Added decode string

BitTorrent/Bencode/BEncoder+decode.swift

@@ -66,5 +66,16 @@ public extension BEncoder {
         return byteStream.nextBytes(numberOfBytes)!
     }
 
+    public class func decodeString(data: NSData) throws -> String {
+        return try self.decodeString(NSDataByteStream(data: data));
+    }
+
+    class func decodeString(byteStream: ByteStream) throws -> String {
+        let data = try self.decodeByteString(byteStream)
+        guard let result = String(asciiData: data) else {
+            throw AsciiError.Invalid
+        }
+        return result
+    }
     
 }

BitTorrent/Utilities/Ascii.swift

@@ -111,16 +111,15 @@ extension Character {
 
 extension String {
     
+    init?(asciiData: NSData) {
+        self.init(data: asciiData, encoding: NSASCIIStringEncoding)
+    }
+    
     func asciiValue() throws -> NSData {
-        let data = NSMutableData()
-        for character in self.utf8 {
-            if UnicodeScalar(character).isASCII() {
-                data.appendData(character.toData())
-            } else {
-                throw AsciiError.Invalid
-            }
+        guard let result = (self as NSString).dataUsingEncoding(NSASCIIStringEncoding) else {
+            throw AsciiError.Invalid
         }
-        return data
+        return result
     }
     
 }

BitTorrentTests/Bencode/BEncoderDecodeTests.swift

@@ -117,5 +117,19 @@ class BEncoderDecodeTests: XCTestCase {
         }
 
     }
+    
+    func testDecodeEmptyString() {
+        let emptyString = ""
+        let input = BEncoder.encodeString(emptyString)
+        let result = try! BEncoder.decodeString(input)
+        XCTAssertEqual(emptyString, result)
+    }
+    
+    func testDecodeString() {
+        let string = "A simple test string"
+        let input = BEncoder.encodeString(string)
+        let result = try! BEncoder.decodeString(input)
+        XCTAssertEqual(string, result)
+    }
 
 }