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

pkg/shelf/lib/src/handlers/logger.dart

Index: pkg/shelf/lib/src/handlers/logger.dart
diff --git a/pkg/shelf/lib/src/handlers/logger.dart b/pkg/shelf/lib/src/handlers/logger.dart
index 2e95cf99268fec4f505e8414de26282f110a96c7..e949c9bc29c22a461feb834f778e9c61f8f3f71e 100644
--- a/pkg/shelf/lib/src/handlers/logger.dart
+++ b/pkg/shelf/lib/src/handlers/logger.dart
@@ -6,6 +6,7 @@ library shelf.handlers.logger;
 
 import 'package:stack_trace/stack_trace.dart';
 
+import '../hijack_exception.dart';
 import '../middleware.dart';
 import '../util.dart';
 
@@ -37,6 +38,8 @@ Middleware logRequests({void logger(String msg, bool isError)}) =>
 
       return response;
     }, onError: (error, stackTrace) {
+      if (error is HijackException) throw error;

[kevmoo, 2014/05/07 19:28:22]

Is this something we want to generalize? A base class for "functional
exceptions".

Having to special case any more of these will be annoying.

[nweiz, 2014/05/19 20:10:29]

As per our in-person discussion, I think we're unlikely to want additional
exceptions that work this way.

+
       var msg = _getErrorMessage(startTime, request.url, request.method,
           watch.elapsed, error, stackTrace);