啊，手废了，废了~
第一篇讲的是同步、异步调用源码走向Android-OKHTTP底层原理浅析（一）
第二篇讲的是重定向拦截器、桥拦截器的工作内容Android-OKHttp底层原理浅析（二）
第三篇讲的是缓存拦截器、连接拦截器的工作内容Android-OKhttp底层原理浅析（三）
开撸！CallServerInterceptor——呼叫服务拦截器
@Override public Response intercept(Chain chain) throws IOException {
HttpCodec httpCodec = ((RealInterceptorChain) chain).httpStream();
StreamAllocation streamAllocation = ((RealInterceptorChain) chain).streamAllocation();
Request request = chain.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);
}
// Write the request body, unless an "Expect: 100-continue" expectation failed.
if (responseBuilder == null) {
Sink requestBodyOut = httpCodec.createRequestBody(request, request.body().contentLength());
BufferedSink bufferedRequestBody = Okio.buffer(requestBodyOut);
request.body().writeTo(bufferedRequestBody);
bufferedRequestBody.close();
}
}
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;
}
pia，代码出来了，来，扣
这里把之前兄弟们传下来的数据都给拿了出来（都大结局了）httpCodec, streamAllocation, request
httpStream.writeRequestHeaders(request);
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();
}
}
上面代码是写入请求头信息跟写入请求体信息
httpCodec.finishRequest();
这里结束请求了
if (responseBuilder == null) {
responseBuilder = httpCodec.readResponseHeaders(false);
}
接下来这里获取响应头的信息
Response response = responseBuilder
.request(request)
.handshake(streamAllocation.connection().handshake())
.sentRequestAtMillis(sentRequestMillis)
.receivedResponseAtMillis(System.currentTimeMillis())
.build();
这里构建了Response, 传入原请求，握手的情况，请求的时间，接收到响应的时间
if (forWebSocket && code == 101) {
response = response.newBuilder()
.body(Util.EMPTY_RESPONSE)
.build();
} else {
response = response.newBuilder()
.body(httpCodec.openResponseBody(response))
.build();
}
这里将body修改为空响应，或者是响应体信息
最后就是返回response给上个拦截器了。
总结一下这边所做的内容就是
1，获取一些从上层的各个拦截器处理完成后传入的对象
2，写入请求头信息
3，写入请求体信息
4，结束请求
5，读取响应头信息
6，读取响应体信息或标记为空响应信息
7，判断请求头是否有close标记，是则断开连接
8，如果有协议异常，抛出
9，返回响应数据至上层拦截器
这边做的事情，其实很多都是上一个拦截器（ConnectInterceptor ）已经准备好的，也有一些数据是一路传了下来比如httpCodec, streamAllocation, request，在这边主要是做了一个请求的发起以及数据的响应。
ok，最后一个官方拦截器讲完了，我为啥要说“官方”呢，因为这里还有我们可以自定义的拦截器，回到我们最初的拦截器集合代码那里
List<Interceptor> interceptors = new ArrayList<>();
interceptors.addAll(client.interceptors());
interceptors.add(retryAndFollowUpInterceptor);
interceptors.add(new BridgeInterceptor(client.cookieJar()));
interceptors.add(new CacheInterceptor(client.internalCache()));
interceptors.add(new ConnectInterceptor(client));
if (!forWebSocket) {
interceptors.addAll(client.networkInterceptors());
}
interceptors.add(new CallServerInterceptor(forWebSocket));
其中interceptors.addAll(client.interceptors())跟 interceptors.addAll(client.networkInterceptors())都是我们可以自行添加的，不同的是前后顺序的区别，第一个
interceptors.addAll(client.interceptors())
是在请求发送前，以及网络响应后所执行的拦截器，比如我们的HttpLoggingInterceptor拦截器，插入的就是这个位置
HttpLoggingInterceptor.Level level = HttpLoggingInterceptor.Level.BODY;
HttpLoggingInterceptor loggingInterceptor = new HttpLoggingInterceptor(new HttpLoggingInterceptor.Logger() {
@Override
public void log(String message) {
Utils.logAll("OkHttpClient", message);
}
});
loggingInterceptor.setLevel(level);
okHttpClient = new OkHttpClient.Builder()
.cookieJar(new CookieJarImpl(new MemoryCookieStore()))
.addInterceptor(loggingInterceptor)
.build();
而如果插入到networkInterceptors这个位置呢，就有一定的区别，因为这是处于第六个拦截器，这时的请求已经经过了前面几个拦截器的处理，比如重定向，请求跟响应的处理等，这里可以得到更多的信息。当然相反的，这里获取到的响应也是最初的（他是CallServerInterceptor的上一层），没有经过其他拦截器的响应处理，是否需要这些数据就看各自的需求了。
好了，okhttp的底层原理暂时告一段落，其实里面的内容真的很庞大，要一个一个点去深挖我觉得是很耗费精力的，与其如此不如先把流程走透，学习他人的设计想法跟思路，这是我们提升自己代码技巧最直观最实际的做法。
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