Swallow errors in subscriptions.

pkg/http_multi_server/test/http_multi_server_test.dart

Index: pkg/http_multi_server/test/http_multi_server_test.dart
diff --git a/pkg/http_multi_server/test/http_multi_server_test.dart b/pkg/http_multi_server/test/http_multi_server_test.dart
index a3d9062067bced9da28b8452eccec18c0212a906..3e6f73b5bc1ab0c1fa5fe53cf536b3e0c3b835ea 100644
--- a/pkg/http_multi_server/test/http_multi_server_test.dart
+++ b/pkg/http_multi_server/test/http_multi_server_test.dart
@@ -108,7 +108,7 @@ void main() {
       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")));
@@ -117,6 +117,24 @@ void main() {
   });
 }
 
+/// 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));