content: /*
   * Copyright 2020  Google LLC
   *
   * 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 com.taobao.arthas.grpcweb.proxy;
  
  import io.grpc.*;
  import io.grpc.ClientCall.Listener;
  import io.grpc.ForwardingClientCall.SimpleForwardingClientCall;
  import io.grpc.ForwardingClientCallListener.SimpleForwardingClientCallListener;
  
  import java.util.concurrent.CountDownLatch;
  
  class GrpcWebClientInterceptor implements ClientInterceptor {
  
      private final CountDownLatch latch;
      private final SendGrpcWebResponse sendResponse;
  
      GrpcWebClientInterceptor(CountDownLatch latch, SendGrpcWebResponse send) {
          this.latch = latch;
          sendResponse = send;
      }
  
      @Override
      public <ReqT, RespT> ClientCall<ReqT, RespT> interceptCall(MethodDescriptor<ReqT, RespT> method,
              CallOptions callOptions, Channel channel) {
          return new SimpleForwardingClientCall<ReqT, RespT>(channel.newCall(method, callOptions)) {
              @Override
              public void start(Listener<RespT> responseListener, Metadata headers) {
                  super.start(new MetadataResponseListener<RespT>(responseListener), headers);
              }
          };
      }
  
      class MetadataResponseListener<T> extends SimpleForwardingClientCallListener<T> {
          private boolean headersSent = false;
  
          MetadataResponseListener(Listener<T> responseListener) {
              super(responseListener);
          }
  
          @Override
          public void onHeaders(Metadata h) {
              sendResponse.writeHeaders(h);
              headersSent = true;
          }
  
          @Override
          public void onClose(Status s, Metadata t) {
              // TODO 这个函数会在 onCompleted 之前回调，这里有点奇怪
              if (!headersSent) {
                  // seems, sometimes onHeaders() is not called before this method is called!
                  // so far, they are the error cases. let onError() method in ClientListener
                  // handle this call. Could ignore this.
                  // TODO is this correct? what if onError() never gets called?
              } else {
                  sendResponse.writeTrailer(s, t);
                  latch.countDown();
              }
              super.onClose(s, t);
          }
      }
  }
  