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OKHttp源码解析(6)----拦截器CallServerInterceptor

This is the last interceptor in the chain. It makes a network call to the server. 这是链中最后一个拦截器，它向服务器发起了一次网络访问

请求服务拦截器，负责向服务器发送请求数据、从服务器读取响应数据

源码解析

@Override public Response intercept(Chain chain) throws IOException {
    RealInterceptorChain realChain = (RealInterceptorChain) chain;
    HttpCodec httpCodec = realChain.httpStream();
    StreamAllocation streamAllocation = realChain.streamAllocation();
    RealConnection connection = (RealConnection) realChain.connection();
    Request request = realChain.request();

    long sentRequestMillis = System.currentTimeMillis();
     // 整理请求头并写入
    httpCodec.writeRequestHeaders(request);

    Response.Builder responseBuilder = null;
     // 检查是否为有 body 的请求方法
    if (HttpMethod.permitsRequestBody(request.method()) && request.body() != null) {
      // If there is a "Expect: 100-continue" header on the request, wait for a "HTTP/1.1 100
      // Continue" response before transmitting the request body. If we do not get that, return what
      // we did get (such as a 4xx response) without ever transmitting the request body.
      // 如果有 Expect: 100-continue在请求头中，那么要等服务器的响应。100-continue协议需要在post数据前，
      征询服务器情况，看服务器是否处理POST的数据
      if ("100-continue".equalsIgnoreCase(request.header("Expect"))) {
      //发送100-continue的请求
        httpCodec.flushRequest();
        //如果有中间级的响应，返回null
        responseBuilder = httpCodec.readResponseHeaders(true);
      }

      if (responseBuilder == null) {
        // Write the request body if the "Expect: 100-continue" expectation was met.
        // 写入请求体
        Sink requestBodyOut = httpCodec.createRequestBody(request, request.body().contentLength());
        BufferedSink bufferedRequestBody = Okio.buffer(requestBodyOut);
        request.body().writeTo(bufferedRequestBody);
        bufferedRequestBody.close();
      } 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();
      }
    }
    //发送最终的请求
    httpCodec.finishRequest();
     // 得到响应头
    if (responseBuilder == null) {
      responseBuilder = httpCodec.readResponseHeaders(false);
    }

    Response response = responseBuilder
        .request(request)
        .handshake(streamAllocation.connection().handshake())
        .sentRequestAtMillis(sentRequestMillis)
        .receivedResponseAtMillis(System.currentTimeMillis())
        .build();

    int code = response.code();
     // 如果为 web socket 且状态码是 101 ，那么 body 为空
    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();
    }
     // 如果请求头中有 close 那么断开连接
    if ("close".equalsIgnoreCase(response.request().header("Connection"))
        || "close".equalsIgnoreCase(response.header("Connection"))) {
      streamAllocation.noNewStreams();
    }
     // 抛出协议异常
    if ((code == 204 || code == 205) && response.body().contentLength() > 0) {
      throw new ProtocolException(
          "HTTP " + code + " had non-zero Content-Length: " + response.body().contentLength());
    }

    return response;
  }

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原文 https://juejin.im/post/5c0791695188251ba9057d23

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