Expose content shell's remote debugging URL.

lib/src/util/io.dart

 // Copyright (c) 2015, 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 test.util.io;
 
 import 'dart:async';
 import 'dart:convert';
 import 'dart:io';
 import 'dart:mirrors';
@@ skipping 177 matching lines @@
 /// returned.
 String libraryPath(Symbol libraryName, {String packageRoot}) {
   var lib = currentMirrorSystem().findLibrary(libraryName);
   if (lib.uri.scheme != 'package') return p.fromUri(lib.uri);
 
   // TODO(nweiz): is there a way to avoid assuming this is being run next to a
   // packages directory?.
   if (packageRoot == null) packageRoot = p.absolute('packages');
   return p.join(packageRoot, p.fromUri(lib.uri.path));
 }
+
+/// Repeatedly finds a probably-unused port on localhost and passes it to
+/// [tryPort] until it binds successfully.
+///
+/// [tryPort] should return a non-`null` value or a Future completing to a
+/// non-`null` value once it binds successfully. This value will be returned
+/// by [getUnusedPort] in turn.
+///
+/// This is necessary for ensuring that our port binding isn't flaky for
+/// applications that don't print out the bound port.
+Future getUnusedPort(tryPort(int port)) {
+  var value;
+  return Future.doWhile(() async {
+    var socket = await RawServerSocket.bind(InternetAddress.LOOPBACK_IP_V4, 0);
+    var port = socket.port;
+    await socket.close();
+
+    value = await tryPort(port);
+    return value == null;
+  }).then((_) => value);
+}