Change default authority for UDS connections. (#577)

We were using path to the UDS socket itself, which is incorrect `:authority` value. 

This was tripping checks in some HTTP2 protocol implementations.

Instead default `:authority` to `localhost`, which in line with other gRPC implementations.

Fixes #576

CHANGELOG.md

@@ -3,6 +3,10 @@
 * Expose a stream for connection state changes on ClientChannel to address
   [#428](https://github.com/grpc/grpc-dart/issues/428).
   This allows users to react to state changes in the connection.
+* Fix [#576](https://github.com/grpc/grpc-dart/issues/576): set default
+  `:authority` value for UDS connections to `localhost` instead of using
+  UDS path. Using path triggers checks in HTTP2 servers which
+  attempt to validate `:authority` value.
 
 ## 3.0.2
 

lib/src/client/http2_connection.dart

@@ -355,10 +355,23 @@ class _SocketTransportConnector implements ClientTransportConnector {
 
   @override
   String get authority {
-    final host =
-        _host is String ? _host as String : (_host as InternetAddress).host;
-    return _options.credentials.authority ??
-        (_port == 443 ? host : '$host:$_port');
+    return _options.credentials.authority ?? _makeAuthority();
+  }
+
+  String _makeAuthority() {
+    final host = _host;
+    final portSuffix = _port == 443 ? '' : ':$_port';
+    final hostName;
+    if (host is String) {
+      hostName = '$host';
+    } else {
+      host as InternetAddress;
+      if (host.type == InternetAddressType.unix) {
+        return 'localhost'; // UDS don't have a meaningful authority.
+      }
+      hostName = host.host;
+    }
+    return '$hostName$portSuffix';
   }
 
   @override

test/common.dart

@@ -16,6 +16,21 @@ import 'dart:async';
 import 'dart:io';
 import 'package:test/test.dart';
 
+/// Test functionality for Unix domain socket.
+void testUds(String name, FutureOr<void> Function(InternetAddress) testCase) {
+  if (Platform.isWindows) {
+    return;
+  }
+
+  test(name, () async {
+    final tempDir = await Directory.systemTemp.createTemp();
+    final address = InternetAddress(tempDir.path + '/socket',
+        type: InternetAddressType.unix);
+    addTearDown(() => tempDir.delete(recursive: true));
+    await testCase(address);
+  });
+}
+
 /// Test functionality for both TCP and Unix domain sockets.
 void testTcpAndUds(
     String name, FutureOr<void> Function(InternetAddress) testCase,
@@ -25,15 +40,5 @@ void testTcpAndUds(
     await testCase(address.first);
   });
 
-  if (Platform.isWindows) {
-    return;
-  }
-
-  test('$name (over uds)', () async {
-    final tempDir = await Directory.systemTemp.createTemp();
-    final address = InternetAddress(tempDir.path + '/socket',
-        type: InternetAddressType.unix);
-    addTearDown(() => tempDir.delete(recursive: true));
-    await testCase(address);
-  });
+  testUds('$name (over uds)', testCase);
 }

test/round_trip_test.dart

@@ -23,10 +23,12 @@ class TestClient extends Client {
 }
 
 class TestService extends Service {
+  final String? expectedAuthority;
+
   @override
   String get $name => 'test.TestService';
 
-  TestService() {
+  TestService({this.expectedAuthority}) {
     $addMethod(ServiceMethod<int, int>('stream', stream, false, true,
         (List<int> value) => value[0], (int value) => [value]));
   }
@@ -35,12 +37,20 @@ class TestService extends Service {
   static const requestInfiniteStream = 2;
 
   Stream<int> stream(ServiceCall call, Future request) async* {
+    checkMetadata(call.clientMetadata);
+
     final isInfinite = 2 == await request;
     for (var i = 1; i <= 3 || isInfinite; i++) {
       yield i;
       await Future.delayed(Duration(milliseconds: 100));
     }
   }
+
+  void checkMetadata(Map<String, String>? metadata) {
+    if (expectedAuthority != null) {
+      expect(metadata![':authority'], equals(expectedAuthority));
+    }
+  }
 }
 
 class TestServiceWithOnMetadataException extends TestService {
@@ -93,6 +103,22 @@ Future<void> main() async {
     server.shutdown();
   });
 
+  testUds('UDS provides valid default authority', (address) async {
+    // round trip test of insecure connection.
+    final server = Server([TestService(expectedAuthority: 'localhost')]);
+    await server.serve(address: address, port: 0);
+
+    final channel = FixedConnectionClientChannel(Http2ClientConnection(
+      address,
+      server.port!,
+      ChannelOptions(credentials: ChannelCredentials.insecure()),
+    ));
+    final testClient = TestClient(channel);
+    expect(await testClient.stream(TestService.requestFiniteStream).toList(),
+        [1, 2, 3]);
+    server.shutdown();
+  });
+
   testTcpAndUds('round trip with outgoing and incoming compression',
       (address) async {
     final server = Server(