Add support for HttpServer.defaultResponseHeaders to HttpMultiServer.

pkg/http_multi_server/lib/http_multi_server.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 http_multi_server;
 
 import 'dart:async';
 import 'dart:io';
 
+import 'src/multi_headers.dart';
 import 'src/utils.dart';
 
 /// An implementation of `dart:io`'s [HttpServer] that wraps multiple servers
 /// and forwards methods to all of them.
 ///
 /// This is useful for serving the same application on multiple network
 /// interfaces while still having a unified way of controlling the servers. In
 /// particular, it supports serving on both the IPv4 and IPv6 loopback addresses
 /// using [HttpMultiServer.loopback].
 class HttpMultiServer extends StreamView<HttpRequest> implements HttpServer {
   /// The wrapped servers.
   final Set<HttpServer> _servers;
 
+  /// Returns the default value of the `Server` header for all responses
+  /// generated by each server.
+  ///
+  /// If the wrapped servers have different default values, it's not defined
+  /// which value is returned.
   String get serverHeader => _servers.first.serverHeader;
   set serverHeader(String value) {
     for (var server in _servers) {
       server.serverHeader = value;
     }
   }
 
-  HttpHeaders get defaultResponseHeaders =>
-      throw new UnsupportedError('defaultResponseHeaders not supported');
+  /// Returns the default set of headers added to all response objects.
+  ///
+  /// If the wrapped servers have different default headers, it's not defined
+  /// which header is returned for accessor methods.
+  final HttpHeaders defaultResponseHeaders;
 
   Duration get idleTimeout => _servers.first.idleTimeout;
   set idleTimeout(Duration value) {
     for (var server in _servers) {
       server.idleTimeout = value;
     }
   }
 
   /// Returns the port that one of the wrapped servers is listening on.
   ///
@@ skipping 12 matching lines @@
       server.sessionTimeout = value;
     }
   }
 
   /// Creates an [HttpMultiServer] wrapping [servers].
   ///
   /// All [servers] should have the same configuration and none should be
   /// listened to when this is called.
   HttpMultiServer(Iterable<HttpServer> servers)
       : _servers = servers.toSet(),
+        defaultResponseHeaders = new MultiHeaders(
+            servers.map((server) => server.defaultResponseHeaders)),
         super(mergeStreams(servers));
 
   /// Creates an [HttpServer] listening on all available loopback addresses for
   /// this computer.
   ///
   /// If this computer supports both IPv4 and IPv6, this returns an
   /// [HttpMultiServer] listening to [port] on both loopback addresses.
   /// Otherwise, it returns a normal [HttpServer] listening only on the IPv4
   /// address.
   ///
@@ skipping 56 matching lines @@
     for (var server in _servers) {
       var subInfo = server.connectionsInfo();
       info.total += subInfo.total;
       info.active += subInfo.active;
       info.idle += subInfo.idle;
       info.closing += subInfo.closing;
     }
     return info;
   }
 }