okhttp3 拦截器源码分析

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今天给你们分析一下OKhttp3拦截器的调度源码。

先来看看拦截器总流程图

拦截器流程.png

下面是简单的一个okhttp3的get请求的例子。

OkHttpClient client = new OkHttpClient();        
Request request = new Request.Builder()
  .url("http://www.baidu.com")
  .build();

client.newCall(request).enqueue(new Callback() {
  @Override
  public void onFailure(Call call, IOException e) {
    Log.d("OkHttp", "Call Failed:" + e.getMessage());
  }

  @Override
  public void onResponse(Call call, Response response) throws IOException {
    Log.d("OkHttp", "Call succeeded:" + response.message());
  }
});
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（1）建立OkHttpClient的时候会初始化很是多的东西，分发器、协议、代理、拦截器、cookie、缓存、socket工厂等等一系列的东西
（2）Request是使用了建造者模式来设置一些请求参数,包括请求形式get/put、请求地址等
（3）OkHttpClient.newCall会调用RealCall.newRealCall

/**
   * Prepares the {@code request} to be executed at some point in the future.
   */
  @Override public Call newCall(Request request) {
    return RealCall.newRealCall(this, request, false /* for web socket */);
  }
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（4）OKHttpClient里面dipatcher会调用enqueue

@Override public void enqueue(Callback responseCallback) {
    synchronized (this) {
      if (executed) throw new IllegalStateException("Already Executed");
      executed = true;
    }
    captureCallStackTrace();
    eventListener.callStart(this);
    client.dispatcher().enqueue(new AsyncCall(responseCallback));
  }

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（5）Dispatcher会调用excute AsyncCall

synchronized void enqueue(AsyncCall call) {
    if (runningAsyncCalls.size() < maxRequests && runningCallsForHost(call) < maxRequestsPerHost) {
      runningAsyncCalls.add(call);
      executorService().execute(call);
    } else {
      readyAsyncCalls.add(call);
    }
  }
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（6）AsyncCall继承于Runnable，其主要调用在excute函数中
能够看到其主要是使用getResponseWithInterceptorChain()开始调用拦截链的

@Override protected void execute() {
      boolean signalledCallback = false;
      try {
        Response response = getResponseWithInterceptorChain();
        if (retryAndFollowUpInterceptor.isCanceled()) {
          signalledCallback = true;
          responseCallback.onFailure(RealCall.this, new IOException("Canceled"));
        } else {
          signalledCallback = true;
          responseCallback.onResponse(RealCall.this, response);
        }
      } catch (IOException e) {
        if (signalledCallback) {
          // Do not signal the callback twice!
          Platform.get().log(INFO, "Callback failure for " + toLoggableString(), e);
        } else {
          eventListener.callFailed(RealCall.this, e);
          responseCallback.onFailure(RealCall.this, e);
        }
      } finally {
        client.dispatcher().finished(this);
      }
    }
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（7）拦截链包含多个不一样的拦截器，构建一个ReaInterceptorChain，调用proceed执行链。

Response getResponseWithInterceptorChain() throws IOException {
    // Build a full stack of interceptors.
    List<Interceptor> interceptors = new ArrayList<>();
    interceptors.addAll(client.interceptors());
    interceptors.add(retryAndFollowUpInterceptor);  //重试重定向拦截器
    interceptors.add(new BridgeInterceptor(client.cookieJar()));  //内容桥接拦截
    interceptors.add(new CacheInterceptor(client.internalCache()));  //缓存拦截器
    interceptors.add(new ConnectInterceptor(client));      //链接拦截器
    if (!forWebSocket) {
      interceptors.addAll(client.networkInterceptors());     
    }
    interceptors.add(new CallServerInterceptor(forWebSocket));  //像服务器发送真正的访问

    Interceptor.Chain chain = new RealInterceptorChain(interceptors, null, null, null, 0,
        originalRequest, this, eventListener, client.connectTimeoutMillis(),
        client.readTimeoutMillis(), client.writeTimeoutMillis());

    return chain.proceed(originalRequest);
  }
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（8）这里会经过interceptor.intercept调用下一个调用链对象

public Response proceed(Request request, StreamAllocation streamAllocation, HttpCodec httpCodec,
      RealConnection connection) throws IOException {
   ....
    // Call the next interceptor in the chain.
    RealInterceptorChain next = new RealInterceptorChain(interceptors, streamAllocation, httpCodec,
        connection, index + 1, request, call, eventListener, connectTimeout, readTimeout,
        writeTimeout);
    Interceptor interceptor = interceptors.get(index);
    Response response = interceptor.intercept(next);

  ....

    return response;
  }
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（9）这里RetryAndFollowUpInterceptor拦截器，
重要功能在于
在网络请求失败后进行重试；
当服务器返回当前请求须要进行重定向时直接发起新的请求，并在条件容许状况下复用当前链接；

@Override public Response intercept(Chain chain) throws IOException {
    Request request = chain.request();
    RealInterceptorChain realChain = (RealInterceptorChain) chain;
    Call call = realChain.call();
    EventListener eventListener = realChain.eventListener();
    //建立流分配
    streamAllocation = new StreamAllocation(client.connectionPool(), createAddress(request.url()),
        call, eventListener, callStackTrace);

    int followUpCount = 0;
    Response priorResponse = null;
    while (true) {
      if (canceled) {
        streamAllocation.release();
        throw new IOException("Canceled");
      }

      Response response;
      boolean releaseConnection = true;
      try {
        response = realChain.proceed(request, streamAllocation, null, null); //获取下一个拦截器的响应
        releaseConnection = false;
      } catch (RouteException e) {
        // The attempt to connect via a route failed. The request will not have been sent.
        //通道失败，不会发送请求
        if (!recover(e.getLastConnectException(), false, request)) {
          throw e.getLastConnectException();
        }
        releaseConnection = false;
        continue;
      } catch (IOException e) {
        // An attempt to communicate with a server failed. The request may have been sent.
        boolean requestSendStarted = !(e instanceof ConnectionShutdownException);
        if (!recover(e, requestSendStarted, request)) throw e;
        releaseConnection = false;
        continue;
      } finally {
        // We're throwing an unchecked exception. Release any resources. if (releaseConnection) { streamAllocation.streamFailed(null); streamAllocation.release(); } } // Attach the prior response if it exists. Such responses never have a body. if (priorResponse != null) { response = response.newBuilder() .priorResponse(priorResponse.newBuilder() .body(null) .build()) .build(); } Request followUp = followUpRequest(response); //重定向和重试请求 if (followUp == null) { if (!forWebSocket) { streamAllocation.release(); } return response; } closeQuietly(response.body()); if (++followUpCount > MAX_FOLLOW_UPS) { streamAllocation.release(); throw new ProtocolException("Too many follow-up requests: " + followUpCount); } if (followUp.body() instanceof UnrepeatableRequestBody) { streamAllocation.release(); throw new HttpRetryException("Cannot retry streamed HTTP body", response.code()); } if (!sameConnection(response, followUp.url())) { streamAllocation.release(); streamAllocation = new StreamAllocation(client.connectionPool(), createAddress(followUp.url()), call, eventListener, callStackTrace); } else if (streamAllocation.codec() != null) { throw new IllegalStateException("Closing the body of " + response + " didn't close its backing stream. Bad interceptor?"); } request = followUp; priorResponse = response; } } 复制代码

关键在于response = realChain.proceed(request, streamAllocation, null, null)调用下一个拦截器
（10）BridgeInterceptor主要做用
设置内容长度，内容编码
设置gzip压缩，并在接收到内容后进行解压。省去了应用层处理数据解压的麻烦
添加cookie
设置其余报头，如User-Agent,Host,Keep-alive等。其中Keep-Alive是实现多路复用的必要步骤

@Override public Response intercept(Chain chain) throws IOException {
    Request userRequest = chain.request();
    Request.Builder requestBuilder = userRequest.newBuilder();

    RequestBody body = userRequest.body();
    //构建报头Header内容
    if (body != null) {
      MediaType contentType = body.contentType();
      if (contentType != null) {
        requestBuilder.header("Content-Type", contentType.toString());
      }

      long contentLength = body.contentLength();
      if (contentLength != -1) {
        requestBuilder.header("Content-Length", Long.toString(contentLength));
        requestBuilder.removeHeader("Transfer-Encoding");
      } else {
        requestBuilder.header("Transfer-Encoding", "chunked");
        requestBuilder.removeHeader("Content-Length");
      }
    }

    if (userRequest.header("Host") == null) {
      requestBuilder.header("Host", hostHeader(userRequest.url(), false));
    }

    if (userRequest.header("Connection") == null) {
      requestBuilder.header("Connection", "Keep-Alive");
    }

    // If we add an "Accept-Encoding: gzip" header field we're responsible for also decompressing // the transfer stream. boolean transparentGzip = false; if (userRequest.header("Accept-Encoding") == null && userRequest.header("Range") == null) { transparentGzip = true; requestBuilder.header("Accept-Encoding", "gzip"); } //构建Cookie内容 List<Cookie> cookies = cookieJar.loadForRequest(userRequest.url()); if (!cookies.isEmpty()) { requestBuilder.header("Cookie", cookieHeader(cookies)); } if (userRequest.header("User-Agent") == null) { requestBuilder.header("User-Agent", Version.userAgent()); } Response networkResponse = chain.proceed(requestBuilder.build()); //交托给下一个拦截器 HttpHeaders.receiveHeaders(cookieJar, userRequest.url(), networkResponse.headers()); Response.Builder responseBuilder = networkResponse.newBuilder() .request(userRequest); //gzip压缩内容 if (transparentGzip && "gzip".equalsIgnoreCase(networkResponse.header("Content-Encoding")) && HttpHeaders.hasBody(networkResponse)) { GzipSource responseBody = new GzipSource(networkResponse.body().source()); Headers strippedHeaders = networkResponse.headers().newBuilder() .removeAll("Content-Encoding") .removeAll("Content-Length") .build(); responseBuilder.headers(strippedHeaders); String contentType = networkResponse.header("Content-Type"); responseBuilder.body(new RealResponseBody(contentType, -1L, Okio.buffer(responseBody))); } return responseBuilder.build(); } 复制代码

（11）CacheInterceptor负责缓存管理
当网络请求有符合要求的Cache时直接返回Cache
当服务器返回内容有改变时更新当前cache
若是当前cache失效，删除。

@Override public Response intercept(Chain chain) throws IOException {
    Response cacheCandidate = cache != null
        ? cache.get(chain.request())
        : null;

    long now = System.currentTimeMillis();

    CacheStrategy strategy = new CacheStrategy.Factory(now, chain.request(), cacheCandidate).get();
    Request networkRequest = strategy.networkRequest;
    Response cacheResponse = strategy.cacheResponse;

    if (cache != null) {
      cache.trackResponse(strategy);
    }

    if (cacheCandidate != null && cacheResponse == null) {
      closeQuietly(cacheCandidate.body()); // The cache candidate wasn't applicable. Close it. } // If we're forbidden from using the network and the cache is insufficient, fail.
    if (networkRequest == null && cacheResponse == null) {
      return new Response.Builder()
          .request(chain.request())
          .protocol(Protocol.HTTP_1_1)
          .code(504)
          .message("Unsatisfiable Request (only-if-cached)")
          .body(Util.EMPTY_RESPONSE)
          .sentRequestAtMillis(-1L)
          .receivedResponseAtMillis(System.currentTimeMillis())
          .build();
    }

    // If we don't need the network, we're done.
    if (networkRequest == null) {
      return cacheResponse.newBuilder()
          .cacheResponse(stripBody(cacheResponse))
          .build();
    }

    Response networkResponse = null;
    try {
      networkResponse = chain.proceed(networkRequest);
    } finally {
      // If we're crashing on I/O or otherwise, don't leak the cache body.
      if (networkResponse == null && cacheCandidate != null) {
        closeQuietly(cacheCandidate.body());
      }
    }

    // If we have a cache response too, then we're doing a conditional get. //返回缓存的内容 if (cacheResponse != null) { if (networkResponse.code() == HTTP_NOT_MODIFIED) { Response response = cacheResponse.newBuilder() .headers(combine(cacheResponse.headers(), networkResponse.headers())) .sentRequestAtMillis(networkResponse.sentRequestAtMillis()) .receivedResponseAtMillis(networkResponse.receivedResponseAtMillis()) .cacheResponse(stripBody(cacheResponse)) .networkResponse(stripBody(networkResponse)) .build(); networkResponse.body().close(); // Update the cache after combining headers but before stripping the // Content-Encoding header (as performed by initContentStream()). //若是Header的内容更改，就更新缓存 cache.trackConditionalCacheHit(); cache.update(cacheResponse, response); return response; } else { closeQuietly(cacheResponse.body()); } } Response response = networkResponse.newBuilder() .cacheResponse(stripBody(cacheResponse)) .networkResponse(stripBody(networkResponse)) .build(); if (cache != null) { if (HttpHeaders.hasBody(response) && CacheStrategy.isCacheable(response, networkRequest)) { // Offer this request to the cache. CacheRequest cacheRequest = cache.put(response); return cacheWritingResponse(cacheRequest, response); } if (HttpMethod.invalidatesCache(networkRequest.method())) { try { cache.remove(networkRequest); } catch (IOException ignored) { // The cache cannot be written. } } } return response; } 复制代码

（12）ConnectInterceptor配置链接RealConnection

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

    // We need the network to satisfy this request. Possibly for validating a conditional GET.
    boolean doExtensiveHealthChecks = !request.method().equals("GET");
    HttpCodec httpCodec = streamAllocation.newStream(client, chain, doExtensiveHealthChecks);
    RealConnection connection = streamAllocation.connection();  //找到合适的链接，返回链接池负责链接

    return realChain.proceed(request, streamAllocation, httpCodec, connection);
  }
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（13）CallServerInterceptor调用链接服务器请求

@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();

    realChain.eventListener().requestHeadersStart(realChain.call());  //响应请求头开始的回调
    httpCodec.writeRequestHeaders(request);      //写入请求头到请求中
    realChain.eventListener().requestHeadersEnd(realChain.call(), request);  //响应请求头结束的回调

    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();
        realChain.eventListener().responseHeadersStart(realChain.call());
        responseBuilder = httpCodec.readResponseHeaders(true);
      }

      if (responseBuilder == null) {
        // Write the request body if the "Expect: 100-continue" expectation was met.
        realChain.eventListener().requestBodyStart(realChain.call());
        long contentLength = request.body().contentLength();
        CountingSink requestBodyOut =
            new CountingSink(httpCodec.createRequestBody(request, contentLength));
        BufferedSink bufferedRequestBody = Okio.buffer(requestBodyOut);  //构建请求数据流

        request.body().writeTo(bufferedRequestBody);  //请求写到数据流
        bufferedRequestBody.close(); 
        realChain.eventListener()
            .requestBodyEnd(realChain.call(), requestBodyOut.successfulCount);  //调用请求结束
      } 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) {
      realChain.eventListener().responseHeadersStart(realChain.call());  //读取响应头
      responseBuilder = httpCodec.readResponseHeaders(false);
    }

    Response response = responseBuilder             //读取响应消息
        .request(request)
        .handshake(streamAllocation.connection().handshake())
        .sentRequestAtMillis(sentRequestMillis)
        .receivedResponseAtMillis(System.currentTimeMillis())
        .build();

    realChain.eventListener()
        .responseHeadersEnd(realChain.call(), response);        //调用响应头回调

    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;
}
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（14）添加拦截器。okhttp3中拦截器自定义拦截类型有两种，一种是应用拦截器，一种是网络拦截器。两种拦截器都须要继承Interceptor。

Application Interceptors应用拦截器

*不须要担忧中间过程的响应,如重定向和重试.
*老是只调用一次,即便HTTP响应是从缓存中获取.
*观察应用程序的初衷. 不关心OkHttp注入的头信息如: If-None-Match.
*容许短路而不调用 Chain.proceed(),即停止调用.
*容许重试,使 Chain.proceed()调用屡次
经过addInterceptor函数添加

Network Interceptors网络拦截器

*可以对中间的响应进行操做好比重定向和重试。
*当发生网络短路时，不调用缓存的响应结果。
*监控数据，就像数据再网络上传输同样。
*访问承载请求的链接Connection。
经过addNetworkInterceptor函数添加

查看一下RealCall中的拦截器排序

Response getResponseWithInterceptorChain() throws IOException {
    // Build a full stack of interceptors.
    List<Interceptor> interceptors = new ArrayList<>();
    interceptors.addAll(client.interceptors());  //自定义的应用拦截器，是一开始添加的因此能够截断请求和一些初始化拦截
    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());  //自定义网络拦截器，在真正请求前调用，能够拦截改变一切默认的参数。
    }
    interceptors.add(new CallServerInterceptor(forWebSocket));  //真正请求的拦截器

    Interceptor.Chain chain = new RealInterceptorChain(interceptors, null, null, null, 0,
        originalRequest, this, eventListener, client.connectTimeoutMillis(),
        client.readTimeoutMillis(), client.writeTimeoutMillis());

    return chain.proceed(originalRequest);
  }
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拦截器的源码就分析到这里了。