servlet: force always sending end_stream in trailer frame (Fixes grpc…

…#10124)

Signed-off-by: hypnoce <hypnoce@donarproject.org>

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

@@ -0,0 +1,52 @@
+/*
+ * Copyright 2023 The gRPC Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package io.grpc.servlet;
+
+import io.grpc.ForwardingServerCall;
+import io.grpc.Metadata;
+import io.grpc.ServerCall;
+import io.grpc.ServerCallHandler;
+import io.grpc.ServerInterceptor;
+import io.grpc.Status;
+
+class ForceTrailersServerInterceptor implements ServerInterceptor {
+  @Override
+  public <ReqT, RespT> ServerCall.Listener<ReqT> interceptCall(
+      ServerCall<ReqT, RespT> call,
+      Metadata headers,
+      ServerCallHandler<ReqT, RespT> next) {
+    ServerCall<ReqT, RespT> interceptedCall =
+        new ForwardingServerCall.SimpleForwardingServerCall<ReqT, RespT>(call) {
+      private boolean headersSent = false;
+
+      @Override
+      public void sendHeaders(Metadata headers) {
+        super.sendHeaders(headers);
+        headersSent = true;
+      }
+
+      @Override
+      public void close(Status status, Metadata trailers) {
+        if (!headersSent) {
+          sendHeaders(new Metadata());
+        }
+        super.close(status, trailers);
+      }
+    };
+    return next.startCall(interceptedCall, headers);
+  }
+}

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

@@ -33,6 +33,7 @@
 import io.grpc.Metadata;
 import io.grpc.Server;
 import io.grpc.ServerBuilder;
+import io.grpc.ServerInterceptor;
 import io.grpc.ServerStreamTracer;
 import io.grpc.Status;
 import io.grpc.internal.GrpcUtil;
@@ -46,6 +47,7 @@
 import java.io.File;
 import java.io.IOException;
 import java.net.SocketAddress;
+import java.util.ArrayList;
 import java.util.Collections;
 import java.util.List;
 import java.util.concurrent.ScheduledExecutorService;
@@ -72,6 +74,7 @@ public final class ServletServerBuilder extends ForwardingServerBuilder<ServletS
   private boolean internalCaller;
   private boolean usingCustomScheduler;
   private InternalServerImpl internalServer;
+  private final List<ServerInterceptor> interceptors = new ArrayList<>();
 
   public ServletServerBuilder() {
     serverImplBuilder = new ServerImplBuilder(this::buildTransportServers);
@@ -102,6 +105,7 @@ public ServletAdapter buildServletAdapter() {
   }
 
   private ServerTransportListener buildAndStart() {
+    interceptors.forEach(serverImplBuilder::intercept);
     Server server;
     try {
       internalCaller = true;
@@ -176,6 +180,25 @@ 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() {
+    interceptors.add(0, new ForceTrailersServerInterceptor());
+    return this;
+  }
+
+  @Override
+  public ServletServerBuilder intercept(ServerInterceptor interceptor) {
+    interceptors.add(checkNotNull(interceptor, "interceptor"));
+    return this;
+  }
+
   /**
    * Provides a custom scheduled executor service to the server builder.
    *

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()
+            .maxInboundMessageSize(AbstractInteropTest.MAX_MESSAGE_SIZE);
   }
 
   @Override
@@ -112,28 +114,4 @@ protected boolean metricsExpected() {
   @Ignore("Tomcat is broken on client GOAWAY")
   @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() {}
 }