Support Request hijacking in Shelf, using a similar API to Rack.

pkg/shelf/test/shelf_io_test.dart

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library shelf_io_test;
 
 import 'dart:async';
 import 'dart:convert';
 import 'dart:io';
 
@@ skipping 167 matching lines @@
         return syncHandler(request);
       });
     });
 
     return _schedulePost(body: 'test body').then((response) {
       expect(response.statusCode, HttpStatus.OK);
       expect(response.stream.bytesToString(), completion('Hello from /'));
     });
   });
 
+  test('supports request hijacking', () {
+    _scheduleServer((request) {
+      expect(request.method, 'POST');
+
+      request.hijack(expectAsync((stream, sink) {
+        expect(stream.first, completion(equals("Hello".codeUnits)));
+
+        sink.add((
+            "HTTP/1.1 404 Not Found\r\n"
+            "Date: Mon, 23 May 2005 22:38:34 GMT\r\n"
+            "Content-Length: 13\r\n"
+            "\r\n"
+            "Hello, world!").codeUnits);
+        sink.close();
+      }));
+    });
+
+    return _schedulePost(body: "Hello").then((response) {
+      expect(response.statusCode, HttpStatus.NOT_FOUND);
+      expect(response.headers["date"], "Mon, 23 May 2005 22:38:34 GMT");
+      expect(response.stream.bytesToString(),
+          completion(equals("Hello, world!")));
+    });
+  });
+
+  test('reports an error if a HijackException is thrown without hijacking', () {
+    _scheduleServer((request) => throw const HijackException());
+
+    return _scheduleGet().then((response) {
+      expect(response.statusCode, HttpStatus.INTERNAL_SERVER_ERROR);
+    });
+  });
+
   test('passes asynchronous exceptions to the parent error zone', () {
     return runZoned(() {
       return shelf_io.serve((request) {
         new Future(() => throw 'oh no');
         return syncHandler(request);
       }, 'localhost', 0).then((server) {
         return http.get('http://localhost:${server.port}').then((response) {
           expect(response.statusCode, HttpStatus.OK);
           expect(response.body, 'Hello from /');
           server.close();
@@ skipping 47 matching lines @@
 
     var request = new http.Request('POST',
         Uri.parse('http://localhost:$_serverPort/'));
 
     if (headers != null) request.headers.addAll(headers);
     if (body != null) request.body = body;
 
     return request.send();
   });
 }