springcloud gateway nullpointerexception (NettyRoutingFilter)

最近在做一个下载功能时，发现直接调用服务是可以下载的，但是通过gateway路由下载会报NPE异常，具体如下

java.lang.NullPointerException: null
        at java.util.concurrent.ConcurrentHashMap.putVal(ConcurrentHashMap.java:1011) ~[na:1.8.0_111]
        at java.util.concurrent.ConcurrentHashMap.put(ConcurrentHashMap.java:1006) ~[na:1.8.0_111]
        at org.springframework.cloud.gateway.filter.NettyRoutingFilter.lambda$filter$3(NettyRoutingFilter.java:117) ~[spring-cloud-gateway-core-2.0.0.RELEASE.jar!/:2.0.0.RELEASE]
        at reactor.core.publisher.FluxPeek$PeekSubscriber.onNext(FluxPeek.java:177) ~[reactor-core-3.1.8.RELEASE.jar!/:3.1.8.RELEASE]
        at reactor.core.publisher.FluxMap$MapSubscriber.onNext(FluxMap.java:108) ~[reactor-core-3.1.8.RELEASE.jar!/:3.1.8.RELEASE]
        at reactor.core.publisher.FluxRetryPredicate$RetryPredicateSubscriber.onNext(FluxRetryPredicate.java:81) ~[reactor-core-3.1.8.RELEASE.jar!/:3.1.8.RELEASE]
        at reactor.core.publisher.MonoCreate$DefaultMonoSink.success(MonoCreate.java:146) ~[reactor-core-3.1.8.RELEASE.jar!/:3.1.8.RELEASE]
        at reactor.ipc.netty.channel.PooledClientContextHandler.fireContextActive(PooledClientContextHandler.java:85) ~[reactor-netty-0.7.8.RELEASE.jar!/:0.7.8.RELEASE]
        at reactor.ipc.netty.http.client.HttpClientOperations.onInboundNext(HttpClientOperations.java:578) ~[reactor-netty-0.7.8.RELEASE.jar!/:0.7.8.RELEASE]
        at reactor.ipc.netty.channel.ChannelOperationsHandler.channelRead(ChannelOperationsHandler.java:136) ~[reactor-netty-0.7.8.RELEASE.jar!/:0.7.8.RELEASE]
        at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:362) ~[netty-transport-4.1.25.Final.jar!/:4.1.25.Final]
        at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:348) ~[netty-transport-4.1.25.Final.jar!/:4.1.25.Final]
        at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:340) ~[netty-transport-4.1.25.Final.jar!/:4.1.25.Final]
        at io.netty.channel.CombinedChannelDuplexHandler$DelegatingChannelHandlerContext.fireChannelRead(CombinedChannelDuplexHandler.java:438) ~[netty-transport-4.1.25.Final.jar!/:4.1.25.Final]
        at io.netty.handler.codec.ByteToMessageDecoder.fireChannelRead(ByteToMessageDecoder.java:310) ~[netty-codec-4.1.25.Final.jar!/:4.1.25.Final]
        at io.netty.handler.codec.ByteToMessageDecoder.channelRead(ByteToMessageDecoder.java:284) ~[netty-codec-4.1.25.Final.jar!/:4.1.25.Final]
        at io.netty.channel.CombinedChannelDuplexHandler.channelRead(CombinedChannelDuplexHandler.java:253) ~[netty-transport-4.1.25.Final.jar!/:4.1.25.Final]
        at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:362) ~[netty-transport-4.1.25.Final.jar!/:4.1.25.Final]
        at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:348) ~[netty-transport-4.1.25.Final.jar!/:4.1.25.Final]
        at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:340) ~[netty-transport-4.1.25.Final.jar!/:4.1.25.Final]
        at io.netty.channel.DefaultChannelPipeline$HeadContext.channelRead(DefaultChannelPipeline.java:1434) ~[netty-transport-4.1.25.Final.jar!/:4.1.25.Final]
        at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:362) ~[netty-transport-4.1.25.Final.jar!/:4.1.25.Final]
        at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:348) ~[netty-transport-4.1.25.Final.jar!/:4.1.25.Final]
        at io.netty.channel.DefaultChannelPipeline.fireChannelRead(DefaultChannelPipeline.java:965) ~[netty-transport-4.1.25.Final.jar!/:4.1.25.Final]
        at io.netty.channel.epoll.AbstractEpollStreamChannel$EpollStreamUnsafe.epollInReady(AbstractEpollStreamChannel.java:808) ~[netty-transport-native-epoll-4.1.25.Final.jar!/:4.1.25.Final]
        at io.netty.channel.epoll.EpollEventLoop.processReady(EpollEventLoop.java:408) ~[netty-transport-native-epoll-4.1.25.Final.jar!/:4.1.25.Final]
        at io.netty.channel.epoll.EpollEventLoop.run(EpollEventLoop.java:308) ~[netty-transport-native-epoll-4.1.25.Final.jar!/:4.1.25.Final]
        at io.netty.util.concurrent.SingleThreadEventExecutor$5.run(SingleThreadEventExecutor.java:884) ~[netty-common-4.1.25.Final.jar!/:4.1.25.Final]
        at java.lang.Thread.run(Thread.java:745) ~[na:1.8.0_111]

分析异常 发现其中和spring gateway有关的是这句

 at org.springframework.cloud.gateway.filter.NettyRoutingFilter.lambda$filter$3(NettyRoutingFilter.java:117) ~[spring-cloud-gateway-core-2.0.0.RELEASE.jar!/:2.0.0.RELEASE]

定位到相关的代码片段查看 org.springframework.cloud.gateway.filter.NettyRoutingFilter

return this.httpClient.request(method, url, req -> {
            final HttpClientRequest proxyRequest = req.options(NettyPipeline.SendOptions::flushOnEach)
                    .headers(httpHeaders)
                    .chunkedTransfer(chunkedTransfer)
                    .failOnServerError(false)
                    .failOnClientError(false);

            if (preserveHost) {
                String host = request.getHeaders().getFirst(HttpHeaders.HOST);
                proxyRequest.header(HttpHeaders.HOST, host);
            }

            return proxyRequest.sendHeaders() //I shouldn't need this
                    .send(request.getBody().map(dataBuffer ->
                            ((NettyDataBuffer)dataBuffer).getNativeBuffer()));
        }).doOnNext(res -> {
            ServerHttpResponse response = exchange.getResponse();
            // put headers and status so filters can modify the response
            HttpHeaders headers = new HttpHeaders();

            res.responseHeaders().forEach(entry -> headers.add(entry.getKey(), entry.getValue()));

            exchange.getAttributes().put("original_response_content_type", headers.getContentType());

            HttpHeaders filteredResponseHeaders = HttpHeadersFilter.filter(
                    this.headersFilters.getIfAvailable(), headers, exchange, Type.RESPONSE);

            response.getHeaders().putAll(filteredResponseHeaders);
            HttpStatus status = HttpStatus.resolve(res.status().code());
            if (status != null) {
                response.setStatusCode(status);
            } else if (response instanceof AbstractServerHttpResponse) {
                // https://jira.spring.io/browse/SPR-16748
                ((AbstractServerHttpResponse) response).setStatusCodeValue(res.status().code());
            } else {
                throw new IllegalStateException("Unable to set status code on response: " +res.status().code()+", "+response.getClass());
            }

            // Defer committing the response until all route filters have run
            // Put client response as ServerWebExchange attribute and write response later NettyWriteResponseFilter
            exchange.getAttributes().put(CLIENT_RESPONSE_ATTR, res);
        }).then(chain.filter(exchange));

出问题的为这句

exchange.getAttributes().put("original_response_content_type", headers.getContentType());

因为ConcurrentHashMap不允许出现null值，可见此时header中的ContentType为空导致。像下载文件，或者在controller中进行跳转时，都会出现这种情况。

这个bug在spring cloud gateway的github上作者已经说明的解决方案：将springcloud gateway升级至2.0.1或以上的版本即可，我之前使用的是2.0.0，对应

springcloud的版本 为 Finchley.RELEASE

我升级到了2.0.2 对应springcloud的版本为 Finchley.SR2   对应部分的代码

    return responseMono.doOnNext(res -> {
            ServerHttpResponse response = exchange.getResponse();
            // put headers and status so filters can modify the response
            HttpHeaders headers = new HttpHeaders();

            res.responseHeaders().forEach(entry -> headers.add(entry.getKey(), entry.getValue()));

            String contentTypeValue = headers.getFirst(HttpHeaders.CONTENT_TYPE);
            if (StringUtils.hasLength(contentTypeValue)) {
                exchange.getAttributes().put(ORIGINAL_RESPONSE_CONTENT_TYPE_ATTR, contentTypeValue);
            }

            HttpHeaders filteredResponseHeaders = HttpHeadersFilter.filter(
                    this.headersFilters.getIfAvailable(), headers, exchange, Type.RESPONSE);

            response.getHeaders().putAll(filteredResponseHeaders);
            HttpStatus status = HttpStatus.resolve(res.status().code());
            if (status != null) {
                response.setStatusCode(status);
            } else if (response instanceof AbstractServerHttpResponse) {
                // https://jira.spring.io/browse/SPR-16748
                ((AbstractServerHttpResponse) response).setStatusCodeValue(res.status().code());
            } else {
                throw new IllegalStateException("Unable to set status code on response: " +res.status().code()+", "+response.getClass());
            }

            // Defer committing the response until all route filters have run
            // Put client response as ServerWebExchange attribute and write response later NettyWriteResponseFilter
            exchange.getAttributes().put(CLIENT_RESPONSE_ATTR, res);
        })
                .onErrorMap(t -> properties.getResponseTimeout() != null && t instanceof ReadTimeoutException,
                        t -> new TimeoutException("Response took longer than timeout: " +
                                properties.getResponseTimeout()))
                .then(chain.filter(exchange));

可以看到关键部分的代码 和之前的相比较 已经做了判空

　　　　　　String contentTypeValue = headers.getFirst(HttpHeaders.CONTENT_TYPE);
            if (StringUtils.hasLength(contentTypeValue)) {
                exchange.getAttributes().put(ORIGINAL_RESPONSE_CONTENT_TYPE_ATTR, contentTypeValue);
            }