Grpc-web Handle empty trailers (#247)

* Grpc-web Handle empty trailers

CHANGELOG.md

@@ -1,5 +1,6 @@
 ## 2.1.3
 
+* Fix bug in grpc-web when receiving an empty trailer.
 * Fix a state bug in the server.
 
 ## 2.1.2

lib/src/client/transport/web_streams.dart

@@ -118,7 +118,8 @@ class _GrpcWebConversionSink extends ChunkedConversionSink<ByteBuffer> {
   }
 
   Map<String, String> _parseHttp1Headers(String stringData) {
-    final chunks = stringData.trim().split('\r\n');
+    final trimmed = stringData.trim();
+    final chunks = trimmed == '' ? [] : trimmed.split('\r\n');
     final headers = <String, String>{};
     for (final chunk in chunks) {
       final pos = chunk.indexOf(':');

test/client_tests/client_xhr_transport_test.dart

@@ -121,6 +121,68 @@ void main() {
     });
   });
 
+  test('Stream handles trailers properly', () async {
+    final trailers = <String, String>{
+      'trailer_1': 'value_1',
+      'trailer_2': 'value_2'
+    };
+
+    final connection = MockXhrClientConnection();
+
+    final stream = connection.makeRequest('test_path', Duration(seconds: 10),
+        {}, (error) => fail(error.toString()));
+
+    final encodedTrailers = frame(trailers.entries
+        .map((e) => '${e.key}:${e.value}')
+        .join('\r\n')
+        .codeUnits);
+    encodedTrailers[0] = 0x80; // Mark this frame as trailers.
+    final encodedString = String.fromCharCodes(encodedTrailers);
+
+    stream.incomingMessages.listen((message) {
+      expect(message, TypeMatcher<GrpcMetadata>());
+      if (message is GrpcMetadata) {
+        message.metadata.forEach((key, value) {
+          expect(value, trailers[key]);
+        });
+      }
+    });
+    when(connection.latestRequest.getResponseHeader('Content-Type'))
+        .thenReturn('application/grpc+proto');
+    when(connection.latestRequest.responseHeaders).thenReturn({});
+    when(connection.latestRequest.readyState)
+        .thenReturn(HttpRequest.HEADERS_RECEIVED);
+    when(connection.latestRequest.response).thenReturn(encodedString);
+    connection.latestRequest.readyStateChangeController.add(null);
+    connection.latestRequest.progressController.add(null);
+  });
+
+  test('Stream handles empty trailers properly', () async {
+    final connection = MockXhrClientConnection();
+
+    final stream = connection.makeRequest('test_path', Duration(seconds: 10),
+        {}, (error) => fail(error.toString()));
+
+    final encoded = frame(''.codeUnits);
+    encoded[0] = 0x80; // Mark this frame as trailers.
+    final encodedString = String.fromCharCodes(encoded);
+
+    stream.incomingMessages.listen((message) {
+      expect(message, TypeMatcher<GrpcMetadata>());
+      if (message is GrpcMetadata) {
+        message.metadata.isEmpty;
+      }
+    });
+    when(connection.latestRequest.getResponseHeader('Content-Type'))
+        .thenReturn('application/grpc+proto');
+    when(connection.latestRequest.responseHeaders).thenReturn({});
+    when(connection.latestRequest.readyState)
+        .thenReturn(HttpRequest.HEADERS_RECEIVED);
+    when(connection.latestRequest.response).thenReturn(encodedString);
+    connection.latestRequest.readyStateChangeController.add(null);
+    connection.latestRequest.progressController.add(null);
+  });
+
   test('Stream deserializes data properly', () async {
     final metadata = <String, String>{
       'parameter_1': 'value_1',