Support Request hijacking in Shelf, using a similar API to Rack.

pkg/shelf/lib/src/handlers/logger.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.
 
 library shelf.handlers.logger;
 
 import 'package:stack_trace/stack_trace.dart';
 
+import '../hijack_exception.dart';
 import '../middleware.dart';
 import '../util.dart';
 
 /// Middleware which prints the time of the request, the elapsed time for the
 /// inner handlers, the response's status code and the request URI.
 ///
 /// [logger] takes two paramaters.
 ///
 /// `msg` includes the request time, duration, request method, and requested
 /// path.
@@ skipping 11 matching lines @@
     var watch = new Stopwatch()..start();
 
     return syncFuture(() => innerHandler(request)).then((response) {
       var msg = _getMessage(startTime, response.statusCode, request.url,
           request.method, watch.elapsed);
 
       logger(msg, false);
 
       return response;
     }, onError: (error, stackTrace) {
+      if (error is HijackException) throw error;
+
       var msg = _getErrorMessage(startTime, request.url, request.method,
           watch.elapsed, error, stackTrace);
 
       logger(msg, true);
 
       throw error;
     });
   };
 };
 
@@ skipping 19 matching lines @@
   return '$msg\n$chain';
 }
 
 void _defaultLogger(String msg, bool isError) {
   if (isError) {
     print('[ERROR] $msg');
   } else {
     print(msg);
   }
 }