现象

使用Spring Cloud Gateway时，在线上偶尔出现异常，但是很少且很难复现。

在压测的最后几条日志也会出现，当时没有放在心上，线上是不是会有error告警，故此花时间研究一番。

[4eee5339] Error [reactor.netty.ReactorNetty$InternalNettyException: java.nio.channels.ClosedChannelException] for HTTP GET "/xxx", but ServerHttpResponse already committed (200 OK)

分析

观察日志异常提示为：请求的channel被关闭了，导致异常，但是后端的处理已经返回200了，在流出过程中发现了异常。

处理过程如下：

• Spring Framework 5开始使用反应式编程（Reactive Programming，也有叫响应式）
• 当结果处理过程中发现request的channel已被关闭，出现ClosedChannelException异常时，会使用onErrorResume处理异常，调用handleUnresolvedError方法处理，handleUnresolvedError方法中经过检查发现不是内部错误，而且外部请求断开了，输出对应的错误日志。

• package org.springframework.web.server.adapter;
  ...
  public class HttpWebHandlerAdapter extends WebHandlerDecorator implements HttpHandler {
  ...
  
  @Override
  	public Mono<Void> handle(ServerHttpRequest request, ServerHttpResponse response) {
  		if (this.forwardedHeaderTransformer != null) {
  			request = this.forwardedHeaderTransformer.apply(request);
  		}
  		ServerWebExchange exchange = createExchange(request, response);
  
  		LogFormatUtils.traceDebug(logger, traceOn ->
  				exchange.getLogPrefix() + formatRequest(exchange.getRequest()) +
  						(traceOn ? ", headers=" + formatHeaders(exchange.getRequest().getHeaders()) : ""));
  
  		return getDelegate().handle(exchange)
  				.doOnSuccess(aVoid -> logResponse(exchange))
  				.onErrorResume(ex -> handleUnresolvedError(exchange, ex)) //处理过程发现异常
  				.then(Mono.defer(response::setComplete));
  	}
  
  ..
  
  /**
  * 处理异常过程
  */
  private Mono<Void> handleUnresolvedError(ServerWebExchange exchange, Throwable ex) {
  		ServerHttpRequest request = exchange.getRequest();
  		ServerHttpResponse response = exchange.getResponse();
  		String logPrefix = exchange.getLogPrefix();
  
  		// Sometimes a remote call error can look like a disconnected client.
  		// Try to set the response first before the "isDisconnectedClient" check.
  
  		if (response.setStatusCode(HttpStatus.INTERNAL_SERVER_ERROR)) {
  			logger.error(logPrefix + "500 Server Error for " + formatRequest(request), ex);
  			return Mono.empty();
  		}
  		else if (isDisconnectedClientError(ex)) {
  			if (lostClientLogger.isTraceEnabled()) {
  				lostClientLogger.trace(logPrefix + "Client went away", ex);
  			}
  			else if (lostClientLogger.isDebugEnabled()) {
  				lostClientLogger.debug(logPrefix + "Client went away: " + ex +
  						" (stacktrace at TRACE level for '" + DISCONNECTED_CLIENT_LOG_CATEGORY + "')");
  			}
  			return Mono.empty();
  		}
  		else {
              //日志异常输出的内容
  			// After the response is committed, propagate errors to the server...
  			logger.error(logPrefix + "Error [" + ex + "] for " + formatRequest(request) +
  					", but ServerHttpResponse already committed (" + response.getStatusCode() + ")");
  			return Mono.error(ex);
  		}
  	}
  }

• 观察nginx日志，发现对应的请求状态码为499
• 
• nginx状态499表示客户端主动断开了连接，

处理办法

方法1：

参考Nginx状态码499原因分析和处理

方法2:

貌似在reactor-netty项目正在修复中，关注issue：https://github.com/reactor/reactor-netty/pull/1106

PS：待验证……汗