Make daemon server work on ipv6-only machines. (#144359)

Retry binding on ipv6 if binding on ipv4 failed.

Author: chingjun

packages/flutter_tools/lib/src/commands/daemon.dart

@@ -73,7 +73,7 @@ class DaemonCommand extends FlutterCommand {
         throwToolExit('Invalid port for `--listen-on-tcp-port`: $error');
       }
 
-      await _DaemonServer(
+      await DaemonServer(
         port: port,
         logger: StdoutLogger(
           terminal: globals.terminal,
@@ -100,12 +100,14 @@ class DaemonCommand extends FlutterCommand {
   }
 }
 
-class _DaemonServer {
-  _DaemonServer({
+@visibleForTesting
+class DaemonServer {
+  DaemonServer({
     this.port,
     required this.logger,
     this.notifyingLogger,
-  });
+    @visibleForTesting Future<ServerSocket> Function(InternetAddress address, int port) bind = ServerSocket.bind,
+  }) : _bind = bind;
 
   final int? port;
 
@@ -115,8 +117,20 @@ class _DaemonServer {
   // Logger that sends the message to the other end of daemon connection.
   final NotifyingLogger? notifyingLogger;
 
+  final Future<ServerSocket> Function(InternetAddress address, int port) _bind;
+
   Future<void> run() async {
-    final ServerSocket serverSocket = await ServerSocket.bind(InternetAddress.loopbackIPv4, port!);
+    ServerSocket? serverSocket;
+    try {
+      serverSocket = await _bind(InternetAddress.loopbackIPv4, port!);
+    } on SocketException {
+      logger.printTrace('Bind on $port failed with IPv4, retrying on IPv6');
+    }
+
+    // If binding on IPv4 failed, try binding on IPv6.
+    // Omit try catch here, let the failure fallthrough.
+    serverSocket ??= await _bind(InternetAddress.loopbackIPv6, port!);
+
     logger.printStatus('Daemon server listening on ${serverSocket.port}');
 
     final StreamSubscription<Socket> subscription = serverSocket.listen(

packages/flutter_tools/test/general.shard/commands/daemon_test.dart

@@ -0,0 +1,96 @@
+// Copyright 2014 The Flutter Authors. 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 'package:flutter_tools/src/base/io.dart';
+import 'package:flutter_tools/src/base/logger.dart';
+import 'package:flutter_tools/src/commands/daemon.dart';
+import 'package:test/fake.dart';
+
+import '../../src/common.dart';
+
+void main() {
+  testWithoutContext('binds on ipv4 normally', () async {
+    final FakeServerSocket socket = FakeServerSocket();
+    final BufferLogger logger = BufferLogger.test();
+
+    int bindCalledTimes = 0;
+    final List<Object?> bindAddresses = <Object?>[];
+    final List<int> bindPorts = <int>[];
+
+    final DaemonServer server = DaemonServer(
+      port: 123,
+      logger: logger,
+      bind: (Object? address, int port) async {
+        bindCalledTimes++;
+        bindAddresses.add(address);
+        bindPorts.add(port);
+        return socket;
+      },
+    );
+    await server.run();
+    expect(bindCalledTimes, 1);
+    expect(bindAddresses, <Object?>[InternetAddress.loopbackIPv4]);
+    expect(bindPorts, <int>[123]);
+  });
+
+  testWithoutContext('binds on ipv6 if ipv4 failed normally', () async {
+    final FakeServerSocket socket = FakeServerSocket();
+    final BufferLogger logger = BufferLogger.test();
+
+    int bindCalledTimes = 0;
+    final List<Object?> bindAddresses = <Object?>[];
+    final List<int> bindPorts = <int>[];
+
+    final DaemonServer server = DaemonServer(
+      port: 123,
+      logger: logger,
+      bind: (Object? address, int port) async {
+        bindCalledTimes++;
+        bindAddresses.add(address);
+        bindPorts.add(port);
+        if (address == InternetAddress.loopbackIPv4) {
+          throw const SocketException('fail');
+        }
+        return socket;
+      },
+    );
+    await server.run();
+    expect(bindCalledTimes, 2);
+    expect(bindAddresses, <Object?>[InternetAddress.loopbackIPv4, InternetAddress.loopbackIPv6]);
+    expect(bindPorts, <int>[123, 123]);
+  });
+}
+
+class FakeServerSocket extends Fake implements ServerSocket {
+  FakeServerSocket();
+
+  @override
+  int get port => 1;
+
+  bool closeCalled = false;
+  final StreamController<Socket> controller = StreamController<Socket>();
+
+  @override
+  StreamSubscription<Socket> listen(
+    void Function(Socket event)? onData, {
+    Function? onError,
+    void Function()? onDone,
+    bool? cancelOnError,
+  }) {
+    // Close the controller immediately for testing purpose.
+    scheduleMicrotask(() {
+      controller.close();
+    });
+    return controller.stream.listen(onData,
+        onError: onError, onDone: onDone, cancelOnError: cancelOnError);
+  }
+
+  @override
+  Future<ServerSocket> close() async {
+    closeCalled = true;
+    return this;
+  }
+}