servlet: Avoid sending Trailers-Only responses

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

@@ -1103,9 +1103,8 @@ public void earlyServerClose_noServerHeaders() throws Exception {
     Metadata clientStreamTrailers =
         clientStreamListener.awaitTrailers(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)));

interop-testing/src/main/java/io/grpc/testing/integration/AbstractInteropTest.java

@@ -1113,7 +1113,10 @@ public void deadlineExceeded() throws Exception {
           Pattern.matches("CallOptions deadline exceeded after .*s. \\[.*\\]", desc)
           // If server expires first, it'd reset the stream and client would generate a different
           // message
-          || desc.startsWith("ClientCall was cancelled at or after deadline."));
+          || desc.startsWith("ClientCall was cancelled at or after deadline.")
+          // If server expires first and sends the status instead of resetting the stream (e.g.,
+          // servlet based servers), the client sees the server's status
+          || desc.equals("context timed out"));
     }
 
     assertStatsTrace("grpc.testing.TestService/EmptyCall", Status.Code.OK);

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

@@ -280,11 +280,15 @@ public void writeTrailers(Metadata trailers, boolean headersSent, Status status)
             new Object[] {logId, trailers, headersSent, status});
       }
       if (!headersSent) {
-        writeHeadersToServletResponse(trailers);
-      } else {
-        serializeHeaders(trailers,
-            (k, v) -> trailerSupplier.get().merge(k, v, (oldV, newV) -> oldV + "," + newV));
+        // Don't send a Trailers-Only response (status in the response headers). Some containers,
+        // like Tomcat, don't set END_STREAM on that HEADERS frame and instead terminate the stream
+        // with an empty DATA frame, which the client treats as a protocol error, discarding the
+        // status. Send (empty) headers followed by real trailers instead.
+        writeHeadersToServletResponse(new Metadata());
+        resp.setTrailerFields(trailerSupplier);
       }
+      serializeHeaders(trailers,
+          (k, v) -> trailerSupplier.get().merge(k, v, (oldV, newV) -> oldV + "," + newV));
 
       writer.complete();
     }

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

@@ -112,29 +112,4 @@ protected boolean metricsExpected() {
   @Ignore("Tomcat is broken on client GOAWAY")
   @Test
   public void gracefulShutdown() {}
-
-  @Override
-  @Ignore("Tomcat is not able to send trailer only")
-  @Test
-  public void specialStatusMessage() {}
-
-  @Override
-  @Ignore("Tomcat is not able to send trailer only")
-  @Test
-  public void unimplementedMethod() {}
-
-  @Override
-  @Ignore("Tomcat is not able to send trailer only")
-  @Test
-  public void statusCodeAndMessage() {}
-
-  @Override
-  @Ignore("Tomcat is not able to send trailer only")
-  @Test
-  public void emptyStream() {}
-
-  @Override
-  @Ignore("Tomcat is not able to send trailer only")
-  @Test
-  public void timeoutOnSleepingServer() {}
 }

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

@@ -261,21 +261,6 @@ 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