Rip out the last dart:io dependency from pkg/http.

pkg/http/lib/browser_client.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 http.browser_client;
+
+import 'dart:async';
+import 'dart:html';
+import 'dart:typed_data';
+
+import 'package:stack_trace/stack_trace.dart';
+
+import 'src/base_client.dart';
+import 'src/base_request.dart';
+import 'src/byte_stream.dart';
+import 'src/exception.dart';
+import 'src/streamed_response.dart';
+
+// TODO(nweiz): Move this under src/, re-export from lib/http.dart, and use this
+// automatically from [new Client] once we can create an HttpRequest using
+// mirrors on dart2js (issue 18541) and dart2js doesn't crash on pkg/collection
+// (issue 18535).
+
+/// A `dart:html`-based HTTP client that runs in the browser and is backed by
+/// XMLHttpRequests.
+///
+/// This client inherits some of the limitations of XMLHttpRequest. It ignores
+/// the [BaseRequest.contentLength], [BaseRequest.persistentConnection],
+/// [BaseRequest.followRedirects], and [BaseRequest.maxRedirects] fields. It is
+/// also unable to stream requests or responses; a request will only be sent and
+/// a response will only be returned once all the data is available.
+class BrowserClient extends BaseClient {
+  /// The currently active XHRs.
+  ///
+  /// These are aborted if the client is closed.
+  final _xhrs = new Set<HttpRequest>();
+
+  /// Creates a new HTTP client.
+  BrowserClient();
+
+  /// Sends an HTTP request and asynchronously returns the response.
+  Future<StreamedResponse> send(BaseRequest request) {
+    return request.finalize().toBytes().then((bytes) {
+      var xhr = new HttpRequest();
+      _xhrs.add(xhr);
+      xhr.open(request.method, request.url.toString(), async: true);
+      xhr.responseType = 'blob';
+      request.headers.forEach(xhr.setRequestHeader);
+
+      var completer = new Completer();
+      xhr.onLoad.first.then((_) {
+        // TODO(nweiz): Set the response type to "arraybuffer" when issue 18542
+        // is fixed.
+        var blob = xhr.response == null ? new Blob([]) : xhr.response;
+        var reader = new FileReader();
+
+        reader.onLoad.first.then((_) {
+          var body = reader.result;
+          completer.complete(new StreamedResponse(
+              new ByteStream.fromBytes(body),
+              xhr.status,
+              contentLength: body.length,
+              request: request,
+              headers: xhr.responseHeaders,
+              reasonPhrase: xhr.statusText));
+        });
+
+        reader.onError.first.then((error) {
+          completer.complete(
+              new ClientException(error.toString(), request.url),
+              new Chain.current());
+        });
+
+        reader.readAsArrayBuffer(blob);
+      });
+
+      xhr.onError.first.then((_) {
+        // Unfortunately, the underlying XMLHttpRequest API doesn't expose any
+        // specific information about the error itself.
+        completer.completeError(
+            new ClientException("XMLHttpRequest error.", request.url),
+            new Chain.current());
+      });
+
+      xhr.send(bytes);
+      return completer.future.whenComplete(() => _xhrs.remove(xhr));
+    });
+  }
+
+  /// Closes the client.
+  ///
+  /// This terminates all active requests.
+  void close() {
+    for (var xhr in _xhrs) {
+      xhr.abort();
+    }
+  }
+}