Attempt to reduce flakiness rate of io test

tests/standalone/io/socket_source_address_test.dart

 // Copyright (c) 2013, 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.
 //
 
 import "dart:async";
 import "dart:io";
 
 import "package:async_helper/async_helper.dart";
 import "package:expect/expect.dart";
 
+import 'test_utils.dart' show freeIPv4AndIPv6Port, retry;
+
 Future throws(Function f, Function check) async {
   try {
     await f();
     Expect.fail('Did not throw');
   } catch (e) {
     if (check != null) {
       if (!check(e)) {
         Expect.fail('Unexpected: $e');
       }
     }
   }
 }
 
 Future testArguments(connectFunction) async {
+  int freePort = await freeIPv4AndIPv6Port();
+
   var sourceAddress;
   asyncStart();
-  var server = await ServerSocket.bind(InternetAddress.LOOPBACK_IP_V4, 0);
+  var server = await ServerSocket.bind(InternetAddress.LOOPBACK_IP_V4,
+                                       freePort);
   server.listen((_) {
     throw 'Unexpected connection from address $sourceAddress';
   }, onDone: () => asyncEnd());
 
   asyncStart();
   // Illegal type for sourceAddress.
   for (sourceAddress in ['www.google.com', 'abc']) {
     await throws(() => connectFunction('127.0.0.1',
                                        server.port,
                                        sourceAddress: sourceAddress),
@@ skipping 27 matching lines @@
 // IPv6 addresses to use as source address when connecting locally.
 var ipV6SourceAddresses = [InternetAddress.LOOPBACK_IP_V6,
                            InternetAddress.ANY_IP_V6,
                            '::1',
                            '::'];
 
 Future testConnect(InternetAddress bindAddress,
                    bool v6Only,
                    Function connectFunction,
                    Function closeDestroyFunction) async {
+  int freePort = await freeIPv4AndIPv6Port();
+
   var successCount = 0;
   if (!v6Only) successCount += ipV4SourceAddresses.length;
   if (bindAddress.type == InternetAddressType.IP_V6) {
      successCount += ipV6SourceAddresses.length;
   }
   var count = 0;
   var allConnected = new Completer();
   if (successCount == 0) allConnected.complete();
 
   asyncStart();
-  var server = await ServerSocket.bind(bindAddress, 0, v6Only: v6Only);
+  var server = await ServerSocket.bind(bindAddress, freePort, v6Only: v6Only);
   server.listen((s) {
     s.destroy();
     count++;
     if (count == successCount) allConnected.complete();
   }, onDone: () => asyncEnd());
 
   asyncStart();
 
   // Connect with IPv4 source addesses.
   for (var sourceAddress in ipV4SourceAddresses) {
@@ skipping 26 matching lines @@
                                          sourceAddress: sourceAddress),
                    (e) => e is SocketException);
     }
   }
 
   await allConnected.future;
   await server.close();
   asyncEnd();
 }
 
-main() {
-  testArguments(RawSocket.connect);
-  testArguments(Socket.connect);
-  testConnect(
-      InternetAddress.ANY_IP_V4, false, RawSocket.connect, (s) => s.close());
-  testConnect(
-      InternetAddress.ANY_IP_V4, false, Socket.connect, (s) => s.destroy());
-  testConnect(
-      InternetAddress.ANY_IP_V6, false, RawSocket.connect, (s) => s.close());
-  testConnect(
-      InternetAddress.ANY_IP_V6, false, Socket.connect, (s) => s.destroy());
-  testConnect(
-      InternetAddress.ANY_IP_V6, true, RawSocket.connect, (s) => s.close());
-  testConnect(
-      InternetAddress.ANY_IP_V6, true, Socket.connect, (s) => s.destroy());
+main() async {
+  asyncStart();
+
+  await retry(() async {
+    await testArguments(RawSocket.connect);
+  });
+  await retry(() async {
+    await testArguments(Socket.connect);
+  });
+
+  await retry(() async {
+    await testConnect(
+        InternetAddress.ANY_IP_V4, false, RawSocket.connect, (s) => s.close());
+  });
+  await retry(() async {
+    await testConnect(
+        InternetAddress.ANY_IP_V4, false, Socket.connect, (s) => s.destroy());
+  });
+  await retry(() async {
+    await testConnect(
+        InternetAddress.ANY_IP_V6, false, RawSocket.connect, (s) => s.close());
+  });
+  await retry(() async {
+    await testConnect(
+        InternetAddress.ANY_IP_V6, false, Socket.connect, (s) => s.destroy());
+  });
+  await retry(() async {
+    await testConnect(
+        InternetAddress.ANY_IP_V6, true, RawSocket.connect, (s) => s.close());
+  });
+  await retry(() async {
+    await testConnect(
+        InternetAddress.ANY_IP_V6, true, Socket.connect, (s) => s.destroy());
+  });
+
+  asyncEnd();
 }