Swallow errors in subscriptions.

pkg/http_multi_server/test/http_multi_server_test.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.test;
 
 import 'dart:async';
 import 'dart:io';
 
 import 'package:http/http.dart' as http;
@@ skipping 90 matching lines @@
 
     test("listens on all localhost interfaces", () {
       server.listen((request) {
         request.response.write("got request");
         request.response.close();
       });
 
       expect(http.read("http://127.0.0.1:${server.port}/"),
           completion(equals("got request")));
 
-      return supportsIpV6.then((supportsIpV6) {
+      return _supportsIpV6.then((supportsIpV6) {
         if (!supportsIpV6) return;
         expect(http.read("http://[::1]:${server.port}/"),
             completion(equals("got request")));
       });
     });
   });
 }
 
+/// A cache for [supportsIpV6].
+bool _supportsIpV6Cache;
+
+/// Returns whether this computer supports binding to IPv6 addresses.
+Future<bool> get _supportsIpV6 {
+  if (_supportsIpV6Cache != null) return new Future.value(_supportsIpV6Cache);
+
+  return ServerSocket.bind(InternetAddress.LOOPBACK_IP_V6, 0).then((socket) {
+    _supportsIpV6Cache = true;
+    socket.close();
+    return true;
+  }).catchError((error) {
+    if (error is! SocketException) throw error;
+    _supportsIpV6Cache = false;
+    return false;
+  });
+}

[nweiz, 2014/07/09 02:02:01]

I'm kind of uncomfortable about using different IPv6-detection logic in the
tests than we do in the library. If we can't trust this logic to be accurate
everywhere, how can we trust that the test won't be flaky?

+
 /// Makes a GET request to the root of [server] and returns the response.
 Future<http.Response> _get(HttpServer server) => http.get(_urlFor(server));
 
 /// Makes a GET request to the root of [server] and returns the response body.
 Future<String> _read(HttpServer server) => http.read(_urlFor(server));
 
 /// Returns the URL for the root of [server].
 String _urlFor(HttpServer server) =>
     "http://${server.address.host}:${server.port}/";