Add support for controlling HttpResponse.bufferOutput to shelf_io.

lib/shelf_io.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.
 
 /// A Shelf adapter for handling [HttpRequest] objects from `dart:io`.
 ///
 /// One can provide an instance of [HttpServer] as the `requests` parameter in
 /// [serveRequests].
 ///
-/// The `dart:io` adapter supports request hijacking; see [Request.hijack].
+/// This adapter supports request hijacking; see [Request.hijack]. It also
+/// supports the `"shelf.io.buffer_output"` `Response.context` property. If this
+/// property is `true` (the default), streamed responses will be buffered to
+/// improve performance; if it's `false`, all chunks will be pushed over the
+/// wire as they're received. See [`HttpResponse.bufferOutput`][bufferOutput]
+/// for more information.
+///
+/// [bufferOutput]: https://api.dartlang.org/apidocs/channels/stable/dartdoc-viewer/dart:io.HttpResponse#id_bufferOutput
 library shelf.io;
 
 import 'dart:async';
 import 'dart:io';
 
 import 'package:stack_trace/stack_trace.dart';
 
 import 'shelf.dart';
 import 'src/util.dart';
 
@@ skipping 50 matching lines @@
       // If the request wasn't hijacked, we shouldn't be seeing this exception.
       return _logError(
           "Caught HijackException, but the request wasn't hijacked.",
           stackTrace);
     }
 
     return _logError('Error thrown by handler.\n$error', stackTrace);
   }).then((response) {
     if (response == null) {
       response = _logError('null response from handler.');
-    } else if (!shelfRequest.canHijack) {
-      var message = new StringBuffer()
-        ..writeln("Got a response for hijacked request "
-            "${shelfRequest.method} ${shelfRequest.requestedUri}:")
-        ..writeln(response.statusCode);
-      response.headers
-          .forEach((key, value) => message.writeln("${key}: ${value}"));
-      throw new Exception(message.toString().trim());
+    } else if (shelfRequest.canHijack) {
+      return _writeResponse(response, request.response);
     }
 
-    return _writeResponse(response, request.response);
+    var message = new StringBuffer()
+      ..writeln("Got a response for hijacked request "
+          "${shelfRequest.method} ${shelfRequest.requestedUri}:")
+      ..writeln(response.statusCode);
+    response.headers
+        .forEach((key, value) => message.writeln("${key}: ${value}"));
+    throw new Exception(message.toString().trim());
   }).catchError((error, stackTrace) {
     // Ignore HijackExceptions.
     if (error is! HijackException) throw error;
   });
 }
 
 /// Creates a new [Request] from the provided [HttpRequest].
 Request _fromHttpRequest(HttpRequest request) {
   var headers = {};
   request.headers.forEach((k, v) {
     // Multiple header values are joined with commas.
     // See http://tools.ietf.org/html/draft-ietf-httpbis-p1-messaging-21#page-22
     headers[k] = v.join(',');
   });
 
   onHijack(callback) {
     return request.response
         .detachSocket(writeHeaders: false)
         .then((socket) => callback(socket, socket));
   }
 
   return new Request(request.method, request.requestedUri,
       protocolVersion: request.protocolVersion,
       headers: headers,
       body: request,
       onHijack: onHijack);
 }
 
 Future _writeResponse(Response response, HttpResponse httpResponse) {
+  if (response.context.containsKey("shelf.io.buffer_output")) {
+    httpResponse.bufferOutput = response.context["shelf.io.buffer_output"];
+  }
+
   httpResponse.statusCode = response.statusCode;
 
   response.headers.forEach((header, value) {
     if (value == null) return;
     httpResponse.headers.set(header, value);
   });
 
   if (!response.headers.containsKey(HttpHeaders.SERVER)) {
     httpResponse.headers.set(HttpHeaders.SERVER, 'dart:io with Shelf');
   }
@@ skipping 15 matching lines @@
     chain = new Chain.forTrace(stackTrace);
   }
   chain = chain
       .foldFrames((frame) => frame.isCore || frame.package == 'shelf').terse;
 
   stderr.writeln('ERROR - ${new DateTime.now()}');
   stderr.writeln(message);
   stderr.writeln(chain);
   return new Response.internalServerError();
 }