Signal chain++

Loop condition++
Dots--
2014-01-21 12:58:11 -08:00 · 2014-01-21 12:56:54 -08:00 · 2014-01-21 12:56:00 -08:00 · 2014-01-21 12:55:57 -08:00 · 2014-01-21 12:55:28 -08:00 · 2014-01-21 12:55:22 -08:00
65 changed files with 2929 additions and 655 deletions
@@ -4,3 +4,6 @@
 [submodule "External/Mantle"]
 	path = External/Mantle
 	url = https://github.com/github/Mantle.git
+[submodule "External/OHHTTPStubs"]
+	path = External/OHHTTPStubs
+	url = https://github.com/github/OHHTTPStubs
@@ -19,6 +19,8 @@ Support](#server-support) below.
 Squirrel’s installer is also designed to be fault tolerant, and ensure that any
 updates installed are valid.

+![:shipit:](http://shipitsquirrel.github.io/images/ship%20it%20squirrel.png)
+
 # Adopting Squirrel

 1. Add the Squirrel repository as a git submodule
@@ -36,30 +38,38 @@ Once Squirrel is added to your project, you need to configure and start it.

 - (void)applicationDidFinishLaunching:(NSNotification *)notification {
 	self.updater = [[SQRLUpdater alloc] initWithUpdateRequest:[NSURLRequest requestWithURL:[NSURL URLWithString:@"https://mycompany.com/myapp/latest"]]];
-	[self.updater startAutomaticChecksWithInterval:/* 4 Hours */ 60 * 60 * 4];
-	[self.updater checkForUpdates];
+
+	// Check for updates every 4 hours.
+	[self.updater startAutomaticChecksWithInterval:60 * 60 * 4];
 }
 ```

-Squirrel will periodically request and automatically download any updates.
+Squirrel will periodically request and automatically download any updates. When
+your application terminates, any downloaded update will be automatically
+installed.

-Before your application terminates, it should tell Squirrel to install any
-updates that it has downloaded:
+## Update Notifications
+
+To know when an update is ready to be installed, you can subscribe to the
+`updates` signal on `SQRLUpdater`:

 ```objc
- (NSApplicationTerminateReply)applicationShouldTerminate:(NSApplication *)sender {
-	[self.updater installUpdateIfNeeded:^(BOOL success, NSError *error) {
-		if (success) {
-			NSLog(@"Successfully installed an update");
-		} else {
-			NSLog(@"Failed to update: %@", error);
-		}
+[self.updater.updates subscribeNext:^(SQRLDownloadedUpdate *downloadedUpdate) {
+    NSLog(@"An update is ready to install: %@", downloadedUpdate);
+}];
+```

-		[sender replyToApplicationShouldTerminate:YES];
-	}];
+If you've been notified of an available update, and don't want to wait for it to
+be installed automatically, you can terminate the app to begin the installation
+process immediately.

-	return NSTerminateLater;
-}
+If you want to install a downloaded update and automatically relaunch afterward,
+`SQRLUpdater` can do that:
+
+```objc
+[[self.updater relaunchToInstallUpdate] subscribeError:^(NSError *error) {
+    NSLog(@"Error preparing update: %@", error);
+}];
 ```

 # Update JSON Format
@@ -100,7 +110,6 @@ will check for an update again at the interval you specify.

 # User Interface

-Squirrel does not provide an updates interface, if you want to display available
-updates, subscribe to the `SQRLUpdaterUpdateAvailableNotification` notification.
-
-![:shipit:](http://shipitsquirrel.github.io/images/ship%20it%20squirrel.png)
+Squirrel does not provide any GUI components for presenting updates. If you want
+to indicate updates to the user, make sure to [listen for downloaded
+updates](#update-notifications).
@@ -7,20 +7,42 @@
 	objects = {

 /* Begin PBXBuildFile section */
+		5316AF7A188EFC1800C070DF /* RACSignal+SQRLFileManagerExtensions.h in Headers */ = {isa = PBXBuildFile; fileRef = 5316AF78188EFC1800C070DF /* RACSignal+SQRLFileManagerExtensions.h */; };
+		5316AF7B188EFC1800C070DF /* RACSignal+SQRLFileManagerExtensions.m in Sources */ = {isa = PBXBuildFile; fileRef = 5316AF79188EFC1800C070DF /* RACSignal+SQRLFileManagerExtensions.m */; };
+		5316AF95188EFFA100C070DF /* RACSignal+SQRLFileManagerExtensions.m in Sources */ = {isa = PBXBuildFile; fileRef = 5316AF79188EFC1800C070DF /* RACSignal+SQRLFileManagerExtensions.m */; };
+		5316AFA8188F002100C070DF /* SQRLDownload+Private.h in Headers */ = {isa = PBXBuildFile; fileRef = 5316AFA6188F002100C070DF /* SQRLDownload+Private.h */; };
+		5316AFAC188F0A8E00C070DF /* NSData+SQRLExtensions.h in Headers */ = {isa = PBXBuildFile; fileRef = 5316AFAA188F0A8E00C070DF /* NSData+SQRLExtensions.h */; };
+		5316AFAD188F0A8E00C070DF /* NSData+SQRLExtensions.m in Sources */ = {isa = PBXBuildFile; fileRef = 5316AFAB188F0A8E00C070DF /* NSData+SQRLExtensions.m */; };
 		533076EB17EB688300BDCCE0 /* IOKit.framework in Frameworks */ = {isa = PBXBuildFile; fileRef = D097B9BC17BB4777006C3FEB /* IOKit.framework */; };
+		53390936184F6219009FA41F /* NSHTTPURLResponse+SQRLExtensions.h in Headers */ = {isa = PBXBuildFile; fileRef = 53390934184F6219009FA41F /* NSHTTPURLResponse+SQRLExtensions.h */; };
+		53390937184F6219009FA41F /* NSHTTPURLResponse+SQRLExtensions.m in Sources */ = {isa = PBXBuildFile; fileRef = 53390935184F6219009FA41F /* NSHTTPURLResponse+SQRLExtensions.m */; };
+		5339094A184F6322009FA41F /* NSHTTPURLResponseExtensionsSpec.m in Sources */ = {isa = PBXBuildFile; fileRef = 53390949184F6322009FA41F /* NSHTTPURLResponseExtensionsSpec.m */; };
 		534FF35B17D8E8B90020A51A /* unused-helper in Copy LoginItems */ = {isa = PBXBuildFile; fileRef = D0B1DDCB17B487D90059C355 /* unused-helper */; };
 		534FF36117D8E90A0020A51A /* Foundation.framework in Frameworks */ = {isa = PBXBuildFile; fileRef = F60CA7EA179FC4F60069F69A /* Foundation.framework */; };
 		534FF36717D8E90A0020A51A /* InfoPlist.strings in Resources */ = {isa = PBXBuildFile; fileRef = 534FF36517D8E90A0020A51A /* InfoPlist.strings */; };
 		534FF36A17D8E90A0020A51A /* main.m in Sources */ = {isa = PBXBuildFile; fileRef = 534FF36917D8E90A0020A51A /* main.m */; };
 		534FF37317D8E9370020A51A /* com.github.Squirrel.TestApplication.TestService.xpc in Copy XPCServices */ = {isa = PBXBuildFile; fileRef = 534FF36017D8E90A0020A51A /* com.github.Squirrel.TestApplication.TestService.xpc */; };
+		53542FC0184F86EC003A6AFD /* Mantle.framework in Copy Frameworks */ = {isa = PBXBuildFile; fileRef = D0A56BA41804B1FD00A84EDC /* Mantle.framework */; };
+		53542FCE184F86F1003A6AFD /* ReactiveCocoa.framework in Copy Frameworks */ = {isa = PBXBuildFile; fileRef = D0F3F05617E83A1D003AFA6B /* ReactiveCocoa.framework */; };
+		53542FCF184F870C003A6AFD /* Mantle.framework in Frameworks */ = {isa = PBXBuildFile; fileRef = D0A56BA41804B1FD00A84EDC /* Mantle.framework */; };
+		53542FD2184F8736003A6AFD /* SQRLDownloadedUpdateSpec.m in Sources */ = {isa = PBXBuildFile; fileRef = 53542FD1184F8736003A6AFD /* SQRLDownloadedUpdateSpec.m */; };
+		536CD4E2183E5D7F000C0FD1 /* SQRLDownload.h in Headers */ = {isa = PBXBuildFile; fileRef = 536CD4E0183E5D7F000C0FD1 /* SQRLDownload.h */; };
+		536CD4E3183E5D7F000C0FD1 /* SQRLDownload.m in Sources */ = {isa = PBXBuildFile; fileRef = 536CD4E1183E5D7F000C0FD1 /* SQRLDownload.m */; };
 		53710D7417D8F59700A992DE /* SQRLDeepCodesignSpec.m in Sources */ = {isa = PBXBuildFile; fileRef = 53710D7317D8F59700A992DE /* SQRLDeepCodesignSpec.m */; };
 		53710D8417D8F5CB00A992DE /* deep-codesign in Resources */ = {isa = PBXBuildFile; fileRef = 53710D7F17D8F5C300A992DE /* deep-codesign */; };
 		5395C0E317E9D013001648E8 /* SQRLUpdateSpec.m in Sources */ = {isa = PBXBuildFile; fileRef = 5395C0E217E9D013001648E8 /* SQRLUpdateSpec.m */; };
-		53A60408182134F9002DB2C7 /* Squirrel-Constants.h in Headers */ = {isa = PBXBuildFile; fileRef = 53A60406182134F9002DB2C7 /* Squirrel-Constants.h */; settings = {ATTRIBUTES = (Public, ); }; };
-		53A60409182134F9002DB2C7 /* Squirrel-Constants.m in Sources */ = {isa = PBXBuildFile; fileRef = 53A60407182134F9002DB2C7 /* Squirrel-Constants.m */; };
-		53A6040A182134F9002DB2C7 /* Squirrel-Constants.m in Sources */ = {isa = PBXBuildFile; fileRef = 53A60407182134F9002DB2C7 /* Squirrel-Constants.m */; };
 		53AACF4B17E9CA0500B41027 /* SQRLUpdate.h in Headers */ = {isa = PBXBuildFile; fileRef = 53AACF4917E9CA0500B41027 /* SQRLUpdate.h */; settings = {ATTRIBUTES = (Public, ); }; };
 		53AACF4C17E9CA0500B41027 /* SQRLUpdate.m in Sources */ = {isa = PBXBuildFile; fileRef = 53AACF4A17E9CA0500B41027 /* SQRLUpdate.m */; };
+		53B0360B184E5C860079FB77 /* SQRLHTTPServer.m in Sources */ = {isa = PBXBuildFile; fileRef = 53B0360A184E5C860079FB77 /* SQRLHTTPServer.m */; };
+		53B70030181E9460000FFBD0 /* OHHTTPStubs.framework in Frameworks */ = {isa = PBXBuildFile; fileRef = 53B70025181E944F000FFBD0 /* OHHTTPStubs.framework */; };
+		53C3186F1816C38A0074B481 /* SQRLDownloadManager.h in Headers */ = {isa = PBXBuildFile; fileRef = 53C318691816C38A0074B481 /* SQRLDownloadManager.h */; };
+		53C318701816C38A0074B481 /* SQRLDownloadManager.m in Sources */ = {isa = PBXBuildFile; fileRef = 53C3186A1816C38A0074B481 /* SQRLDownloadManager.m */; };
+		53C318711816C38A0074B481 /* SQRLURLConnection.h in Headers */ = {isa = PBXBuildFile; fileRef = 53C3186B1816C38A0074B481 /* SQRLURLConnection.h */; };
+		53C318721816C38A0074B481 /* SQRLURLConnection.m in Sources */ = {isa = PBXBuildFile; fileRef = 53C3186C1816C38A0074B481 /* SQRLURLConnection.m */; };
+		53C318731816C38A0074B481 /* SQRLResumableDownload.h in Headers */ = {isa = PBXBuildFile; fileRef = 53C3186D1816C38A0074B481 /* SQRLResumableDownload.h */; };
+		53C318741816C38A0074B481 /* SQRLResumableDownload.m in Sources */ = {isa = PBXBuildFile; fileRef = 53C3186E1816C38A0074B481 /* SQRLResumableDownload.m */; };
+		53C3187C1816CCD70074B481 /* SQRLDownloadManagerSpec.m in Sources */ = {isa = PBXBuildFile; fileRef = 53C318791816CCD70074B481 /* SQRLDownloadManagerSpec.m */; };
+		53C3187D1816CCD70074B481 /* SQRLURLConnectionSpec.m in Sources */ = {isa = PBXBuildFile; fileRef = 53C3187A1816CCD70074B481 /* SQRLURLConnectionSpec.m */; };
 		D000218F17BACEFF0050109A /* SQRLZipArchiver.m in Sources */ = {isa = PBXBuildFile; fileRef = D000218D17BACEFF0050109A /* SQRLZipArchiver.m */; };
 		D000219717BAD34D0050109A /* TestApplication.app.zip in Resources */ = {isa = PBXBuildFile; fileRef = D000219617BAD34D0050109A /* TestApplication.app.zip */; };
 		D000219917BAD35C0050109A /* SQRLZipArchiverSpec.m in Sources */ = {isa = PBXBuildFile; fileRef = D000219817BAD35C0050109A /* SQRLZipArchiverSpec.m */; };
@@ -109,6 +131,34 @@
 			remoteGlobalIDString = 534FF35F17D8E90A0020A51A;
 			remoteInfo = TestService;
 		};
+		53B70020181E944F000FFBD0 /* PBXContainerItemProxy */ = {
+			isa = PBXContainerItemProxy;
+			containerPortal = 53E1E674181E942300ED813C /* OHHTTPStubs.xcodeproj */;
+			proxyType = 2;
+			remoteGlobalIDString = 09793579161B6251006DB5D5;
+			remoteInfo = "OHHTTPStubs-iOS";
+		};
+		53B70022181E944F000FFBD0 /* PBXContainerItemProxy */ = {
+			isa = PBXContainerItemProxy;
+			containerPortal = 53E1E674181E942300ED813C /* OHHTTPStubs.xcodeproj */;
+			proxyType = 2;
+			remoteGlobalIDString = 098368CE168FC7920082B1A4;
+			remoteInfo = UnitTests;
+		};
+		53B70024181E944F000FFBD0 /* PBXContainerItemProxy */ = {
+			isa = PBXContainerItemProxy;
+			containerPortal = 53E1E674181E942300ED813C /* OHHTTPStubs.xcodeproj */;
+			proxyType = 2;
+			remoteGlobalIDString = F6C37BA016F6C8680082B630;
+			remoteInfo = OHHTTPStubs;
+		};
+		53B7002E181E9456000FFBD0 /* PBXContainerItemProxy */ = {
+			isa = PBXContainerItemProxy;
+			containerPortal = 53E1E674181E942300ED813C /* OHHTTPStubs.xcodeproj */;
+			proxyType = 1;
+			remoteGlobalIDString = F6C37B9F16F6C8680082B630;
+			remoteInfo = OHHTTPStubs;
+		};
 		D014AC1617B9793A007D79D0 /* PBXContainerItemProxy */ = {
 			isa = PBXContainerItemProxy;
 			containerPortal = D0C22BCE179CC00E00158214 /* Project object */;
@@ -361,6 +411,8 @@
 			dstPath = "";
 			dstSubfolderSpec = 10;
 			files = (
+				53542FCE184F86F1003A6AFD /* ReactiveCocoa.framework in Copy Frameworks */,
+				53542FC0184F86EC003A6AFD /* Mantle.framework in Copy Frameworks */,
 				D08D4E4917B451F20012B22D /* Squirrel.framework in Copy Frameworks */,
 			);
 			name = "Copy Frameworks";
@@ -380,11 +432,22 @@
 /* End PBXCopyFilesBuildPhase section */

 /* Begin PBXFileReference section */
+		5316AF78188EFC1800C070DF /* RACSignal+SQRLFileManagerExtensions.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = "RACSignal+SQRLFileManagerExtensions.h"; sourceTree = "<group>"; };
+		5316AF79188EFC1800C070DF /* RACSignal+SQRLFileManagerExtensions.m */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.objc; path = "RACSignal+SQRLFileManagerExtensions.m"; sourceTree = "<group>"; };
+		5316AFA6188F002100C070DF /* SQRLDownload+Private.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = "SQRLDownload+Private.h"; sourceTree = "<group>"; };
+		5316AFAA188F0A8E00C070DF /* NSData+SQRLExtensions.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = "NSData+SQRLExtensions.h"; sourceTree = "<group>"; };
+		5316AFAB188F0A8E00C070DF /* NSData+SQRLExtensions.m */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.objc; path = "NSData+SQRLExtensions.m"; sourceTree = "<group>"; };
+		53390934184F6219009FA41F /* NSHTTPURLResponse+SQRLExtensions.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = "NSHTTPURLResponse+SQRLExtensions.h"; sourceTree = "<group>"; };
+		53390935184F6219009FA41F /* NSHTTPURLResponse+SQRLExtensions.m */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.objc; path = "NSHTTPURLResponse+SQRLExtensions.m"; sourceTree = "<group>"; };
+		53390949184F6322009FA41F /* NSHTTPURLResponseExtensionsSpec.m */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.objc; path = NSHTTPURLResponseExtensionsSpec.m; sourceTree = "<group>"; };
 		534FF36017D8E90A0020A51A /* com.github.Squirrel.TestApplication.TestService.xpc */ = {isa = PBXFileReference; explicitFileType = wrapper.cfbundle; includeInIndex = 0; path = com.github.Squirrel.TestApplication.TestService.xpc; sourceTree = BUILT_PRODUCTS_DIR; };
 		534FF36417D8E90A0020A51A /* TestService-Info.plist */ = {isa = PBXFileReference; lastKnownFileType = text.plist.xml; path = "TestService-Info.plist"; sourceTree = "<group>"; };
 		534FF36617D8E90A0020A51A /* en */ = {isa = PBXFileReference; lastKnownFileType = text.plist.strings; name = en; path = en.lproj/InfoPlist.strings; sourceTree = "<group>"; };
 		534FF36817D8E90A0020A51A /* TestService-Prefix.pch */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.c.h; path = "TestService-Prefix.pch"; sourceTree = "<group>"; };
 		534FF36917D8E90A0020A51A /* main.m */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.c.objc; path = main.m; sourceTree = "<group>"; };
+		53542FD1184F8736003A6AFD /* SQRLDownloadedUpdateSpec.m */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.objc; path = SQRLDownloadedUpdateSpec.m; sourceTree = "<group>"; };
+		536CD4E0183E5D7F000C0FD1 /* SQRLDownload.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = SQRLDownload.h; sourceTree = "<group>"; };
+		536CD4E1183E5D7F000C0FD1 /* SQRLDownload.m */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.objc; path = SQRLDownload.m; sourceTree = "<group>"; };
 		53710D7317D8F59700A992DE /* SQRLDeepCodesignSpec.m */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.objc; path = SQRLDeepCodesignSpec.m; sourceTree = "<group>"; };
 		53710D7D17D8F5C300A992DE /* bootstrap */ = {isa = PBXFileReference; lastKnownFileType = text.script.sh; path = bootstrap; sourceTree = "<group>"; };
 		53710D7E17D8F5C300A992DE /* cibuild */ = {isa = PBXFileReference; lastKnownFileType = text.script.sh; path = cibuild; sourceTree = "<group>"; };
@@ -394,10 +457,19 @@
 		53710D8217D8F5C300A992DE /* targets.awk */ = {isa = PBXFileReference; lastKnownFileType = text; path = targets.awk; sourceTree = "<group>"; };
 		53710D8317D8F5C300A992DE /* xcodebuild.awk */ = {isa = PBXFileReference; lastKnownFileType = text; path = xcodebuild.awk; sourceTree = "<group>"; };
 		5395C0E217E9D013001648E8 /* SQRLUpdateSpec.m */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.objc; path = SQRLUpdateSpec.m; sourceTree = "<group>"; };
-		53A60406182134F9002DB2C7 /* Squirrel-Constants.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = "Squirrel-Constants.h"; sourceTree = "<group>"; };
-		53A60407182134F9002DB2C7 /* Squirrel-Constants.m */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.objc; path = "Squirrel-Constants.m"; sourceTree = "<group>"; };
 		53AACF4917E9CA0500B41027 /* SQRLUpdate.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = SQRLUpdate.h; sourceTree = "<group>"; };
 		53AACF4A17E9CA0500B41027 /* SQRLUpdate.m */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.objc; path = SQRLUpdate.m; sourceTree = "<group>"; };
+		53B03609184E5C860079FB77 /* SQRLHTTPServer.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = SQRLHTTPServer.h; sourceTree = "<group>"; };
+		53B0360A184E5C860079FB77 /* SQRLHTTPServer.m */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.objc; path = SQRLHTTPServer.m; sourceTree = "<group>"; };
+		53C318691816C38A0074B481 /* SQRLDownloadManager.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = SQRLDownloadManager.h; sourceTree = "<group>"; };
+		53C3186A1816C38A0074B481 /* SQRLDownloadManager.m */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.objc; path = SQRLDownloadManager.m; sourceTree = "<group>"; };
+		53C3186B1816C38A0074B481 /* SQRLURLConnection.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = SQRLURLConnection.h; sourceTree = "<group>"; };
+		53C3186C1816C38A0074B481 /* SQRLURLConnection.m */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.objc; path = SQRLURLConnection.m; sourceTree = "<group>"; };
+		53C3186D1816C38A0074B481 /* SQRLResumableDownload.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = SQRLResumableDownload.h; sourceTree = "<group>"; };
+		53C3186E1816C38A0074B481 /* SQRLResumableDownload.m */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.objc; path = SQRLResumableDownload.m; sourceTree = "<group>"; };
+		53C318791816CCD70074B481 /* SQRLDownloadManagerSpec.m */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.objc; path = SQRLDownloadManagerSpec.m; sourceTree = "<group>"; };
+		53C3187A1816CCD70074B481 /* SQRLURLConnectionSpec.m */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.objc; path = SQRLURLConnectionSpec.m; sourceTree = "<group>"; };
+		53E1E674181E942300ED813C /* OHHTTPStubs.xcodeproj */ = {isa = PBXFileReference; lastKnownFileType = "wrapper.pb-project"; name = OHHTTPStubs.xcodeproj; path = External/ReactiveCocoa/external/specta/../../../OHHTTPStubs/OHHTTPStubs/OHHTTPStubs.xcodeproj; sourceTree = "<group>"; };
 		D000218C17BACEFF0050109A /* SQRLZipArchiver.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = SQRLZipArchiver.h; sourceTree = "<group>"; };
 		D000218D17BACEFF0050109A /* SQRLZipArchiver.m */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.objc; path = SQRLZipArchiver.m; sourceTree = "<group>"; };
 		D000219617BAD34D0050109A /* TestApplication.app.zip */ = {isa = PBXFileReference; lastKnownFileType = archive.zip; path = TestApplication.app.zip; sourceTree = "<group>"; };
@@ -521,6 +593,7 @@
 			isa = PBXFrameworksBuildPhase;
 			buildActionMask = 2147483647;
 			files = (
+				53542FCF184F870C003A6AFD /* Mantle.framework in Frameworks */,
 				D0F3F06417E83B0B003AFA6B /* ReactiveCocoa.framework in Frameworks */,
 				D08D4E4717B451E50012B22D /* Squirrel.framework in Frameworks */,
 				D08D4E0D17B451500012B22D /* Cocoa.framework in Frameworks */,
@@ -545,6 +618,7 @@
 			isa = PBXFrameworksBuildPhase;
 			buildActionMask = 2147483647;
 			files = (
+				53B70030181E9460000FFBD0 /* OHHTTPStubs.framework in Frameworks */,
 				D0A56BCF1804B8FC00A84EDC /* Mantle.framework in Frameworks */,
 				D093682417FF732200BA0EAE /* ServiceManagement.framework in Frameworks */,
 				D0F3F06817E83B27003AFA6B /* ReactiveCocoa.framework in Frameworks */,
@@ -596,13 +670,30 @@
 			path = script;
 			sourceTree = "<group>";
 		};
-		53A603F7182134D3002DB2C7 /* Supporting Files */ = {
+		53B70015181E944F000FFBD0 /* Products */ = {
 			isa = PBXGroup;
 			children = (
-				53A60406182134F9002DB2C7 /* Squirrel-Constants.h */,
-				53A60407182134F9002DB2C7 /* Squirrel-Constants.m */,
+				53B70021181E944F000FFBD0 /* libOHHTTPStubs-iOS.a */,
+				53B70023181E944F000FFBD0 /* UnitTests.octest */,
+				53B70025181E944F000FFBD0 /* OHHTTPStubs.framework */,
 			);
-			name = "Supporting Files";
+			name = Products;
+			sourceTree = "<group>";
+		};
+		53C3185A1816C3730074B481 /* Downloads */ = {
+			isa = PBXGroup;
+			children = (
+				53C318691816C38A0074B481 /* SQRLDownloadManager.h */,
+				53C3186A1816C38A0074B481 /* SQRLDownloadManager.m */,
+				536CD4E0183E5D7F000C0FD1 /* SQRLDownload.h */,
+				536CD4E1183E5D7F000C0FD1 /* SQRLDownload.m */,
+				5316AFA6188F002100C070DF /* SQRLDownload+Private.h */,
+				53C3186D1816C38A0074B481 /* SQRLResumableDownload.h */,
+				53C3186E1816C38A0074B481 /* SQRLResumableDownload.m */,
+				53C3186B1816C38A0074B481 /* SQRLURLConnection.h */,
+				53C3186C1816C38A0074B481 /* SQRLURLConnection.m */,
+			);
+			name = Downloads;
 			sourceTree = "<group>";
 		};
 		D00F5B8217E82CFB009A4818 /* Extensions */ = {
@@ -610,6 +701,8 @@
 			children = (
 				D00F5B8917E82D15009A4818 /* NSProcessInfo+SQRLVersionExtensions.h */,
 				D00F5B8A17E82D15009A4818 /* NSProcessInfo+SQRLVersionExtensions.m */,
+				5316AFAA188F0A8E00C070DF /* NSData+SQRLExtensions.h */,
+				5316AFAB188F0A8E00C070DF /* NSData+SQRLExtensions.m */,
 			);
 			name = Extensions;
 			sourceTree = "<group>";
@@ -644,6 +737,10 @@
 				D0964B3B17F2E20B00D88BF7 /* NSBundle+SQRLVersionExtensions.m */,
 				D0EDBE9A17B0C68E0058BC3C /* NSError+SQRLVerbosityExtensions.h */,
 				D0EDBE9B17B0C68E0058BC3C /* NSError+SQRLVerbosityExtensions.m */,
+				53390934184F6219009FA41F /* NSHTTPURLResponse+SQRLExtensions.h */,
+				53390935184F6219009FA41F /* NSHTTPURLResponse+SQRLExtensions.m */,
+				5316AF78188EFC1800C070DF /* RACSignal+SQRLFileManagerExtensions.h */,
+				5316AF79188EFC1800C070DF /* RACSignal+SQRLFileManagerExtensions.m */,
 			);
 			name = Extensions;
 			sourceTree = "<group>";
@@ -666,7 +763,8 @@
 				534FF36217D8E90A0020A51A /* TestService */,
 				D08D4E0F17B451500012B22D /* Supporting Files */,
 			);
-			path = TestApplication;
+			name = TestApplication;
+			path = ../TestApplication;
 			sourceTree = "<group>";
 		};
 		D08D4E0F17B451500012B22D /* Supporting Files */ = {
@@ -753,7 +851,6 @@
 				D0EDBE9F17B0C6930058BC3C /* Shared */,
 				D0C22BE0179CC00E00158214 /* Squirrel */,
 				D0C22BF6179CC00E00158214 /* SquirrelTests */,
-				D08D4E0E17B451500012B22D /* TestApplication */,
 				D014AC0317B97885007D79D0 /* ShipIt */,
 				D0C22BD9179CC00E00158214 /* Frameworks */,
 				53710D7C17D8F5C300A992DE /* Scripts */,
@@ -780,6 +877,7 @@
 			children = (
 				D097B9BC17BB4777006C3FEB /* IOKit.framework */,
 				D014ABB917B97403007D79D0 /* ServiceManagement.framework */,
+				53E1E674181E942300ED813C /* OHHTTPStubs.xcodeproj */,
 				D0F3F01417E83918003AFA6B /* Expecta.xcodeproj */,
 				D0A56B961804B1FD00A84EDC /* Mantle.xcodeproj */,
 				D0F3F04A17E83A1D003AFA6B /* ReactiveCocoa.xcodeproj */,
@@ -820,6 +918,7 @@
 		D0C22BF6179CC00E00158214 /* SquirrelTests */ = {
 			isa = PBXGroup;
 			children = (
+				D08D4E0E17B451500012B22D /* TestApplication */,
 				D0C22C4E179CC18000158214 /* Specs */,
 				D0C22BF7179CC00E00158214 /* Supporting Files */,
 			);
@@ -831,6 +930,8 @@
 			children = (
 				D049059E180558B7004E683E /* SQRLTestUpdate.h */,
 				D049059F180558B7004E683E /* SQRLTestUpdate.m */,
+				53B03609184E5C860079FB77 /* SQRLHTTPServer.h */,
+				53B0360A184E5C860079FB77 /* SQRLHTTPServer.m */,
 				D000219617BAD34D0050109A /* TestApplication.app.zip */,
 				D09D244917B59AB30001FAF8 /* TestApplication 2.1.app */,
 				D0C22BF8179CC00E00158214 /* SquirrelTests-Info.plist */,
@@ -908,6 +1009,7 @@
 			isa = PBXGroup;
 			children = (
 				D0964B2817F2DEE700D88BF7 /* Updates */,
+				53C3185A1816C3730074B481 /* Downloads */,
 				D0964B3417F2DEF500D88BF7 /* Archives */,
 				D0964B3517F2DF3100D88BF7 /* IPC */,
 			);
@@ -918,6 +1020,7 @@
 			isa = PBXGroup;
 			children = (
 				D00F5B8D17E82DE6009A4818 /* NSProcessInfoExtensionsSpec.m */,
+				53390949184F6322009FA41F /* NSHTTPURLResponseExtensionsSpec.m */,
 				D0EDBEE017B0E3650058BC3C /* SQRLCodeSignatureVerifierSpec.m */,
 				53710D7317D8F59700A992DE /* SQRLDeepCodesignSpec.m */,
 				D049059A180554BA004E683E /* SQRLDirectoryManagerSpec.m */,
@@ -929,6 +1032,9 @@
 				D0C22C4F179CC18C00158214 /* SQRLUpdaterSpec.m */,
 				5395C0E217E9D013001648E8 /* SQRLUpdateSpec.m */,
 				D000219817BAD35C0050109A /* SQRLZipArchiverSpec.m */,
+				53C318791816CCD70074B481 /* SQRLDownloadManagerSpec.m */,
+				53C3187A1816CCD70074B481 /* SQRLURLConnectionSpec.m */,
+				53542FD1184F8736003A6AFD /* SQRLDownloadedUpdateSpec.m */,
 			);
 			name = Specs;
 			sourceTree = "<group>";
@@ -940,7 +1046,6 @@
 				D0A56BF61804BABB00A84EDC /* Code Signing */,
 				D0A56BE71804BA2400A84EDC /* State */,
 				D06B58BC18032BE800656D97 /* Transactions */,
-				53A603F7182134D3002DB2C7 /* Supporting Files */,
 			);
 			name = Shared;
 			path = Squirrel;
@@ -989,12 +1094,19 @@
 			isa = PBXHeadersBuildPhase;
 			buildActionMask = 2147483647;
 			files = (
+				53C318711816C38A0074B481 /* SQRLURLConnection.h in Headers */,
 				D0964B3C17F2E20B00D88BF7 /* NSBundle+SQRLVersionExtensions.h in Headers */,
 				D0C22C4C179CC15100158214 /* SQRLUpdater.h in Headers */,
+				5316AFAC188F0A8E00C070DF /* NSData+SQRLExtensions.h in Headers */,
 				D0C22C52179CC23900158214 /* Squirrel.h in Headers */,
+				5316AFA8188F002100C070DF /* SQRLDownload+Private.h in Headers */,
+				53390936184F6219009FA41F /* NSHTTPURLResponse+SQRLExtensions.h in Headers */,
 				D0964B3817F2E01500D88BF7 /* SQRLDownloadedUpdate.h in Headers */,
 				53AACF4B17E9CA0500B41027 /* SQRLUpdate.h in Headers */,
-				53A60408182134F9002DB2C7 /* Squirrel-Constants.h in Headers */,
+				5316AF7A188EFC1800C070DF /* RACSignal+SQRLFileManagerExtensions.h in Headers */,
+				53C318731816C38A0074B481 /* SQRLResumableDownload.h in Headers */,
+				536CD4E2183E5D7F000C0FD1 /* SQRLDownload.h in Headers */,
+				53C3186F1816C38A0074B481 /* SQRLDownloadManager.h in Headers */,
 				D00F5B8B17E82D15009A4818 /* NSProcessInfo+SQRLVersionExtensions.h in Headers */,
 			);
 			runOnlyForDeploymentPostprocessing = 0;
@@ -1089,11 +1201,11 @@
 				D0C22BEA179CC00E00158214 /* Sources */,
 				D0C22BEB179CC00E00158214 /* Frameworks */,
 				D0C22BEC179CC00E00158214 /* Resources */,
-				D0C22BED179CC00E00158214 /* ShellScript */,
 			);
 			buildRules = (
 			);
 			dependencies = (
+				53B7002F181E9456000FFBD0 /* PBXTargetDependency */,
 				D0F3F03317E83924003AFA6B /* PBXTargetDependency */,
 				D0F3F03517E83924003AFA6B /* PBXTargetDependency */,
 				D08D4E4C17B4520C0012B22D /* PBXTargetDependency */,
@@ -1134,6 +1246,10 @@
 					ProductGroup = D0A56B971804B1FD00A84EDC /* Products */;
 					ProjectRef = D0A56B961804B1FD00A84EDC /* Mantle.xcodeproj */;
 				},
+				{
+					ProductGroup = 53B70015181E944F000FFBD0 /* Products */;
+					ProjectRef = 53E1E674181E942300ED813C /* OHHTTPStubs.xcodeproj */;
+				},
 				{
 					ProductGroup = D0F3F04B17E83A1D003AFA6B /* Products */;
 					ProjectRef = D0F3F04A17E83A1D003AFA6B /* ReactiveCocoa.xcodeproj */;
@@ -1155,6 +1271,27 @@
 /* End PBXProject section */

 /* Begin PBXReferenceProxy section */
+		53B70021181E944F000FFBD0 /* libOHHTTPStubs-iOS.a */ = {
+			isa = PBXReferenceProxy;
+			fileType = archive.ar;
+			path = "libOHHTTPStubs-iOS.a";
+			remoteRef = 53B70020181E944F000FFBD0 /* PBXContainerItemProxy */;
+			sourceTree = BUILT_PRODUCTS_DIR;
+		};
+		53B70023181E944F000FFBD0 /* UnitTests.octest */ = {
+			isa = PBXReferenceProxy;
+			fileType = wrapper.cfbundle;
+			path = UnitTests.octest;
+			remoteRef = 53B70022181E944F000FFBD0 /* PBXContainerItemProxy */;
+			sourceTree = BUILT_PRODUCTS_DIR;
+		};
+		53B70025181E944F000FFBD0 /* OHHTTPStubs.framework */ = {
+			isa = PBXReferenceProxy;
+			fileType = wrapper.framework;
+			path = OHHTTPStubs.framework;
+			remoteRef = 53B70024181E944F000FFBD0 /* PBXContainerItemProxy */;
+			sourceTree = BUILT_PRODUCTS_DIR;
+		};
 		D0964B1C17F2DD4500D88BF7 /* libReactiveCocoa-Mac.a */ = {
 			isa = PBXReferenceProxy;
 			fileType = archive.ar;
@@ -1340,22 +1477,6 @@
 		};
 /* End PBXResourcesBuildPhase section */

-/* Begin PBXShellScriptBuildPhase section */
-		D0C22BED179CC00E00158214 /* ShellScript */ = {
-			isa = PBXShellScriptBuildPhase;
-			buildActionMask = 2147483647;
-			files = (
-			);
-			inputPaths = (
-			);
-			outputPaths = (
-			);
-			runOnlyForDeploymentPostprocessing = 0;
-			shellPath = /bin/sh;
-			shellScript = "# Run the unit tests in this test bundle.\n\"${SYSTEM_DEVELOPER_DIR}/Tools/RunUnitTests\"\n";
-		};
-/* End PBXShellScriptBuildPhase section */
-
 /* Begin PBXSourcesBuildPhase section */
 		534FF35C17D8E90A0020A51A /* Sources */ = {
 			isa = PBXSourcesBuildPhase;
@@ -1373,9 +1494,9 @@
 				D014AC1117B9789C007D79D0 /* SQRLInstaller.m in Sources */,
 				D043F77217FF40C90012F996 /* SQRLTerminationListener.m in Sources */,
 				D014AC0517B97885007D79D0 /* ShipIt-main.m in Sources */,
+				5316AF95188EFFA100C070DF /* RACSignal+SQRLFileManagerExtensions.m in Sources */,
 				D014AC1917B979A8007D79D0 /* SQRLCodeSignature.m in Sources */,
 				D06B58B618032B1500656D97 /* RACSignal+SQRLTransactionExtensions.m in Sources */,
-				53A6040A182134F9002DB2C7 /* Squirrel-Constants.m in Sources */,
 				D014AC1A17B979AA007D79D0 /* NSError+SQRLVerbosityExtensions.m in Sources */,
 				D0D2B6271804E903000EA901 /* SQRLDirectoryManager.m in Sources */,
 				D0964B3E17F2E20B00D88BF7 /* NSBundle+SQRLVersionExtensions.m in Sources */,
@@ -1396,19 +1517,25 @@
 			isa = PBXSourcesBuildPhase;
 			buildActionMask = 2147483647;
 			files = (
+				5316AFAD188F0A8E00C070DF /* NSData+SQRLExtensions.m in Sources */,
 				D0964B3D17F2E20B00D88BF7 /* NSBundle+SQRLVersionExtensions.m in Sources */,
 				F6F2ED8417A33C4900F4D220 /* SQRLCodeSignature.m in Sources */,
 				D0D2B6261804E903000EA901 /* SQRLDirectoryManager.m in Sources */,
+				53C318741816C38A0074B481 /* SQRLResumableDownload.m in Sources */,
+				5316AF7B188EFC1800C070DF /* RACSignal+SQRLFileManagerExtensions.m in Sources */,
 				D0964B3917F2E01500D88BF7 /* SQRLDownloadedUpdate.m in Sources */,
 				D014ABB817B96CB3007D79D0 /* SQRLShipItLauncher.m in Sources */,
+				53C318721816C38A0074B481 /* SQRLURLConnection.m in Sources */,
 				D000218F17BACEFF0050109A /* SQRLZipArchiver.m in Sources */,
 				D0C22C4D179CC15100158214 /* SQRLUpdater.m in Sources */,
 				D0EDBE9D17B0C68E0058BC3C /* NSError+SQRLVerbosityExtensions.m in Sources */,
 				53AACF4C17E9CA0500B41027 /* SQRLUpdate.m in Sources */,
 				D0A56BEB1804BA3C00A84EDC /* SQRLShipItState.m in Sources */,
-				53A60409182134F9002DB2C7 /* Squirrel-Constants.m in Sources */,
+				53C318701816C38A0074B481 /* SQRLDownloadManager.m in Sources */,
 				D00F5B8C17E82D15009A4818 /* NSProcessInfo+SQRLVersionExtensions.m in Sources */,
+				536CD4E3183E5D7F000C0FD1 /* SQRLDownload.m in Sources */,
 				D06B58B518032B1500656D97 /* RACSignal+SQRLTransactionExtensions.m in Sources */,
+				53390937184F6219009FA41F /* NSHTTPURLResponse+SQRLExtensions.m in Sources */,
 			);
 			runOnlyForDeploymentPostprocessing = 0;
 		};
@@ -1418,15 +1545,20 @@
 			files = (
 				5395C0E317E9D013001648E8 /* SQRLUpdateSpec.m in Sources */,
 				D000219917BAD35C0050109A /* SQRLZipArchiverSpec.m in Sources */,
+				53542FD2184F8736003A6AFD /* SQRLDownloadedUpdateSpec.m in Sources */,
 				D043F77E17FF43640012F996 /* SQRLTerminationListener.m in Sources */,
 				D09D244117B595470001FAF8 /* SQRLInstallerSpec.m in Sources */,
 				D0C22C50179CC18C00158214 /* SQRLUpdaterSpec.m in Sources */,
 				D0EDBEDD17B0DB3E0058BC3C /* SQRLTestCase.m in Sources */,
+				5339094A184F6322009FA41F /* NSHTTPURLResponseExtensionsSpec.m in Sources */,
+				53C3187C1816CCD70074B481 /* SQRLDownloadManagerSpec.m in Sources */,
 				D06B58D118035B5A00656D97 /* SQRLTerminationListenerSpec.m in Sources */,
 				D0EDBEE117B0E3650058BC3C /* SQRLCodeSignatureVerifierSpec.m in Sources */,
 				53710D7417D8F59700A992DE /* SQRLDeepCodesignSpec.m in Sources */,
 				D00F5B8E17E82DE6009A4818 /* NSProcessInfoExtensionsSpec.m in Sources */,
+				53B0360B184E5C860079FB77 /* SQRLHTTPServer.m in Sources */,
 				D049059B180554BA004E683E /* SQRLDirectoryManagerSpec.m in Sources */,
+				53C3187D1816CCD70074B481 /* SQRLURLConnectionSpec.m in Sources */,
 				D061E40217FD580D00CC134A /* SQRLInstaller.m in Sources */,
 				D04905A0180558B7004E683E /* SQRLTestUpdate.m in Sources */,
 				D049059D18055671004E683E /* SQRLShipItStateSpec.m in Sources */,
@@ -1441,6 +1573,11 @@
 			target = 534FF35F17D8E90A0020A51A /* TestService */;
 			targetProxy = 534FF37017D8E9170020A51A /* PBXContainerItemProxy */;
 		};
+		53B7002F181E9456000FFBD0 /* PBXTargetDependency */ = {
+			isa = PBXTargetDependency;
+			name = OHHTTPStubs;
+			targetProxy = 53B7002E181E9456000FFBD0 /* PBXContainerItemProxy */;
+		};
 		D014AC1717B9793A007D79D0 /* PBXTargetDependency */ = {
 			isa = PBXTargetDependency;
 			target = D014AC0017B97885007D79D0 /* ShipIt */;
@@ -20,6 +20,20 @@
               ReferencedContainer = "container:Squirrel.xcodeproj">
            </BuildableReference>
         </BuildActionEntry>
+         <BuildActionEntry
+            buildForTesting = "YES"
+            buildForRunning = "YES"
+            buildForProfiling = "NO"
+            buildForArchiving = "NO"
+            buildForAnalyzing = "YES">
+            <BuildableReference
+               BuildableIdentifier = "primary"
+               BlueprintIdentifier = "D0C22BEE179CC00E00158214"
+               BuildableName = "SquirrelTests.octest"
+               BlueprintName = "SquirrelTests"
+               ReferencedContainer = "container:Squirrel.xcodeproj">
+            </BuildableReference>
+         </BuildActionEntry>
      </BuildActionEntries>
   </BuildAction>
   <TestAction
@@ -0,0 +1,19 @@
+//
+//  NSData+SQRLExtensions.h
+//  Squirrel
+//
+//  Created by Keith Duncan on 21/01/2014.
+//  Copyright (c) 2014 GitHub. All rights reserved.
+//
+
+#import <Foundation/Foundation.h>
+
+@interface NSData (SQRLExtensions)
+
+// Returns an NSData for the SHA1 hash of the receiver.
+- (NSData *)sqrl_SHA1Hash;
+
+// Returns the base16 encoding of the receiver.
+- (NSString *)sqrl_base16String;
+
+@end
@@ -0,0 +1,31 @@
+//
+//  NSData+SQRLExtensions.m
+//  Squirrel
+//
+//  Created by Keith Duncan on 21/01/2014.
+//  Copyright (c) 2014 GitHub. All rights reserved.
+//
+
+#import "NSData+SQRLExtensions.h"
+
+#import <CommonCrypto/CommonCrypto.h>
+
+@implementation NSData (SQRLExtensions)
+
+- (NSData *)sqrl_SHA1Hash {
+	unsigned char hash[CC_SHA1_DIGEST_LENGTH];
+	CC_SHA1(self.bytes, (CC_LONG)self.length, hash);
+	return [NSData dataWithBytes:hash length:sizeof(hash) / sizeof(*hash)];
+}
+
+- (NSString *)sqrl_base16String {
+	NSMutableString *base16 = [NSMutableString stringWithCapacity:self.length * 2];
+	uint8_t *bytes = (uint8_t *)self.bytes;
+	for (NSUInteger idx = 0; idx < self.length; idx++) {
+		uint8_t byte = *(bytes + idx);
+		[base16 appendFormat:@"%02hhx", byte];
+	}
+	return base16;
+}
+
+@end
@@ -0,0 +1,18 @@
+//
+//  NSHTTPURLResponse+SQRLExtensions.h
+//  Squirrel
+//
+//  Created by Keith Duncan on 04/12/2013.
+//  Copyright (c) 2013 GitHub. All rights reserved.
+//
+
+#import <Foundation/Foundation.h>
+
+@interface NSHTTPURLResponse (SQRLExtensions)
+
+// Case insensitively look up a header field value.
+//
+// Returns the value of the header if present or nil otherwise.
+- (NSString *)sqrl_valueForHTTPHeaderField:(NSString *)field;
+
+@end
@@ -0,0 +1,26 @@
+//
+//  NSHTTPURLResponse+SQRLExtensions.m
+//  Squirrel
+//
+//  Created by Keith Duncan on 04/12/2013.
+//  Copyright (c) 2013 GitHub. All rights reserved.
+//
+
+#import "NSHTTPURLResponse+SQRLExtensions.h"
+
+#import <ReactiveCocoa/ReactiveCocoa.h>
+
+@implementation NSHTTPURLResponse (SQRLExtensions)
+
+- (NSString *)sqrl_valueForHTTPHeaderField:(NSString *)field {
+	return [[[self.allHeaderFields.rac_signal
+		filter:^ BOOL (RACTuple *keyValuePair) {
+			return [keyValuePair[0] caseInsensitiveCompare:field] == NSOrderedSame;
+		}]
+		reduceEach:^(NSString *key, NSString *value) {
+			return value;
+		}]
+		first];
+}
+
+@end
@@ -0,0 +1,15 @@
+//
+//  RACSignal+SQRLFileManagerExtensions.h
+//  Squirrel
+//
+//  Created by Keith Duncan on 21/01/2014.
+//  Copyright (c) 2014 GitHub. All rights reserved.
+//
+
+#import <ReactiveCocoa/ReactiveCocoa.h>
+
+@interface RACSignal (SQRLFileManagerExtensions)
+
+- (RACSignal *)sqrl_tryCreateDirectory;
+
+@end
@@ -0,0 +1,21 @@
+//
+//  RACSignal+SQRLFileManagerExtensions.m
+//  Squirrel
+//
+//  Created by Keith Duncan on 21/01/2014.
+//  Copyright (c) 2014 GitHub. All rights reserved.
+//
+
+#import "RACSignal+SQRLFileManagerExtensions.h"
+
+@implementation RACSignal (SQRLFileManagerExtensions)
+
+- (RACSignal *)sqrl_tryCreateDirectory {
+	return [[self
+		try:^(NSURL *directoryURL, NSError **errorRef) {
+			return [NSFileManager.defaultManager createDirectoryAtURL:directoryURL withIntermediateDirectories:YES attributes:nil error:errorRef];
+		}]
+		setNameWithFormat:@"%@ -sqrl_tryCreateDirectory", self];
+}
+
+@end
@@ -97,15 +97,12 @@ static RACDisposable *SQRLCreateTransaction(NSString *name, NSString *descriptio
 		va_end(args);
 	}

-	return [[RACSignal createSignal:^(id<RACSubscriber> subscriber) {
-		RACDisposable *transactionDisposable = SQRLCreateTransaction(name, description);
-		RACDisposable *subscriptionDisposable = [self subscribe:subscriber];
-
-		return [RACDisposable disposableWithBlock:^{
-			[subscriptionDisposable dispose];
-			[transactionDisposable dispose];
-		}];
-	}] setNameWithFormat:@"[%@] -sqrl_addTransactionWithName: %@ description: %@", self.name, name, description];
+	return [[RACSignal
+		create:^(id<RACSubscriber> subscriber) {
+			[subscriber.disposable addDisposable:SQRLCreateTransaction(name, description)];
+			[self subscribe:subscriber];
+		}]
+		setNameWithFormat:@"[%@] -sqrl_addTransactionWithName: %@ description: %@", self.name, name, description];
 }

 - (RACSignal *)sqrl_addSubscriptionTransactionWithName:(NSString *)name description:(NSString *)descriptionFormat, ... {
@@ -117,13 +114,13 @@ static RACDisposable *SQRLCreateTransaction(NSString *name, NSString *descriptio
 		va_end(args);
 	}

-	return [[RACSignal createSignal:^(id<RACSubscriber> subscriber) {
-		RACDisposable *transactionDisposable = SQRLCreateTransaction(name, description);
-		RACDisposable *subscriptionDisposable = [self subscribe:subscriber];
-		[transactionDisposable dispose];
-
-		return subscriptionDisposable;
-	}] setNameWithFormat:@"[%@] -sqrl_addSubscriptionTransactionWithName: %@ description: %@", self.name, name, description];
+	return [[RACSignal
+		create:^(id<RACSubscriber> subscriber) {
+			RACDisposable *transactionDisposable = SQRLCreateTransaction(name, description);
+			[self subscribe:subscriber];
+			[transactionDisposable dispose];
+		}]
+		setNameWithFormat:@"[%@] -sqrl_addSubscriptionTransactionWithName: %@ description: %@", self.name, name, description];
 }

@end
@@ -9,6 +9,16 @@
 #import <Foundation/Foundation.h>
 #import <Mantle/Mantle.h>

+// The domain for errors originating within SQRLCodeSignature.
+extern NSString * const SQRLCodeSignatureErrorDomain;
+
+// The bundle did not pass codesign verification.
+extern const NSInteger SQRLCodeSignatureErrorDidNotPass;
+
+// A static code object could not be created for the target bundle or running
+// code.
+extern const NSInteger SQRLCodeSignatureErrorCouldNotCreateStaticCode;
+
@class RACSignal;

 // Implements the verification of Apple code signatures.
@@ -10,7 +10,11 @@
 #import <ReactiveCocoa/EXTScope.h>
 #import <ReactiveCocoa/ReactiveCocoa.h>
 #import <Security/Security.h>
-#import "Squirrel-Constants.h"
+
+NSString * const SQRLCodeSignatureErrorDomain = @"SQRLCodeSignatureErrorDomain";
+
+const NSInteger SQRLCodeSignatureErrorDidNotPass = -1;
+const NSInteger SQRLCodeSignatureErrorCouldNotCreateStaticCode = -2;

@interface SQRLCodeSignature ()

@@ -79,7 +83,7 @@
 - (RACSignal *)verifyBundleAtURL:(NSURL *)bundleURL {
 	NSParameterAssert(bundleURL != nil);

-	return [[RACSignal createSignal:^ RACDisposable * (id<RACSubscriber> subscriber) {
+	return [[RACSignal create:^(id<RACSubscriber> subscriber) {
 		SecStaticCodeRef staticCode = NULL;
 		
 		OSStatus result = SecStaticCodeCreateWithPath((__bridge CFURLRef)bundleURL, kSecCSDefaultFlags, &staticCode);
@@ -95,9 +99,11 @@
 			NSString *failureReason = CFBridgingRelease(SecCopyErrorMessageString(result, NULL));
 			if (failureReason != nil) userInfo[NSLocalizedFailureReasonErrorKey] = failureReason;
 			
-			[subscriber sendError:[NSError errorWithDomain:SQRLErrorDomain code:SQRLCodeSignatureErrorCouldNotCreateStaticCode userInfo:userInfo]];
-			return nil;
+			[subscriber sendError:[NSError errorWithDomain:SQRLCodeSignatureErrorDomain code:SQRLCodeSignatureErrorCouldNotCreateStaticCode userInfo:userInfo]];
+			return;
 		}
+
+		if (subscriber.disposable.disposed) return;
 		
 		CFErrorRef validityError = NULL;
 		result = SecStaticCodeCheckValidityWithErrors(staticCode, kSecCSCheckAllArchitectures, (__bridge SecRequirementRef)self.requirement, &validityError);
@@ -114,12 +120,11 @@
 			if (failureReason != nil) userInfo[NSLocalizedFailureReasonErrorKey] = failureReason;
 			if (validityError != NULL) userInfo[NSUnderlyingErrorKey] = (__bridge NSError *)validityError;
 			
-			[subscriber sendError:[NSError errorWithDomain:SQRLErrorDomain code:SQRLCodeSignatureErrorDidNotPass userInfo:userInfo]];
-			return nil;
+			[subscriber sendError:[NSError errorWithDomain:SQRLCodeSignatureErrorDomain code:SQRLCodeSignatureErrorDidNotPass userInfo:userInfo]];
+			return;
 		}
 		
 		[subscriber sendCompleted];
-		return nil;
 	}] setNameWithFormat:@"-verifyCodeSignatureOfBundle: %@", bundleURL];
 }

@@ -26,14 +26,27 @@
 //                 on-disk locations for. This must not be nil.
 - (instancetype)initWithApplicationIdentifier:(NSString *)appIdentifier;

-// Finds or creates an Application Support folder.
+// Finds or creates an Application Support subdirectory for the receiver’s
+// application identifier.
 //
 // Returns a signal which synchronously sends a URL then completes, or errors.
- (RACSignal *)applicationSupportURL;
+@property (readonly, nonatomic) RACSignal *applicationSupportURL;
+
+// Finds or creates a downloads directory to store update downloads in prior to
+// installation. This is an applicationSupportURL subdirectory.
+//
+// Returns a signal which sends a URL then completes, or errors.
+@property (readonly, nonatomic) RACSignal *downloadDirectoryURL;
+
+// Creates a new directory to unpack a downloaded update into prior to
+// installation. This is an applicationSupportURL subdirectory.
+//
+// Returns a signal which sends a URL then completes, or errors.
+- (RACSignal *)createUniqueUpdateDirectoryURL;

 // Determines where archived `SQRLShipItState` should be saved.
 //
 // Returns a signal which synchronously sends a URL then completes, or errors.
- (RACSignal *)shipItStateURL;
+@property (readonly, nonatomic) RACSignal *shipItStateURL;

@end
@@ -8,6 +8,8 @@

 #import "SQRLDirectoryManager.h"
 #import <ReactiveCocoa/ReactiveCocoa.h>
+#import <ReactiveCocoa/EXTScope.h>
+#import "RACSignal+SQRLFileManagerExtensions.h"

@interface SQRLDirectoryManager ()

@@ -53,25 +55,65 @@

 #pragma mark Folder URLs

+ (NSString *)fileSystemNameForIdentifier:(NSString *)identifier {
+	// Periods are problematic in the filesystem because they denote file type.
+	// A directory can become a package which can be undesirable.
+	return [identifier stringByReplacingOccurrencesOfString:@"." withString:@"~"];
+}
+
 - (RACSignal *)applicationSupportURL {
-	return [[RACSignal
+	return [[[[RACSignal
 		defer:^{
 			NSError *error = nil;
-			NSURL *folderURL = [NSFileManager.defaultManager URLForDirectory:NSApplicationSupportDirectory inDomain:NSUserDomainMask appropriateForURL:nil create:YES error:&error];
-			if (folderURL == nil) {
+			NSURL *directoryURL = [NSFileManager.defaultManager URLForDirectory:NSApplicationSupportDirectory inDomain:NSUserDomainMask appropriateForURL:nil create:YES error:&error];
+			if (directoryURL == nil) {
 				return [RACSignal error:error];
 			}

-			folderURL = [folderURL URLByAppendingPathComponent:self.applicationIdentifier];
-			if (![NSFileManager.defaultManager createDirectoryAtURL:folderURL withIntermediateDirectories:YES attributes:nil error:&error]) {
-				return [RACSignal error:error];
-			}
-
-			return [RACSignal return:folderURL];
+			return [RACSignal return:directoryURL];
 		}]
+		map:^ (NSURL *directoryURL) {
+			RACSignal *identifierComponents = [@[ self.applicationIdentifier, @"com.github.Squirrel" ].rac_signal
+				map:^(NSString *name) {
+					return [self.class fileSystemNameForIdentifier:name];
+				}];
+
+			RACSignal *pathComponents = [directoryURL.pathComponents.rac_signal concat:identifierComponents];
+			return [NSURL fileURLWithPathComponents:[pathComponents array]];
+		}]
+		sqrl_tryCreateDirectory]
 		setNameWithFormat:@"%@ -applicationSupportURL", self];
 }

+- (RACSignal *)downloadDirectoryURL {
+	return [[[[self
+		applicationSupportURL]
+		map:^(NSURL *directoryURL) {
+			return [directoryURL URLByAppendingPathComponent:@"downloads"];
+		}]
+		sqrl_tryCreateDirectory]
+		setNameWithFormat:@"%@ -downloadDirectoryURL", self];
+}
+
+- (RACSignal *)createUniqueUpdateDirectoryURL {
+	return [[[[self
+		applicationSupportURL]
+		map:^(NSURL *directoryURL) {
+			// noindex so that Spotlight doesn't pick up apps pending update and
+			// add them to the Launch Services database.
+			return [[directoryURL URLByAppendingPathComponent:NSProcessInfo.processInfo.globallyUniqueString] URLByAppendingPathExtension:@"noindex"];
+		}]
+		try:^(NSURL *directoryURL, NSError **errorRef) {
+			// Explicitly just provide the owner with permission, discarding the
+			// current umask. This matches the `mkdtemp` behaviour.
+			NSDictionary *directoryAttributes = @{
+				NSFilePosixPermissions: @(S_IRWXU),
+			};
+			return [NSFileManager.defaultManager createDirectoryAtURL:directoryURL withIntermediateDirectories:YES attributes:directoryAttributes error:errorRef];
+		}]
+		setNameWithFormat:@"%@ -createUniqueUpdateDirectoryURL", self];
+}
+
 - (RACSignal *)shipItStateURL {
 	return [[[self
 		applicationSupportURL]
@@ -0,0 +1,21 @@
+//
+//  SQRLDownload+Private.h
+//  Squirrel
+//
+//  Created by Keith Duncan on 21/01/2014.
+//  Copyright (c) 2014 GitHub. All rights reserved.
+//
+
+#import "SQRLDownload.h"
+
+@interface SQRLDownload ()
+
+// Designated initialiser.
+//
+// request - Must not be nil. The request this download is for.
+// fileURL - Must not be nil. The file location to save received data to.
+//
+// Returns an initialised download suitable for saving response data.
+- (instancetype)initWithRequest:(NSURLRequest *)request fileURL:(NSURL *)fileURL;
+
+@end
@@ -0,0 +1,31 @@
+//
+//  SQRLDownload.h
+//  Squirrel
+//
+//  Created by Keith Duncan on 21/11/2013.
+//  Copyright (c) 2013 GitHub. All rights reserved.
+//
+
+#import <Mantle/Mantle.h>
+
+@class RACSignal;
+
+// A download is a file which holds the response body for a request and can be
+// resumed by a subsequent request if the initial transfer is interrupted.
+//
+// Don't create a download directly, instead retrieve one from
+// `SQRLDownloadManager`.
+@interface SQRLDownload : MTLModel
+
+// The `request` the receiver was initialised with.
+@property (readonly, copy, nonatomic) NSURLRequest *request;
+
+// The `fileURL` the receiver was initialised with.
+@property (readonly, copy, nonatomic) NSURL *fileURL;
+
+// Calculate a request suitable for resuming the download.
+//
+// Returns a signal which sends an `NSURLRequest` then completes.
+@property (readonly, nonatomic) RACSignal *resumableRequest;
+
+@end
@@ -0,0 +1,29 @@
+//
+//  SQRLDownload.m
+//  Squirrel
+//
+//  Created by Keith Duncan on 21/11/2013.
+//  Copyright (c) 2013 GitHub. All rights reserved.
+//
+
+#import "SQRLDownload.h"
+#import "SQRLDownload+Private.h"
+
+#import <ReactiveCocoa/ReactiveCocoa.h>
+
+@implementation SQRLDownload
+
+- (instancetype)initWithRequest:(NSURLRequest *)request fileURL:(NSURL *)fileURL {
+	return [self initWithDictionary:@{
+		@keypath(self.request): request,
+		@keypath(self.fileURL): fileURL,
+	} error:NULL];
+}
+
+- (RACSignal *)resumableRequest {
+	return [[RACSignal
+		return:self.request]
+		setNameWithFormat:@"%@ %s", self, sel_getName(_cmd)];
+}
+
+@end
@@ -0,0 +1,61 @@
+//
+//  SQRLDownloadController.h
+//  Squirrel
+//
+//  Created by Keith Duncan on 26/09/2013.
+//  Copyright (c) 2013 GitHub. All rights reserved.
+//
+
+#import <Foundation/Foundation.h>
+
+@class SQRLDownload;
+@class SQRLResumableDownload;
+@class RACSignal;
+@class SQRLDirectoryManager;
+
+// Stores metadata for download resumption, and manages the disk locations for
+// where they're stored.
+@interface SQRLDownloadManager : NSObject
+
+// Default download manager, initializes a download manager with the current
+// application directory manager. Stores downloads in
+// `directoryManager.downloadDirectoryURL`.
+ (instancetype)defaultDownloadManager;
+
+// Designated initialiser.
+//
+// directoryManager - Must not be nil.
+//
+// Returns a download manager which can resume previously started downloads for
+// the initialised directory manager's application.
+- (instancetype)initWithDirectoryManager:(SQRLDirectoryManager *)directoryManager;
+
+// Clean the resumable download state, removes downloaded data and tracking
+// state.
+//
+// Returns a signal which errors or completes when all file operations have been
+// attempted.
+- (RACSignal *)removeAllResumableDownloads;
+
+// Retrieve a previously started download, or initialise a new download.
+//
+// Previously started downloads may have been removed and require
+// reinitialising.
+//
+// request - The request you are performing and require a disk location to save
+//           the response body to. Must not be nil.
+//
+// Returns a signal which sends an `SQRLDownload` object then completes, or
+// errors.
+- (RACSignal *)downloadForRequest:(NSURLRequest *)request;
+
+// Store metadata for a download so that it can be resumed later.
+//
+// download - The download being stored for future resumption. Must not be nil.
+// request  - The request for which the download can be resumed. Must not be
+//            nil.
+//
+// Returns a signal which completes or errors.
+- (RACSignal *)setDownload:(SQRLResumableDownload *)download forRequest:(NSURLRequest *)request;
+
+@end
@@ -0,0 +1,239 @@
+//
+//  SQRLDownloadController.m
+//  Squirrel
+//
+//  Created by Keith Duncan on 26/09/2013.
+//  Copyright (c) 2013 GitHub. All rights reserved.
+//
+
+#import "SQRLDownloadManager.h"
+
+#import <ReactiveCocoa/ReactiveCocoa.h>
+
+#import "SQRLDirectoryManager.h"
+#import "SQRLDownload.h"
+#import "SQRLDownload+Private.h"
+#import "SQRLResumableDownload.h"
+
+#import "NSData+SQRLExtensions.h"
+
+@interface SQRLDownloadManager ()
+@property (nonatomic, strong, readonly) SQRLDirectoryManager *directoryManager;
+@property (nonatomic, assign, readonly) dispatch_queue_t queue;
+
+// Reads the download index.
+//
+// Returns a signal which sends the download index at time of read then
+// completes, or errors.
+- (RACSignal *)readDownloadIndex;
+
+// Write a new download index.
+//
+// block - Map from the old download index to the new download index. Writing
+//         is serialised, subsequent writers will receive the output of the
+//         previous map block. If the output of the map is equal to the input
+//         no write is attempted and the returned signal completes.
+//
+// Returns a signal which completes or errors.
+- (RACSignal *)writeDownloadIndexWithBlock:(NSDictionary * (^)(NSMutableDictionary *))block;
+@end
+
+@implementation SQRLDownloadManager
+
+ (instancetype)defaultDownloadManager {
+	static SQRLDownloadManager *defaultDownloadManager;
+	static dispatch_once_t defaultDownloadManagerPredicate;
+
+	dispatch_once(&defaultDownloadManagerPredicate, ^{
+		defaultDownloadManager = [[self alloc] initWithDirectoryManager:SQRLDirectoryManager.currentApplicationManager];
+	});
+
+	return defaultDownloadManager;
+}
+
+- (id)initWithDirectoryManager:(SQRLDirectoryManager *)directoryManager {
+	NSParameterAssert(directoryManager != nil);
+
+	self = [super init];
+	if (self == nil) return nil;
+
+	_directoryManager = directoryManager;
+
+	_queue = dispatch_queue_create("com.github.Squirrel.SQRLDownloadManager.queue", DISPATCH_QUEUE_CONCURRENT);
+	dispatch_set_target_queue(_queue, dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0));
+
+	return self;
+}
+
+- (void)dealloc {
+	if (_queue != NULL) dispatch_release(_queue);
+}
+
+- (RACSignal *)removeAllResumableDownloads {
+	return [[[RACSignal
+		merge:@[
+			[self downloadStoreIndexFileLocation],
+			[self.directoryManager downloadDirectoryURL]
+		]]
+		flattenMap:^ (NSURL *location) {
+			return [[RACSignal
+				defer:^{
+					NSError *error;
+					BOOL remove = [NSFileManager.defaultManager removeItemAtURL:location error:&error];
+					return (remove ? [RACSignal empty] : [RACSignal error:error]);
+				}]
+				catch:^(NSError *error) {
+					if ([error.domain isEqualToString:NSCocoaErrorDomain] && error.code == NSFileNoSuchFileError) return [RACSignal empty];
+					return [RACSignal error:error];
+				}];
+		}]
+		setNameWithFormat:@"%@ %s", self, sel_getName(_cmd)];
+}
+
+- (RACSignal *)downloadStoreIndexFileLocation {
+	return [[[self.directoryManager
+		applicationSupportURL]
+		map:^(NSURL *directory) {
+			return [directory URLByAppendingPathComponent:@"DownloadIndex.plist"];
+		}]
+		setNameWithFormat:@"%@ %s", self, sel_getName(_cmd)];
+}
+
+- (RACSignal *)readDownloadIndex {
+	return [[[self
+		downloadStoreIndexFileLocation]
+		flattenMap:^(NSURL *location) {
+			return [RACSignal
+				create:^(id<RACSubscriber> subscriber) {
+					dispatch_async(self.queue, ^{
+						if (subscriber.disposable.disposed) return;
+
+						NSError *error;
+						NSDictionary *propertyList = [self readPropertyListWithContentsOfURL:location error:&error];
+						if (propertyList == nil) {
+							[subscriber sendError:error];
+							return;
+						}
+
+						[subscriber sendNext:propertyList];
+						[subscriber sendCompleted];
+					});
+				}];
+		}]
+		setNameWithFormat:@"%@ %s", self, sel_getName(_cmd)];
+}
+
+- (RACSignal *)writeDownloadIndexWithBlock:(NSDictionary * (^)(NSMutableDictionary *))block {
+	NSParameterAssert(block != nil);
+
+	return [[[self
+		downloadStoreIndexFileLocation]
+		flattenMap:^(NSURL *location) {
+			return [RACSignal create:^(id<RACSubscriber> subscriber) {
+				dispatch_barrier_async(self.queue, ^{
+					if (subscriber.disposable.disposed) return;
+
+					NSError *error;
+					NSDictionary *propertyList = [self readPropertyListWithContentsOfURL:location error:&error];
+					if (propertyList == nil) {
+						[subscriber sendError:error];
+						return;
+					}
+
+					NSDictionary *newPropertyList = block([propertyList mutableCopy]);
+					if ([newPropertyList isEqual:propertyList]) {
+						[subscriber sendCompleted];
+						return;
+					}
+
+					NSData *newData = [NSKeyedArchiver archivedDataWithRootObject:newPropertyList];
+					if (newData == nil) {
+						NSDictionary *errorInfo = @{ NSURLErrorKey: location };
+						[subscriber sendError:[NSError errorWithDomain:NSCocoaErrorDomain code:NSPropertyListWriteStreamError userInfo:errorInfo]];
+						return;
+					}
+
+					BOOL write = [newData writeToURL:location options:NSDataWritingAtomic error:&error];
+					if (!write) {
+						[subscriber sendError:error];
+						return;
+					}
+
+					[subscriber sendCompleted];
+				});
+			}];
+		}]
+		setNameWithFormat:@"%@ %s", self, sel_getName(_cmd)];
+}
+
+- (NSDictionary *)readPropertyListWithContentsOfURL:(NSURL *)location error:(NSError **)errorRef {
+	NSData *propertyListData = [NSData dataWithContentsOfURL:location options:NSDataReadingUncached error:NULL];
+	if (propertyListData == nil) {
+		return @{};
+	}
+
+	NSDictionary *propertyList = [NSKeyedUnarchiver unarchiveObjectWithData:propertyListData];
+	if (propertyList == nil) {
+		if (errorRef != NULL) {
+			NSDictionary *errorInfo = @{ NSURLErrorKey: location };
+			*errorRef = [NSError errorWithDomain:NSCocoaErrorDomain code:NSPropertyListReadCorruptError userInfo:errorInfo];
+		}
+		return nil;
+	}
+
+	return propertyList;
+}
+
+ (NSString *)keyForURL:(NSURL *)URL {
+	return URL.absoluteString;
+}
+
+ (NSString *)fileNameForURL:(NSURL *)URL {
+	NSString *key = [self keyForURL:URL];
+	return [[[key dataUsingEncoding:NSUTF8StringEncoding] sqrl_SHA1Hash] sqrl_base16String];
+}
+
+- (RACSignal *)downloadForRequest:(NSURLRequest *)request {
+	NSParameterAssert(request != nil);
+
+	return [[[[self
+		readDownloadIndex]
+		map:^(NSDictionary *index) {
+			NSString *key = [self.class keyForURL:request.URL];
+			return index[key];
+		}]
+		flattenMap:^(SQRLResumableDownload *download) {
+			if (download != nil) return [RACSignal return:download];
+
+			return [[[self.directoryManager
+				downloadDirectoryURL]
+				map:^(NSURL *downloadDirectory) {
+					return [downloadDirectory URLByAppendingPathComponent:[self.class fileNameForURL:request.URL]];
+				}]
+				map:^(NSURL *location) {
+					return [[SQRLDownload alloc] initWithRequest:request fileURL:location];
+				}];
+		}]
+		setNameWithFormat:@"%@ %s", self, sel_getName(_cmd)];
+}
+
+- (RACSignal *)setDownload:(SQRLResumableDownload *)download forRequest:(NSURLRequest *)request {
+	NSParameterAssert(download.response != nil);
+	NSParameterAssert(request != nil);
+
+	return [[self
+		writeDownloadIndexWithBlock:^(NSMutableDictionary *index) {
+			NSString *key = [self.class keyForURL:request.URL];
+
+			if (download != nil) {
+				index[key] = download;
+			} else {
+				[index removeObjectForKey:key];
+			}
+
+			return index;
+		}]
+		setNameWithFormat:@"%@ %s", self, sel_getName(_cmd)];
+}
+
+@end
@@ -11,7 +11,7 @@
@class SQRLUpdate;

 // A SQRLUpdate that has been successfully downloaded to disk.
-@interface SQRLDownloadedUpdate : MTLModel
+@interface SQRLDownloadedUpdate : MTLModel <MTLJSONSerializing>

 // The application bundle representing the downloaded and unarchived update.
@property (nonatomic, strong, readonly) NSBundle *bundle;
@@ -7,6 +7,7 @@
 //

 #import "SQRLDownloadedUpdate.h"
+#import "SQRLUpdate.h"
 #import <ReactiveCocoa/ReactiveCocoa.h>

@interface SQRLDownloadedUpdate ()
@@ -40,9 +41,15 @@
 #pragma mark MTLJSONSerializing

 + (NSDictionary *)JSONKeyPathsByPropertyKey {
-	return [super.JSONKeyPathsByPropertyKey mtl_dictionaryByAddingEntriesFromDictionary:@{
-		@keypath(SQRLDownloadedUpdate.new, bundleURL): NSNull.null
-	}];
+	return @{};
+}
+
+ (NSValueTransformer *)updateJSONTransformer {
+	return [MTLValueTransformer mtl_JSONDictionaryTransformerWithModelClass:SQRLUpdate.class];
+}
+
+ (NSValueTransformer *)bundleURLJSONTransformer {
+	return [NSValueTransformer valueTransformerForName:MTLURLValueTransformerName];
 }

@end
@@ -8,6 +8,9 @@

 #import <Foundation/Foundation.h>

+// The domain for errors originating within SQRLInstaller.
+extern NSString * const SQRLInstallerErrorDomain;
+
 // There was an error copying the target bundle to the backup location.
 extern const NSInteger SQRLInstallerErrorBackupFailed;

@@ -31,7 +34,9 @@ extern const NSInteger SQRLInstallerErrorInvalidState;
 // There was an error moving a bundle across volumes.
 extern const NSInteger SQRLInstallerErrorMovingAcrossVolumes;

-@class RACCommand;
+@class RACSignal;
+@class RACAction;
+@class SQRLShipItState;
@class SQRLDirectoryManager;

 // Performs the installation of an update, using the `SQRLShipItState` on disk,
@@ -41,21 +46,20 @@ extern const NSInteger SQRLInstallerErrorMovingAcrossVolumes;
 // terminated.
@interface SQRLInstaller : NSObject

-// When executed with a `SQRLShipItState`, attempts to install the update or
-// resume an in-progress installation.
+// Attempts to install the update or resume an in-progress installation.
 //
-// Each execution will complete or error on an unspecified scheduler when
+// Returns a signal which completes or errors on an unspecified scheduler when
 // installation has completed or failed.
-@property (nonatomic, strong, readonly) RACCommand *installUpdateCommand;
+- (RACSignal *)installUpdateWithState:(SQRLShipItState *)state;

-// When executed with a `SQRLShipItState`, aborts an installation, and attempts
-// to restore the old version of the application if necessary.
+// Aborts an installation, and attempts to restore the old version of the
+// application if necessary.
 //
-// This must not be executed while `installUpdateCommand` is executing.
+// This must not be executed while `installUpdateWithState:` is executing.
 //
-// Each execution will complete or error on an unspecified scheduler once
+// Returns a signal while completes or errors on an unspecified scheduler once
 // aborting/recovery has finished.
-@property (nonatomic, strong, readonly) RACCommand *abortInstallationCommand;
+- (RACSignal *)abortInstallationWithState:(SQRLShipItState *)state;

 // Initializes an installer using the given directory manager to read and write the
 // state of the installation.
@@ -18,7 +18,8 @@
 #import <ReactiveCocoa/EXTScope.h>
 #import <ReactiveCocoa/ReactiveCocoa.h>
 #import <sys/xattr.h>
-#import "Squirrel-Constants.h"
+
+NSString * const SQRLInstallerErrorDomain = @"SQRLInstallerErrorDomain";

 const NSInteger SQRLInstallerErrorBackupFailed = -1;
 const NSInteger SQRLInstallerErrorReplacingTarget = -2;
@@ -144,44 +145,34 @@ typedef struct {
 	if (self == nil) return nil;

 	_directoryManager = directoryManager;
-
-	@weakify(self);
-
-	RACSignal *aborting = [[[[RACObserve(self, abortInstallationCommand)
-		ignore:nil]
-		map:^(RACCommand *command) {
-			return command.executing;
-		}]
-		switchToLatest]
-		setNameWithFormat:@"aborting"];
-
-	_installUpdateCommand = [[RACCommand alloc] initWithEnabled:[aborting not] signalBlock:^(SQRLShipItState *state) {
-		@strongify(self);
-		NSParameterAssert(state != nil);
-
-		return [[self
-			resumeInstallationFromState:state]
-			sqrl_addTransactionWithName:NSLocalizedString(@"Updating", nil) description:NSLocalizedString(@"%@ is being updated, and interrupting the process could corrupt the application", nil), state.targetBundleURL.path];
-	}];
-
-	_abortInstallationCommand = [[RACCommand alloc] initWithEnabled:[self.installUpdateCommand.executing not] signalBlock:^(SQRLShipItState *state) {
-		@strongify(self);
-		NSParameterAssert(state != nil);
-
-		return [[[RACSignal
-			zip:@[
-				[self getRequiredKey:@keypath(state.targetBundleURL) fromState:state],
-				[self getRequiredKey:@keypath(state.codeSignature) fromState:state]
-			] reduce:^(NSURL *targetBundleURL, SQRLCodeSignature *codeSignature) {
-				return [self verifyBundleAtURL:targetBundleURL usingSignature:codeSignature recoveringUsingBackupAtURL:state.backupBundleURL];
-			}]
-			flatten]
-			sqrl_addTransactionWithName:NSLocalizedString(@"Aborting update", nil) description:NSLocalizedString(@"An update to %@ is being rolled back, and interrupting the process could corrupt the application", nil), state.targetBundleURL.path];
-	}];
 	
 	return self;
 }

+#pragma mark Actions
+
+- (RACSignal *)installUpdateWithState:(SQRLShipItState *)state {
+	NSParameterAssert(state != nil);
+
+	return [[self
+		resumeInstallationFromState:state]
+		sqrl_addTransactionWithName:NSLocalizedString(@"Updating", nil) description:NSLocalizedString(@"%@ is being updated, and interrupting the process could corrupt the application", nil), state.targetBundleURL.path];
+}
+
+- (RACSignal *)abortInstallationWithState:(SQRLShipItState *)state {
+	NSParameterAssert(state != nil);
+
+	return [[[RACSignal
+		zip:@[
+			[self getRequiredKey:@keypath(state.targetBundleURL) fromState:state],
+			[self getRequiredKey:@keypath(state.codeSignature) fromState:state]
+		] reduce:^(NSURL *targetBundleURL, SQRLCodeSignature *codeSignature) {
+			return [self verifyBundleAtURL:targetBundleURL usingSignature:codeSignature recoveringUsingBackupAtURL:state.backupBundleURL];
+		}]
+		flatten]
+		sqrl_addTransactionWithName:NSLocalizedString(@"Aborting update", nil) description:NSLocalizedString(@"An update to %@ is being rolled back, and interrupting the process could corrupt the application", nil), state.targetBundleURL.path];
+}
+
 #pragma mark Installer State

 - (RACSignal *)getRequiredKey:(NSString *)key fromState:(SQRLShipItState *)state {
@@ -210,7 +201,6 @@ typedef struct {
 		{ .installerState = SQRLInstallerStateBackingUp, .selector = @selector(backUpWithState:) },
 		{ .installerState = SQRLInstallerStateInstalling, .selector = @selector(installWithState:) },
 		{ .installerState = SQRLInstallerStateVerifyingInPlace, .selector = @selector(verifyInPlaceWithState:) },
-		{ .installerState = SQRLInstallerStateRelaunching, .selector = @selector(relaunchWithState:) },
 	};

 	const size_t tableCount = sizeof(dispatchTablePrototype) / sizeof(*dispatchTablePrototype);
@@ -235,7 +225,7 @@ typedef struct {
 				NSLocalizedRecoverySuggestionErrorKey: NSLocalizedString(@"Try installing the update again.", nil)
 			};

-			return [RACSignal error:[NSError errorWithDomain:SQRLErrorDomain code:SQRLInstallerErrorInvalidState userInfo:userInfo]];
+			return [RACSignal error:[NSError errorWithDomain:SQRLInstallerErrorDomain code:SQRLInstallerErrorInvalidState userInfo:userInfo]];
 		}

 		SEL selector = dispatchTable[tableIndex].selector;
@@ -262,13 +252,12 @@ typedef struct {
 			nextState = dispatchTable[tableIndex + 1].installerState;
 		}

-		return [[step
+		return [[[step
 			doCompleted:^{
 				NSLog(@"Completed state %i", (int)installerState);
 			}]
-			then:^{
-				return [RACSignal return:@(nextState)];
-			}];
+			ignoreValues]
+			concat:[RACSignal return:@(nextState)]];
 	}];

 	return [[self
@@ -365,11 +354,9 @@ typedef struct {
 					// failure. Try recovering it if it did.
 					return [[self
 						verifyBundleAtURL:targetBundleURL usingSignature:codeSignature recoveringUsingBackupAtURL:backupBundleURL]
-						then:^{
-							// Recovery succeeded, but we still want to pass
-							// through the original error.
-							return [RACSignal error:error];
-						}];
+						// Recovery succeeded, but we still want to pass
+						// through the original error.
+						concat:[RACSignal error:error]];
 				}];
 		}]
 		flatten]
@@ -387,37 +374,14 @@ typedef struct {
 		] reduce:^(NSURL *targetBundleURL, NSURL *backupBundleURL, SQRLCodeSignature *codeSignature) {
 			return [[self
 				verifyBundleAtURL:targetBundleURL usingSignature:codeSignature recoveringUsingBackupAtURL:backupBundleURL]
-				then:^{
-					return [[self
-						deleteBackupAtURL:backupBundleURL]
-						catchTo:[RACSignal empty]];
-				}];
+				concat:[[self
+					deleteBackupAtURL:backupBundleURL]
+					catchTo:[RACSignal empty]]];
 		}]
 		flatten]
 		setNameWithFormat:@"%@ -verifyInPlaceWithState: %@", self, state];
 }

- (RACSignal *)relaunchWithState:(SQRLShipItState *)state {
-	return [[[[RACSignal
-		defer:^{
-			if (state.relaunchAfterInstallation) {
-				return [self getRequiredKey:@keypath(state.targetBundleURL) fromState:state];
-			} else {
-				return [RACSignal empty];
-			}
-		}]
-		deliverOn:RACScheduler.mainThreadScheduler]
-		flattenMap:^(NSURL *bundleURL) {
-			NSError *error = nil;
-			if ([NSWorkspace.sharedWorkspace launchApplicationAtURL:bundleURL options:NSWorkspaceLaunchDefault configuration:nil error:&error]) {
-				return [RACSignal empty];
-			} else {
-				return [RACSignal error:error];
-			}
-		}]
-		setNameWithFormat:@"%@ -relaunch", self];
-}
-
 #pragma mark Backing Up

 - (RACSignal *)backUpBundleAtURL:(NSURL *)targetBundleURL {
@@ -459,26 +423,23 @@ typedef struct {
 - (RACSignal *)deleteBackupAtURL:(NSURL *)backupURL {
 	NSParameterAssert(backupURL != nil);

-	return [[[RACSignal
+	return [[RACSignal
 		defer:^{
 			NSError *error = nil;
-			if ([NSFileManager.defaultManager removeItemAtURL:backupURL error:&error]) {
-				return [RACSignal empty];
-			} else {
+			if (![NSFileManager.defaultManager removeItemAtURL:backupURL error:&error]) {
 				return [RACSignal error:error];
 			}
-		}]
-		then:^{
+
 			// Also remove the temporary directory that the backup lived in.
 			NSURL *temporaryDirectoryURL = backupURL.URLByDeletingLastPathComponent;

 			// However, use rmdir() to skip it in case there are other files
 			// contained within (for whatever reason).
-			if (rmdir(temporaryDirectoryURL.path.fileSystemRepresentation) == 0) {
-				return [RACSignal empty];
-			} else {
+			if (rmdir(temporaryDirectoryURL.path.fileSystemRepresentation) != 0) {
 				return [RACSignal error:[NSError errorWithDomain:NSPOSIXErrorDomain code:errno userInfo:nil]];
 			}
+
+			return [RACSignal empty];
 		}]
 		setNameWithFormat:@"%@ -deleteBackupAtURL: %@", self, backupURL];
 }
@@ -492,10 +453,11 @@ typedef struct {
 		catch:^(NSError *error) {
 			if (backupBundleURL == nil) return [RACSignal error:error];

-			return [[[[self
-				installItemAtURL:bundleURL fromURL:backupBundleURL]
-				initially:^{
+			return [[[RACSignal
+				defer:^{
 					[NSFileManager.defaultManager removeItemAtURL:bundleURL error:NULL];
+
+					return [self installItemAtURL:bundleURL fromURL:backupBundleURL];
 				}]
 				doCompleted:^{
 					NSLog(@"Restored backup bundle to %@", bundleURL);
@@ -516,9 +478,7 @@ typedef struct {

 	return [[[[self
 		verifyBundleAtURL:targetURL usingSignature:signature recoveringUsingBackupAtURL:nil]
-		then:^{
-			return [RACSignal return:@YES];
-		}]
+		concat:[RACSignal return:@YES]]
 		catch:^(NSError *error) {
 			BOOL directory;
 			if ([NSFileManager.defaultManager fileExistsAtPath:sourceURL.path isDirectory:&directory]) {
@@ -584,7 +544,7 @@ typedef struct {
 				return YES;
 			}];

-			return enumerator.rac_sequence.signal;
+			return [enumerator.rac_promise start];
 		}]
 		flattenMap:^(NSURL *URL) {
 			const char *path = URL.path.fileSystemRepresentation;
@@ -618,7 +578,7 @@ typedef struct {
 		NSLocalizedRecoverySuggestionErrorKey: NSLocalizedString(@"Try installing the update again.", nil)
 	};

-	return [NSError errorWithDomain:SQRLErrorDomain code:SQRLInstallerErrorMissingInstallationData userInfo:userInfo];
+	return [NSError errorWithDomain:SQRLInstallerErrorDomain code:SQRLInstallerErrorMissingInstallationData userInfo:userInfo];
 }

 - (NSError *)errorByAddingDescription:(NSString *)description code:(NSInteger)code toError:(NSError *)error {
@@ -627,7 +587,7 @@ typedef struct {
 	if (description != nil) userInfo[NSLocalizedDescriptionKey] = description;
 	if (error != nil) userInfo[NSUnderlyingErrorKey] = error;

-	return [NSError errorWithDomain:SQRLErrorDomain code:code userInfo:userInfo];
+	return [NSError errorWithDomain:SQRLInstallerErrorDomain code:code userInfo:userInfo];
 }

@end
@@ -0,0 +1,27 @@
+//
+//  SQRLResumableDownload.h
+//  Squirrel
+//
+//  Created by Keith Duncan on 30/09/2013.
+//  Copyright (c) 2013 GitHub. All rights reserved.
+//
+
+#import <Foundation/Foundation.h>
+
+#import "SQRLDownload.h"
+
+// A download which has already been started and already has partial data.
+@interface SQRLResumableDownload : SQRLDownload
+
+// Designated initialiser.
+//
+// request  - See `SQRLDownload`.
+// response - HTTP response whose body is being downloaded to `fileURL`.
+//            Must not be nil.
+// fileURL  - See `SQRLDownload`.
+- (instancetype)initWithRequest:(NSURLRequest *)request response:(NSHTTPURLResponse *)response fileURL:(NSURL *)fileURL;
+
+// The `response` the receiver was initialised with.
+@property (readonly, copy, nonatomic) NSHTTPURLResponse *response;
+
+@end
@@ -0,0 +1,66 @@
+//
+//  SQRLResumableDownload.m
+//  Squirrel
+//
+//  Created by Keith Duncan on 30/09/2013.
+//  Copyright (c) 2013 GitHub. All rights reserved.
+//
+
+#import "SQRLResumableDownload.h"
+
+#import <ReactiveCocoa/ReactiveCocoa.h>
+
+#import "NSHTTPURLResponse+SQRLExtensions.h"
+
+@implementation SQRLResumableDownload
+
+- (instancetype)initWithRequest:(NSURLRequest *)request response:(NSHTTPURLResponse *)response fileURL:(NSURL *)fileURL {
+	NSParameterAssert(request != nil);
+	NSParameterAssert(response != nil);
+	NSParameterAssert(fileURL != nil);
+
+	return [self initWithDictionary:@{
+		@keypath(self.request): request,
+		@keypath(self.response): response,
+		@keypath(self.fileURL): fileURL,
+	} error:NULL];
+}
+
+- (BOOL)isEqual:(SQRLResumableDownload *)object {
+	if (self == object) return YES;
+	if (![object isKindOfClass:self.class]) return NO;
+
+	if (!(self.response == nil && object.response == nil) && ![self responseEqual:object.response]) return NO;
+	if (![object.fileURL isEqual:self.fileURL]) return NO;
+
+	return YES;
+}
+
+- (BOOL)responseEqual:(NSHTTPURLResponse *)response {
+	if (![response.URL isEqual:self.response.URL]) return NO;
+	if (response.statusCode != self.response.statusCode) return NO;
+	if (![response.allHeaderFields isEqual:self.response.allHeaderFields]) return NO;
+	return YES;
+}
+
+- (RACSignal *)resumableRequest {
+	return [[[super
+		resumableRequest]
+		map:^ NSURLRequest * (NSURLRequest *request) {
+			NSHTTPURLResponse *response = self.response;
+			NSString *ETag = [response sqrl_valueForHTTPHeaderField:@"ETag"];
+			if (ETag == nil) return request;
+
+			NSNumber *alreadyDownloadedSize = nil;
+			BOOL getAlreadyDownloadedSize = [self.fileURL getResourceValue:&alreadyDownloadedSize forKey:NSURLFileSizeKey error:NULL];
+			if (!getAlreadyDownloadedSize) return request;
+
+			NSMutableURLRequest *newRequest = [request mutableCopy];
+			[newRequest setValue:ETag forHTTPHeaderField:@"If-Range"];
+			[newRequest setValue:[NSString stringWithFormat:@"%llu-", alreadyDownloadedSize.unsignedLongLongValue] forHTTPHeaderField:@"Range"];
+			return newRequest;
+		}]
+		setNameWithFormat:@"%@ %s", self, sel_getName(_cmd)];
+}
+
+@end
@@ -10,6 +10,12 @@

@class RACSignal;

+// The domain for errors originating within SQRLShipItLauncher.
+extern NSString * const SQRLShipItLauncherErrorDomain;
+
+// The ShipIt service could not be started.
+extern const NSInteger SQRLShipItLauncherErrorCouldNotStartService;
+
 // Responsible for launching the ShipIt service to actually install an update.
@interface SQRLShipItLauncher : NSObject

@@ -13,7 +13,10 @@
 #import <Security/Security.h>
 #import <ServiceManagement/ServiceManagement.h>
 #import <launch.h>
-#import "Squirrel-Constants.h"
+
+NSString * const SQRLShipItLauncherErrorDomain = @"SQRLShipItLauncherErrorDomain";
+
+const NSInteger SQRLShipItLauncherErrorCouldNotStartService = 1;

@implementation SQRLShipItLauncher

@@ -68,7 +71,7 @@

 + (RACSignal *)shipItAuthorization {
 	return [[RACSignal
-		createSignal:^(id<RACSubscriber> subscriber) {
+		create:^(id<RACSubscriber> subscriber) {
 			AuthorizationItem rightItems[] = {
 				{
 					.name = kSMRightModifySystemDaemons,
@@ -112,9 +115,9 @@
 				[subscriber sendError:[NSError errorWithDomain:NSOSStatusErrorDomain code:authorizationError userInfo:nil]];
 			}

-			return [RACDisposable disposableWithBlock:^{
+			[subscriber.disposable addDisposable:[RACDisposable disposableWithBlock:^{
 				if (authorization != NULL) AuthorizationFree(authorization, kAuthorizationFlagDestroyRights);
-			}];
+			}]];
 		}]
 		setNameWithFormat:@"+shipItAuthorization"];
 }
@@ -129,13 +132,11 @@

 			CFErrorRef cfError;
 			if (!SMJobRemove(domain, (__bridge CFStringRef)self.shipItJobLabel, (__bridge AuthorizationRef)authorization, true, &cfError)) {
-				#if DEBUG
-				NSLog(@"Could not remove previous ShipIt job: %@", cfError);
-				#endif
+				NSError *error = CFBridgingRelease(cfError);
+				cfError = NULL;

-				if (cfError != NULL) {
-					CFRelease(cfError);
-					cfError = NULL;
+				if (![error.domain isEqual:(__bridge id)kSMErrorDomainLaunchd] || error.code != kSMErrorJobNotFound) {
+					NSLog(@"Could not remove previous ShipIt job: %@", error);
 				}
 			}

@@ -8,6 +8,22 @@

 #import <Mantle/Mantle.h>

+// The domain for errors originating within `SQRLShipItState`.
+extern NSString * const SQRLShipItStateErrorDomain;
+
+// A required property was `nil` upon initialization.
+//
+// The `userInfo` dictionary for this error will contain
+// `SQRLShipItStatePropertyErrorKey`.
+extern const NSInteger SQRLShipItStateErrorMissingRequiredProperty;
+
+// The saved state on disk could not be unarchived, possibly because it's
+// invalid.
+extern const NSInteger SQRLShipItStateErrorUnarchiving;
+
+// The state object could not be archived.
+extern const NSInteger SQRLShipItStateErrorArchiving;
+
 // Associated with an NSString indicating the required property key that did not
 // have a value upon initialization.
 extern NSString * const SQRLShipItStatePropertyErrorKey;
@@ -25,9 +41,6 @@ extern NSString * const SQRLShipItStatePropertyErrorKey;
 //                                        update bundle.
 // SQRLInstallerStateVerifyingInPlace   - Verifying that the target bundle is
 //                                        still valid after updating.
-// SQRLInstallerStateRelaunching        - Relaunching the updated application.
-//                                        This state will be entered even if
-//                                        there's no relaunching to do.
 //
 // Note that these values must remain backwards compatible, so ShipIt doesn't
 // start up in a weird mode on a newer version.
@@ -37,7 +50,6 @@ typedef enum : NSInteger {
 	SQRLInstallerStateBackingUp,
 	SQRLInstallerStateInstalling,
 	SQRLInstallerStateVerifyingInPlace,
-	SQRLInstallerStateRelaunching
 } SQRLInstallerState;

@class RACSignal;
@@ -8,10 +8,14 @@

 #import "SQRLShipItState.h"
 #import <ReactiveCocoa/ReactiveCocoa.h>
-#import "Squirrel-Constants.h"

+NSString * const SQRLShipItStateErrorDomain = @"SQRLShipItStateErrorDomain";
 NSString * const SQRLShipItStatePropertyErrorKey = @"SQRLShipItStatePropertyErrorKey";

+const NSInteger SQRLShipItStateErrorMissingRequiredProperty = 1;
+const NSInteger SQRLShipItStateErrorUnarchiving = 2;
+const NSInteger SQRLShipItStateErrorArchiving = 3;
+
@implementation SQRLShipItState

 #pragma mark Lifecycle
@@ -29,7 +33,7 @@ NSString * const SQRLShipItStatePropertyErrorKey = @"SQRLShipItStatePropertyErro
 				NSLocalizedRecoverySuggestionErrorKey: [NSString stringWithFormat:NSLocalizedString(@"\"%@\" must not be set to nil.", nil), key]
 			};

-			*error = [NSError errorWithDomain:SQRLErrorDomain code:SQRLShipItStateErrorMissingRequiredProperty userInfo:userInfo];
+			*error = [NSError errorWithDomain:SQRLShipItStateErrorDomain code:SQRLShipItStateErrorMissingRequiredProperty userInfo:userInfo];
 		}

 		return NO;
@@ -74,7 +78,7 @@ NSString * const SQRLShipItStatePropertyErrorKey = @"SQRLShipItStatePropertyErro
 					NSLocalizedRecoverySuggestionErrorKey: NSLocalizedString(@"An unknown error occurred while unarchiving.", nil)
 				};

-				return [RACSignal error:[NSError errorWithDomain:SQRLErrorDomain code:SQRLShipItStateErrorUnarchiving userInfo:userInfo]];
+				return [RACSignal error:[NSError errorWithDomain:SQRLShipItStateErrorDomain code:SQRLShipItStateErrorUnarchiving userInfo:userInfo]];
 			}

 			return [RACSignal return:state];
@@ -93,7 +97,7 @@ NSString * const SQRLShipItStatePropertyErrorKey = @"SQRLShipItStatePropertyErro
 				NSLocalizedRecoverySuggestionErrorKey: NSLocalizedString(@"An unknown error occurred while archiving.", nil)
 			};

-			return [RACSignal error:[NSError errorWithDomain:SQRLErrorDomain code:SQRLShipItStateErrorArchiving userInfo:userInfo]];
+			return [RACSignal error:[NSError errorWithDomain:SQRLShipItStateErrorDomain code:SQRLShipItStateErrorArchiving userInfo:userInfo]];
 		}

 		return [RACSignal return:data];
@@ -45,7 +45,7 @@
 	return [[[[RACSignal
 		defer:^{
 			NSArray *apps = [NSRunningApplication runningApplicationsWithBundleIdentifier:self.bundleIdentifier];
-			return [apps.rac_sequence signalWithScheduler:RACScheduler.immediateScheduler];
+			return apps.rac_signal;
 		}]
 		filter:^(NSRunningApplication *application) {
 			return [application.bundleURL.URLByStandardizingPath isEqual:self.bundleURL];
@@ -60,7 +60,7 @@

 - (RACSignal *)waitForTerminationOfProcessIdentifier:(pid_t)processIdentifier {
 	return [[RACSignal
-		createSignal:^(id<RACSubscriber> subscriber) {
+		create:^(id<RACSubscriber> subscriber) {
 			dispatch_source_t source = dispatch_source_create(DISPATCH_SOURCE_TYPE_PROC, processIdentifier, DISPATCH_PROC_EXIT, dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0));

 			dispatch_source_set_registration_handler(source, ^{
@@ -72,10 +72,10 @@
 			});

 			dispatch_resume(source);
-			return [RACDisposable disposableWithBlock:^{
+			[subscriber.disposable addDisposable:[RACDisposable disposableWithBlock:^{
 				dispatch_source_cancel(source);
 				dispatch_release(source);
-			}];
+			}]];
 		}]
 		setNameWithFormat:@"%@ -waitForTerminationOfProcessIdentifier: %i", self, (int)processIdentifier];
 }
@@ -0,0 +1,49 @@
+//
+//  SQRLURLConnection.h
+//  Squirrel
+//
+//  Created by Keith Duncan on 25/09/2013.
+//  Copyright (c) 2013 GitHub. All rights reserved.
+//
+
+#import <Foundation/Foundation.h>
+
+@class SQRLDownloadManager;
+@class RACSignal;
+
+// Resumably download a remote resource.
+//
+// If the resource has previously been downloaded this operation may return the
+// URL of an existing file, contingent on the server matching the ETag of the
+// original response.
+@interface SQRLURLConnection : NSObject
+
+// This is the designated initialiser. The body of the response is streamed to
+// disk. If the response includes an ETag the download can be resumed
+// automatically by subsequent download operations initialised with a request of
+// equal URL.
+//
+// request - Must not be nil, the request is issued with NSURLConnection.
+- (instancetype)initWithRequest:(NSURLRequest *)request __attribute__((nonnull (1)));
+
+// Starts accumulating the resource body in memory, cancels when the
+// subscription is disposed.
+//
+// Returns a signal when sends a tuple of `NSURLResponse` and `NSData`, then
+// completes or errors.
+- (RACSignal *)retrieve;
+
+// Starts downloading the resource body to disk, resuming from a previous
+// download if possible, cancels when the subscription is disposed.
+//
+// downloadManager - Must be non nil, determines where the downloads will be
+//                   stored and resumed from. For a previously started download
+//                   to be resumed, an equivalent download manager should be
+//                   provided.
+//
+// Returns a signal which sends a tuple of `NSURLResponse` and a file
+// scheme `NSURL` where the resource has been stored on disk, then completes, or
+// errors.
+- (RACSignal *)download:(SQRLDownloadManager *)downloadManager __attribute__((nonnull (1)));
+
+@end
@@ -0,0 +1,257 @@
+//
+//  SQRLURLConnection.m
+//  Squirrel
+//
+//  Created by Keith Duncan on 25/09/2013.
+//  Copyright (c) 2013 GitHub. All rights reserved.
+//
+
+#import "SQRLURLConnection.h"
+
+#import <ReactiveCocoa/ReactiveCocoa.h>
+#import <ReactiveCocoa/EXTScope.h>
+
+#import "SQRLDownloadManager.h"
+#import "SQRLResumableDownload.h"
+
+@interface SQRLURLConnection ()
+// The request the downloader was initialised with.
+@property (nonatomic, copy, readonly) NSURLRequest *request;
+
+// Listens for invocations of `selector` on the receiver.
+//
+// The first argument of `selector` must be an `NSURLConnection` object.
+//
+// Returns a signal which sends the _second_ argument of `selector`, or
+// RACUnit if there is only one argument, then completes when the receiver
+// deallocates.
+- (RACSignal *)signalForDelegateSelector:(SEL)selector;
+
+// Subscribes to the connection delegate selectors and starts a connection for
+// `request`.
+//
+// request - The request to perform, must not be nil.
+// mapData - For each response, map the data received for that response to a
+//           result.
+//
+// Returns a signal which sends a tuple of the last response, and the first
+// value from the last `mapData`, then completes, or errors.
+- (RACSignal *)connectionSignalWithRequest:(NSURLRequest *)request mapData:(RACSignal * (^)(NSURLResponse *, RACSignal *))mapData;
+
+@end
+
+@implementation SQRLURLConnection
+
+- (instancetype)initWithRequest:(NSURLRequest *)request {
+	NSParameterAssert(request != nil);
+
+	self = [self init];
+	if (self == nil) return nil;
+
+	_request = [request copy];
+
+	return self;
+}
+
+- (RACSignal *)signalForDelegateSelector:(SEL)selector {
+	NSParameterAssert(selector != NULL);
+
+	return [[self
+		rac_signalForSelector:selector]
+		map:^(RACTuple *args) {
+			return args[1] ?: RACUnit.defaultUnit;
+		}];
+}
+
+- (RACSignal *)connectionSignalWithRequest:(NSURLRequest *)request mapData:(RACSignal * (^)(NSURLResponse *, RACSignal *))mapData {
+	return [[RACSignal
+		create:^(id<RACSubscriber> subscriber) {
+			// A signal that will error if the connection fails for any reason.
+			RACSignal *errors = [[self
+				signalForDelegateSelector:@selector(connection:didFailWithError:)]
+				flattenMap:^(NSError *error) {
+					return [RACSignal error:error];
+				}];
+
+			// Sends (or replays) RACUnit when the connection has finished
+			// loading successfully.
+			RACSignal *finished = [[[[self
+				signalForDelegateSelector:@selector(connectionDidFinishLoading:)]
+				take:1]
+				promiseOnScheduler:RACScheduler.immediateScheduler]
+				start];
+
+			// A signal of all `NSURLResponse`s received on the connection.
+			RACSignal *responses = [[self
+				signalForDelegateSelector:@selector(connection:didReceiveResponse:)]
+				takeUntil:finished];
+
+			// A signal of all `NSData` received on the connection.
+			RACSignal *data = [[self
+				signalForDelegateSelector:@selector(connection:didReceiveData:)]
+				takeUntil:finished];
+
+			[[[[[RACSignal
+				merge:@[ responses, errors ]]
+				takeUntil:finished]
+				map:^(NSURLResponse *response) {
+					return [RACSignal
+						zip:@[
+							[RACSignal return:response],
+							mapData(response, data),
+						]];
+				}]
+				switchToLatest]
+				subscribe:subscriber];
+
+			NSOperationQueue *delegateQueue = [[NSOperationQueue alloc] init];
+			delegateQueue.maxConcurrentOperationCount = 1;
+
+			NSURLConnection *connection = [[NSURLConnection alloc] initWithRequest:request delegate:self startImmediately:NO];
+			connection.delegateQueue = delegateQueue;
+
+			[connection start];
+
+			[subscriber.disposable addDisposable:[RACDisposable disposableWithBlock:^{
+				[connection cancel];
+			}]];
+		}]
+		setNameWithFormat:@"%@ %s %@", self, sel_getName(_cmd), request];
+}
+
+#pragma mark Download
+
+- (RACSignal *)truncateDownload:(SQRLDownload *)download {
+	NSParameterAssert(download != nil);
+
+	return [[[[RACSignal
+		defer:^{
+			NSError *error = nil;
+			BOOL remove = [NSFileManager.defaultManager removeItemAtURL:download.fileURL error:&error];
+			return (remove ? [RACSignal empty] : [RACSignal error:error]);
+		}]
+		catch:^(NSError *error) {
+			if ([error.domain isEqualToString:NSCocoaErrorDomain] && error.code == NSFileNoSuchFileError) return [RACSignal empty];
+			return [RACSignal error:error];
+		}]
+		concat:[RACSignal return:download]]
+		setNameWithFormat:@"%@ %s %@", self, sel_getName(_cmd), download];
+}
+
+- (RACSignal *)recordDownload:(SQRLResumableDownload *)download downloadManager:(SQRLDownloadManager *)downloadManager {
+	NSParameterAssert(download != nil);
+	NSParameterAssert(downloadManager != nil);
+
+	return [[[downloadManager
+		setDownload:download forRequest:self.request]
+		concat:[RACSignal return:download]]
+		setNameWithFormat:@"%@ %s %@", self, sel_getName(_cmd), download];
+}
+
+- (RACSignal *)prepareDownload:(SQRLDownload *)download downloadManager:(SQRLDownloadManager *)downloadManager forResponse:(NSURLResponse *)response {
+	return [[RACSignal
+		defer:^{
+			if (![response isKindOfClass:NSHTTPURLResponse.class]) {
+				return [self truncateDownload:download];
+			}
+
+			NSHTTPURLResponse *httpResponse = (id)response;
+
+			RACSignal *downloadSignal;
+			if (httpResponse.statusCode != 206 /* Partial Data */) {
+				downloadSignal = [self truncateDownload:download];
+			} else {
+				downloadSignal = [RACSignal empty];
+			}
+
+			SQRLResumableDownload *newDownload = [[SQRLResumableDownload alloc] initWithRequest:self.request response:httpResponse fileURL:download.fileURL];
+
+			return [[downloadSignal
+				ignoreValues]
+				concat:[self recordDownload:newDownload downloadManager:downloadManager]];
+		}]
+		setNameWithFormat:@"%@ %s %@", self, sel_getName(_cmd), response];
+}
+
+- (BOOL)appendData:(NSData *)data toURL:(NSURL *)fileURL error:(NSError **)errorRef {
+	NSOutputStream *outputStream = [NSOutputStream outputStreamWithURL:fileURL append:YES];
+
+	[outputStream open];
+	@onExit {
+		[outputStream close];
+	};
+
+	uint8_t const *bytes = data.bytes;
+	size_t length = data.length;
+	while (length > 0) {
+		NSInteger written = [outputStream write:bytes maxLength:length];
+		if (written == -1) {
+			NSError *streamError = outputStream.streamError;
+			if ([streamError.domain isEqualToString:NSPOSIXErrorDomain] && streamError.code == EINTR) continue;
+
+			if (errorRef != NULL) *errorRef = streamError;
+			return NO;
+		}
+		
+		bytes += written;
+		length -= written;
+	}
+
+	return YES;
+}
+
+#pragma mark Start
+
+- (RACSignal *)retrieve {
+	return [[self
+		connectionSignalWithRequest:self.request mapData:^(id _, RACSignal *data) {
+			return [data
+				aggregateWithStart:[NSMutableData data] reduce:^(NSMutableData *running, NSData *data) {
+					[running appendData:data];
+					return running;
+				}];
+		}]
+		setNameWithFormat:@"%@ %s", self, sel_getName(_cmd)];
+}
+
+- (RACSignal *)download:(SQRLDownloadManager *)downloadManager {
+	NSParameterAssert(downloadManager != nil);
+
+	RACSignal *download = [[[downloadManager
+		downloadForRequest:self.request]
+		promiseOnScheduler:RACScheduler.immediateScheduler]
+		deferred];
+
+	return [[[download
+		flattenMap:^(SQRLDownload *download) {
+			return [download resumableRequest];
+		}]
+		flattenMap:^(NSURLRequest *request) {
+			return [self connectionSignalWithRequest:request mapData:^(NSURLResponse *response, RACSignal *data) {
+				RACSignal *downloadURL = [[[[download
+					flattenMap:^(SQRLDownload *download) {
+						return [self prepareDownload:download downloadManager:downloadManager forResponse:response];
+					}]
+					map:^(SQRLDownload *download) {
+						return download.fileURL;
+					}]
+					promiseOnScheduler:RACScheduler.immediateScheduler]
+					deferred];
+
+				return [[[[data
+					map:^(NSData *bodyData) {
+						return [[downloadURL
+							try:^(NSURL *fileURL, NSError **errorRef) {
+								return [self appendData:bodyData toURL:fileURL error:errorRef];
+							}]
+							ignoreValues];
+					}]
+					concat]
+					ignoreValues]
+					concat:downloadURL];
+			}];
+		}]
+		setNameWithFormat:@"%@ download: %@", self, downloadManager];
+}
+
+@end
@@ -14,6 +14,8 @@ NSString * const SQRLUpdateJSONReleaseNotesKey = @"notes";
 NSString * const SQRLUpdateJSONNameKey = @"name";
 NSString * const SQRLUpdateJSONPublicationDateKey = @"pub_date";

+NSString * const SQRLUpdateErrorDomain = @"SQRLUpdateErrorDomain";
+
@implementation SQRLUpdate

 #pragma mark Lifecycle
@@ -50,7 +52,7 @@ NSString * const SQRLUpdateJSONPublicationDateKey = @"pub_date";

 			*error = [NSError errorWithDomain:NSCocoaErrorDomain code:NSKeyValueValidationError userInfo:userInfo];
 		}
-		
+
 		return NO;
 	}

@@ -61,10 +63,10 @@ NSString * const SQRLUpdateJSONPublicationDateKey = @"pub_date";

 + (NSDictionary *)JSONKeyPathsByPropertyKey {
 	return @{
-		@keypath(SQRLUpdate.new, releaseNotes): @"notes",
-		@keypath(SQRLUpdate.new, releaseName): @"name",
-		@keypath(SQRLUpdate.new, releaseDate): @"pub_date",
-		@keypath(SQRLUpdate.new, updateURL): @"url",
+		@keypath(SQRLUpdate.new, releaseNotes): SQRLUpdateJSONReleaseNotesKey,
+		@keypath(SQRLUpdate.new, releaseName): SQRLUpdateJSONNameKey,
+		@keypath(SQRLUpdate.new, releaseDate): SQRLUpdateJSONPublicationDateKey,
+		@keypath(SQRLUpdate.new, updateURL): SQRLUpdateJSONURLKey,
 	};
 }

@@ -94,8 +96,8 @@ NSString * const SQRLUpdateJSONPublicationDateKey = @"pub_date";
 		}

 		// If neither match, try removing the ':' in the time zone
-		static NSRegularExpression *timeZoneSuffix = nil;
-		static dispatch_once_t timeZoneSuffixPredicate = 0;
+		static NSRegularExpression *timeZoneSuffix;
+		static dispatch_once_t timeZoneSuffixPredicate;
 		dispatch_once(&timeZoneSuffixPredicate, ^ {
 			timeZoneSuffix = [NSRegularExpression regularExpressionWithPattern:@"([-+])([0-9]{2}):([0-9]{2})$" options:0 error:NULL];
 		});
@@ -134,16 +136,30 @@ NSString * const SQRLUpdateJSONPublicationDateKey = @"pub_date";

 - (BOOL)validateUpdateURL:(NSURL **)updateURLPtr error:(NSError **)error {
 	NSURL *updateURL = *updateURLPtr;
-	if (![updateURL isKindOfClass:NSURL.class] || updateURL.scheme == nil || updateURL.host == nil || updateURL.path == nil) {
+	if (![updateURL isKindOfClass:NSURL.class]) {
 		if (error != NULL) {
 			NSDictionary *userInfo = @{
 				NSLocalizedDescriptionKey: NSLocalizedString(@"Validation failed", nil),
 				NSLocalizedRecoverySuggestionErrorKey: [NSString stringWithFormat:NSLocalizedString(@"An invalid updateURL was given to SQRLUpdate: %@", nil), updateURL]
 			};
-
 			*error = [NSError errorWithDomain:NSCocoaErrorDomain code:NSKeyValueValidationError userInfo:userInfo];
 		}
-		
+
+		return NO;
+	}
+
+	BOOL valid = (updateURL.scheme != nil);
+	valid &= ([updateURL.scheme isEqualToString:@"file"] || updateURL.host != nil);
+	valid &= (updateURL.path != nil);
+	if (!valid) {
+		if (error != NULL) {
+			NSDictionary *userInfo = @{
+				NSLocalizedDescriptionKey: NSLocalizedString(@"Validation failed", nil),
+				NSLocalizedRecoverySuggestionErrorKey: [NSString stringWithFormat:NSLocalizedString(@"Update URLs must have a scheme, a host and a path: %@", nil), updateURL]
+			};
+			*error = [NSError errorWithDomain:NSCocoaErrorDomain code:NSKeyValueValidationError userInfo:userInfo];
+		}
+
 		return NO;
 	}

@@ -6,6 +6,35 @@
 //  Copyright (c) 2013 GitHub. All rights reserved.
 //

+// The domain for errors originating within SQRLUpdater.
+extern NSString * const SQRLUpdaterErrorDomain;
+
+// The downloaded update does not contain an app bundle, or it was deleted on
+// disk before we could get to it.
+extern const NSInteger SQRLUpdaterErrorMissingUpdateBundle;
+
+// An error occurred in the out-of-process updater while it was setting up.
+extern const NSInteger SQRLUpdaterErrorPreparingUpdateJob;
+
+// The code signing requirement for the running application could not be
+// retrieved.
+extern const NSInteger SQRLUpdaterErrorRetrievingCodeSigningRequirement;
+
+// The server sent a response that we didn't understand.
+//
+// Includes `SQRLUpdaterServerDataErrorKey` in the error's `userInfo`.
+extern const NSInteger SQRLUpdaterErrorInvalidServerResponse;
+
+// The server sent a response body that we didn't understand.
+//
+// Includes `SQRLUpdaterServerDataErrorKey` in the error's `userInfo`.
+extern const NSInteger SQRLUpdaterErrorInvalidServerBody;
+
+// The server sent update JSON that we didn't understand.
+//
+// Includes `SQRLUpdaterJSONObjectErrorKey` in the error's `userInfo`.
+extern const NSInteger SQRLUpdaterErrorInvalidJSON;
+
 // Associated with the `NSData` received from the server when an error with code
 // `SQRLUpdaterErrorInvalidServerResponse` is generated.
 extern NSString * const SQRLUpdaterServerDataErrorKey;
@@ -14,7 +43,7 @@ extern NSString * const SQRLUpdaterServerDataErrorKey;
 // error with code `SQRLUpdaterErrorInvalidJSON` is generated.
 extern NSString * const SQRLUpdaterJSONObjectErrorKey;

-@class RACCommand;
+@class RACAction;
@class RACDisposable;
@class RACSignal;

@@ -23,21 +52,14 @@ extern NSString * const SQRLUpdaterJSONObjectErrorKey;

 // Kicks off a check for updates.
 //
-// If an update is available, it will be sent on `updates` once downloaded.
-@property (nonatomic, strong, readonly) RACCommand *checkForUpdatesCommand;
+// If an update is available, it will be sent on
+// `[checkForUpdatesAction deferred]` and `updates` once downloaded.
+@property (nonatomic, strong, readonly) RACAction *checkForUpdatesAction;

 // Sends an `SQRLDownloadedUpdate` object on the main thread whenever a new
-// update is available.
-//
-// This signal is actually just `checkForUpdatesCommand.executionSignals`,
-// flattened for convenience.
+// update is available. Completes when the receiver deallocates.
@property (nonatomic, strong, readonly) RACSignal *updates;

-// Whether or not to relaunch after installing an update.
-//
-// This will be reset to NO whenever update installation fails.
-@property (atomic) BOOL shouldRelaunch;
-
 // The request that will be sent to check for updates.
 //
 // The default value is the argument that was originally passed to
@@ -75,6 +97,21 @@ extern NSString * const SQRLUpdaterJSONObjectErrorKey;
 // checking.
 - (RACDisposable *)startAutomaticChecksWithInterval:(NSTimeInterval)interval;

+// Terminates the running application to install any available update, then
+// automatically relaunches the app after updating.
+//
+// This method is only useful if you want the application to automatically
+// relaunch. Otherwise, you can simply use `-[NSApplication terminate:]` or any
+// other exit mechanism.
+//
+// After invoking this method, the receiver is responsible for terminating the
+// application upon success. The app must not be terminated in any other way
+// unless an error occurs.
+//
+// Returns a signal that will error on the main scheduler if anything goes
+// wrong before termination. The signal will never complete.
+- (RACSignal *)relaunchToInstallUpdate;
+
@end

@interface SQRLUpdater (Unavailable)
@@ -17,16 +17,30 @@
 #import "SQRLShipItLauncher.h"
 #import "SQRLShipItState.h"
 #import "SQRLUpdate.h"
+#import "SQRLDownloadedUpdate.h"
 #import "SQRLZipArchiver.h"
 #import <ReactiveCocoa/EXTScope.h>
 #import <ReactiveCocoa/ReactiveCocoa.h>
-#import "Squirrel-Constants.h"
+#import "SQRLURLConnection.h"
+#import "SQRLURLConnection.h"
+#import "SQRLDownloadManager.h"

+NSString * const SQRLUpdaterErrorDomain = @"SQRLUpdaterErrorDomain";
 NSString * const SQRLUpdaterServerDataErrorKey = @"SQRLUpdaterServerDataErrorKey";
 NSString * const SQRLUpdaterJSONObjectErrorKey = @"SQRLUpdaterJSONObjectErrorKey";

+const NSInteger SQRLUpdaterErrorMissingUpdateBundle = 2;
+const NSInteger SQRLUpdaterErrorPreparingUpdateJob = 3;
+const NSInteger SQRLUpdaterErrorRetrievingCodeSigningRequirement = 4;
+const NSInteger SQRLUpdaterErrorInvalidServerResponse = 5;
+const NSInteger SQRLUpdaterErrorInvalidJSON = 6;
+const NSInteger SQRLUpdaterErrorInvalidServerBody = 7;
+
@interface SQRLUpdater ()

+// The directory manager used for downloads and unpacks.
+@property (nonatomic, strong, readonly) SQRLDirectoryManager *directoryManager;
+
 // The code signature for the running application, used to check updates before
 // sending them to ShipIt.
@property (nonatomic, strong, readonly) SQRLCodeSignature *signature;
@@ -55,22 +69,25 @@ NSString * const SQRLUpdaterJSONObjectErrorKey = @"SQRLUpdaterJSONObjectErrorKey
 // errors, on a background thread.
 - (RACSignal *)downloadAndPrepareUpdate:(SQRLUpdate *)update;

-// Downloads the archived bundle associated with the given update.
+// Downloads the update archive for the given update.
 //
 // update            - Describes the update to install. This must not be nil.
-// downloadDirectory - A directory in which to create a temporary directory for this
-//                     download. This must not be nil.
+// downloadDirectory - A directory in which to create a temporary directory for
+//                     this download. This must not be nil.
 //
-// Returns a signal which sends an unarchived `NSBundle` then completes, or
-// errors, on a background thread.
- (RACSignal *)downloadBundleForUpdate:(SQRLUpdate *)update intoDirectory:(NSURL *)downloadDirectory;
+// Returns a signal which sends an NSURL of the downloaded update archive then
+// completes, or errors, on a background thread.
+- (RACSignal *)downloadArchiveForUpdate:(SQRLUpdate *)update intoDirectory:(NSURL *)downloadDirectory;

-// Creates a unique directory in which to save the update bundle, for later use
-// by ShipIt.
+// Unpacks an update archive.
 //
-// Returns a signal which sends an `NSURL` then completes, or errors, on an
-// unspecified thread.
- (RACSignal *)uniqueTemporaryDirectoryForUpdate;
+// archiveURL   - The location of the update archive, currently only ZIP
+//                archives are supported. Must not be nil.
+// directoryURL - A directory in which to place the unpacked contents of the
+//                archive. Must not be nil.
+//
+// Returns a signal which completes or errors.
+- (RACSignal *)unpackArchiveAtURL:(NSURL *)archiveURL intoDirectory:(NSURL *)directoryURL;

 // Recursively searches the given directory for an application bundle that has
 // the same identifier as the running application.
@@ -103,16 +120,27 @@ NSString * const SQRLUpdaterJSONObjectErrorKey = @"SQRLUpdaterJSONObjectErrorKey
 // Returns a signal which completes or errors on a background thread.
 - (RACSignal *)prepareUpdateForInstallation:(SQRLDownloadedUpdate *)update;

+// Verifies that an existing state is innocuous, and therefore safe to
+// overwrite.
+//
+// This won't be the case if, for example, an update is currently being
+// installed.
+//
+// Returns a signal which sends `existingState` then completes upon successful
+// validation, or errors otherwise.
+- (RACSignal *)validateExistingState:(SQRLShipItState *)existingState;
+
@end

-@implementation SQRLUpdater
+@implementation SQRLUpdater {
+	RACSubject *_updates;
+}

 #pragma mark Properties

 - (RACSignal *)updates {
-	return [[self.checkForUpdatesCommand.executionSignals
-		concat]
-		setNameWithFormat:@"%@ -updates", self];
+	return [_updates
+		deliverOn:RACScheduler.mainThreadScheduler];
 }

 #pragma mark Lifecycle
@@ -131,39 +159,29 @@ NSString * const SQRLUpdaterJSONObjectErrorKey = @"SQRLUpdaterJSONObjectErrorKey
 	_updateRequest = [updateRequest copy];
 	_updateClass = SQRLUpdate.class;

+	_directoryManager = SQRLDirectoryManager.currentApplicationManager;
+
 	NSError *error = nil;
 	_signature = [SQRLCodeSignature currentApplicationSignature:&error];
 	NSAssert(_signature != nil, @"Could not get code signature for running application: %@", error);

-	BOOL updatesDisabled = (getenv("DISABLE_UPDATE_CHECK") != NULL);
-
 	@weakify(self);
-	_checkForUpdatesCommand = [[RACCommand alloc] initWithEnabled:[RACSignal return:@(!updatesDisabled)] signalBlock:^(id _) {
-		@strongify(self);
-		NSParameterAssert(self.updateRequest != nil);
+	_checkForUpdatesAction = [[[RACSignal
+		defer:^{
+			@strongify(self);
+			return [RACSignal return:self.updateRequest];
+		}]
+		flattenMap:^(NSURLRequest *request) {
+			@strongify(self);
+			return [self checkForUpdates:request];
+		}]
+		action];

-		// TODO: Maybe allow this to be an argument to the command?
-		NSMutableURLRequest *request = [self.updateRequest mutableCopy];
-		[request setValue:@"application/json" forHTTPHeaderField:@"Accept"];
+	_updates = [[RACSubject
+		subject]
+		setNameWithFormat:@"%@ updates", self];

-		return [[[[[[NSURLConnection
-			rac_sendAsynchronousRequest:request]
-			reduceEach:^(id _, NSData *data) {
-				return data;
-			}]
-			flattenMap:^(NSData *data) {
-				return [self updateFromJSONData:data];
-			}]
-			flattenMap:^(SQRLUpdate *update) {
-				return [self downloadAndPrepareUpdate:update];
-			}]
-			doError:^(id _) {
-				self.shouldRelaunch = NO;
-			}]
-			deliverOn:RACScheduler.mainThreadScheduler];
-	}];
-
-	_shipItLauncher = [[[RACSignal
+	_shipItLauncher = [[[[RACSignal
 		defer:^{
 			NSURL *targetURL = NSRunningApplication.currentApplication.bundleURL;

@@ -175,31 +193,80 @@ NSString * const SQRLUpdaterJSONObjectErrorKey = @"SQRLUpdaterJSONObjectErrorKey
 			// wait for another, more canonical error.
 			return [SQRLShipItLauncher launchPrivileged:(gotWritable && !targetWritable.boolValue)];
 		}]
-		replayLazily]
+		promiseOnScheduler:RACScheduler.immediateScheduler]
+		deferred]
 		setNameWithFormat:@"shipItLauncher"];
-	
+
 	return self;
 }

+- (void)dealloc {
+	[_updates sendCompleted];
+}
+
 #pragma mark Checking for Updates

 - (RACDisposable *)startAutomaticChecksWithInterval:(NSTimeInterval)interval {
 	@weakify(self);

-	return [[[[[RACSignal
+	return [[[[RACSignal
 		interval:interval onScheduler:[RACScheduler schedulerWithPriority:RACSchedulerPriorityBackground]]
 		flattenMap:^(id _) {
 			@strongify(self);
-			return [[self.checkForUpdatesCommand
-				execute:RACUnit.defaultUnit]
+
+			return [[[self.checkForUpdatesAction
+				deferred]
+				ignoreValues]
 				catch:^(NSError *error) {
 					NSLog(@"Error checking for updates: %@", error);
 					return [RACSignal empty];
 				}];
 		}]
 		takeUntil:self.rac_willDeallocSignal]
-		publish]
-		connect];
+		subscribeCompleted:^{}];
+}
+
+- (RACSignal *)checkForUpdates:(NSURLRequest *)request {
+	NSParameterAssert(request != nil);
+
+	BOOL updatesDisabled = (getenv("DISABLE_UPDATE_CHECK") != NULL);
+	if (updatesDisabled) return [RACSignal empty];
+
+	NSMutableURLRequest *newRequest = [request mutableCopy];
+	[newRequest setValue:@"application/json" forHTTPHeaderField:@"Accept"];
+
+	return [[[[[[NSURLConnection
+		rac_sendAsynchronousRequest:newRequest]
+		reduceEach:^(NSURLResponse *response, NSData *bodyData) {
+		if ([response isKindOfClass:NSHTTPURLResponse.class]) {
+			NSHTTPURLResponse *httpResponse = (id)response;
+			if (!(httpResponse.statusCode >= 200 && httpResponse.statusCode <= 299)) {
+				NSDictionary *errorInfo = @{
+					NSLocalizedDescriptionKey: NSLocalizedString(@"Update check failed", nil),
+					NSLocalizedRecoverySuggestionErrorKey: NSLocalizedString(@"The server sent an invalid response. Try again later.", nil),
+					SQRLUpdaterServerDataErrorKey: bodyData,
+				};
+				NSError *error = [NSError errorWithDomain:SQRLUpdaterErrorDomain code:SQRLUpdaterErrorInvalidServerResponse userInfo:errorInfo];
+				return [RACSignal error:error];
+			}
+
+			if (httpResponse.statusCode == 204 /* No Content */) {
+				return [RACSignal empty];
+			}
+		}
+
+		return [RACSignal return:bodyData];
+	}]
+	flatten]
+	flattenMap:^(NSData *data) {
+		return [self updateFromJSONData:data];
+	}]
+	flattenMap:^(SQRLUpdate *update) {
+		return [self downloadAndPrepareUpdate:update];
+	}]
+	doNext:^(SQRLDownloadedUpdate *update) {
+		[self->_updates sendNext:update];
+	}];
 }

 - (RACSignal *)updateFromJSONData:(NSData *)data {
@@ -216,7 +283,7 @@ NSString * const SQRLUpdaterJSONObjectErrorKey = @"SQRLUpdaterJSONObjectErrorKey
 				userInfo[SQRLUpdaterServerDataErrorKey] = data;
 				if (error != nil) userInfo[NSUnderlyingErrorKey] = error;

-				return [RACSignal error:[NSError errorWithDomain:SQRLErrorDomain code:SQRLUpdaterErrorInvalidServerResponse userInfo:userInfo]];
+				return [RACSignal error:[NSError errorWithDomain:SQRLUpdaterErrorDomain code:SQRLUpdaterErrorInvalidServerBody userInfo:userInfo]];
 			}

 			Class updateClass = self.updateClass;
@@ -233,7 +300,7 @@ NSString * const SQRLUpdaterJSONObjectErrorKey = @"SQRLUpdaterJSONObjectErrorKey
 				userInfo[SQRLUpdaterJSONObjectErrorKey] = JSON;
 				if (error != nil) userInfo[NSUnderlyingErrorKey] = error;

-				return [RACSignal error:[NSError errorWithDomain:SQRLErrorDomain code:SQRLUpdaterErrorInvalidJSON userInfo:userInfo]];
+				return [RACSignal error:[NSError errorWithDomain:SQRLUpdaterErrorDomain code:SQRLUpdaterErrorInvalidJSON userInfo:userInfo]];
 			}

 			return [RACSignal return:update];
@@ -241,14 +308,21 @@ NSString * const SQRLUpdaterJSONObjectErrorKey = @"SQRLUpdaterJSONObjectErrorKey
 		setNameWithFormat:@"%@ -updateFromJSONData:", self];
 }

+#pragma Download
+
 - (RACSignal *)downloadAndPrepareUpdate:(SQRLUpdate *)update {
 	NSParameterAssert(update != nil);

-	return [[[self
-		uniqueTemporaryDirectoryForUpdate]
+	return [[[self.directoryManager
+		createUniqueUpdateDirectoryURL]
 		flattenMap:^(NSURL *downloadDirectory) {
-			return [[[self
-				downloadBundleForUpdate:update intoDirectory:downloadDirectory]
+			return [[[[[[self
+				downloadArchiveForUpdate:update intoDirectory:downloadDirectory]
+				flattenMap:^(NSURL *updateArchiveURL) {
+					return [self unpackArchiveAtURL:updateArchiveURL intoDirectory:downloadDirectory];
+				}]
+				ignoreValues]
+				concat:[self updateBundleMatchingCurrentApplicationInDirectory:downloadDirectory]]
 				flattenMap:^(NSBundle *updateBundle) {
 					return [self verifyAndPrepareUpdate:update fromBundle:updateBundle];
 				}]
@@ -262,74 +336,65 @@ NSString * const SQRLUpdaterJSONObjectErrorKey = @"SQRLUpdaterJSONObjectErrorKey
 		setNameWithFormat:@"%@ -downloadAndPrepareUpdate: %@", self, update];
 }

- (RACSignal *)downloadBundleForUpdate:(SQRLUpdate *)update intoDirectory:(NSURL *)downloadDirectory {
+- (RACSignal *)downloadArchiveForUpdate:(SQRLUpdate *)update intoDirectory:(NSURL *)downloadDirectory {
 	NSParameterAssert(update != nil);
 	NSParameterAssert(downloadDirectory != nil);

-	return [[[[[RACSignal
+	return [[[RACSignal
 		defer:^{
 			NSURL *zipDownloadURL = update.updateURL;
 			NSMutableURLRequest *zipDownloadRequest = [NSMutableURLRequest requestWithURL:zipDownloadURL];
 			[zipDownloadRequest setValue:@"application/zip" forHTTPHeaderField:@"Accept"];

-			return [[[NSURLConnection
-				rac_sendAsynchronousRequest:zipDownloadRequest]
-				reduceEach:^(id _, NSData *data) {
-					return data;
-				}]
-				flattenMap:^(NSData *data) {
-					NSURL *zipOutputURL = [downloadDirectory URLByAppendingPathComponent:zipDownloadURL.lastPathComponent];
+			SQRLURLConnection *connection = [[SQRLURLConnection alloc] initWithRequest:zipDownloadRequest];

-					NSError *error = nil; 
-					if ([data writeToURL:zipOutputURL options:NSDataWritingAtomic error:&error]) {
-						return [RACSignal return:zipOutputURL];
-					} else {
-						return [RACSignal error:error];
+			SQRLDownloadManager *downloadManager = [[SQRLDownloadManager alloc] initWithDirectoryManager:self.directoryManager];
+
+			return [[[[connection
+				download:downloadManager]
+				reduceEach:^(NSURLResponse *response, NSURL *bodyLocation) {
+					if ([response isKindOfClass:NSHTTPURLResponse.class]) {
+						NSHTTPURLResponse *httpResponse = (id)response;
+						if (!(httpResponse.statusCode >= 200 && httpResponse.statusCode <= 299)) {
+							NSDictionary *errorInfo = @{
+								NSLocalizedDescriptionKey: NSLocalizedString(@"Update download failed", nil),
+								NSLocalizedRecoverySuggestionErrorKey: NSLocalizedString(@"The server sent an invalid response. Try again later.", nil),
+							};
+							NSError *error = [NSError errorWithDomain:SQRLUpdaterErrorDomain code:SQRLUpdaterErrorInvalidServerResponse userInfo:errorInfo];
+							return [RACSignal error:error];
+						}
 					}
-				}];
+
+					return [[RACSignal
+						return:bodyLocation]
+						tryMap:^ NSURL * (NSURL *bodyLocation, NSError **errorRef) {
+							NSURL *updateLocation = [downloadDirectory URLByAppendingPathComponent:response.suggestedFilename];
+							if (![NSFileManager.defaultManager moveItemAtURL:bodyLocation toURL:updateLocation error:errorRef]) return nil;
+							return updateLocation;
+						}];
+				}]
+				flatten]
+				concat:[[downloadManager
+					removeAllResumableDownloads]
+					catchTo:RACSignal.empty]];
 		}]
 		doNext:^(NSURL *zipOutputURL) {
 			NSLog(@"Download completed to: %@", zipOutputURL);
 		}]
-		flattenMap:^(NSURL *zipOutputURL) {
-			return [SQRLZipArchiver unzipArchiveAtURL:zipOutputURL intoDirectoryAtURL:downloadDirectory];
-		}]
-		then:^{
-			return [self updateBundleMatchingCurrentApplicationInDirectory:downloadDirectory];
-		}]
-		setNameWithFormat:@"%@ -downloadBundleForUpdate: %@ intoDirectory: %@", self, update, downloadDirectory];
+		setNameWithFormat:@"%@ -downloadArchiveForUpdate: %@ intoDirectory: %@", self, update, downloadDirectory];
 }

 #pragma mark File Management

- (RACSignal *)uniqueTemporaryDirectoryForUpdate {
-	return [[[RACSignal
+- (RACSignal *)unpackArchiveAtURL:(NSURL *)archiveURL intoDirectory:(NSURL *)directoryURL {
+	NSParameterAssert(archiveURL != nil);
+	NSParameterAssert(directoryURL != nil);
+
+	return [[RACSignal
 		defer:^{
-			SQRLDirectoryManager *directoryManager = [[SQRLDirectoryManager alloc] initWithApplicationIdentifier:SQRLShipItLauncher.shipItJobLabel];
-			return [directoryManager applicationSupportURL];
+			return [SQRLZipArchiver unzipArchiveAtURL:archiveURL intoDirectoryAtURL:directoryURL];
 		}]
-		flattenMap:^(NSURL *appSupportURL) {
-			NSURL *updateDirectoryTemplate = [appSupportURL URLByAppendingPathComponent:@"update.XXXXXXX"];
-			char *updateDirectoryCString = strdup(updateDirectoryTemplate.path.fileSystemRepresentation);
-			@onExit {
-				free(updateDirectoryCString);
-			};
-			
-			if (mkdtemp(updateDirectoryCString) == NULL) {
-				int code = errno;
-
-				NSDictionary *userInfo = @{
-					NSLocalizedDescriptionKey: NSLocalizedString(@"Could not create temporary directory", nil),
-					NSURLErrorKey: updateDirectoryTemplate
-				};
-
-				return [RACSignal error:[NSError errorWithDomain:NSPOSIXErrorDomain code:code userInfo:userInfo]];
-			}
-
-			NSString *updateDirectoryPath = [NSFileManager.defaultManager stringWithFileSystemRepresentation:updateDirectoryCString length:strlen(updateDirectoryCString)];
-			return [RACSignal return:[NSURL fileURLWithPath:updateDirectoryPath isDirectory:YES]];
-		}]
-		setNameWithFormat:@"%@ -uniqueTemporaryDirectoryForUpdate", self];
+		setNameWithFormat:@"%@ unpackArchiveAtURL: %@ intoDirectory: %@", self, archiveURL, directoryURL];
 }

 - (RACSignal *)updateBundleMatchingCurrentApplicationInDirectory:(NSURL *)directory {
@@ -342,25 +407,28 @@ NSString * const SQRLUpdaterJSONObjectErrorKey = @"SQRLUpdaterJSONObjectErrorKey
 				NSLog(@"Error enumerating item %@ within directory %@: %@", URL, directory, error);
 				return YES;
 			}];
-			
-			NSURL *updateBundleURL = [enumerator.rac_sequence objectPassingTest:^(NSURL *URL) {
-				NSString *type = nil;
-				NSError *error = nil;
-				if (![URL getResourceValue:&type forKey:NSURLTypeIdentifierKey error:&error]) {
-					NSLog(@"Error retrieving UTI for item at %@: %@", URL, error);
-					return NO;
-				}

-				if (!UTTypeConformsTo((__bridge CFStringRef)type, kUTTypeApplicationBundle)) return NO;
+			NSURL *updateBundleURL = [[[enumerator.rac_promise
+				start]
+				filter:^(NSURL *URL) {
+					NSString *type = nil;
+					NSError *error = nil;
+					if (![URL getResourceValue:&type forKey:NSURLTypeIdentifierKey error:&error]) {
+						NSLog(@"Error retrieving UTI for item at %@: %@", URL, error);
+						return NO;
+					}

-				NSBundle *bundle = [NSBundle bundleWithURL:URL];
-				if (bundle == nil) {
-					NSLog(@"Could not open application bundle at %@", URL);
-					return NO;
-				}
+					if (!UTTypeConformsTo((__bridge CFStringRef)type, kUTTypeApplicationBundle)) return NO;

-				return [bundle.bundleIdentifier isEqual:NSRunningApplication.currentApplication.bundleIdentifier];
-			}];
+					NSBundle *bundle = [NSBundle bundleWithURL:URL];
+					if (bundle == nil) {
+						NSLog(@"Could not open application bundle at %@", URL);
+						return NO;
+					}
+
+					return [bundle.bundleIdentifier isEqual:NSRunningApplication.currentApplication.bundleIdentifier];
+				}]
+				first];

 			if (updateBundleURL != nil) {
 				return [RACSignal return:updateBundleURL];
@@ -369,7 +437,7 @@ NSString * const SQRLUpdaterJSONObjectErrorKey = @"SQRLUpdaterJSONObjectErrorKey
 					NSLocalizedDescriptionKey: [NSString stringWithFormat:NSLocalizedString(@"Could not locate update bundle for %@ within %@", nil), NSRunningApplication.currentApplication.bundleIdentifier, directory],
 				};

-				return [RACSignal error:[NSError errorWithDomain:SQRLErrorDomain code:SQRLUpdaterErrorMissingUpdateBundle userInfo:userInfo]];
+				return [RACSignal error:[NSError errorWithDomain:SQRLUpdaterErrorDomain code:SQRLUpdaterErrorMissingUpdateBundle userInfo:userInfo]];
 			}
 		}]
 		map:^(NSURL *URL) {
@@ -378,6 +446,15 @@ NSString * const SQRLUpdaterJSONObjectErrorKey = @"SQRLUpdaterJSONObjectErrorKey
 		setNameWithFormat:@"%@ -applicationBundleMatchingCurrentApplicationInDirectory: %@", self, directory];
 }

+- (RACSignal *)shipItStateURL {
+	return [[RACSignal
+		defer:^{
+			SQRLDirectoryManager *directoryManager = [[SQRLDirectoryManager alloc] initWithApplicationIdentifier:SQRLShipItLauncher.shipItJobLabel];
+			return directoryManager.shipItStateURL;
+		}]
+		setNameWithFormat:@"%@ -shipItStateURL", self];
+}
+
 #pragma mark Installing Updates

 - (RACSignal *)verifyAndPrepareUpdate:(SQRLUpdate *)update fromBundle:(NSBundle *)updateBundle {
@@ -386,53 +463,75 @@ NSString * const SQRLUpdaterJSONObjectErrorKey = @"SQRLUpdaterJSONObjectErrorKey

 	return [[[[self.signature
 		verifyBundleAtURL:updateBundle.bundleURL]
-		then:^{
-			SQRLDownloadedUpdate *downloadedUpdate = [[SQRLDownloadedUpdate alloc] initWithUpdate:update bundle:updateBundle];
-			return [RACSignal return:downloadedUpdate];
-		}]
+		concat:[RACSignal return:[[SQRLDownloadedUpdate alloc] initWithUpdate:update bundle:updateBundle]]]
 		flattenMap:^(SQRLDownloadedUpdate *downloadedUpdate) {
-			return [[self prepareUpdateForInstallation:downloadedUpdate] then:^{
-				return [RACSignal return:downloadedUpdate];
-			}];
+			return [[self
+				prepareUpdateForInstallation:downloadedUpdate]
+				concat:[RACSignal return:downloadedUpdate]];
 		}]
 		setNameWithFormat:@"%@ -verifyAndPrepareUpdate: %@ fromBundle: %@", self, update, updateBundle];
 }

+- (RACSignal *)validateExistingState:(SQRLShipItState *)existingState {
+	return [[RACSignal
+		defer:^{
+			if (existingState.installerState != SQRLInstallerStateNothingToDo) {
+				// If this happens, shit is crazy, because it implies that an
+				// update is being installed over us right now.
+				NSDictionary *userInfo = @{
+					NSLocalizedDescriptionKey: NSLocalizedString(@"Installation in progress", nil),
+					NSLocalizedRecoverySuggestionErrorKey: [NSString stringWithFormat:NSLocalizedString(@"An update for %@ is already in progress.", nil), NSRunningApplication.currentApplication.bundleIdentifier],
+				};
+
+				return [RACSignal error:[NSError errorWithDomain:SQRLUpdaterErrorDomain code:SQRLUpdaterErrorPreparingUpdateJob userInfo:userInfo]];
+			}
+
+			return [RACSignal return:existingState];
+		}]
+		setNameWithFormat:@"%@ -validateExistingState: %@", self, existingState];
+}
+
 - (RACSignal *)prepareUpdateForInstallation:(SQRLDownloadedUpdate *)update {
 	NSParameterAssert(update != nil);

-	return [[[[RACSignal
-		defer:^{
-			SQRLDirectoryManager *directoryManager = [[SQRLDirectoryManager alloc] initWithApplicationIdentifier:SQRLShipItLauncher.shipItJobLabel];
-			RACSignal *stateLocation = directoryManager.shipItStateURL;
-			return [[[[SQRLShipItState
-				readUsingURL:stateLocation]
-				catchTo:[RACSignal empty]]
-				flattenMap:^(SQRLShipItState *existingState) {
-					if (existingState.installerState != SQRLInstallerStateNothingToDo) {
-						// If this happens, shit is crazy, because it implies that an
-						// update is being installed over us right now.
-						NSDictionary *userInfo = @{
-							NSLocalizedDescriptionKey: NSLocalizedString(@"Installation in progress", nil),
-							NSLocalizedRecoverySuggestionErrorKey: [NSString stringWithFormat:NSLocalizedString(@"An update for %@ is already in progress.", nil), NSRunningApplication.currentApplication.bundleIdentifier],
-						};
-
-						return [RACSignal error:[NSError errorWithDomain:SQRLErrorDomain code:SQRLUpdaterErrorPreparingUpdateJob userInfo:userInfo]];
-					}
-
-					return [RACSignal empty];
-				}]
-				then:^{
-					SQRLShipItState *state = [[SQRLShipItState alloc] initWithTargetBundleURL:NSRunningApplication.currentApplication.bundleURL updateBundleURL:update.bundle.bundleURL bundleIdentifier:NSRunningApplication.currentApplication.bundleIdentifier codeSignature:self.signature];
-					state.relaunchAfterInstallation = self.shouldRelaunch;
-					return [state writeUsingURL:stateLocation];
-				}];
-		}]
-		then:^{
-			return self.shipItLauncher;
+	return [[[[[[[[SQRLShipItState
+		readUsingURL:self.shipItStateURL]
+		catchTo:[RACSignal empty]]
+		flattenMap:^(SQRLShipItState *existingState) {
+			return [self validateExistingState:existingState];
 		}]
+		ignoreValues]
+		concat:[RACSignal defer:^{
+			SQRLShipItState *state = [[SQRLShipItState alloc] initWithTargetBundleURL:NSRunningApplication.currentApplication.bundleURL updateBundleURL:update.bundle.bundleURL bundleIdentifier:NSRunningApplication.currentApplication.bundleIdentifier codeSignature:self.signature];
+			return [state writeUsingURL:self.shipItStateURL];
+		}]]
+		concat:self.shipItLauncher]
 		sqrl_addTransactionWithName:NSLocalizedString(@"Preparing update", nil) description:NSLocalizedString(@"An update for %@ is being prepared. Interrupting the process could corrupt the application.", nil), NSRunningApplication.currentApplication.bundleIdentifier]
 		setNameWithFormat:@"%@ -prepareUpdateForInstallation: %@", self, update];
 }

+- (RACSignal *)relaunchToInstallUpdate {
+	return [[[[[[[[[SQRLShipItState
+		readUsingURL:self.shipItStateURL]
+		flattenMap:^(SQRLShipItState *existingState) {
+			return [self validateExistingState:existingState];
+		}]
+		flattenMap:^(SQRLShipItState *state) {
+			state.relaunchAfterInstallation = YES;
+			return [[state
+				writeUsingURL:self.shipItStateURL]
+				sqrl_addTransactionWithName:NSLocalizedString(@"Preparing to relaunch", nil) description:NSLocalizedString(@"%@ is preparing to relaunch to install an update. Interrupting the process could corrupt the application.", nil), NSRunningApplication.currentApplication.bundleIdentifier];
+		}]
+		deliverOn:RACScheduler.mainThreadScheduler]
+		doCompleted:^{
+			[NSApp terminate:self];
+		}]
+		// Never allow `completed` to escape this signal chain (in case
+		// -terminate: is asynchronous or something crazy).
+		concat:[RACSignal never]]
+		promiseOnScheduler:RACScheduler.immediateScheduler]
+		deferred]
+		setNameWithFormat:@"%@ -relaunchToInstallUpdate", self];
+}
+
@end
@@ -10,10 +10,17 @@

@class RACSignal;

+extern NSString * const SQRLZipArchiverErrorDomain;
+
 // Associated with an NSNumber containing the code that a shell task exited
 // with.
 extern NSString * const SQRLZipArchiverExitCodeErrorKey;

+// `SQRLZipArchiver` tried to invoke the shell and failed.
+//
+// Contains `SQRLZipArchiverExitStatusErrorKey` in the `userInfo` dictionary.
+extern const NSInteger SQRLZipArchiverShellTaskFailed;
+
 // Uses `ditto` on the command line to zip and unzip archives.
@interface SQRLZipArchiver : NSObject

@@ -9,9 +9,10 @@
 #import "SQRLZipArchiver.h"
 #import <ReactiveCocoa/EXTScope.h>
 #import <ReactiveCocoa/ReactiveCocoa.h>
-#import "Squirrel-Constants.h"

+NSString * const SQRLZipArchiverErrorDomain = @"SQRLZipArchiverErrorDomain";
 NSString * const SQRLZipArchiverExitCodeErrorKey = @"SQRLZipArchiverExitCodeErrorKey";
+const NSInteger SQRLZipArchiverShellTaskFailed = 1;

@interface SQRLZipArchiver () {
 	RACSubject *_taskTerminated;
@@ -129,25 +130,23 @@ NSString * const SQRLZipArchiverExitCodeErrorKey = @"SQRLZipArchiverExitCodeErro
 		// This is important because the signals on `self` complete upon
 		// dealloc.
 		return:self]
-		then:^{
-			return [RACSignal
-				zip:@[ self.taskTerminated, self.standardErrorData ]
-				reduce:^(NSNumber *exitStatus, NSData *errorData) {
-					if (exitStatus.intValue == 0) return [RACSignal empty];
+		ignoreValues]
+		concat:[RACSignal
+			zip:@[ self.taskTerminated, self.standardErrorData ]
+			reduce:^(NSNumber *exitStatus, NSData *errorData) {
+				if (exitStatus.intValue == 0) return [RACSignal empty];

-					NSMutableDictionary *userInfo = [NSMutableDictionary dictionary];
-					userInfo[SQRLZipArchiverExitCodeErrorKey] = exitStatus;
+				NSMutableDictionary *userInfo = [NSMutableDictionary dictionary];
+				userInfo[SQRLZipArchiverExitCodeErrorKey] = exitStatus;

-					NSString *errorString = [[NSString alloc] initWithData:errorData encoding:NSUTF8StringEncoding];
-					errorString = [errorString stringByTrimmingCharactersInSet:NSCharacterSet.whitespaceAndNewlineCharacterSet];
-					if (errorString.length > 0) userInfo[NSLocalizedDescriptionKey] = errorString;
+				NSString *errorString = [[NSString alloc] initWithData:errorData encoding:NSUTF8StringEncoding];
+				errorString = [errorString stringByTrimmingCharactersInSet:NSCharacterSet.whitespaceAndNewlineCharacterSet];
+				if (errorString.length > 0) userInfo[NSLocalizedDescriptionKey] = errorString;

-					return [RACSignal error:[NSError errorWithDomain:SQRLErrorDomain code:SQRLZipArchiverShellTaskFailed userInfo:userInfo]];
-				}];
-		}]
+				return [RACSignal error:[NSError errorWithDomain:SQRLZipArchiverErrorDomain code:SQRLZipArchiverShellTaskFailed userInfo:userInfo]];
+			}]]
 		take:1]
 		flatten]
-		replay]
 		setNameWithFormat:@"-launchWithArguments: %@", arguments];

 	self.dittoTask.arguments = arguments;
@@ -24,6 +24,9 @@
 // updating will abort.
 static const NSUInteger SQRLShipItMaximumInstallationAttempts = 3;

+// The domain for errors generated here.
+static NSString * const SQRLShipItErrorDomain = @"SQRLShipItErrorDomain";
+
 // Waits for all instances of the target application (as described in the
 // `state`) to exit, then sends completed.
 static RACSignal *waitForTerminationIfNecessary(SQRLShipItState *state) {
@@ -52,16 +55,15 @@ int main(int argc, const char * argv[]) {
 		SQRLDirectoryManager *directoryManager = [[SQRLDirectoryManager alloc] initWithApplicationIdentifier:@(jobLabel)];
 		RACSignal *stateLocation = directoryManager.shipItStateURL;

-		[[[[[[SQRLShipItState
+		[[[[[[[SQRLShipItState
 			readUsingURL:stateLocation]
 			flattenMap:^(SQRLShipItState *state) {
 				return waitForTerminationIfNecessary(state);
 			}]
-			then:^{
-				// Read the latest state, in case it was modified by the
-				// controlling application in the meantime.
-				return [SQRLShipItState readUsingURL:stateLocation];
-			}]
+			ignoreValues]
+			// Read the latest state, in case it was modified by the
+			// controlling application in the meantime.
+			concat:[SQRLShipItState readUsingURL:stateLocation]]
 			catch:^(NSError *error) {
 				NSLog(@"Error reading saved installer state: %@", error);

@@ -73,11 +75,14 @@ int main(int argc, const char * argv[]) {
 				SQRLInstaller *installer = [[SQRLInstaller alloc] initWithDirectoryManager:directoryManager];

 				NSUInteger attempt = (freshInstall ? 1 : state.installationStateAttempt + 1);
+				RACSignal *action;
+
 				if (attempt > SQRLShipItMaximumInstallationAttempts) {
-					return [[[installer.abortInstallationCommand
-						execute:state]
-						initially:^{
+					action = [[RACSignal
+						defer:^{
 							NSLog(@"Too many attempts to install from state %i, aborting update", (int)state.installerState);
+
+							return [installer abortInstallationWithState:state];
 						}]
 						catch:^(NSError *error) {
 							NSLog(@"Error aborting installation: %@", error);
@@ -86,9 +91,8 @@ int main(int argc, const char * argv[]) {
 							return [RACSignal empty];
 						}];
 				} else {
-					return [[[[[state
-						writeUsingURL:stateLocation]
-						initially:^{
+					action = [[[[RACSignal
+						defer:^{
 							if (freshInstall) {
 								NSLog(@"Beginning installation");
 								state.installerState = SQRLInstallerStateClearingQuarantine;
@@ -97,15 +101,39 @@ int main(int argc, const char * argv[]) {
 							}

 							state.installationStateAttempt = attempt;
+
+							return [state writeUsingURL:stateLocation];
 						}]
-						then:^{
-							return [installer.installUpdateCommand execute:state];
-						}]
+						concat:[installer installUpdateWithState:state]]
 						doCompleted:^{
 							NSLog(@"Installation completed successfully");
 						}]
 						sqrl_addTransactionWithName:NSLocalizedString(@"Updating", nil) description:NSLocalizedString(@"%@ is being updated, and interrupting the process could corrupt the application", nil), state.targetBundleURL.path];
 				}
+
+				if (state.relaunchAfterInstallation) {
+					// Relaunch regardless of whether installation succeeds or
+					// fails.
+					action = [[action
+						deliverOn:RACScheduler.mainThreadScheduler]
+						doFinished:^{
+							NSURL *bundleURL = state.targetBundleURL;
+							if (bundleURL == nil) {
+								NSLog(@"Missing target bundle URL, cannot relaunch application");
+								return;
+							}
+
+							NSError *error = nil;
+							if (![NSWorkspace.sharedWorkspace launchApplicationAtURL:bundleURL options:NSWorkspaceLaunchDefault configuration:nil error:&error]) {
+								NSLog(@"Could not relaunch application at %@: %@", bundleURL, error);
+								return;
+							}
+
+							NSLog(@"Application relaunched at %@", bundleURL);
+						}];
+				}
+
+				return action;
 			}]
 			subscribeError:^(NSError *error) {
 				NSLog(@"Installation error: %@", error);
@@ -1,71 +0,0 @@
-//
-//  Squirrel-Constants.h
-//  Squirrel
-//
-//  Created by Keith Duncan on 30/10/2013.
-//  Copyright (c) 2013 GitHub. All rights reserved.
-//
-
-#import <Foundation/Foundation.h>
-
-// Error domain for errors originating in Squirrel.
-extern NSString * const SQRLErrorDomain;
-
-// Error codes for errors originating in Squirrel.
-//
-// SQRLCodeSignatureErrorDidNotPass - The bundle did not pass codesign
-// verification.
-//
-// SQRLCodeSignatureErrorCouldNotCreateStaticCode - A static code object could
-// not be created for the target bundle or running code.
-//
-// SQRLShipItStateErrorMissingRequiredProperty - A required property was `nil`
-// upon initialization. Includes `SQRLShipItStatePropertyErrorKey` in the
-// error's `userInfo` dictionary.
-//
-// SQRLShipItStateErrorUnarchiving - The saved state on disk could not be
-// unarchived, possibly because it's invalid.
-//
-// SQRLShipItStateErrorArchiving - The state object could not be archived.
-//
-// SQRLUpdaterErrorMissingUpdateBundle - The downloaded update does not contain
-// an app bundle, or it was deleted on disk before we could get to it.
-//
-// SQRLUpdaterErrorPreparingUpdateJob - An error occurred in the out-of-process
-// updater while it was setting up.
-//
-// SQRLUpdaterErrorRetrievingCodeSigningRequirement - The code signing
-// requirement for the running application could not be retrieved.
-//
-// SQRLUpdaterErrorInvalidServerResponse - The server sent a response that we
-// didn't understand. Includes `SQRLUpdaterServerDataErrorKey` in the error's
-// `userInfo` dictionary.
-//
-// SQRLUpdaterErrorInvalidJSON - The server sent update JSON that we didn't
-// understand. Includes `SQRLUpdaterJSONObjectErrorKey` in the error's
-// `userInfo` dictionary.
-//
-// SQRLZipArchiverShellTaskFailed - `SQRLZipArchiver` tried to invoke the shell
-// and failed. Includes `SQRLZipArchiverExitStatusErrorKey` in the error's
-// `userInfo` dictionary.
-//
-// SQRLShipItLauncherErrorCouldNotStartService - The ShipIt service could not be
-// started.
-typedef enum : NSInteger {
-	SQRLCodeSignatureErrorDidNotPass = -1,
-	SQRLCodeSignatureErrorCouldNotCreateStaticCode = -2,
-
-	SQRLShipItStateErrorMissingRequiredProperty = -100,
-	SQRLShipItStateErrorUnarchiving = -101,
-	SQRLShipItStateErrorArchiving = -102,
-
-	SQRLUpdaterErrorMissingUpdateBundle = -200,
-	SQRLUpdaterErrorPreparingUpdateJob = -201,
-	SQRLUpdaterErrorRetrievingCodeSigningRequirement = -202,
-	SQRLUpdaterErrorInvalidServerResponse = -203,
-	SQRLUpdaterErrorInvalidJSON = -204,
-
-	SQRLZipArchiverShellTaskFailed = -300,
-
-	SQRLShipItLauncherErrorCouldNotStartService = -400,
-} SQRLErrorCode;
@@ -1,11 +0,0 @@
-//
-//  Squirrel-Constants.m
-//  Squirrel
-//
-//  Created by Keith Duncan on 30/10/2013.
-//  Copyright (c) 2013 GitHub. All rights reserved.
-//
-
-#import "Squirrel-Constants.h"
-
-NSString * const SQRLErrorDomain = @"SQRLErrorDomain";
@@ -0,0 +1,23 @@
+//
+//  NSHTTPURLResponseExtensionsSpec.m
+//  Squirrel
+//
+//  Created by Keith Duncan on 04/12/2013.
+//  Copyright (c) 2013 GitHub. All rights reserved.
+//
+
+#import "NSHTTPURLResponse+SQRLExtensions.h"
+
+SpecBegin(NSHTTPURLResponseExtensions)
+
+it(@"should perform case insensitive key look up", ^{
+	NSDictionary *headers = @{
+		@"ETag": @"foo",
+	};
+	NSHTTPURLResponse *response = [[NSHTTPURLResponse alloc] initWithURL:[NSURL URLWithString:@"http://localhost"] statusCode:200 HTTPVersion:(__bridge NSString *)kCFHTTPVersion1_1 headerFields:headers];
+
+	expect([response sqrl_valueForHTTPHeaderField:@"etag"]).to.equal(@"foo");
+	expect([response sqrl_valueForHTTPHeaderField:@"ETAG"]).to.equal(@"foo");
+});
+
+SpecEnd
@@ -7,7 +7,6 @@
 //

 #import "SQRLCodeSignature.h"
-#import "Squirrel-Constants.h"

 SpecBegin(SQRLCodeSignature)

@@ -55,7 +54,7 @@ describe(@"code signature changes", ^{
 		expect(success).to.beFalsy();

 		expect(error).notTo.beNil();
-		expect(error.domain).to.equal(SQRLErrorDomain);
+		expect(error.domain).to.equal(SQRLCodeSignatureErrorDomain);
 		expect(error.code).to.equal(SQRLCodeSignatureErrorDidNotPass);
 	});

@@ -67,7 +66,7 @@ describe(@"code signature changes", ^{
 		expect(success).to.beFalsy();

 		expect(error).notTo.beNil();
-		expect(error.domain).to.equal(SQRLErrorDomain);
+		expect(error.domain).to.equal(SQRLCodeSignatureErrorDomain);
 		expect(error.code).to.equal(SQRLCodeSignatureErrorDidNotPass);
 	});
 });
@@ -81,7 +80,7 @@ describe(@"main executable changes", ^{
 		expect(success).to.beFalsy();

 		expect(error).notTo.beNil();
-		expect(error.domain).to.equal(SQRLErrorDomain);
+		expect(error.domain).to.equal(SQRLCodeSignatureErrorDomain);
 		expect(error.code).to.equal(SQRLCodeSignatureErrorCouldNotCreateStaticCode);
 	});

@@ -93,7 +92,7 @@ describe(@"main executable changes", ^{
 		expect(success).to.beFalsy();

 		expect(error).notTo.beNil();
-		expect(error.domain).to.equal(SQRLErrorDomain);
+		expect(error.domain).to.equal(SQRLCodeSignatureErrorDomain);
 		expect(error.code).to.equal(SQRLCodeSignatureErrorDidNotPass);
 	});
 });
@@ -114,7 +113,7 @@ describe(@"helper executable changes", ^{
 		expect(success).to.beFalsy();

 		expect(error).notTo.beNil();
-		expect(error.domain).to.equal(SQRLErrorDomain);
+		expect(error.domain).to.equal(SQRLCodeSignatureErrorDomain);
 		expect(error.code).to.equal(SQRLCodeSignatureErrorDidNotPass);
 	});

@@ -126,7 +125,7 @@ describe(@"helper executable changes", ^{
 		expect(success).to.beFalsy();

 		expect(error).notTo.beNil();
-		expect(error.domain).to.equal(SQRLErrorDomain);
+		expect(error.domain).to.equal(SQRLCodeSignatureErrorDomain);
 		expect(error.code).to.equal(SQRLCodeSignatureErrorDidNotPass);
 	});
 });
@@ -147,7 +146,7 @@ describe(@"resource changes", ^{
 		expect(success).to.beFalsy();

 		expect(error).notTo.beNil();
-		expect(error.domain).to.equal(SQRLErrorDomain);
+		expect(error.domain).to.equal(SQRLCodeSignatureErrorDomain);
 		expect(error.code).to.equal(SQRLCodeSignatureErrorDidNotPass);
 	});

@@ -159,7 +158,7 @@ describe(@"resource changes", ^{
 		expect(success).to.beFalsy();

 		expect(error).notTo.beNil();
-		expect(error.domain).to.equal(SQRLErrorDomain);
+		expect(error.domain).to.equal(SQRLCodeSignatureErrorDomain);
 		expect(error.code).to.equal(SQRLCodeSignatureErrorDidNotPass);
 	});
 });
@@ -179,7 +178,7 @@ describe(@"framework changes", ^{
 		expect(success).to.beFalsy();

 		expect(error).notTo.beNil();
-		expect(error.domain).to.equal(SQRLErrorDomain);
+		expect(error.domain).to.equal(SQRLCodeSignatureErrorDomain);
 		expect(error.code).to.equal(SQRLCodeSignatureErrorDidNotPass);
 	});

@@ -191,7 +190,7 @@ describe(@"framework changes", ^{
 		expect(success).to.beFalsy();

 		expect(error).notTo.beNil();
-		expect(error.domain).to.equal(SQRLErrorDomain);
+		expect(error.domain).to.equal(SQRLCodeSignatureErrorDomain);
 		expect(error.code).to.equal(SQRLCodeSignatureErrorDidNotPass);
 	});
 });
@@ -60,12 +60,16 @@ void (^deepCodesignTestApplication)(void) = ^{

 	NSTask *deepCodesignTask = [[NSTask alloc] init];
 	deepCodesignTask.launchPath = deepCodesignLocation.path;
+	deepCodesignTask.standardError = [NSPipe pipe];
+	deepCodesignTask.standardOutput = [NSPipe pipe];
+
 	NSMutableDictionary *environment = environmentSuitableForChildProcess();
 	[environment addEntriesFromDictionary:@{
 		@"CODE_SIGN_IDENTITY": @"-",
 		@"CONFIGURATION_BUILD_DIR": testApplicationLocation.URLByDeletingLastPathComponent.path,
 		@"FULL_PRODUCT_NAME": testApplicationLocation.lastPathComponent,
 	}];
+
 	deepCodesignTask.environment = environment;

 	[deepCodesignTask launch];
@@ -106,7 +110,7 @@ it(@"should deep sign the test application", ^{
 	deepCodesignTestApplication();
 });

-it(@"should deep verify after signing", ^{
+xit(@"should deep verify after signing", ^{
 	expect(deepVerify()).to.beFalsy();
 	deepCodesignTestApplication();
 	expect(deepVerify()).to.beTruthy();
@@ -0,0 +1,87 @@
+//
+//  SQRLDownloadControllerSpec.m
+//  Squirrel
+//
+//  Created by Keith Duncan on 27/09/2013.
+//  Copyright (c) 2013 GitHub. All rights reserved.
+//
+
+#import "SQRLDownloadManager.h"
+#import "SQRLResumableDownload.h"
+#import "NSError+SQRLVerbosityExtensions.h"
+#import <ReactiveCocoa/ReactiveCocoa.h>
+
+SpecBegin(SQRLDownloadManager)
+
+__block SQRLDownloadManager *downloadManager = nil;
+
+beforeAll(^{
+	downloadManager = SQRLDownloadManager.defaultDownloadManager;
+
+	NSError *removeError = nil;
+	BOOL remove = [[downloadManager removeAllResumableDownloads] waitUntilCompleted:&removeError];
+	if (!remove) {
+		if ([removeError.domain isEqualToString:NSCocoaErrorDomain] && removeError.code == NSFileNoSuchFileError) return;
+		
+		NSLog(@"Couldn’t remove resumable downloads %@", removeError.sqrl_verboseDescription);
+	}
+});
+
+NSURL * (^newTestURL)() = ^ () {
+	return [[NSURL alloc] initWithScheme:@"http" host:@"localhost" path:[@"/" stringByAppendingString:NSProcessInfo.processInfo.globallyUniqueString]];
+};
+
+NSURL * (^newDownloadURL)() = ^ () {
+	NSError *error = nil;
+	SQRLResumableDownload *download = [[downloadManager downloadForRequest:[NSURLRequest requestWithURL:newTestURL()]] firstOrDefault:nil success:NULL error:&error];
+	expect(download).notTo.beNil();
+	expect(error).to.beNil();
+
+	NSURL *downloadURL = download.fileURL;
+	expect(downloadURL).notTo.beNil();
+
+	return downloadURL;
+};
+
+it(@"should return a file that doesn't exist yet for new URLs", ^{
+	NSURL *downloadURL = newDownloadURL();
+
+	BOOL exists = [NSFileManager.defaultManager fileExistsAtPath:downloadURL.path];
+	expect(exists).to.beFalsy();
+});
+
+it(@"should return a path in a writable directory for new URLs", ^{
+	NSURL *downloadURL = newDownloadURL();
+
+	BOOL writable = [NSFileManager.defaultManager isWritableFileAtPath:downloadURL.URLByDeletingLastPathComponent.path];
+	expect(writable).to.beTruthy();
+});
+
+it(@"should return the same path for the same URL", ^{
+	NSURL *testURL = newTestURL();
+
+	SQRLDownload *download1 = [[downloadManager downloadForRequest:[NSURLRequest requestWithURL:testURL]] first];
+	SQRLDownload *download2 = [[downloadManager downloadForRequest:[NSURLRequest requestWithURL:testURL]] first];
+	expect(download1).notTo.beNil();
+	expect(download1).to.equal(download2);
+});
+
+it(@"should remember a response", ^{
+	NSURLRequest *request = [NSURLRequest requestWithURL:newTestURL()];
+	NSHTTPURLResponse *response = [[NSHTTPURLResponse alloc] initWithURL:request.URL statusCode:200 HTTPVersion:(__bridge NSString *)kCFHTTPVersion1_1 headerFields:@{ @"ETag": NSProcessInfo.processInfo.globallyUniqueString }];
+
+	SQRLDownload *initialDownload = [[downloadManager downloadForRequest:request] first];
+
+	SQRLResumableDownload *newDownload = [[SQRLResumableDownload alloc] initWithRequest:request response:response fileURL:initialDownload.fileURL];
+	expect(newDownload).notTo.equal(initialDownload);
+
+	NSError *error = nil;
+	BOOL setNewDownload = [[downloadManager setDownload:newDownload forRequest:request] waitUntilCompleted:&error];
+	expect(setNewDownload).to.beTruthy();
+	expect(error).to.beNil();
+
+	SQRLResumableDownload *resumedDownload = [[downloadManager downloadForRequest:request] first];
+	expect(newDownload).to.equal(resumedDownload);
+});
+
+SpecEnd
@@ -0,0 +1,40 @@
+//
+//  SQRLDownloadedUpdateSpec.m
+//  Squirrel
+//
+//  Created by Keith Duncan on 04/12/2013.
+//  Copyright (c) 2013 GitHub. All rights reserved.
+//
+
+SpecBegin(SQRLDownloadedUpdate)
+
+it(@"should serialise to JSON", ^{
+	NSError *error = nil;
+	SQRLUpdate *update = [SQRLUpdate modelWithDictionary:@{
+		@keypath(SQRLUpdate.new, updateURL) : [NSURL URLWithString:@"http://fake.domain/path"],
+	} error:&error];
+	expect(update).notTo.beNil();
+
+	NSURL *testApplicationURL = [self createTestApplicationUpdate];
+	NSBundle *testApplicationBundle = [NSBundle bundleWithURL:testApplicationURL];
+	expect(testApplicationBundle).notTo.beNil();
+
+	SQRLDownloadedUpdate *downloadedUpdate = [[SQRLDownloadedUpdate alloc] initWithUpdate:update bundle:testApplicationBundle];
+	expect(downloadedUpdate).notTo.beNil();
+
+	NSDictionary *JSONDictionary = [MTLJSONAdapter JSONDictionaryFromModel:downloadedUpdate];
+	expect(JSONDictionary).notTo.beNil();
+
+	NSData *JSONData = [NSJSONSerialization dataWithJSONObject:JSONDictionary options:0 error:&error];
+	expect(JSONData).notTo.beNil();
+	expect(error).to.beNil();
+
+	JSONDictionary = [NSJSONSerialization JSONObjectWithData:JSONData options:0 error:&error];
+	expect(JSONDictionary).notTo.beNil();
+
+	SQRLDownloadedUpdate *downloadedUpdate2 = [MTLJSONAdapter modelOfClass:SQRLDownloadedUpdate.class fromJSONDictionary:JSONDictionary error:&error];
+	expect(downloadedUpdate2).to.equal(downloadedUpdate);
+	expect(error).to.beNil();
+});
+
+SpecEnd
@@ -0,0 +1,18 @@
+//
+//  SQRLHTTPServer.h
+//  Squirrel
+//
+//  Created by Keith Duncan on 03/12/2013.
+//  Copyright (c) 2013 GitHub. All rights reserved.
+//
+
+#import <Foundation/Foundation.h>
+
+@interface SQRLHTTPServer : NSObject
+
+- (NSURL *)start:(NSError **)errorRef;
+- (void)invalidate;
+
+@property (copy, nonatomic) CFHTTPMessageRef (^responseBlock)(CFHTTPMessageRef request);
+
+@end
@@ -0,0 +1,165 @@
+//
+//  SQRLHTTPServer.m
+//  Squirrel
+//
+//  Created by Keith Duncan on 03/12/2013.
+//  Copyright (c) 2013 GitHub. All rights reserved.
+//
+
+#import "SQRLHTTPServer.h"
+
+#import <sys/socket.h>
+#import <netinet/in.h>
+
+@interface SQRLHTTPServer ()
+@property (assign, nonatomic) dispatch_source_t listenerSource;
+@property (strong, nonatomic) NSMutableArray *cleanupBlocks;
+@end
+
+@implementation SQRLHTTPServer
+
+- (id)init {
+	self = [super init];
+	if (self == nil) return nil;
+
+	_cleanupBlocks = [[NSMutableArray alloc] init];
+
+	return self;
+}
+
+- (void)dealloc {
+	[self invalidate];
+}
+
+- (NSURL *)start:(NSError **)errorRef {
+	NSParameterAssert(self.listenerSource == NULL);
+
+	int listenSocket = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
+
+	struct sockaddr_in listenAddress = {
+		.sin_len = sizeof(listenAddress),
+		.sin_family = AF_INET,
+		.sin_port = 0,
+		.sin_addr = {
+			.s_addr = htonl(INADDR_LOOPBACK),
+		},
+	};
+	int bindError = bind(listenSocket, (struct sockaddr const *)&listenAddress, listenAddress.sin_len);
+	if (bindError != 0) {
+		close(listenSocket);
+
+		if (errorRef != NULL) *errorRef = [NSError errorWithDomain:NSPOSIXErrorDomain code:bindError userInfo:nil];
+		return nil;
+	}
+
+	listen(listenSocket, 128);
+
+	dispatch_source_t source = dispatch_source_create(DISPATCH_SOURCE_TYPE_READ, listenSocket, 0, NULL);
+	dispatch_source_set_event_handler(source, ^{
+		int connectionSocket = accept(listenSocket, NULL, NULL);
+		// Wait to close the connection until after the test case is complete.
+		// We need NSURLConnection to timeout, closing the connection causes it
+		// to error immediately.
+		[self addCleanupBlock:^{
+			close(connectionSocket);
+		}];
+
+		CFHTTPMessageRef request = (__bridge CFHTTPMessageRef)CFBridgingRelease(CFHTTPMessageCreateEmpty(kCFAllocatorDefault, true));
+
+		while (1) {
+			uint8_t buffer;
+			ssize_t readLength = read(connectionSocket, &buffer, 1);
+			if (readLength < 0) {
+				return;
+			}
+
+			CFHTTPMessageAppendBytes(request, (UInt8 const *)&buffer, readLength);
+			if (!CFHTTPMessageIsHeaderComplete(request)) {
+				continue;
+			}
+
+			// Doesn't support reading requests with a body for simplicity
+			NSString *contentLength = CFBridgingRelease(CFHTTPMessageCopyHeaderFieldValue(request, CFSTR("Content-Length")));
+			if (contentLength != nil) {
+				return;
+			}
+
+			break;
+		}
+
+		NSLog(@"Received Request:");
+		NSLog(@"%@", [[NSString alloc] initWithData:CFBridgingRelease(CFHTTPMessageCopySerializedMessage(request)) encoding:NSASCIIStringEncoding]);
+
+		CFHTTPMessageRef response = self.responseBlock(request);
+		NSData *responseData = CFBridgingRelease(CFHTTPMessageCopySerializedMessage(response));
+
+		NSLog(@"Sending Response:");
+		NSLog(@"%@", [[NSString alloc] initWithData:responseData encoding:NSASCIIStringEncoding]);
+
+		size_t bufferLength = responseData.length;
+		uint8_t const *buffer = responseData.bytes;
+
+		while (1) {
+			ssize_t writeLength = write(connectionSocket, buffer, bufferLength);
+			if (writeLength < 0) {
+				return;
+			}
+
+			buffer += writeLength;
+			bufferLength -= writeLength;
+
+			if (bufferLength == 0) {
+				break;
+			}
+		}
+	});
+	dispatch_source_set_cancel_handler(source, ^{
+		close(listenSocket);
+	});
+	dispatch_resume(source);
+
+	struct sockaddr_storage localAddress = {};
+	socklen_t localAddressLength = sizeof(localAddress);
+	int localAddressError = getsockname(listenSocket, (struct sockaddr *)&localAddress, &localAddressLength);
+	if (localAddressError != 0) {
+		dispatch_release(source);
+
+		if (errorRef != NULL) *errorRef = [NSError errorWithDomain:NSPOSIXErrorDomain code:localAddressError userInfo:nil];
+		return nil;
+	}
+
+	self.listenerSource = source;
+
+	// IPv4 and IPv6 address transport layer port fields are at the same offset
+	// and are the same size
+	in_port_t port = ntohs(((struct sockaddr_in *)&localAddress)->sin_port);
+
+	return [NSURL URLWithString:[NSString stringWithFormat:@"http://localhost:%ld/", (unsigned long)port]];
+}
+
+- (void)invalidate {
+	dispatch_source_t listenerSource = self.listenerSource;
+	if (listenerSource == NULL) return;
+
+	dispatch_source_cancel(listenerSource);
+	dispatch_release(listenerSource);
+
+	self.listenerSource = NULL;
+
+	[self performCleanup];
+}
+
+- (void)addCleanupBlock:(void (^)(void))block {
+	[self.cleanupBlocks addObject:[block copy]];
+}
+
+- (void)performCleanup {
+	NSArray *blocks = [self.cleanupBlocks copy];
+	[self.cleanupBlocks removeAllObjects];
+
+	for (void (^currentBlock)(void) in blocks) {
+		currentBlock();
+	}
+}
+
+@end
@@ -77,7 +77,7 @@ it(@"should install an update in process", ^{
 	expect(installer).notTo.beNil();

 	NSError *installError = nil;
-	BOOL install = [[installer.installUpdateCommand execute:state] asynchronouslyWaitUntilCompleted:&installError];
+	BOOL install = [[installer installUpdateWithState:state] asynchronouslyWaitUntilCompleted:&installError];
 	expect(install).to.beTruthy();
 	expect(installError).to.beNil();
 });
@@ -104,6 +104,28 @@ it(@"should not install an update after too many attempts", ^{
 	expect(self.testApplicationBundleVersion).to.equal(SQRLTestApplicationOriginalShortVersionString);
 });

+it(@"should relaunch even after failing to install an update", ^{
+	NSURL *targetURL = self.testApplicationURL;
+	NSURL *backupURL = [self.temporaryDirectoryURL URLByAppendingPathComponent:@"TestApplication.app.bak"];
+	expect([NSFileManager.defaultManager moveItemAtURL:targetURL toURL:backupURL error:NULL]).to.beTruthy();
+
+	SQRLShipItState *state = [[SQRLShipItState alloc] initWithTargetBundleURL:targetURL updateBundleURL:updateURL bundleIdentifier:nil codeSignature:self.testApplicationSignature];
+	state.backupBundleURL = backupURL;
+	state.installerState = SQRLInstallerStateInstalling;
+	state.installationStateAttempt = 4;
+	state.relaunchAfterInstallation = YES;
+	expect([[state writeUsingURL:self.shipItDirectoryManager.shipItStateURL] waitUntilCompleted:NULL]).to.beTruthy();
+
+	[self launchShipIt];
+
+	__block NSError *error = nil;
+	expect([[self.testApplicationSignature verifyBundleAtURL:targetURL] waitUntilCompleted:&error]).will.beTruthy();
+	expect(error).to.beNil();
+
+	expect([NSRunningApplication runningApplicationsWithBundleIdentifier:@"com.github.Squirrel.TestApplication"].count).will.equal(1);
+	expect(self.testApplicationBundleVersion).to.equal(SQRLTestApplicationOriginalShortVersionString);
+});
+
 describe(@"signal handling", ^{
 	__block NSURL *targetURL;

@@ -117,6 +139,9 @@ describe(@"signal handling", ^{

 		[self launchShipIt];

+		// Wait until ShipIt has transitioned by at least one state.
+		expect([[[SQRLShipItState readUsingURL:self.shipItDirectoryManager.shipItStateURL] asynchronousFirstOrDefault:nil success:NULL error:NULL] installerState]).willNot.equal(SQRLInstallerStateNothingToDo);
+
 		// Apply a random delay before sending the termination signal, to
 		// fuzz out race conditions.
 		NSTimeInterval delay = arc4random_uniform(50) / 1000.0;
@@ -136,26 +161,26 @@ describe(@"signal handling", ^{
 	});

 	it(@"should handle SIGHUP", ^{
-		system("killall -v -HUP ShipIt");
+		system("killall -HUP ShipIt");
 	});

 	it(@"should handle SIGTERM", ^{
-		system("killall -v -TERM ShipIt");
+		system("killall -TERM ShipIt");
 	});

 	it(@"should handle SIGINT", ^{
-		system("killall -v -INT ShipIt");
+		system("killall -INT ShipIt");
 	});

 	it(@"should handle SIGQUIT", ^{
-		system("killall -v -QUIT ShipIt");
+		system("killall -QUIT ShipIt");
 	});

 	it(@"should handle SIGKILL", ^{
 		// SIGKILL is unique in that it'll always terminate ShipIt, so send it
 		// a few times to really test resumption.
 		for (int i = 0; i < 3; i++) {
-			system("killall -v -KILL ShipIt");
+			system("killall -KILL ShipIt");

 			// Wait at least for the launchd throttle interval.
 			NSTimeInterval delay = 2 + (arc4random_uniform(100) / 1000.0);
@@ -40,7 +40,8 @@ it(@"should wait until one instance terminates", ^{
 	expect(observedApp).will.equal(app);
 	expect(completed).to.beFalsy();

-	expect([app terminate]).to.beTruthy();
+	[app forceTerminate];
+	expect(app.terminated).will.beTruthy();
 	expect(completed).will.beTruthy();
 });

@@ -55,10 +56,12 @@ it(@"should wait until multiple instances terminate", ^{

 	expect(completed).to.beFalsy();

-	expect([app1 terminate]).to.beTruthy();
+	[app1 forceTerminate];
+	expect(app1.terminated).will.beTruthy();
 	expect(completed).to.beFalsy();

-	expect([app2 terminate]).to.beTruthy();
+	[app2 forceTerminate];
+	expect(app2.terminated).will.beTruthy();
 	expect(completed).will.beTruthy();
 });

@@ -88,4 +88,11 @@ extern NSString * const SQRLBundleShortVersionStringKey;
 // automatically be unmounted and deleted at the end of the example.
 - (NSURL *)createAndMountDiskImageNamed:(NSString *)name fromDirectory:(NSURL *)directoryURL;

+// Add a block to cleanup after each example has run
+//
+// Blocks are run in reverse order, i.e. LIFO
+//
+// block - The block to invoke after the current example has finished
+- (void)addCleanupBlock:(dispatch_block_t)block;
+
@end
@@ -51,6 +51,10 @@ static void SQRLSignalHandler(int sig) {
 // all copied test data.
@property (nonatomic, copy, readonly) NSURL *baseTemporaryDirectoryURL;

+// Returns an _unlaunched_ task that will follow log files at the given paths,
+// then pipe that output through this process.
+ (NSTask *)tailTaskWithPaths:(RACSignal *)paths;
+
@end

@implementation SQRLTestCase
@@ -71,27 +75,27 @@ static void SQRLSignalHandler(int sig) {
 		@"otest-x86_64.ShipIt",
 	];

-	RACSequence *URLs = [folders.rac_sequence flattenMap:^(NSString *folder) {
-		NSURL *baseURL = [appSupportURL URLByAppendingPathComponent:folder];
-		return @[
-			[baseURL URLByAppendingPathComponent:@"ShipIt_stdout.log"],
-			[baseURL URLByAppendingPathComponent:@"ShipIt_stderr.log"]
-		].rac_sequence;
-	}];
-
-	for (NSURL *URL in URLs) {
-		[[NSData data] writeToURL:URL atomically:YES];
-	}
-
-	NSArray *args = [[[URLs
-		map:^(NSURL *URL) {
-			return URL.path;
+	RACSignal *logLocations = [[[[folders.rac_signal
+		flattenMap:^(NSString *folder) {
+			return [folder stringsByAppendingPaths:@[
+				@"ShipIt_stdout.log",
+				@"ShipIt_stderr.log",
+			]].rac_signal;
 		}]
-		startWith:@"-f"]
-		array];
+		map:^(NSString *path) {
+			return [appSupportURL URLByAppendingPathComponent:path];
+		}]
+		doNext:^(NSURL *location) {
+			[[NSData data] writeToURL:location atomically:YES];
+		}]
+		map:^(NSURL *location) {
+			return location.path;
+		}];

-	NSTask *readShipIt = [NSTask launchedTaskWithLaunchPath:@"/usr/bin/tail" arguments:args];
-	NSAssert([readShipIt isRunning], @"Could not start task %@ with arguments: %@", readShipIt, args);
+	NSTask *readShipIt = [self tailTaskWithPaths:logLocations];
+	[readShipIt launch];
+
+	NSAssert([readShipIt isRunning], @"Could not start task %@", readShipIt);

 	atexit_b(^{
 		[readShipIt terminate];
@@ -131,6 +135,24 @@ static void SQRLSignalHandler(int sig) {
 	[self.exampleCleanupBlocks addObject:[block copy]];
 }

+#pragma mark Logging
+
+ (NSTask *)tailTaskWithPaths:(RACSignal *)paths {
+	NSPipe *outputPipe = [NSPipe pipe];
+	NSFileHandle *outputHandle = outputPipe.fileHandleForReading;
+
+	outputHandle.readabilityHandler = ^(NSFileHandle *handle) {
+		NSString *output = [[NSString alloc] initWithData:handle.availableData encoding:NSUTF8StringEncoding];
+		NSLog(@"\n%@", output);
+	};
+
+	NSTask *task = [[NSTask alloc] init];
+	task.launchPath = @"/usr/bin/tail";
+	task.standardOutput = outputPipe;
+	task.arguments = [[paths startWith:@"-f"] array];
+	return task;
+}
+
 #pragma mark Temporary Directory

 - (NSURL *)baseTemporaryDirectoryURL {
@@ -176,7 +198,9 @@ static void SQRLSignalHandler(int sig) {
 		NSURL *testAppLog = [fixtureURL.URLByDeletingLastPathComponent URLByAppendingPathComponent:@"TestApplication.log"];
 		[[NSData data] writeToURL:testAppLog atomically:YES];

-		NSTask *readTestApp = [NSTask launchedTaskWithLaunchPath:@"/usr/bin/tail" arguments:@[ @"-f", testAppLog.path ]];
+		NSTask *readTestApp = [self.class tailTaskWithPaths:[RACSignal return:testAppLog.path]];
+		[readTestApp launch];
+
 		STAssertTrue([readTestApp isRunning], @"Could not start task %@ to read %@", readTestApp, testAppLog);

 		[self addCleanupBlock:^{
@@ -301,11 +325,7 @@ static void SQRLSignalHandler(int sig) {

 	[self addCleanupBlock:^{
 		// Remove ShipIt's launchd job so it doesn't relaunch itself.
-		CFErrorRef removeError = NULL;
-		if (!SMJobRemove(kSMDomainUserLaunchd, (__bridge CFStringRef)SQRLShipItLauncher.shipItJobLabel, NULL, true, &removeError)) {
-			NSLog(@"Could not remove ShipIt job after tests: %@", removeError);
-			if (removeError != NULL) CFRelease(removeError);
-		}
+		SMJobRemove(kSMDomainUserLaunchd, (__bridge CFStringRef)SQRLShipItLauncher.shipItJobLabel, NULL, true, NULL);

 		NSError *lookupError = nil;
 		NSURL *stateURL = [[self.shipItDirectoryManager shipItStateURL] firstOrDefault:nil success:NULL error:&lookupError];
@@ -0,0 +1,311 @@
+//
+//  SQRLURLConnectionSpec.m
+//  Squirrel
+//
+//  Created by Keith Duncan on 27/09/2013.
+//  Copyright (c) 2013 GitHub. All rights reserved.
+//
+
+#import "SQRLURLConnection.h"
+#import "SQRLDownloadManager.h"
+#import "SQRLResumableDownload.h"
+#import <ReactiveCocoa/EXTScope.h>
+#import "NSError+SQRLVerbosityExtensions.h"
+#import "SQRLHTTPServer.h"
+
+SpecBegin(SQRLURLConnection);
+
+__block SQRLDownloadManager *downloadManager;
+
+beforeAll(^{
+	downloadManager = SQRLDownloadManager.defaultDownloadManager;
+
+	NSError *removeError = nil;
+	BOOL remove = [[downloadManager
+		removeAllResumableDownloads]
+		waitUntilCompleted:&removeError];
+	expect(remove).to.beTruthy();
+	expect(removeError).to.beNil();
+});
+
+beforeEach(^{
+	Expecta.asynchronousTestTimeout = 60.;
+});
+
+afterAll(^{
+	Expecta.asynchronousTestTimeout = 1.;
+});
+
+describe(@"file scheme URLs", ^{
+	NSURL *fileLocation = [self.temporaryDirectoryURL URLByAppendingPathComponent:@"test"];
+	NSData *testContents = [@"test" dataUsingEncoding:NSUTF8StringEncoding];
+
+	NSError *error;
+	BOOL write = [testContents writeToURL:fileLocation options:0 error:&error];
+	expect(write).to.beTruthy();
+	expect(error).to.beNil();
+
+	NSURLRequest *request = [NSURLRequest requestWithURL:fileLocation];
+
+	__block SQRLURLConnection *connection;
+
+	beforeEach(^{
+		connection = [[SQRLURLConnection alloc] initWithRequest:request];
+	});
+
+	void (^testBodyEqualTestContents)(NSData *) = ^ (NSData *body) {
+		expect(body.length).to.equal(testContents.length);
+		expect(body).to.equal(testContents);
+	};
+
+	it(@"should retrieve file:// scheme URLs", ^{
+		NSError *error;
+		RACTuple *result = [[connection retrieve] firstOrDefault:nil success:NULL error:&error];
+		expect(result).notTo.beNil();
+		expect(error).to.beNil();
+
+		testBodyEqualTestContents(result[1]);
+	});
+
+	it(@"should download file:// scheme URLs", ^{
+		NSError *error;
+		RACTuple *result = [[connection download:downloadManager] firstOrDefault:nil success:NULL error:&error];
+		expect(result).notTo.beNil();
+		expect(error).to.beNil();
+
+		NSURL *location = result[1];
+
+		NSData *body = [NSData dataWithContentsOfURL:location options:0 error:&error];
+		expect(error).to.beNil();
+		testBodyEqualTestContents(body);
+	});
+});
+
+static NSData * (^stringTimes)(NSString *, NSUInteger) = ^ (NSString *string, NSUInteger times) {
+	NSData *stringData = [string dataUsingEncoding:NSUTF8StringEncoding];
+	NSMutableData *data = [NSMutableData dataWithCapacity:(stringData.length + 2) * times];
+	for (NSUInteger idx = 0; idx < times; idx++) {
+		[data appendData:stringData];
+		[data appendData:[NSData dataWithBytes:"\r\n" length:2]];
+	}
+	return data;
+};
+
+static SQRLHTTPServer * (^newHttpServer)(SQRLTestCase *) = ^ (SQRLTestCase *self) {
+	SQRLHTTPServer *server = [[SQRLHTTPServer alloc] init];
+
+	[self addCleanupBlock:^{
+		[server invalidate];
+	}];
+
+	return server;
+};
+
+it(@"should resume a download", ^{
+	// Start server
+
+	SQRLHTTPServer *server = newHttpServer(self);
+
+	NSError *error = nil;
+	NSURL *baseURL = [server start:&error];
+	expect(baseURL).notTo.beNil();
+	expect(error).to.beNil();
+
+	error = nil;
+
+
+	// Prepare half response
+
+	NSData *firstHalf = stringTimes(@"the quick brown fox", 100);
+	NSData *secondHalf = stringTimes(@"jumped over the lazy doge", 100);
+
+	NSString *ETag = NSProcessInfo.processInfo.globallyUniqueString;
+
+	CFHTTPMessageRef serverResponse = (__bridge CFHTTPMessageRef)CFBridgingRelease(CFHTTPMessageCreateResponse(kCFAllocatorDefault, 200, NULL, kCFHTTPVersion1_1));
+	NSDictionary *responseHeaders = @{
+		@"Content-Length": [@(firstHalf.length + secondHalf.length) stringValue],
+		@"ETag": ETag,
+	};
+	[responseHeaders enumerateKeysAndObjectsUsingBlock:^(NSString *key, NSString *obj, BOOL *stop) {
+		CFHTTPMessageSetHeaderFieldValue(serverResponse, (__bridge CFStringRef)key, (__bridge CFStringRef)obj);
+	}];
+	CFHTTPMessageSetBody(serverResponse, (__bridge CFDataRef)firstHalf);
+
+	server.responseBlock = ^ (CFHTTPMessageRef request) {
+		NSString *ifRange = CFBridgingRelease(CFHTTPMessageCopyHeaderFieldValue(request, CFSTR("If-Range")));
+		expect(ifRange).to.beNil();
+
+		NSString *range = CFBridgingRelease(CFHTTPMessageCopyHeaderFieldValue(request, CFSTR("Range")));
+		expect(range).to.beNil();
+
+		return serverResponse;
+	};
+
+
+	// Issue first request
+
+	NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:baseURL];
+	request.timeoutInterval = 1.;
+	SQRLURLConnection *connection = [[SQRLURLConnection alloc] initWithRequest:request];
+	RACTuple *result = [[connection download:downloadManager] firstOrDefault:nil success:NULL error:&error];
+	expect(result).to.beNil();
+	expect(error).notTo.beNil();
+
+	error = nil;
+
+	SQRLResumableDownload *download = [[downloadManager downloadForRequest:request] firstOrDefault:nil success:NULL error:&error];
+	expect(download).notTo.beNil();
+	expect(error).to.beNil();
+
+	NSData *downloadedData = [NSData dataWithContentsOfURL:download.fileURL options:0 error:&error];
+	expect(downloadedData.length).to.equal(firstHalf.length);
+	expect(downloadedData).to.equal(firstHalf);
+	expect(error).to.beNil();
+
+
+	// Prepare remainder response
+
+	serverResponse = CFHTTPMessageCreateResponse(kCFAllocatorDefault, 206, NULL, kCFHTTPVersion1_1);
+	responseHeaders = @{
+		@"Content-Length": [@(secondHalf.length) stringValue],
+		@"Range": [NSString stringWithFormat:@"%lu-%lu", firstHalf.length, secondHalf.length - 1],
+		@"ETag": ETag,
+	};
+	[responseHeaders enumerateKeysAndObjectsUsingBlock:^(NSString *key, NSString *obj, BOOL *stop) {
+		CFHTTPMessageSetHeaderFieldValue(serverResponse, (__bridge CFStringRef)key, (__bridge CFStringRef)obj);
+	}];
+	CFHTTPMessageSetBody(serverResponse, (__bridge CFDataRef)secondHalf);
+
+	server.responseBlock = ^ (CFHTTPMessageRef request) {
+		NSString *ifRange = CFBridgingRelease(CFHTTPMessageCopyHeaderFieldValue(request, CFSTR("If-Range")));
+		expect(ifRange).to.equal(ETag);
+
+		NSString *range = CFBridgingRelease(CFHTTPMessageCopyHeaderFieldValue(request, CFSTR("Range")));
+		expect(range).to.equal(([NSString stringWithFormat:@"%lu-", firstHalf.length]));
+
+		return serverResponse;
+	};
+
+
+	// Issue second request
+
+	connection = [[SQRLURLConnection alloc] initWithRequest:request];
+	result = [[connection download:downloadManager] firstOrDefault:nil success:NULL error:&error];
+	expect(result).notTo.beNil();
+	expect(error).to.beNil();
+
+	NSURL *location = result[1];
+
+	NSMutableData *fullBody = [firstHalf mutableCopy];
+	[fullBody appendData:secondHalf];
+
+	downloadedData = [NSData dataWithContentsOfURL:location options:0 error:&error];
+	expect(downloadedData.length).to.equal(fullBody.length);
+	expect(downloadedData).to.equal(fullBody);
+	expect(error).to.beNil();
+});
+
+it(@"should not resume downloads for a response with a different ETag", ^{
+	// Start server
+
+	SQRLHTTPServer *server = newHttpServer(self);
+
+	NSError *error = nil;
+	NSURL *baseURL = [server start:&error];
+	expect(baseURL).notTo.beNil();
+	expect(error).to.beNil();
+
+	error = nil;
+
+
+	// Prepare first response
+
+	NSData *firstBody = stringTimes(@"the quick brown fox", 100);
+	NSString *firstETag = NSProcessInfo.processInfo.globallyUniqueString;
+
+	CFHTTPMessageRef serverResponse = (__bridge CFHTTPMessageRef)CFBridgingRelease(CFHTTPMessageCreateResponse(kCFAllocatorDefault, 200, NULL, kCFHTTPVersion1_1));
+	NSDictionary *responseHeaders = @{
+		// Claim the response to be longer so that the connection will timeout
+		// waiting for the extra bytes
+		@"Content-Length": [@(firstBody.length + 100) stringValue],
+		@"ETag": firstETag,
+	};
+	[responseHeaders enumerateKeysAndObjectsUsingBlock:^(NSString *key, NSString *obj, BOOL *stop) {
+		CFHTTPMessageSetHeaderFieldValue(serverResponse, (__bridge CFStringRef)key, (__bridge CFStringRef)obj);
+	}];
+	CFHTTPMessageSetBody(serverResponse, (__bridge CFDataRef)firstBody);
+
+	server.responseBlock = ^ (CFHTTPMessageRef request) {
+		NSString *ifRange = CFBridgingRelease(CFHTTPMessageCopyHeaderFieldValue(request, CFSTR("If-Range")));
+		expect(ifRange).to.beNil();
+
+		NSString *range = CFBridgingRelease(CFHTTPMessageCopyHeaderFieldValue(request, CFSTR("Range")));
+		expect(range).to.beNil();
+
+		return serverResponse;
+	};
+
+
+	// Issue first request
+
+	NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:baseURL];
+	request.timeoutInterval = 1.;
+	SQRLURLConnection *connection = [[SQRLURLConnection alloc] initWithRequest:request];
+	RACTuple *result = [[connection download:downloadManager] firstOrDefault:nil success:NULL error:&error];
+	expect(result).to.beNil();
+	expect(error).notTo.beNil();
+
+	error = nil;
+
+	SQRLResumableDownload *download = [[downloadManager downloadForRequest:request] firstOrDefault:nil success:NULL error:&error];
+	expect(download).notTo.beNil();
+	expect(error).to.beNil();
+
+	NSData *downloadedData = [NSData dataWithContentsOfURL:download.fileURL options:0 error:&error];
+	expect(downloadedData.length).to.equal(firstBody.length);
+	expect(downloadedData).to.equal(firstBody);
+	expect(error).to.beNil();
+
+
+	// Prepare second response
+
+	NSData *secondBody = stringTimes(@"jumps over the lazy doge", 100);
+	NSString *secondETag = NSProcessInfo.processInfo.globallyUniqueString;
+
+	serverResponse = (__bridge CFHTTPMessageRef)CFBridgingRelease(CFHTTPMessageCreateResponse(kCFAllocatorDefault, 200, NULL, kCFHTTPVersion1_1));
+	responseHeaders = @{
+		@"Content-Length": [@(secondBody.length) stringValue],
+		@"ETag": secondETag,
+	};
+	[responseHeaders enumerateKeysAndObjectsUsingBlock:^(NSString *key, NSString *obj, BOOL *stop) {
+		CFHTTPMessageSetHeaderFieldValue(serverResponse, (__bridge CFStringRef)key, (__bridge CFStringRef)obj);
+	}];
+	CFHTTPMessageSetBody(serverResponse, (__bridge CFDataRef)secondBody);
+
+	server.responseBlock = ^ (CFHTTPMessageRef request) {
+		NSString *ifRange = CFBridgingRelease(CFHTTPMessageCopyHeaderFieldValue(request, CFSTR("If-Range")));
+		expect(ifRange).to.equal(firstETag);
+
+		NSString *range = CFBridgingRelease(CFHTTPMessageCopyHeaderFieldValue(request, CFSTR("Range")));
+		expect(range).to.equal(([NSString stringWithFormat:@"%lu-", firstBody.length]));
+
+		return serverResponse;
+	};
+
+
+	// Issue second request
+
+	connection = [[SQRLURLConnection alloc] initWithRequest:request];
+	result = [[connection download:downloadManager] firstOrDefault:nil success:NULL error:&error];
+	expect(result).notTo.beNil();
+	expect(error).to.beNil();
+
+	NSURL *location = result[1];
+
+	downloadedData = [NSData dataWithContentsOfURL:location options:0 error:&error];
+	expect(downloadedData.length).to.equal(secondBody.length);
+	expect(downloadedData).to.equal(secondBody);
+	expect(error).to.beNil();
+});
+
+SpecEnd
@@ -39,13 +39,17 @@ it(@"should validate release name and notes", ^{
 });

 it(@"should parse Central style dates", ^{
-	SQRLUpdate *update = [MTLJSONAdapter modelOfClass:SQRLUpdate.class fromJSONDictionary:@{ @"url": @"http://example.com/update", @"pub_date": @"Tue Sep 17 10:24:27 -0700 2013" } error:NULL];
+	NSError *error = nil;
+	SQRLUpdate *update = [MTLJSONAdapter modelOfClass:SQRLUpdate.class fromJSONDictionary:@{ @"url": @"http://example.com/update", @"pub_date": @"Tue Sep 17 10:24:27 -0700 2013" } error:&error];
 	expect(update.releaseDate).notTo.beNil();
+	expect(error).to.beNil();
 });

 it(@"should parse ISO 8601 dates", ^{
-	SQRLUpdate *update = [MTLJSONAdapter modelOfClass:SQRLUpdate.class fromJSONDictionary:@{ @"url": @"http://example.com/update", @"pub_date": @"2013-09-18T13:17:07+01:00" } error:NULL];
+	NSError *error = nil;
+	SQRLUpdate *update = [MTLJSONAdapter modelOfClass:SQRLUpdate.class fromJSONDictionary:@{ @"url": @"http://example.com/update", @"pub_date": @"2013-09-18T13:17:07+01:00" } error:&error];
 	expect(update.releaseDate).notTo.beNil();
+	expect(error).to.beNil();
 });

 SpecEnd
@@ -8,6 +8,10 @@

 #import "SQRLTestUpdate.h"
 #import "SQRLZipArchiver.h"
+#import "OHHTTPStubs/OHHTTPStubs.h"
+#import "SQRLDirectoryManager.h"
+#import "SQRLURLConnection.h"
+#import "SQRLDownloadManager.h"

 SpecBegin(SQRLUpdater)

@@ -51,10 +55,14 @@ beforeEach(^{

 it(@"should use the application's bundled version of Squirrel and update in-place", ^{
 	NSURL *updateURL = [self createTestApplicationUpdate];
+
+	NSError *error = nil;
 	SQRLTestUpdate *update = [SQRLTestUpdate modelWithDictionary:@{
 		@"updateURL": zipUpdate(updateURL),
 		@"final": @YES
-	} error:NULL];
+	} error:&error];
+	expect(update).notTo.beNil();
+	expect(error).to.beNil();

 	writeUpdate(update);

@@ -130,4 +138,127 @@ it(@"should use the application's bundled version of Squirrel and update in-plac
 	expect(self.testApplicationBundleVersion).will.equal(SQRLTestApplicationUpdatedShortVersionString);
 });

+describe(@"response handling", ^{
+	__block NSURLRequest *localRequest = nil;
+	__block SQRLUpdater *updater = nil;
+
+	before(^{
+		localRequest = [NSURLRequest requestWithURL:[NSURL URLWithString:@"fake://host/path"]];
+		updater = [[SQRLUpdater alloc] initWithUpdateRequest:localRequest];
+	});
+
+	it(@"should return an error for non 2xx code HTTP responses", ^{
+		OHHTTPStubs *stubs = [OHHTTPStubs shouldStubRequestsPassingTest:^(NSURLRequest *request) {
+			return [request.URL isEqual:localRequest.URL];
+		} withStubResponse:^(NSURLRequest *request) {
+			return [OHHTTPStubsResponse responseWithData:nil statusCode:/* Server Error */ 500 responseTime:0 headers:nil];
+		}];
+		[self addCleanupBlock:^{
+			[OHHTTPStubs removeRequestHandler:stubs];
+		}];
+
+		NSError *error = nil;
+		BOOL result = [[updater.checkForUpdatesAction deferred] asynchronouslyWaitUntilCompleted:&error];
+		expect(result).to.beFalsy();
+		expect(error.domain).to.equal(SQRLUpdaterErrorDomain);
+		expect(error.code).to.equal(SQRLUpdaterErrorInvalidServerResponse);
+	});
+
+	it(@"should return an error for non JSON data", ^{
+		OHHTTPStubs *stubs = [OHHTTPStubs shouldStubRequestsPassingTest:^(NSURLRequest *request) {
+			return [request.URL isEqual:localRequest.URL];
+		} withStubResponse:^(NSURLRequest *request) {
+			return [OHHTTPStubsResponse responseWithData:NSData.data statusCode:/* OK */ 200 responseTime:0 headers:nil];
+		}];
+		[self addCleanupBlock:^{
+			[OHHTTPStubs removeRequestHandler:stubs];
+		}];
+
+		NSError *error = nil;
+		BOOL result = [[updater.checkForUpdatesAction deferred] asynchronouslyWaitUntilCompleted:&error];
+		expect(result).to.beFalsy();
+		expect(error.domain).to.equal(SQRLUpdaterErrorDomain);
+		expect(error.code).to.equal(SQRLUpdaterErrorInvalidServerBody);
+	});
+});
+
+it(@"should clean up resumable downloads after a successful download", ^{
+	SQRLDirectoryManager *directoryManager = [[SQRLDirectoryManager alloc] initWithApplicationIdentifier:@"com.github.Squirrel.TestApplication"];
+	SQRLDownloadManager *downloadManager = [[SQRLDownloadManager alloc] initWithDirectoryManager:directoryManager];
+
+	NSError *error = nil;
+	BOOL remove = [[downloadManager removeAllResumableDownloads] asynchronouslyWaitUntilCompleted:&error];
+	expect(remove).to.beTruthy();
+	expect(error).to.beNil();
+
+	NSURL *updateApplicationBundle = [self createTestApplicationUpdate];
+
+	NSURL *firstDownload = zipUpdate(updateApplicationBundle);
+	SQRLURLConnection *connection = [[SQRLURLConnection alloc] initWithRequest:[NSURLRequest requestWithURL:firstDownload]];
+	BOOL download = [[connection download:downloadManager] asynchronouslyWaitUntilCompleted:&error];
+	expect(download).to.beTruthy();
+	expect(error).to.beNil();
+
+	NSURL *downloadDirectory = [[directoryManager downloadDirectoryURL] firstOrDefault:nil success:NULL error:&error];
+	expect(downloadDirectory).notTo.beNil();
+	expect(error).to.beNil();
+
+	NSArray *contents = [NSFileManager.defaultManager contentsOfDirectoryAtURL:downloadDirectory includingPropertiesForKeys:@[] options:0 error:&error];
+	expect(contents.count).to.equal(1);
+
+	SQRLTestUpdate *update = [[SQRLTestUpdate alloc] initWithDictionary:@{
+		@"updateURL": zipUpdate(updateApplicationBundle),
+		@"final": @YES,
+	} error:NULL];
+
+	writeUpdate(update);
+
+	NSRunningApplication *app = launchWithEnvironment(nil);
+	expect(app.terminated).will.beTruthy();
+	expect(self.testApplicationBundleVersion).will.equal(SQRLTestApplicationUpdatedShortVersionString);
+
+	contents = [NSFileManager.defaultManager contentsOfDirectoryAtURL:downloadDirectory includingPropertiesForKeys:@[] options:0 error:&error];
+	if (contents == nil) {
+		expect(error.domain).to.equal(NSCocoaErrorDomain);
+		expect(error.code).to.equal(NSFileReadNoSuchFileError);
+	} else {
+		expect(contents.count).to.equal(0);
+	}
+});
+
+it(@"should unpack update archives into a .noindex directory", ^{
+	NSURL *zippedUpdateLocation = zipUpdate([self createTestApplicationUpdate]);
+
+	SQRLTestUpdate *update = [[SQRLTestUpdate alloc] initWithDictionary:@{
+		@keypath(update.updateURL): zippedUpdateLocation,
+	} error:NULL];
+
+	writeUpdate(update);
+
+	__block SQRLDownloadedUpdate *downloadedUpdate;
+
+	[[[[[NSDistributedNotificationCenter.defaultCenter
+		rac_addObserverForName:@"com.github.Squirrel.TestApplication.updateReceived" object:nil]
+		map:^(NSNotification *notification) {
+			return notification.userInfo[@"update"];
+		}]
+		tryMap:^(NSString *serialisedUpdate, NSError **errorRef) {
+			NSData *JSONData = [serialisedUpdate dataUsingEncoding:NSUTF8StringEncoding];
+			return [NSJSONSerialization JSONObjectWithData:JSONData options:0 error:errorRef];
+		}]
+		tryMap:^(NSDictionary *JSONDictionary, NSError **errorRef) {
+			return [MTLJSONAdapter modelOfClass:SQRLDownloadedUpdate.class fromJSONDictionary:JSONDictionary error:errorRef];
+		}]
+		subscribeNext:^(SQRLDownloadedUpdate *update) {
+			downloadedUpdate = update;
+		}];
+
+	launchWithEnvironment(nil);
+
+	expect(downloadedUpdate).willNot.beNil();
+
+	NSURL *bundleURL = downloadedUpdate.bundle.bundleURL;
+	expect([bundleURL.path rangeOfString:@".noindex"].location).notTo.equal(NSNotFound);
+});
+
 SpecEnd
@@ -8,9 +8,8 @@

 #import "SQRLCodeSignature.h"
 #import "SQRLZipArchiver.h"
-#import "Squirrel-Constants.h"

-SpecBegin(SQRLZipArchiver)
+SpecBegin(SQRLZipOperation)

 it(@"should extract a zip archive created by the Finder", ^{
 	NSURL *zipURL = [[NSBundle bundleForClass:self.class] URLForResource:@"TestApplication.app" withExtension:@"zip"];
@@ -36,7 +35,7 @@ it(@"should fail to extract a nonexistent zip archive", ^{
 	NSLog(@"%@", error);

 	expect(error).notTo.beNil();
-	expect(error.domain).to.equal(SQRLErrorDomain);
+	expect(error.domain).to.equal(SQRLZipArchiverErrorDomain);
 	expect(error.code).to.equal(SQRLZipArchiverShellTaskFailed);
 	expect(error.userInfo[SQRLZipArchiverExitCodeErrorKey]).notTo.equal(0);
 });
@@ -10,6 +10,7 @@
 #import "SQRLDirectoryManager.h"
 #import "SQRLShipItLauncher.h"
 #import "SQRLTestUpdate.h"
+#import "SQRLDownloadedUpdate.h"
 #import <ReactiveCocoa/EXTScope.h>
 #import <ReactiveCocoa/ReactiveCocoa.h>

@@ -70,18 +71,22 @@
 			NSLog(@"***** UPDATE CHECK %lu *****", (unsigned long)updateCheckCount);
 			updateCheckCount++;

-			return [self.updater.checkForUpdatesCommand execute:RACUnit.defaultUnit];
+			return [self.updater.checkForUpdatesAction deferred];
 		}]
 		doNext:^(SQRLDownloadedUpdate *update) {
 			NSLog(@"Got a candidate update: %@", update);
+
+			NSString *serialisedUpdate = [[NSString alloc] initWithData:[NSJSONSerialization dataWithJSONObject:[MTLJSONAdapter JSONDictionaryFromModel:update] options:0 error:NULL] encoding:NSUTF8StringEncoding];
+
+			[NSDistributedNotificationCenter.defaultCenter postNotificationName:@"com.github.Squirrel.TestApplication.updateReceived" object:nil userInfo:@{ @"update": serialisedUpdate }];
 		}]
 		// Retry until we get the expected release.
 		repeat]
-		skipUntilBlock:^(SQRLDownloadedUpdate *download) {
+		skipWhile:^ BOOL (SQRLDownloadedUpdate *download) {
 			SQRLTestUpdate *testUpdate = (id)download.update;
 			NSAssert([testUpdate isKindOfClass:SQRLTestUpdate.class], @"Unexpected update type: %@", testUpdate);

-			return testUpdate.final;
+			return !testUpdate.final;
 		}]
 		take:1]
 		doNext:^(id _) {
@@ -92,12 +97,12 @@
 			NSLog(@"Error in updater: %@", error);
 			return [RACSignal empty];
 		}]
-		then:^{
+		concat:[RACSignal defer:^{
 			NSString *delayString = NSProcessInfo.processInfo.environment[@"SQRLUpdateDelay"];
 			if (delayString == nil) return [RACSignal empty];

 			return [[RACSignal interval:delayString.doubleValue onScheduler:RACScheduler.mainThreadScheduler] take:1];
-		}]
+		}]]
 		subscribeCompleted:^{
 			[NSApp terminate:self];
 		}];
@@ -1,6 +1,66 @@
-These scripts are primarily meant to support the use of
-[Janky](https://github.com/github/janky). To use them, read the contents of this
-repository into a `script` folder:
+# objc-build-scripts
+
+This project is a collection of scripts created with two goals:
+
+ 1. To standardize how Objective-C projects are bootstrapped after cloning
+ 1. To easily build Objective-C projects on continuous integration servers
+
+## Scripts
+
+Right now, there are two important scripts: [`bootstrap`](#bootstrap) and
+[`cibuild`](#cibuild). Both are Bash scripts, to maximize compatibility and
+eliminate pesky system configuration issues (like setting up a working Ruby
+environment).
+
+The structure of the scripts on disk is meant to follow that of a typical Ruby
+project:
+
+```
+script/
+    bootstrap
+    cibuild
+```
+
+### bootstrap
+
+This script is responsible for bootstrapping (initializing) your project after
+it's been checked out. Here, you should install or clone any dependencies that
+are required for a working build and development environment.
+
+By default, the script will verify that [xctool][] is installed, then initialize
+and update submodules recursively. If any submodules contain `script/bootstrap`,
+that will be run as well.
+
+To check that other tools are installed, you can set the `REQUIRED_TOOLS`
+environment variable before running `script/bootstrap`, or edit it within the
+script directly. Note that no installation is performed automatically, though
+this can always be added within your specific project.
+
+### cibuild
+
+This script is responsible for building the project, as you would want it built
+for continuous integration. This is preferable to putting the logic on the CI
+server itself, since it ensures that any changes are versioned along with the
+source.
+
+By default, the script will run [`bootstrap`](#bootstrap), look for any Xcode
+workspace or project in the working directory, then build all targets/schemes
+(as found by `xcodebuild -list`) using [xctool][].
+
+You can also specify the schemes to build by passing them into the script:
+
+```sh
+script/cibuild ReactiveCocoa-Mac ReactiveCocoa-iOS
+```
+
+As with the `bootstrap` script, there are several environment variables that can
+be used to customize behavior. They can be set on the command line before
+invoking the script, or the defaults changed within the script directly.
+
+## Getting Started
+
+To add the scripts to your project, read the contents of this repository into
+a `script` folder:

 ```
 $ git remote add objc-build-scripts https://github.com/jspahrsummers/objc-build-scripts.git
@@ -8,13 +68,15 @@ $ git fetch objc-build-scripts
 $ git read-tree --prefix=script/ -u objc-build-scripts/master
 ```

-Then commit the changes to incorporate the scripts into your own repository's
+Then commit the changes, to incorporate the scripts into your own repository's
 history. You can also freely tweak the scripts for your specific project's
 needs.

-To bring in upstream changes later:
+To merge in upstream changes later:

 ```
 $ git fetch -p objc-build-scripts
-$ git merge -Xsubtree=script objc-build-scripts/master
+$ git merge --ff --squash -Xsubtree=script objc-build-scripts/master
 ```
+
+[xctool]: https://github.com/facebook/xctool
@@ -1,11 +1,73 @@
 #!/bin/bash

-SCRIPT_DIR=$(dirname "$0")
-cd "$SCRIPT_DIR/.."
+export SCRIPT_DIR=$(dirname "$0")

-set -o errexit
+##
+## Configuration Variables
+##

-echo "*** Updating submodules..."
-git submodule sync --quiet
-git submodule update --init
-git submodule foreach --recursive --quiet "git submodule sync --quiet && git submodule update --init"
+config ()
+{
+    # A whitespace-separated list of executables that must be present and locatable.
+    : ${REQUIRED_TOOLS="xctool"}
+    
+    export REQUIRED_TOOLS
+}
+
+##
+## Bootstrap Process
+##
+
+main ()
+{
+    config
+
+    if [ -n "$REQUIRED_TOOLS" ]
+    then
+        echo "*** Checking dependencies..."
+        check_deps
+    fi
+
+    local submodules=$(git submodule status 2>/dev/null)
+    if [ -n "$submodules" ]
+    then
+        echo "*** Updating submodules..."
+        update_submodules
+    fi
+}
+
+check_deps ()
+{
+    for tool in $REQUIRED_TOOLS
+    do
+        which -s "$tool"
+        if [ "$?" -ne "0" ]
+        then
+            echo "*** Error: $tool not found. Please install it and bootstrap again."
+            exit 1
+        fi
+    done
+}
+
+bootstrap_submodule ()
+{
+    local bootstrap="script/bootstrap"
+
+    if [ -e "$bootstrap" ]
+    then
+        echo "*** Bootstrapping $name..."
+        "$bootstrap" >/dev/null
+    else
+        update_submodules
+    fi
+}
+
+update_submodules ()
+{
+    git submodule sync --quiet && git submodule update --init && git submodule foreach --quiet bootstrap_submodule
+}
+
+export -f bootstrap_submodule
+export -f update_submodules
+
+main
@@ -1,129 +1,162 @@
 #!/bin/bash

-SCRIPT_DIR=$(dirname "$0")
-cd "$SCRIPT_DIR/.."
+export SCRIPT_DIR=$(dirname "$0")

 ##
 ## Configuration Variables
 ##

-# The build configuration to use.
-if [ -z "$XCCONFIGURATION" ]
-then
-    XCCONFIGURATION="Test"
-fi
+SCHEMES="$@"

-# The workspace to build.
-#
-# If not set and no workspace is found, the -workspace flag will not be passed
-# to xcodebuild.
-if [ -z "$XCWORKSPACE" ]
-then
-    XCWORKSPACE=$(ls -d *.xcworkspace 2>/dev/null | head -n 1)
-fi
+config ()
+{
+    # The workspace to build.
+    #
+    # If not set and no workspace is found, the -workspace flag will not be passed
+    # to `xctool`.
+    #
+    # Only one of `XCWORKSPACE` and `XCODEPROJ` needs to be set. The former will
+    # take precedence.
+    : ${XCWORKSPACE=$(find_pattern "*.xcworkspace")}

-# A bootstrap script to run before building.
-#
-# If this file does not exist, it is not considered an error.
-BOOTSTRAP="$SCRIPT_DIR/bootstrap"
+    # The project to build.
+    #
+    # If not set and no project is found, the -project flag will not be passed
+    # to `xctool`.
+    #
+    # Only one of `XCWORKSPACE` and `XCODEPROJ` needs to be set. The former will
+    # take precedence.
+    : ${XCODEPROJ=$(find_pattern "*.xcodeproj")}

-# A whitespace-separated list of default targets or schemes to build, if none
-# are specified on the command line.
-#
-# Individual names can be quoted to avoid word splitting.
-DEFAULT_TARGETS=Squirrel
+    # A bootstrap script to run before building.
+    #
+    # If this file does not exist, it is not considered an error.
+    : ${BOOTSTRAP="$SCRIPT_DIR/bootstrap"}

-# Extra build settings to pass to xcodebuild.
-XCODEBUILD_SETTINGS="TEST_AFTER_BUILD=YES"
+    # Extra options to pass to xctool.
+    : ${XCTOOL_OPTIONS="RUN_CLANG_STATIC_ANALYZER=NO"}
+
+    # A whitespace-separated list of default schemes to build.
+    #
+    # Individual names can be quoted to avoid word splitting.
+    : ${SCHEMES:=Squirrel}
+
+    # A source-able file with information about the Keychain, containing our
+    # code-signing certificate.
+    : ${KEYCHAIN_INFO:=/var/lib/jenkins/config/xcodekeychain}
+    
+    export XCWORKSPACE
+    export XCODEPROJ
+    export BOOTSTRAP
+    export XCTOOL_OPTIONS
+    export SCHEMES
+    export KEYCHAIN_INFO
+}

 ##
-## Code-signing Setup
+## Code Signing
 ##

-# A source-able file with information about the Keychain containing our
-# code-signing certificate.
-KEYCHAIN_INFO=/var/lib/jenkins/config/xcodekeychain
-
-if [ -e "$KEYCHAIN_INFO" ]
-then
-    # Unlock the keychain so the certificates it contains can be used for building.
-    . "${KEYCHAIN_INFO}"
-    security unlock-keychain -p "${XCODE_KEYCHAIN_PASSWORD}" "${XCODE_KEYCHAIN}"
-fi
+unlock_keychain ()
+{
+    if [ -e "$KEYCHAIN_INFO" ]
+    then
+        # Unlock the keychain so the certificates it contains can be used for building.
+        . "$KEYCHAIN_INFO"
+        security unlock-keychain -p "$XCODE_KEYCHAIN_PASSWORD" "$XCODE_KEYCHAIN"
+    fi
+}

 ##
 ## Build Process
 ##

-if [ -z "$*" ]
-then
-    # lol recursive shell script
-    if [ -n "$DEFAULT_TARGETS" ]
+main ()
+{
+    config
+    unlock_keychain
+
+    if [ -f "$BOOTSTRAP" ]
    then
-        echo "$DEFAULT_TARGETS" | xargs "$SCRIPT_DIR/cibuild"
-    else
-        xcodebuild -list | awk -f "$SCRIPT_DIR/targets.awk" | xargs "$SCRIPT_DIR/cibuild"
+        echo "*** Bootstrapping..."
+        "$BOOTSTRAP" || exit $?
    fi

-    exit $?
-fi
+    echo "*** The following schemes will be built:"
+    echo "$SCHEMES" | xargs -n 1 echo "  "
+    echo

-if [ -f "$BOOTSTRAP" ]
-then
-    echo "*** Bootstrapping..."
-    bash "$BOOTSTRAP" || exit $?
-fi
+    echo "$SCHEMES" | xargs -n 1 | (
+        local status=0

-echo "*** The following targets will be built:"
+        while read scheme
+        do
+            build_scheme "$scheme" || status=1
+        done

-for target in "$@"
-do
-    echo "$target"
-done
+        exit $status
+    )
+}

-echo "*** Cleaning all targets..."
-xcodebuild -alltargets clean OBJROOT="$PWD/build" SYMROOT="$PWD/build" $XCODEBUILD_SETTINGS
-
-run_xcodebuild ()
+find_pattern ()
 {
-    local scheme=$1
+    ls -d $1 2>/dev/null | head -n 1
+}

+run_xctool ()
+{
    if [ -n "$XCWORKSPACE" ]
    then
-        xcodebuild -workspace "$XCWORKSPACE" -scheme "$scheme" -configuration "$XCCONFIGURATION" build OBJROOT="$PWD/build" SYMROOT="$PWD/build" $XCODEBUILD_SETTINGS
+        xctool -workspace "$XCWORKSPACE" $XCTOOL_OPTIONS "$@" 2>&1
+    elif [ -n "$XCODEPROJ" ]
+    then
+        xctool -project "$XCODEPROJ" $XCTOOL_OPTIONS "$@" 2>&1
    else
-        xcodebuild -scheme "$scheme" -configuration "$XCCONFIGURATION" build OBJROOT="$PWD/build" SYMROOT="$PWD/build" $XCODEBUILD_SETTINGS
+        echo "*** No workspace or project file found."
+        exit 1
    fi
+}

-    local status=$?
-
-    return $status
+parse_build ()
+{
+    awk -f "$SCRIPT_DIR/xctool.awk" 2>&1 >/dev/null
 }

 build_scheme ()
 {
    local scheme=$1

-    run_xcodebuild "$scheme" 2>&1 | awk -f "$SCRIPT_DIR/xcodebuild.awk"
+    echo "*** Cleaning $scheme..."
+    run_xctool -scheme "$scheme" clean >/dev/null || exit $?
+
+    echo "*** Building and testing $scheme..."
+    echo
+
+    local sdkflag=
+    local action=test
+
+    # Determine whether we can run unit tests for this target.
+    run_xctool -scheme "$scheme" run-tests | parse_build

    local awkstatus=$?
-    local xcstatus=${PIPESTATUS[0]}

-    if [ "$xcstatus" -eq "65" ]
+    if [ "$awkstatus" -ne "0" ]
    then
-        # This probably means that there's no scheme by that name. Give up.
-        echo "*** Error building scheme $scheme -- perhaps it doesn't exist"
-    elif [ "$awkstatus" -eq "1" ]
-    then
-        return $awkstatus
+        # Unit tests aren't supported.
+        action=build
    fi

-    return $xcstatus
+    if [ "$awkstatus" -eq "1" ]
+    then
+        # Build for iOS.
+        sdkflag="-sdk iphonesimulator"
+    fi
+
+    run_xctool $sdkflag -scheme "$scheme" $action
 }

-echo "*** Building..."
+export -f build_scheme
+export -f run_xctool
+export -f parse_build

-for scheme in "$@"
-do
-    build_scheme "$scheme" || exit $?
-done
+main
@@ -0,0 +1,12 @@
+BEGIN {
+    FS = "\n";
+}
+
+/Targets:/ {
+    while (getline && $0 != "") {
+        if ($0 ~ /Test/) continue;
+
+        sub(/^ +/, "");
+        print "'" $0 "'";
+    }
+}
@@ -0,0 +1,25 @@
+# Exit statuses:
+#
+# 0 - No errors found.
+# 1 - Wrong SDK. Retry with SDK `iphonesimulator`.
+# 2 - Missing target.
+
+BEGIN {
+    status = 0;
+}
+
+{
+    print;
+}
+
+/Testing with the '(.+)' SDK is not yet supported/ {
+    status = 1;
+}
+
+/does not contain a target named/ {
+    status = 2;
+}
+
+END {
+    exit status;
+}