Add async/await examples (#553)

Examples/GetJSON/GetJSON.swift

@@ -0,0 +1,52 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the AsyncHTTPClient open source project
+//
+// Copyright (c) 2022 Apple Inc. and the AsyncHTTPClient project authors
+// Licensed under Apache License v2.0
+//
+// See LICENSE.txt for license information
+// See CONTRIBUTORS.txt for the list of AsyncHTTPClient project authors
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+//===----------------------------------------------------------------------===//
+
+import AsyncHTTPClient
+import Foundation
+import NIOCore
+import NIOFoundationCompat
+
+struct Comic: Codable {
+    var num: Int
+    var title: String
+    var day: String
+    var month: String
+    var year: String
+    var img: String
+    var alt: String
+    var news: String
+    var link: String
+    var transcript: String
+}
+
+@main
+struct GetJSON {
+    static func main() async throws {
+        let httpClient = HTTPClient(eventLoopGroupProvider: .createNew)
+        do {
+            let request = HTTPClientRequest(url: "https://xkcd.com/info.0.json")
+            let response = try await httpClient.execute(request, timeout: .seconds(30))
+            print("HTTP head", response)
+            let body = try await response.body.collect(upTo: 1024 * 1024) // 1 MB
+            // we use an overload defined in `NIOFoundationCompat` for `decode(_:from:)` to
+            // efficiently decode from a `ByteBuffer`
+            let comic = try JSONDecoder().decode(Comic.self, from: body)
+            dump(comic)
+        } catch {
+            print("request failed:", error)
+        }
+        // it is important to shutdown the httpClient after all requests are done, even if one failed
+        try await httpClient.shutdown()
+    }
+}