聊聊AsyncHttpClient的IOExceptionFilter

序

本文主要研究一下AsyncHttpClient的IOExceptionFilter

IOExceptionFilter

org/asynchttpclient/filter/IOExceptionFilter.java

/**
 * This filter is invoked when an {@link java.io.IOException} occurs during an http transaction.
 */
public interface IOExceptionFilter {

  /**
   * An {@link org.asynchttpclient.AsyncHttpClient} will invoke {@link IOExceptionFilter#filter} and will
   * use the returned {@link FilterContext} to replay the {@link org.asynchttpclient.Request} or abort the processing.
   *
   * @param ctx a {@link FilterContext}
   * @param <T> the handler result type
   * @return {@link FilterContext}. The {@link FilterContext} instance may not the same as the original one.
   * @throws FilterException to interrupt the filter processing.
   */
  <T> FilterContext<T> filter(FilterContext<T> ctx) throws FilterException;
}

IOExceptionFilter接口定义了filter方法，在捕获到IOException的时候执行

ResumableIOExceptionFilter

org/asynchttpclient/handler/resumable/ResumableIOExceptionFilter.java

/**
 * Simple {@link org.asynchttpclient.filter.IOExceptionFilter} that replay the current {@link org.asynchttpclient.Request} using a {@link ResumableAsyncHandler}
 */
public class ResumableIOExceptionFilter implements IOExceptionFilter {
  public <T> FilterContext<T> filter(FilterContext<T> ctx) {
    if (ctx.getIOException() != null && ctx.getAsyncHandler() instanceof ResumableAsyncHandler) {

      Request request = ResumableAsyncHandler.class.cast(ctx.getAsyncHandler()).adjustRequestRange(ctx.getRequest());

      return new FilterContext.FilterContextBuilder<>(ctx).request(request).replayRequest(true).build();
    }
    return ctx;
  }
}

ResumableIOExceptionFilter实现了IOExceptionFilter接口，它在asyncHandler是ResumableAsyncHandler类型的时候执行adjustRequestRange方法获取新的request，然后再通过new FilterContext.FilterContextBuilder<>(ctx).request(request).replayRequest(true).build()返回

ResumableAsyncHandler

org/asynchttpclient/handler/resumable/ResumableAsyncHandler.java

  /**
   * Invoke this API if you want to set the Range header on your {@link Request} based on the last valid bytes
   * position.
   *
   * @param request {@link Request}
   * @return a {@link Request} with the Range header properly set.
   */
  public Request adjustRequestRange(Request request) {

    Long ri = resumableIndex.get(request.getUrl());
    if (ri != null) {
      byteTransferred.set(ri);
    }

    // The Resumable
    if (resumableListener != null && resumableListener.length() > 0 && byteTransferred.get() != resumableListener.length()) {
      byteTransferred.set(resumableListener.length());
    }

    RequestBuilder builder = new RequestBuilder(request);
    if (request.getHeaders().get(RANGE) == null && byteTransferred.get() != 0) {
      builder.setHeader(RANGE, "bytes=" + byteTransferred.get() + "-");
    }
    return builder.build();
  }

adjustRequestRange方法在byteTransferred不等于resumableListener.length()的时候会重置byteTransferred，对于有range的header则重置其bytes参数值

ResponseFiltersInterceptor

org/asynchttpclient/netty/handler/intercept/ResponseFiltersInterceptor.java

  public boolean exitAfterProcessingFilters(Channel channel,
                                            NettyResponseFuture<?> future,
                                            AsyncHandler<?> handler,
                                            HttpResponseStatus status,
                                            HttpHeaders responseHeaders) {

    FilterContext fc = new FilterContext.FilterContextBuilder().asyncHandler(handler).request(future.getCurrentRequest()).responseStatus(status)
            .responseHeaders(responseHeaders).build();

    for (ResponseFilter asyncFilter : config.getResponseFilters()) {
      try {
        fc = asyncFilter.filter(fc);
        // FIXME Is it worth protecting against this?
        assertNotNull("fc", "filterContext");
      } catch (FilterException efe) {
        requestSender.abort(channel, future, efe);
      }
    }

    // The handler may have been wrapped.
    future.setAsyncHandler(fc.getAsyncHandler());

    // The request has changed
    if (fc.replayRequest()) {
      requestSender.replayRequest(future, fc, channel);
      return true;
    }
    return false;
  }

ResponseFiltersInterceptor的exitAfterProcessingFilters方法，对于fc.replayRequest()为true则执行requestSender.replayRequest(future, fc, channel)

replayRequest

org/asynchttpclient/netty/request/NettyRequestSender.java

  public void replayRequest(final NettyResponseFuture<?> future, FilterContext fc, Channel channel) {

    Request newRequest = fc.getRequest();
    future.setAsyncHandler(fc.getAsyncHandler());
    future.setChannelState(ChannelState.NEW);
    future.touch();

    LOGGER.debug("\n\nReplaying Request {}\n for Future {}\n", newRequest, future);
    try {
      future.getAsyncHandler().onRetry();
    } catch (Exception e) {
      LOGGER.error("onRetry crashed", e);
      abort(channel, future, e);
      return;
    }

    channelManager.drainChannelAndOffer(channel, future);
    sendNextRequest(newRequest, future);
  }

NettyRequestSender的replayRequest方法会触发future.getAsyncHandler().onRetry()回调，然后执行channelManager.drainChannelAndOffer(channel, future)及sendNextRequest

applyIoExceptionFiltersAndReplayRequest

org/asynchttpclient/netty/request/NettyRequestSender.java

  public boolean applyIoExceptionFiltersAndReplayRequest(NettyResponseFuture<?> future, IOException e,
                                                         Channel channel) {

    boolean replayed = false;

    @SuppressWarnings({"unchecked", "rawtypes"})
    FilterContext<?> fc = new FilterContext.FilterContextBuilder().asyncHandler(future.getAsyncHandler())
            .request(future.getCurrentRequest()).ioException(e).build();
    for (IOExceptionFilter asyncFilter : config.getIoExceptionFilters()) {
      try {
        fc = asyncFilter.filter(fc);
        assertNotNull(fc, "filterContext");
      } catch (FilterException efe) {
        abort(channel, future, efe);
      }
    }

    if (fc.replayRequest() && future.incrementRetryAndCheck() && future.isReplayPossible()) {
      future.setKeepAlive(false);
      replayRequest(future, fc, channel);
      replayed = true;
    }
    return replayed;
  }

NettyRequestSender的applyIoExceptionFiltersAndReplayRequest方法会遍历config.getIoExceptionFilters()，然后挨个执行fc = asyncFilter.filter(fc)

小结

AsyncHttpClient的IOExceptionFilter接口定义了filter方法，在捕获到IOException的时候执行；ResumableIOExceptionFilter实现了IOExceptionFilter接口，它在asyncHandler是ResumableAsyncHandler类型的时候执行adjustRequestRange方法获取新的request，然后再通过new FilterContext.FilterContextBuilder<>(ctx).request(request).replayRequest(true).build()返回；NettyRequestSender的replayRequest方法会触发future.getAsyncHandler().onRetry()回调，然后执行channelManager.drainChannelAndOffer(channel, future)及sendNextRequest。