OKHttp源码解析（三）

public void readResponse() throws IOException {
        if(this.userResponse == null) {
            if(this.networkRequest == null && this.cacheResponse == null) {
                throw new IllegalStateException("call sendRequest() first!");
            } else if(this.networkRequest != null) {
                Response networkResponse;
                if(this.forWebSocket) {
                    this.transport.writeRequestHeaders(this.networkRequest);
                    networkResponse = this.readNetworkResponse();
                } else if(!this.callerWritesRequestBody) {
                //利用拦截器方式去做答复处理
                    networkResponse = (new HttpEngine.NetworkInterceptorChain(0, this.networkRequest)).proceed(this.networkRequest);
                } else {
                    //这个else分句可以不看
                }
                this.receiveHeaders(networkResponse.headers());
                if(this.cacheResponse != null) {
                    if(validate(this.cacheResponse, networkResponse)) {
                        this.userResponse = this.cacheResponse.newBuilder().request(this.userRequest).priorResponse(stripBody(this.priorResponse)).headers(combine(this.cacheResponse.headers(), networkResponse.headers())).cacheResponse(stripBody(this.cacheResponse)).networkResponse(stripBody(networkResponse)).build();
                        networkResponse.body().close();
                        this.releaseConnection();
                        InternalCache responseCache1 = Internal.instance.internalCache(this.client);
                        responseCache1.trackConditionalCacheHit();
                        responseCache1.update(this.cacheResponse, stripBody(this.userResponse));
                        this.userResponse = this.unzip(this.userResponse);
                        return;
                    }

                    Util.closeQuietly(this.cacheResponse.body());
                }

                this.userResponse = networkResponse.newBuilder().request(this.userRequest).priorResponse(stripBody(this.priorResponse)).cacheResponse(stripBody(this.cacheResponse)).networkResponse(stripBody(networkResponse)).build();
                if(hasBody(this.userResponse)) {
                    this.maybeCache();
                    this.userResponse = this.unzip(this.cacheWritingResponse(this.storeRequest, this.userResponse));
                }

            }
        }
    }

在上篇文章结尾OKHttp源码解析（二） 我们分析到这里第10行的callerWritesRequestBody会为空，所以我会直接进去这个判断，同样在OKHttp源码解析（一） 我们分析过发送请求时使用的拦截器模式，这里对答复的操作也用了同样的方式，不同于请求调用的是intercept，这里用的是proceed，我们就来看看这个方法做了什么

public Response proceed(Request request) throws IOException {
            ++this.calls;
            if(this.index > 0) {
                Interceptor response = (Interceptor)HttpEngine.this.client.networkInterceptors().get(this.index - 1);
                Address code = this.connection().getRoute().getAddress();
                if(!request.url().getHost().equals(code.getUriHost()) || Util.getEffectivePort(request.url()) != code.getUriPort()) {
                    throw new IllegalStateException("network interceptor " + response + " must retain the same host and port");
                }

                if(this.calls > 1) {
                    throw new IllegalStateException("network interceptor " + response + " must call proceed() exactly once");
                }
            }

            if(this.index < HttpEngine.this.client.networkInterceptors().size()) {
            //根据拦截器的数目去相应取出拦截器并执行intercept里面用户自定义的处理方式
                HttpEngine.NetworkInterceptorChain var7 = HttpEngine.this.new NetworkInterceptorChain(this.index + 1, request);
                Interceptor var10 = (Interceptor)HttpEngine.this.client.networkInterceptors().get(this.index);
                Response interceptedResponse = var10.intercept(var7);
                if(var7.calls != 1) {
                    throw new IllegalStateException("network interceptor " + var10 + " must call proceed() exactly once");
                } else {
                    return interceptedResponse;
                }
            } else {
            //写入请求头部
                    HttpEngine.this.transport.writeRequestHeaders(request);
                HttpEngine.this.networkRequest = request;
                if(HttpEngine.this.permitsRequestBody() && request.body() != null) {
                //写入一些请求体
                    Sink var5 = HttpEngine.this.transport.createRequestBody(request, request.body().contentLength());
                    BufferedSink var8 = Okio.buffer(var5);
                    request.body().writeTo(var8);
                    var8.close();
                }
                //将之前写入的数据flush给socket并读取服务器答复
                Response var6 = HttpEngine.this.readNetworkResponse();
                int var9 = var6.code();
                if((var9 == 204 || var9 == 205) && var6.body().contentLength() > 0L) {
                    throw new ProtocolException("HTTP " + var9 + " had non-zero Content-Length: " + var6.body().contentLength());
                } else {
                    return var6;
                }
            }
        }

我们先来看看27行的头部写入是怎么一个写法

public void writeRequestHeaders(Request request) throws IOException {
        this.httpEngine.writingRequestHeaders();
        //组装请求的信息，比如url，请求方式，请求协议
        String requestLine = RequestLine.get(request, this.httpEngine.getConnection().getRoute().getProxy().type(), this.httpEngine.getConnection().getProtocol());
        //将请求头和请求体写入socket
        this.httpConnection.writeRequest(request.headers(), requestLine);
    }

public void writeRequest(Headers headers, String requestLine) throws IOException {
        if(this.state != 0) {
            throw new IllegalStateException("state: " + this.state);
        } else {
            this.sink.writeUtf8(requestLine).writeUtf8("\r\n");
            int i = 0;

            for(int size = headers.size(); i < size; ++i) {
                this.sink.writeUtf8(headers.name(i)).writeUtf8(": ").writeUtf8(headers.value(i)).writeUtf8("\r\n");
            }

            this.sink.writeUtf8("\r\n");
            this.state = 1;
        }
    }

上面的sink就是socket的写入流，在上篇文章我们分析过怎么得到它的，将请求头部和请求体写入socket后，proceed的第37行就要进行flush操作了

private Response readNetworkResponse() throws IOException {
    //执行flush操作
        this.transport.finishRequest();
        //等待服务器相应并读取服务器返回信息组装成我们需要的response
        Response networkResponse = this.transport.readResponseHeaders().request(this.networkRequest).handshake(this.connection.getHandshake()).header(OkHeaders.SENT_MILLIS, Long.toString(this.sentRequestMillis)).header(OkHeaders.RECEIVED_MILLIS, Long.toString(System.currentTimeMillis())).build();
        if(!this.forWebSocket) {
        //组装response的body
            networkResponse = networkResponse.newBuilder().body(this.transport.openResponseBody(networkResponse)).build();
        }

        Internal.instance.setProtocol(this.connection, networkResponse.protocol());
        return networkResponse;
    }

先简单看下第三行finishRequest调用的代码

public void finishRequest() throws IOException {
        this.httpConnection.flush();
    }
public void flush() throws IOException {
        this.sink.flush();
    }

再来看看第5行的组装步骤

public Builder readResponseHeaders() throws IOException {
        return this.httpConnection.readResponse();
    }

public Builder readResponse() throws IOException {
        if(this.state != 1 && this.state != 3) {
            throw new IllegalStateException("state: " + this.state);
        } else {
            try {
                StatusLine e;
                Builder exception1;
                do {
                //从输入流里读出答复并组装成答复消息
                    e = StatusLine.parse(this.source.readUtf8LineStrict());
                    exception1 = (new Builder()).protocol(e.protocol).code(e.code).message(e.message);
                    com.squareup.okhttp.Headers.Builder headersBuilder = new com.squareup.okhttp.Headers.Builder();
                    //答复头部的读取
                    this.readHeaders(headersBuilder);
                    headersBuilder.add(OkHeaders.SELECTED_PROTOCOL, e.protocol.toString());
                    exception1.headers(headersBuilder.build());
                } while(e.code == 100);

                this.state = 4;
                return exception1;
            } catch (EOFException var4) {
                IOException exception = new IOException("unexpected end of stream on " + this.connection + " (recycle count=" + Internal.instance.recycleCount(this.connection) + ")");
                exception.initCause(var4);
                throw exception;
            }
        }
    }

上面的代码我们看到的是对答复头部的读取整理，而readNetworkResponse()第8行则是对服务器答复的body进行整理组装

public ResponseBody openResponseBody(Response response) throws IOException {
        Source source = this.getTransferStream(response);
        //最终返回一个输入流
        return new RealResponseBody(response.headers(), Okio.buffer(source));
    }

    private Source getTransferStream(Response response) throws IOException {
        if(!HttpEngine.hasBody(response)) {
            return this.httpConnection.newFixedLengthSource(0L);
        } else if("chunked".equalsIgnoreCase(response.header("Transfer-Encoding"))) {
            return this.httpConnection.newChunkedSource(this.httpEngine);
        } else {
            long contentLength = OkHeaders.contentLength(response);
            return contentLength != -1L?this.httpConnection.newFixedLengthSource(contentLength):this.httpConnection.newUnknownLengthSource();
        }
    }

在经过这么层层代码的深入（好多代码，看得都乱了吧），我们最终得到了服务器返回的userResponse。。

最后的最后，我们要回到OKHttp源码解析（一） 最后一段代码getResponse的52行得到我们上面分析的userResponse，并关闭相应的连接池，关闭回收socket等”善后“处理。

三篇文章分析到现在，算是把整个OKHttp的流程分析了个大概，OkHttp还有其他的一些部分，比如handshake，连接池的管理等方面的内容，如果有人有发现这方面介绍的好文章可以留言推荐给我看看，大家共同学习，共同进步。