servlet: force always sending end_stream in trailer frame (Fixes #10124)

core/src/testFixtures/java/io/grpc/internal/AbstractTransportTest.java

@@ -1099,9 +1099,9 @@ public void earlyServerClose_noServerHeaders() throws Exception {
     Metadata clientStreamTrailers =
         clientStreamListener.trailers.get(TIMEOUT_MS, TimeUnit.MILLISECONDS);
     checkClientStatus(status, clientStreamStatus);
-    assertEquals(
-        Lists.newArrayList(trailers.getAll(asciiKey)),
-        Lists.newArrayList(clientStreamTrailers.getAll(asciiKey)));
+    assertAsciiMetadataValuesEqual(
+        trailers.getAll(asciiKey),
+        clientStreamTrailers.getAll(asciiKey));
     assertEquals(
         Lists.newArrayList(trailers.getAll(binaryKey)),
         Lists.newArrayList(clientStreamTrailers.getAll(binaryKey)));

servlet/src/jettyTest/java/io/grpc/servlet/JettyTransportTest.java

@@ -69,7 +69,7 @@ public void start(ServerListener listener) throws IOException {
                 listener.transportCreated(new ServletServerBuilder.ServerTransportImpl(scheduler));
         ServletAdapter adapter =
                 new ServletAdapter(serverTransportListener, streamTracerFactories,
-                        Integer.MAX_VALUE);
+                        Integer.MAX_VALUE, false);
         GrpcServlet grpcServlet = new GrpcServlet(adapter);
 
         jettyServer = new Server(0);

servlet/src/main/java/io/grpc/servlet/ServletAdapter.java

@@ -77,15 +77,18 @@ public final class ServletAdapter {
   private final List<? extends ServerStreamTracer.Factory> streamTracerFactories;
   private final int maxInboundMessageSize;
   private final Attributes attributes;
+  private final boolean forceTrailers;
 
   ServletAdapter(
       ServerTransportListener transportListener,
       List<? extends ServerStreamTracer.Factory> streamTracerFactories,
-      int maxInboundMessageSize) {
+      int maxInboundMessageSize,
+      boolean forceTrailers) {
     this.transportListener = transportListener;
     this.streamTracerFactories = streamTracerFactories;
     this.maxInboundMessageSize = maxInboundMessageSize;
     attributes = transportListener.transportReady(Attributes.EMPTY);
+    this.forceTrailers = forceTrailers;
   }
 
   /**
@@ -148,7 +151,8 @@ public void doPost(HttpServletRequest req, HttpServletResponse resp) throws IOEx
                 new InetSocketAddress(req.getLocalAddr(), req.getLocalPort()))
             .build(),
         getAuthority(req),
-        logId);
+        logId,
+        forceTrailers);
 
     transportListener.streamCreated(stream, method, headers);
     stream.transportState().runOnTransportThread(stream.transportState()::onStreamAllocated);

servlet/src/main/java/io/grpc/servlet/ServletServerBuilder.java

@@ -72,6 +72,7 @@ public final class ServletServerBuilder extends ForwardingServerBuilder<ServletS
   private boolean internalCaller;
   private boolean usingCustomScheduler;
   private InternalServerImpl internalServer;
+  private boolean forceTrailers;
 
   public ServletServerBuilder() {
     serverImplBuilder = new ServerImplBuilder(this::buildTransportServers);
@@ -98,7 +99,8 @@ public Server build() {
    * Creates a {@link ServletAdapter}.
    */
   public ServletAdapter buildServletAdapter() {
-    return new ServletAdapter(buildAndStart(), streamTracerFactories, maxInboundMessageSize);
+    return new ServletAdapter(buildAndStart(), streamTracerFactories, maxInboundMessageSize,
+        forceTrailers);
   }
 
   /**
@@ -183,6 +185,19 @@ public ServletServerBuilder maxInboundMessageSize(int bytes) {
     return this;
   }
 
+  /**
+   * Some servlet containers don't support sending trailers only (Tomcat).
+   * They send an empty data frame with an end_stream flag.
+   * This is not supported by gRPC as is expects end_stream flag in trailer or trailer-only frame
+   * To avoid this empty data frame, force the servlet container to either
+   *   - send a header frame, an empty data frame and a trailer frame with end_stream (Tomcat)
+   *   - send a header frame and a trailer frame with end_stream (Jetty, Undertow)
+   */
+  public ServletServerBuilder forceTrailers(boolean forceTrailers) {
+    this.forceTrailers = forceTrailers;
+    return this;
+  }
+
   /**
    * Provides a custom scheduled executor service to the server builder.
    *

servlet/src/main/java/io/grpc/servlet/ServletServerStream.java

@@ -64,14 +64,16 @@ final class ServletServerStream extends AbstractServerStream {
   private final String authority;
   private final InternalLogId logId;
   private final AsyncServletOutputStreamWriter writer;
+  private final boolean forceTrailers;
 
   ServletServerStream(
       AsyncContext asyncCtx,
       StatsTraceContext statsTraceCtx,
       int maxInboundMessageSize,
       Attributes attributes,
       String authority,
-      InternalLogId logId) throws IOException {
+      InternalLogId logId,
+      boolean forceTrailers) throws IOException {
     super(ByteArrayWritableBuffer::new, statsTraceCtx);
     transportState =
         new ServletTransportState(maxInboundMessageSize, statsTraceCtx, new TransportTracer());
@@ -82,6 +84,7 @@ final class ServletServerStream extends AbstractServerStream {
     this.resp = (HttpServletResponse) asyncCtx.getResponse();
     this.writer = new AsyncServletOutputStreamWriter(
         asyncCtx, transportState, logId);
+    this.forceTrailers = forceTrailers;
     resp.getOutputStream().setWriteListener(new GrpcWriteListener());
   }
 
@@ -276,20 +279,30 @@ public void writeTrailers(Metadata trailers, boolean headersSent, Status status)
             new Object[] {logId, trailers, headersSent, status});
       }
       if (!headersSent) {
-        writeHeadersToServletResponse(trailers);
-      } else {
-        byte[][] serializedHeaders = TransportFrameUtil.toHttp2Headers(trailers);
-        for (int i = 0; i < serializedHeaders.length; i += 2) {
-          String key = new String(serializedHeaders[i], StandardCharsets.US_ASCII);
-          String newValue = new String(serializedHeaders[i + 1], StandardCharsets.US_ASCII);
-          trailerSupplier.get().computeIfPresent(key, (k, v) -> v + "," + newValue);
-          trailerSupplier.get().putIfAbsent(key, newValue);
+        if (forceTrailers) {
+          writeHeadersToServletResponse(new Metadata());
+          resp.setTrailerFields(trailerSupplier);
+          serializeTrailers(trailers);
+        } else {
+          writeHeadersToServletResponse(trailers);
         }
+      } else {
+        serializeTrailers(trailers);
       }
 
       writer.complete();
     }
 
+    private void serializeTrailers(Metadata trailers) {
+      byte[][] serializedHeaders = TransportFrameUtil.toHttp2Headers(trailers);
+      for (int i = 0; i < serializedHeaders.length; i += 2) {
+        String key = new String(serializedHeaders[i], StandardCharsets.US_ASCII);
+        String newValue = new String(serializedHeaders[i + 1], StandardCharsets.US_ASCII);
+        trailerSupplier.get().computeIfPresent(key, (k, v) -> v + "," + newValue);
+        trailerSupplier.get().putIfAbsent(key, newValue);
+      }
+    }
+
     @Override
     public void cancel(Status status) {
       if (resp.isCommitted() && Code.DEADLINE_EXCEEDED == status.getCode()) {

servlet/src/tomcatTest/java/io/grpc/servlet/TomcatInteropTest.java

@@ -60,7 +60,9 @@ public static void cleanUp() throws Exception {
 
   @Override
   protected ServerBuilder<?> getServerBuilder() {
-    return new ServletServerBuilder().maxInboundMessageSize(AbstractInteropTest.MAX_MESSAGE_SIZE);
+    return new ServletServerBuilder()
+            .forceTrailers(true)
+            .maxInboundMessageSize(AbstractInteropTest.MAX_MESSAGE_SIZE);
   }
 
   @Override
@@ -113,27 +115,4 @@ protected boolean metricsExpected() {
   @Test
   public void gracefulShutdown() {}
 
-  // FIXME
-  @Override
-  @Ignore("Tomcat is not able to send trailer only")
-  @Test
-  public void specialStatusMessage() {}
-
-  // FIXME
-  @Override
-  @Ignore("Tomcat is not able to send trailer only")
-  @Test
-  public void unimplementedMethod() {}
-
-  // FIXME
-  @Override
-  @Ignore("Tomcat is not able to send trailer only")
-  @Test
-  public void statusCodeAndMessage() {}
-
-  // FIXME
-  @Override
-  @Ignore("Tomcat is not able to send trailer only")
-  @Test
-  public void emptyStream() {}
 }

servlet/src/tomcatTest/java/io/grpc/servlet/TomcatTransportTest.java

@@ -81,7 +81,8 @@ public void start(ServerListener listener) throws IOException {
         ServerTransportListener serverTransportListener =
             listener.transportCreated(new ServerTransportImpl(scheduler));
         ServletAdapter adapter =
-            new ServletAdapter(serverTransportListener, streamTracerFactories, Integer.MAX_VALUE);
+            new ServletAdapter(serverTransportListener, streamTracerFactories, Integer.MAX_VALUE,
+                true);
         GrpcServlet grpcServlet = new GrpcServlet(adapter);
 
         tomcatServer = new Tomcat();
@@ -255,21 +256,6 @@ public void interactionsAfterClientStreamCancelAreNoops() {}
   @Test
   public void clientCancel() {}
 
-  @Override
-  @Ignore("Tomcat does not support trailers only")
-  @Test
-  public void earlyServerClose_noServerHeaders() {}
-
-  @Override
-  @Ignore("Tomcat does not support trailers only")
-  @Test
-  public void earlyServerClose_serverFailure() {}
-
-  @Override
-  @Ignore("Tomcat does not support trailers only")
-  @Test
-  public void earlyServerClose_serverFailure_withClientCancelOnListenerClosed() {}
-
   @Override
   @Ignore("regression since bumping grpc v1.46 to v1.53")
   @Test

servlet/src/undertowTest/java/io/grpc/servlet/UndertowTransportTest.java

@@ -100,7 +100,8 @@ public void start(ServerListener listener) throws IOException {
         ServerTransportListener serverTransportListener =
             listener.transportCreated(new ServerTransportImpl(scheduler));
         ServletAdapter adapter =
-            new ServletAdapter(serverTransportListener, streamTracerFactories, Integer.MAX_VALUE);
+            new ServletAdapter(serverTransportListener, streamTracerFactories, Integer.MAX_VALUE,
+                false);
         GrpcServlet grpcServlet = new GrpcServlet(adapter);
         InstanceFactory<? extends Servlet> instanceFactory =
             () -> new ImmediateInstanceHandle<>(grpcServlet);