okHttp 재시도 메커니즘

Retry And Follow UpInterceptor, 재시도 절차가 뚜렷하고 간략하게 주석을 썼습니다. 관련된 클래스는 주로stream Allocation입니다. 이 클래스는 링크connection, 요청 및 코딩 클래스인 Http Codec, 루트 Reute Selector를 관리하는 데 사용됩니다. 진정으로 사용할 때 뒤에 있는 연결과 요청을 실례화하고 방출합니다.

@Override public Response intercept(Chain chain) throws IOException {
  Request request = chain.request();
  //     connections、stream、routerSelector  
  streamAllocation = new StreamAllocation(
      client.connectionPool(), createAddress(request.url()), callStackTrace);

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

    Response response = null;
    boolean releaseConnection = true;
    try {
      //        
      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.
      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);
      //     ， ssl    、          
      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();
    }

    //      HTTP code，     、    
    Request followUp = followUpRequest(response);

    //        ，    
    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());
    }

    //      host     ，   ，      ，     StreamAllocation
    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;
  }
}