Add an HTTP library that wraps dart:io.

pkg/http/lib/src/streamed_request.dart

+// Copyright (c) 2012, 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 streamed_request;
+
+import 'dart:io';
+import 'dart:uri';
+
+import 'base_request.dart';
+
+/// An HTTP request where the request body is sent asynchronously after the
+/// connection has been established and the headers have been sent.
+///
+/// When the request is sent via [BaseClient.send], only the headers and
+/// whatever data has already been written to [StreamedRequest.stream] will be
+/// sent immediately. More data will be sent as soon as it's written to
+/// [StreamedRequest.stream], and when the stream is closed the request will
+/// end.
+class StreamedRequest extends BaseRequest {
+  /// The stream to which to write data that will be sent as the request body.
+  /// This may be safely written to before the request is sent; the data will be
+  /// buffered.
+  ///
+  /// Closing this signals the end of the request.
+  final OutputStream stream;
+
+  /// The stream from which the [BaseClient] will read the data in [stream] once
+  /// the request has been finalized.
+  final ListInputStream _inputStream;
+
+  /// Creates a new streaming request.
+  StreamedRequest(String method, Uri url)
+    : super(method, url),
+      stream = new ListOutputStream(),
+      _inputStream = new ListInputStream() {
+    // TODO(nweiz): pipe errors from the output stream to the input stream once
+    // issue 3657 is fixed
+    stream.onData = () => _inputStream.write(stream.read());
+    stream.onClosed = _inputStream.markEndOfStream;
+  }
+
+  /// Freezes all mutable fields other than [stream] and returns an [InputStream]
+  /// that emits the data being written to [stream].
+  InputStream finalize() {
+    super.finalize();
+    return _inputStream;
+  }
+}