Adding ext_proc MxN test with ext_proc server send out-of-order respo…

…nse (#37773)

Adding ext_proc MxN test with ext_proc server send out-of-order
response.
This is to address a left-over comments of the initial MxN PR:
#34942.


Fix: #37064

---------

Signed-off-by: Yanjun Xiang <[email protected]>

test/extensions/filters/http/ext_proc/ext_proc_integration_test.cc

@@ -273,12 +273,12 @@ class ExtProcIntegrationTest : public HttpIntegrationTest,
     EXPECT_EQ(std::to_string(status_code), response.headers().getStatusValue());
   }
 
-  void handleUpstreamRequest(bool add_content_length = false) {
+  void handleUpstreamRequest(bool add_content_length = false, int status_code = 200) {
     ASSERT_TRUE(fake_upstreams_[0]->waitForHttpConnection(*dispatcher_, fake_upstream_connection_));
     ASSERT_TRUE(fake_upstream_connection_->waitForNewStream(*dispatcher_, upstream_request_));
     ASSERT_TRUE(upstream_request_->waitForEndStream(*dispatcher_));
     Http::TestResponseHeaderMapImpl response_headers =
-        Http::TestResponseHeaderMapImpl{{":status", "200"}};
+        Http::TestResponseHeaderMapImpl{{":status", std::to_string(status_code)}};
     uint64_t content_length = 100;
     if (add_content_length) {
       response_headers.setContentLength(content_length);
@@ -5180,6 +5180,33 @@ TEST_P(ExtProcIntegrationTest, DuplexStreamedInBothDirection) {
   verifyDownstreamResponse(*response, 200);
 }
 
+// The ext_proc server sends out-of-order response causing Envoy to shutdown the external
+// processing.
+TEST_P(ExtProcIntegrationTest, ServerSendOutOfOrderResponseDuplexStreamed) {
+  const std::string body_sent(8 * 1024, 's');
+  // Enable FULL_DUPLEX_STREAMED body processing in both directions.
+  IntegrationStreamDecoderPtr response = initAndSendDataDuplexStreamedMode(body_sent, true, true);
+
+  // The ext_proc server receives the request headers and body.
+  ProcessingRequest header_request;
+  serverReceiveHeaderDuplexStreamed(header_request);
+  uint32_t total_req_body_msg = serverReceiveBodyDuplexStreamed(body_sent);
+
+  // The ext_proc server should send header response, but it sends back the body response,
+  // which is out-of-order. This cause Envoy to shut down the external processing, and
+  // send the buffered HTTP request headers to the upstream.
+  processor_stream_->startGrpcStream();
+  serverSendBodyRespDuplexStreamed(total_req_body_msg);
+
+  // The backend server processes the request and sends back a 400 response.
+  handleUpstreamRequest(false, 400);
+  // The body received by upstream server is expected to be empty.
+  EXPECT_EQ(upstream_request_->body().toString(), "");
+  // As the external processing is shut down, the response messages are not sent
+  // to the ext_proc server. Instead it is sent to the downstream directly.
+  verifyDownstreamResponse(*response, 400);
+}
+
 // The ext_proc server failed to send response in time trigger Envoy HCM stream_idle_timeout.
 TEST_P(ExtProcIntegrationTest, ServerWaitTooLongBeforeSendRespDuplexStreamed) {
   // Set HCM stream_idle_timeout to be 10s. Note one can also set the