OkHttp3源码详解(三) 拦截器-RetryAndFollowUpInterceptor

最大恢复追逐次数：

private static final int MAX_FOLLOW_UPS = 20;

处理的业务:

1. 实例化StreamAllocation，初始化一个Socket连接对象，获取到输入／输出流（）基于Okio
2. 开启循环，执行下一个调用链（拦截器），等待返回结果（Response）
3. 如果发生错误，判断是否继续请求，否：退出
4. 检查响应是否符合要求，是：返回
5. 关闭响应结果
6. 判断是否达到最大限制数，是：退出
7. 检查是否有相同连接，是：释放，重建连接
8. 重复以上流程

源码

@Override 
public Response intercept(Chain chain) throws IOException {
  // 
  Request request = chain.request();
 // 1. 初始化一个socket连接对象
  streamAllocation = new StreamAllocation(
      client.connectionPool(), createAddress(request.url()), callStackTrace);

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

    Response response = null;
    boolean releaseConnection = true;
    try {
       // 2. 执行下一个拦截器，即BridgeInterceptor
      response = ((RealInterceptorChain) chain).proceed(request, streamAllocation, null, null);
      releaseConnection = false;
    } catch (RouteException e) {
      // The attempt to connect via a route failed. The request will not have been sent.
       // 3. 如果有异常，判断是否要恢复
      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();
    }
 // 4. 检查是否符合要求
    Request followUp = followUpRequest(response);

    if (followUp == null) {
      if (!forWebSocket) {
        streamAllocation.release();
      }
      // 返回结果
      return response;
    }
 // 5. 不符合，关闭响应流
    closeQuietly(response.body());
 // 6. 是否超过最大限制
    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());
    }
 // 7. 是否有相同的连接
    if (!sameConnection(response, followUp.url())) {
      streamAllocation.release();
      streamAllocation = new StreamAllocation(
          client.connectionPool(), createAddress(followUp.url()), 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;
  }
}

初始化连接对象

streamAllocation = new StreamAllocation(
        client.connectionPool(), createAddress(request.url()), callStackTrace);

注意：此处还没有真正的去建立连接，只是初始化一个连接对象

继续下一个拦截器

上面一步初始化好后，将继续执行下一个连接器BridgeInterceptor，

// 这里有个很重的信息，即会将初始化好的连接对象传递给下一个拦截器，也是贯穿整个请求的连击对象，
// 上文我们说过，在拦截器执行过程中，RealInterceptorChain的几个属性字段会一步一步赋值
response = ((RealInterceptorChain) chain).proceed(request, streamAllocation, null, null);

抛出异常
如果抛出异常，将判断是否能够继续连接，以下情况不在，重试：

/**
* 不在继续连接的情况：
* 1. 应用层配置不在连接，默认为true
* 2. 请求Request出错不能继续使用
* 3. 是否可以恢复的
*   3.1、协议错误（ProtocolException）
    3.2、中断异常（InterruptedIOException）
    3.3、SSL握手错误（SSLHandshakeException && CertificateException）
    3.4、certificate pinning错误（SSLPeerUnverifiedException）
* 4. 没用更多线路可供选择
*/
private boolean recover(IOException e, boolean requestSendStarted, Request userRequest) {
  streamAllocation.streamFailed(e);
  // 1. 应用层配置不在连接，默认为true
  // The application layer has forbidden retries.
  if (!client.retryOnConnectionFailure()) return false;

  // 2. 请求Request出错不能继续使用
  // We can't send the request body again.
  if (requestSendStarted && userRequest.body() instanceof UnrepeatableRequestBody) return false;

  //  是否可以恢复的
  // This exception is fatal.
  if (!isRecoverable(e, requestSendStarted)) return false;

  // 4. 没用更多线路可供选择
  // No more routes to attempt.
  if (!streamAllocation.hasMoreRoutes()) return false;

  // For failure recovery, use the same route selector with a new connection.
  return true;
}

 http://lowett.com/categories/Android/Okhttp3/