Rip out dart:io from pkg/http wherever possible.

pkg/http/lib/http.dart

 // Copyright (c) 2013, 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.
 
 /// A composable, [Future]-based library for making HTTP requests.
 ///
 /// ## Installing ##
 ///
 /// Use [pub][] to install this package. Add the following to your
 /// `pubspec.yaml` file.
@@ skipping 41 matching lines @@
 /// to add behavior should create a subclass of [BaseClient] that wraps another
 /// [Client] and adds the desired behavior:
 ///
 ///     class UserAgentClient extends http.BaseClient {
 ///       final String userAgent;
 ///       final http.Client _inner;
 ///
 ///       UserAgentClient(this.userAgent, this._inner);
 ///
 ///       Future<StreamedResponse> send(BaseRequest request) {
-///         request.headers[HttpHeaders.USER_AGENT] = userAgent;
+///         request.headers['user-agent'] = userAgent;
 ///         return _inner.send(request);
 ///       }
 ///     }
 ///
 /// [pub]: http://pub.dartlang.org
 library http;
 
 import 'dart:async';
 import 'dart:convert';
 import 'dart:typed_data';
 
 import 'src/client.dart';
 import 'src/response.dart';
 
 export 'src/base_client.dart';
 export 'src/base_request.dart';
 export 'src/base_response.dart';
 export 'src/byte_stream.dart';
 export 'src/client.dart';
+export 'src/exception.dart';
 export 'src/multipart_file.dart';
 export 'src/multipart_request.dart';
 export 'src/request.dart';
 export 'src/response.dart';
 export 'src/streamed_request.dart';
 export 'src/streamed_response.dart';
 
 /// Sends an HTTP HEAD request with the given headers to the given URL, which
 /// can be a [Uri] or a [String].
 ///
@@ skipping 72 matching lines @@
 /// the same server, you should use a single [Client] for all of those requests.
 ///
 /// For more fine-grained control over the request, use [Request] instead.
 Future<Response> delete(url, {Map<String, String> headers}) =>
   _withClient((client) => client.delete(url, headers: headers));
 
 /// Sends an HTTP GET request with the given headers to the given URL, which can
 /// be a [Uri] or a [String], and returns a Future that completes to the body of
 /// the response as a [String].
 ///
-/// The Future will emit an [HttpException] if the response doesn't have a
+/// The Future will emit a [ClientException] if the response doesn't have a
 /// success status code.
 ///
 /// This automatically initializes a new [Client] and closes that client once
 /// the request is complete. If you're planning on making multiple requests to
 /// the same server, you should use a single [Client] for all of those requests.
 ///
 /// For more fine-grained control over the request and response, use [Request]
 /// instead.
 Future<String> read(url, {Map<String, String> headers}) =>
   _withClient((client) => client.read(url, headers: headers));
 
 /// Sends an HTTP GET request with the given headers to the given URL, which can
 /// be a [Uri] or a [String], and returns a Future that completes to the body of
 /// the response as a list of bytes.
 ///
-/// The Future will emit an [HttpException] if the response doesn't have a
+/// The Future will emit a [ClientException] if the response doesn't have a
 /// success status code.
 ///
 /// This automatically initializes a new [Client] and closes that client once
 /// the request is complete. If you're planning on making multiple requests to
 /// the same server, you should use a single [Client] for all of those requests.
 ///
 /// For more fine-grained control over the request and response, use [Request]
 /// instead.
 Future<Uint8List> readBytes(url, {Map<String, String> headers}) =>
   _withClient((client) => client.readBytes(url, headers: headers));
 
 Future _withClient(Future fn(Client)) {
   var client = new Client();
   var future = fn(client);
   return future.whenComplete(client.close);
 }