Support auto-drain of HttpRequest data.

sdk/lib/io/http_impl.dart

Index: sdk/lib/io/http_impl.dart
diff --git a/sdk/lib/io/http_impl.dart b/sdk/lib/io/http_impl.dart
index dec363306776c1f0c380a365b476abd655bd748f..7e16e5fe4662e3a908d7faf1c39a9227a049bb89 100644
--- a/sdk/lib/io/http_impl.dart
+++ b/sdk/lib/io/http_impl.dart
@@ -23,6 +23,8 @@ class _HttpIncoming extends Stream<List<int>> {
   String method;
   Uri uri;
 
+  bool hasSubscriber = false;
+
   // The transfer length if the length of the message body as it
   // appears in the message (RFC 2616 section 4.4). This can be -1 if
   // the length of the massage body is not known due to transfer
@@ -38,6 +40,7 @@ class _HttpIncoming extends Stream<List<int>> {
                                        {void onError(error),
                                         void onDone(),
                                         bool cancelOnError}) {
+    hasSubscriber = true;
     return _stream.listen(onData,
                           onError: onError,
                           onDone: onDone,
@@ -49,6 +52,7 @@ class _HttpIncoming extends Stream<List<int>> {
 
   void close(bool closing) {
     fullBodyRead = true;
+    hasSubscriber = true;
     _dataCompleter.complete(closing);
   }
 }
@@ -274,7 +278,7 @@ class _HttpClientResponse
   Future<HttpClientResponse> _authenticate(bool proxyAuth) {
     Future<HttpClientResponse> retry() {
       // Drain body and retry.
-      return fold(null, (x, y) {}).then((_) {
+      return drain().then((_) {
           return _httpClient._openUrlFromRequest(_httpRequest.method,
                                                  _httpRequest.uri,
                                                  _httpRequest)
@@ -470,45 +474,56 @@ abstract class _HttpOutboundMessage<T> implements IOSink {
 
   Future<T> get done => _dataSink.done;
 
-  void _writeHeaders() {
-    if (_headersWritten) return;
+  Future _writeHeaders({drainRequest: true}) {
+    if (_headersWritten) return new Future.value();
     _headersWritten = true;
     headers._synchronize();  // Be sure the 'chunked' option is updated.
     bool isServerSide = this is _HttpResponse;
-    if (isServerSide && headers.chunkedTransferEncoding) {
+    if (isServerSide) {
       var response = this;
-      List acceptEncodings =
-          response._httpRequest.headers[HttpHeaders.ACCEPT_ENCODING];
-      List contentEncoding = headers[HttpHeaders.CONTENT_ENCODING];
-      if (acceptEncodings != null &&
-          acceptEncodings
-              .expand((list) => list.split(","))
-              .any((encoding) => encoding.trim().toLowerCase() == "gzip") &&
-          contentEncoding == null) {
-        headers.set(HttpHeaders.CONTENT_ENCODING, "gzip");
-        _asGZip = true;
+      if (headers.chunkedTransferEncoding) {
+        List acceptEncodings =
+            response._httpRequest.headers[HttpHeaders.ACCEPT_ENCODING];
+        List contentEncoding = headers[HttpHeaders.CONTENT_ENCODING];
+        if (acceptEncodings != null &&
+            acceptEncodings
+                .expand((list) => list.split(","))
+                .any((encoding) => encoding.trim().toLowerCase() == "gzip") &&
+            contentEncoding == null) {
+          headers.set(HttpHeaders.CONTENT_ENCODING, "gzip");
+          _asGZip = true;
+        }
+      }
+      if (drainRequest && !response._httpRequest._incoming.hasSubscriber) {
+        return response._httpRequest.drain()
+            // TODO(ajohnsen): Timeout on drain?
+            .catchError((_) {})  // Ignore errors.
+            .then((_) => _writeHeader());
       }
     }
-    _writeHeader();
+    return new Future.sync(_writeHeader);
   }
 
   Future _addStream(Stream<List<int>> stream) {
-    _writeHeaders();
-    int contentLength = headers.contentLength;
-    if (_ignoreBody) {
-      stream.fold(null, (x, y) {}).catchError((_) {});
-      return _headersSink.close();
-    }
-    stream = stream.transform(new _BufferTransformer());
-    if (headers.chunkedTransferEncoding) {
-      if (_asGZip) {
-        stream = stream.transform(new ZLibDeflater(gzip: true, level: 6));
-      }
-      stream = stream.transform(new _ChunkedTransformer());
-    } else if (contentLength >= 0) {
-      stream = stream.transform(new _ContentLengthValidator(contentLength));
-    }
-    return _headersSink.addStream(stream);
+    return _writeHeaders()
+        .then((_) {
+          int contentLength = headers.contentLength;
+          if (_ignoreBody) {
+            stream.drain().catchError((_) {});
+            return _headersSink.close();
+          }
+          stream = stream.transform(new _BufferTransformer());
+          if (headers.chunkedTransferEncoding) {
+            if (_asGZip) {
+              stream = stream.transform(new ZLibDeflater(gzip: true, level: 6));
+            }
+            stream = stream.transform(new _ChunkedTransformer());
+          } else if (contentLength >= 0) {
+            stream = stream.transform(
+                new _ContentLengthValidator(contentLength));
+          }
+          return _headersSink.addStream(stream);
+        });
   }
 
   Future _close() {
@@ -528,8 +543,7 @@ abstract class _HttpOutboundMessage<T> implements IOSink {
             " than 0: ${headers.contentLength}."));
       }
     }
-    _writeHeaders();
-    return _headersSink.close();
+    return _writeHeaders().then((_) => _headersSink.close());
   }
 
   void _writeHeader();  // TODO(ajohnsen): Better name.
@@ -556,6 +570,7 @@ class _HttpOutboundConsumer implements StreamConsumer {
     if (_controller != null) return;
     _controller = new StreamController(onPause: () => _subscription.pause(),
                                        onResume: () => _subscription.resume(),
+                                       onListen: () => _subscription.resume(),
                                        onCancel: _cancel);
     _outbound._addStream(_controller.stream)
         .then((_) {
@@ -608,6 +623,8 @@ class _HttpOutboundConsumer implements StreamConsumer {
           _done(error);
         },
         cancelOnError: true);
+    // Pause the first request.
+    if (_controller == null) _subscription.pause();
     _ensureController();
     return _completer.future;
   }
@@ -682,8 +699,8 @@ class _HttpResponse extends _HttpOutboundMessage<HttpResponse>
 
   Future<Socket> detachSocket() {
     if (_headersWritten) throw new StateError("Headers already sent");
-    _writeHeaders();
     var future = _httpRequest._httpConnection.detachSocket();
+    _writeHeaders(drainRequest: false).then((_) => close());
     // Close connection so the socket is 'free'.
     close();
     done.catchError((_) {
@@ -878,11 +895,11 @@ class _HttpClientRequest extends _HttpOutboundMessage<HttpClientResponse>
     if (followRedirects && response.isRedirect) {
       if (response.redirects.length < maxRedirects) {
         // Redirect and drain response.
-        future = response.fold(null, (x, y) {})
+        future = response.drain()
           .then((_) => response.redirect());
       } else {
         // End with exception, too many redirects.
-        future = response.fold(null, (x, y) {})
+        future = response.drain()
             .then((_) => new Future.error(
                 new RedirectLimitExceededException(response.redirects)));
       }