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okhttp详解3

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上一章分析了sendRequest部分，接下来分析readResponse部分，解决第二章中留下readResponse的问题，直接看代码。

1.HttpEngine.java

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public void readResponse() throws IOException {
    if (userResponse != null) {
      return; // Already ready.
    }
    if (networkRequest == null && cacheResponse == null) {
      throw new IllegalStateException("call sendRequest() first!");
    }
    if (networkRequest == null) {
      return; // No network response to read.
    }

    Response networkResponse;

    if (forWebSocket) {
     ...
    } else if (!callerWritesRequestBody) {
      networkResponse = new NetworkInterceptorChain(0, networkRequest).proceed(networkRequest);
    } else {
      ...
    }

    receiveHeaders(networkResponse.headers());

    // If we have a cache response too, then we're doing a conditional get.
    if (cacheResponse != null) {
      if (validate(cacheResponse, networkResponse)) {
        userResponse = cacheResponse.newBuilder()
            .request(userRequest)
            .priorResponse(stripBody(priorResponse))
            .headers(combine(cacheResponse.headers(), networkResponse.headers()))
            .cacheResponse(stripBody(cacheResponse))
            .networkResponse(stripBody(networkResponse))
            .build();
        networkResponse.body().close();
        releaseConnection();

        // Update the cache after combining headers but before stripping the
        // Content-Encoding header (as performed by initContentStream()).
        InternalCache responseCache = Internal.instance.internalCache(client);
        responseCache.trackConditionalCacheHit();
        responseCache.update(cacheResponse, stripBody(userResponse));
        userResponse = unzip(userResponse);
        return;
      } else {
        closeQuietly(cacheResponse.body());
      }
    }

    userResponse = networkResponse.newBuilder()
        .request(userRequest)
        .priorResponse(stripBody(priorResponse))
        .cacheResponse(stripBody(cacheResponse))
        .networkResponse(stripBody(networkResponse))
        .build();

    if (hasBody(userResponse)) {
      maybeCache();
      userResponse = unzip(cacheWritingResponse(storeRequest, userResponse));
    }
  }

(1)判断userResponse是否被赋值。如果缓存存在并且未失效则在之前一章中sendRequest部分赋值。
(2)forWebSocket为false，也是在HttpEngine实例化时候传递过来。将会走NetworkInterceptorChain(0, networkRequest).proceed(networkRequest)。
(3)将获取的networkResponse赋值转化为userResponse
(4)处理缓存和gzip解压

2.NetworkInterceptorChain.java 

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@Override public Response proceed(Request request) throws IOException {
     calls++;

     if (index > 0) {
      ...
     }

     if (index < client.networkInterceptors().size()) {
	....
     }

     transport.writeRequestHeaders(request);

     //Update the networkRequest with the possibly updated interceptor request.
     networkRequest = request;

     if (permitsRequestBody(request) && request.body() != null) {
       Sink requestBodyOut = transport.createRequestBody(request, request.body().contentLength());
       BufferedSink bufferedRequestBody = Okio.buffer(requestBodyOut);
       request.body().writeTo(bufferedRequestBody);
       bufferedRequestBody.close();
     }

     Response response = readNetworkResponse();

     int code = response.code();
     if ((code == 204 || code == 205) && response.body().contentLength() > 0) {
       throw new ProtocolException(
           "HTTP " + code + " had non-zero Content-Length: " + response.body().contentLength());
     }

     return response;
   }
 }

(1)发送请求头。transport在第一章之前说过，包括两种类型，http1.0对应HttpTransport，spdy/http2.0对应FrameTransport。
(2)发送请求头。
(2)将request body写入到Sink中。
(3)读取Response。

3.HttpEngine.java 

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private Response readNetworkResponse() throws IOException {
    transport.finishRequest();

    Response networkResponse = transport.readResponseHeaders()
        .request(networkRequest)
        .handshake(connection.getHandshake())
        .header(OkHeaders.SENT_MILLIS, Long.toString(sentRequestMillis))
        .header(OkHeaders.RECEIVED_MILLIS, Long.toString(System.currentTimeMillis()))
        .build();

    if (!forWebSocket) {
      networkResponse = networkResponse.newBuilder()
          .body(transport.openResponseBody(networkResponse))
          .build();
    }

    return networkResponse;
  }

(1)首先是完成请求。作用是将上一步中request body Sink数据 发送出去。
(2)创建networkResponse。

###总结

  1. 将请求头和请求body发送出去。
  2. 从transport重获取ResponseHeaders。
  3. 从transport重获取ResponseBody。
  1. 接下来分析transport中的ResponseHeaders和ResponseBody是怎么获取的，因为transport包括两种类型，而且逻辑也比较多所以不放在本章分析。