Summary of OkHttp source code interpretation (XIII) - > call server interceptor

Tags (space separated): learning notes of OkHttp source code

Preface

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Introduction to official website

/** This is the last interceptor in the chain. It makes a network call to the server. */

1. Initiate a real network request
 2. Return the data returned by the server

Main source code

@Override public Response intercept(Chain chain) throws IOException {
    //Interceptor chain
    RealInterceptorChain realChain = (RealInterceptorChain) chain;
    //HttpCodec object source sink two objects input and output / / used to encode request decoding response 
    HttpCodec httpCodec = realChain.httpStream();
    //Other network components used to establish network requests  
    StreamAllocation streamAllocation = realChain.streamAllocation();
    //
    RealConnection connection = (RealConnection) realChain.connection();
    //Network request
    Request request = realChain.request();

    long sentRequestMillis = System.currentTimeMillis();

    realChain.eventListener().requestHeadersStart(realChain.call());
    //Write request header information to socket
    httpCodec.writeRequestHeaders(request);
    realChain.eventListener().requestHeadersEnd(realChain.call(), request);

    Response.Builder responseBuilder = null;
    if (HttpMethod.permitsRequestBody(request.method()) && request.body() != null) {
      // If there's a "Expect: 100-continue" header on the request, wait for a "HTTP/1.1 100
      // Continue" response before transmitting the request body. If we don't get that, return
      // what we did get (such as a 4xx response) without ever transmitting the request body.
      //Ask if the service can send information with the request body
      if ("100-continue".equalsIgnoreCase(request.header("Expect"))) {
        httpCodec.flushRequest();
        realChain.eventListener().responseHeadersStart(realChain.call());
        responseBuilder = httpCodec.readResponseHeaders(true);
      }

      if (responseBuilder == null) {
        // Write the request body if the "Expect: 100-continue" expectation was met.
        realChain.eventListener().requestBodyStart(realChain.call());
        long contentLength = request.body().contentLength();
        CountingSink requestBodyOut =
            new CountingSink(httpCodec.createRequestBody(request, contentLength));
        BufferedSink bufferedRequestBody = Okio.buffer(requestBodyOut);
        //Call the request.body().writeTo() method to write the body information to the socket
        request.body().writeTo(bufferedRequestBody);
        //Close
        bufferedRequestBody.close();
        realChain.eventListener()
            .requestBodyEnd(realChain.call(), requestBodyOut.successfulCount);
      } else if (!connection.isMultiplexed()) {
        // If the "Expect: 100-continue" expectation wasn't met, prevent the HTTP/1 connection
        // from being reused. Otherwise we're still obligated to transmit the request body to
        // leave the connection in a consistent state.
        streamAllocation.noNewStreams();
      }
    }
    //Write operation of network request completed
    httpCodec.finishRequest();

    if (responseBuilder == null) {
      realChain.eventListener().responseHeadersStart(realChain.call());
      //Read response through readResponseHeaders of httpCodec
      responseBuilder = httpCodec.readResponseHeaders(false);
    }
   //Create a response object through streamalallocation request
    Response response = responseBuilder
        .request(request)
        .handshake(streamAllocation.connection().handshake())
        .sentRequestAtMillis(sentRequestMillis)
        .receivedResponseAtMillis(System.currentTimeMillis())
        .build();

    realChain.eventListener()
        .responseHeadersEnd(realChain.call(), response);
    //Get response
    int code = response.code();
    if (forWebSocket && code == 101) {
      // Connection is upgrading, but we need to ensure interceptors see a non-null response body.
      response = response.newBuilder()
          .body(Util.EMPTY_RESPONSE)
          .build();
    } else {
      //Call httpCodec.openResponseBody(response) to create a response
      response = response.newBuilder()
          .body(httpCodec.openResponseBody(response))
          .build();
    }

    if ("close".equalsIgnoreCase(response.request().header("Connection"))
        || "close".equalsIgnoreCase(response.header("Connection"))) {
      //Prevent new streams from creating closed streams and closing connection s    
      streamAllocation.noNewStreams();
    }
    //If the code is 204 or 205, an exception will be thrown
    if ((code == 204 || code == 205) && response.body().contentLength() > 0) {
      throw new ProtocolException(
          "HTTP " + code + " had non-zero Content-Length: " + response.body().contentLength());
    }
    //Finally, return the response
    return response;
  }

• 1. Call httpCodec.writeRequestHeaders(request) to write header information to socket object
• 2. request.body().writeTo(bufferedRequestBody) writes body information to socket
• 3. httpCodec.finishRequest() indicates that the writing of network request is completed
• 4. responseBuilder = httpCodec.readResponseHeaders(false) read the header information of the network request

• 5. Read the body information in the network request through the following code logic

  if (forWebSocket && code == 101) {
    // Connection is upgrading, but we need to ensure interceptors see a non-null response body.
    response = response.newBuilder()
        .body(Util.EMPTY_RESPONSE)
        .build();
  } else {
    response = response.newBuilder()
        .body(httpCodec.openResponseBody(response))
        .build();
  }

General situation of a network request in OkHttp

• 1. Encapsulation of call object to request
• 2. dispatcher distributor distributes requests
• 3. getResponseWithInterceptors() method
  
  • Retryandfollowupinterceptor
  • Cacheinterceptor (CACHE)
  • Bridgeinterceptor (handles request and response objects against actual request and response Transformations / cookies)
  • Connectinterceptor (responsible for establishing intercepting and streaming objects)
  • Callserverinterceptor (completes the final network request and read response)