S2AStub doesn't return responses at front of queue.

Author: rmehta19

s2a/src/main/java/io/grpc/s2a/handshaker/S2AStub.java

@@ -84,6 +84,7 @@ BlockingQueue<Result> getResponses() {
    * @throws IOException if an unexpected response is received, or if the {@code reader} or {@code
    *     writer} calls their {@code onError} method.
    */
+  @SuppressWarnings("CheckReturnValue")
   public SessionResp send(SessionReq req) throws IOException, InterruptedException {
     if (doneWriting && doneReading) {
       logger.log(Level.INFO, "Stream to the S2A is closed.");
@@ -92,9 +93,8 @@ public SessionResp send(SessionReq req) throws IOException, InterruptedException
     createWriterIfNull();
     if (!responses.isEmpty()) {
       IOException exception = null;
-      SessionResp resp = null;
       try {
-        resp = responses.take().getResultOrThrow();
+        responses.take().getResultOrThrow();
       } catch (IOException e) {
         exception = e;
       }
@@ -104,8 +104,9 @@ public SessionResp send(SessionReq req) throws IOException, InterruptedException
             "Received an unexpected response from a host at the S2A's address. The S2A might be"
                 + " unavailable."
                 + exception.getMessage());
+      } else {
+        throw new IOException("Received an unexpected response from a host at the S2A's address.");
       }
-      return resp;
     }
     try {
       writer.onNext(req);

s2a/src/test/java/io/grpc/s2a/handshaker/S2AStubTest.java

@@ -189,26 +189,13 @@ public void send_receiveManyUnexpectedResponse_expectResponsesEmpty() throws Exc
   @Test
   public void send_receiveDelayedResponse() throws Exception {
     writer.sendGetTlsConfigResp();
-    SessionResp resp = stub.send(SessionReq.getDefaultInstance());
-    SessionResp expected =
-        SessionResp.newBuilder()
-            .setGetTlsConfigurationResp(
-                GetTlsConfigurationResp.newBuilder()
-                    .setClientTlsConfiguration(
-                        GetTlsConfigurationResp.ClientTlsConfiguration.newBuilder()
-                            .addCertificateChain(FakeWriter.LEAF_CERT)
-                            .addCertificateChain(FakeWriter.INTERMEDIATE_CERT_2)
-                            .addCertificateChain(FakeWriter.INTERMEDIATE_CERT_1)
-                            .setMinTlsVersion(TLSVersion.TLS_VERSION_1_3)
-                            .setMaxTlsVersion(TLSVersion.TLS_VERSION_1_3)
-                            .addCiphersuites(
-                                Ciphersuite.CIPHERSUITE_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256)
-                            .addCiphersuites(
-                                Ciphersuite.CIPHERSUITE_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384)
-                            .addCiphersuites(
-                                Ciphersuite.CIPHERSUITE_ECDHE_ECDSA_WITH_CHACHA20_POLY1305_SHA256)))
-            .build();
-    assertThat(resp).ignoringRepeatedFieldOrder().isEqualTo(expected);
+    IOException expectedException =
+        assertThrows(IOException.class, () -> stub.send(SessionReq.getDefaultInstance()));
+    assertThat(expectedException)
+        .hasMessageThat()
+        .contains("Received an unexpected response from a host at the S2A's address.");
+
+    assertThat(stub.getResponses()).isEmpty();
   }
 
   @Test