OKHttp3-- 请求服务器拦截器CallServerInterceptor源码分析【十一】

朱雀 2021-12-09 16:34 290阅读 0赞

### CallServerInterceptor ###

*  系列
 *  前言
 *  CallServerInterceptor
 *  总结

# 系列 #

[OKHttp3–详细使用及源码分析系列之初步介绍【一】][OKHttp3]  
[OKHttp3–流程分析 核心类介绍 同步异步请求源码分析【二】][OKHttp3_ _]  
[OKHttp3–Dispatcher分发器源码解析【三】][OKHttp3_Dispatcher]  
[OKHttp3–调用对象RealCall源码解析【四】][OKHttp3_RealCall]  
[OKHttp3–拦截器链RealInterceptorChain源码解析【五】][OKHttp3_RealInterceptorChain]  
[OKHttp3–重试及重定向拦截器RetryAndFollowUpInterceptor源码解析【六】][OKHttp3_RetryAndFollowUpInterceptor]  
[OKHttp3–桥接拦截器BridgeInterceptor源码解析及相关http请求头字段解析【七】][OKHttp3_BridgeInterceptor_http]  
[OKHttp3–缓存拦截器CacheInterceptor源码解析【八】][OKHttp3_CacheInterceptor]  
[OKHttp3-- HTTP缓存机制解析 缓存处理类Cache和缓存策略类CacheStrategy源码分析 【九】][OKHttp3-- HTTP_ _Cache_CacheStrategy_]  
[通过ConnectInterceptor源码掌握OKHttp3网络连接原理 呕心沥血第十弹【十】][ConnectInterceptor_OKHttp3_]

# 前言 #

这篇文章将对OKHttp最后一个拦截器进行解析，总算快要结束了；上一篇文章讲到连接拦截器，即客户端已经与服务端进行了连接，那接下来的操作自然就是发送接收数据了，看看官网的注释

> 这是拦截器链上的最后一个拦截器，向服务器发起网络访问

那接下来就从源码看看它是如何实现发送请求数据，接收响应数据的

# CallServerInterceptor #

@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();
        httpCodec.writeRequestHeaders(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.
          if ("100-continue".equalsIgnoreCase(request.header("Expect"))) {
            httpCodec.flushRequest();
            responseBuilder = httpCodec.readResponseHeaders(true);
          }
    
          if (responseBuilder == null) {
            // Write the request body if the "Expect: 100-continue" expectation was met.
            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();
          }
        }
    
        httpCodec.finishRequest();
    
        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();
        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();
        }
    
        if ("close".equalsIgnoreCase(response.request().header("Connection"))
            || "close".equalsIgnoreCase(response.header("Connection"))) {
          streamAllocation.noNewStreams();
        }
    
        if ((code == 204 || code == 205) && response.body().contentLength() > 0) {
          throw new ProtocolException(
              "HTTP " + code + " had non-zero Content-Length: " + response.body().contentLength());
        }
    
        return response;
      }

这里代码我们分开看

第一部分：获取网络组件

RealInterceptorChain realChain = (RealInterceptorChain) chain;
        HttpCodec httpCodec = realChain.httpStream();
        StreamAllocation streamAllocation = realChain.streamAllocation();
        RealConnection connection = (RealConnection) realChain.connection();
        Request request = realChain.request();

这里通过拦截器链拿到了四个对象

*  HttpCodec ： 封装I/O操作的对象，根据HTTP/1.x，HTTP/2版本，有两个对应的实现类Http1Codec、Http2Codec，可以简单理解为编码我们的请求，解码返回的响应
 *  StreamAllocation：封装了一次网络操作需要的组件，为一个请求分配一个stream
 *  RealConnection： 封装了一次Socket与服务器连接的对象，在OKHttp中将一次连接抽象为Connection，而它是其实现类
 *  Request：封装用户的请求信息的对象

第二部分：发送请求

long sentRequestMillis = System.currentTimeMillis();
        httpCodec.writeRequestHeaders(request);
    
        Response.Builder responseBuilder = null;
        if (HttpMethod.permitsRequestBody(request.method()) && request.body() != null) {
          if ("100-continue".equalsIgnoreCase(request.header("Expect"))) {
            httpCodec.flushRequest();
            responseBuilder = httpCodec.readResponseHeaders(true);
          }
    
          if (responseBuilder == null) {
            Sink requestBodyOut = httpCodec.createRequestBody(request, request.body().contentLength());
            BufferedSink bufferedRequestBody = Okio.buffer(requestBodyOut);
            request.body().writeTo(bufferedRequestBody);
            bufferedRequestBody.close();
          } else if (!connection.isMultiplexed()) {
            streamAllocation.noNewStreams();
          }
        }
    
        httpCodec.finishRequest();

这部分主要是用来发送请求

*  获取发送请求的时间戳，并将请求头信息写入
 *  检测是否为有body的请求方法，接下来有两个判断，分开讲述

第一个if判断的意思是：如果请求头中包含【Expect: 100- Continue】，那么就发送100-continue的请求，然后获取服务器的响应，看服务器是否同意接受请求体，如果服务器的响应码是HTTP\_CONTINUE，即100，那这个responseBuilder 即为null

第二个判断：上面一个判断可以知道如果服务器同意接受请求体数据，那么responseBuilder 为null，接下来就构建输出流BufferedSink对象，将请求体数据写到其缓冲区

第三个判断：也就是responseBuilder 不为null，意思是服务器不同意接受该请求体，且同时这个连接不支持多路复用，也就是说这是一个Http/1.x的请求，那么我们就需要标记该连接不能再被复用，同时关闭相关的Socket

接下来就是将缓存区的数据写到Socket中，发送出去，到这里发送请求已经完成

第三部分：构建响应

if (responseBuilder == null) {
          responseBuilder = httpCodec.readResponseHeaders(false);
        }
    
        Response response = responseBuilder
            .request(request)
            .handshake(streamAllocation.connection().handshake())
            .sentRequestAtMillis(sentRequestMillis)
            .receivedResponseAtMillis(System.currentTimeMillis())
            .build();

首先获取响应头部信息，然后构建响应Response 对象

第四部分：处理响应

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 {
          response = response.newBuilder()
              .body(httpCodec.openResponseBody(response))
              .build();
        }
    
        if ("close".equalsIgnoreCase(response.request().header("Connection"))
            || "close".equalsIgnoreCase(response.header("Connection"))) {
          streamAllocation.noNewStreams();
        }
    
        if ((code == 204 || code == 205) && response.body().contentLength() > 0) {
          throw new ProtocolException(
              "HTTP " + code + " had non-zero Content-Length: " + response.body().contentLength());
        }
    
        return response;

*  如果使用websocket且响应码是101，那么构建一个空响应体的response 对象；否则就根据响应体构建真正的响应对象
 *  如果请求头或者响应头部包含【Connection: close】，意味着该连接不需要保活，那就关闭该连接以及释放相应的资源
 *  如果响应码是204或者205，且响应体长度大于0，也就意味着该次请求成功，但是服务器只返回了响应行和响应头信息，没有响应体，可是这里拿到的响应体长度居然大于0，那就说明出问题了，所以需要抛出一个协议异常

# 总结 #

可以看到最后一个拦截器的代码比较简单，当然了你要是没有看前面的系列文章，可能会觉得有点懵；拦截器链上的五个拦截器分析完了，后续的文章将会介绍下OKHttp中有关WebSocket的知识点

[OKHttp3]: https://blog.csdn.net/qq_30993595/article/details/82079586
[OKHttp3_ _]: https://blog.csdn.net/qq_30993595/article/details/86438864
[OKHttp3_Dispatcher]: https://blog.csdn.net/qq_30993595/article/details/86681210
[OKHttp3_RealCall]: https://blog.csdn.net/qq_30993595/article/details/86686105
[OKHttp3_RealInterceptorChain]: https://blog.csdn.net/qq_30993595/article/details/87475028
[OKHttp3_RetryAndFollowUpInterceptor]: https://blog.csdn.net/qq_30993595/article/details/87523713
[OKHttp3_BridgeInterceptor_http]: https://blog.csdn.net/qq_30993595/article/details/87738481
[OKHttp3_CacheInterceptor]: https://blog.csdn.net/qq_30993595/article/details/87886518
[OKHttp3-- HTTP_ _Cache_CacheStrategy_]: https://blog.csdn.net/qq_30993595/article/details/87941893
[ConnectInterceptor_OKHttp3_]: https://blog.csdn.net/qq_30993595/article/details/94405694