Support follow redirect (-L in curl)

[nightswimmings]

If the proxy target returns a 302 + Location, Spring-Cloud-Gateway does not follow the redirect automatically, it just forwards it to the client so it has to request again (and potentially remap a new route). It would be nice if there was an option/filter to make it follow 302s and resolve the redirection server-side. I don't find such a feature in the documentation so I am wondering if it would make sense

[spencergibb]

I don't know if it would make sense.

[erizzo]

I don't see how it doesn't make sense at least as an option. One purpose of an API gateway is to hide details of internal services and their URLs from external consumers. Handing redirects in the gateway goes directly towards that goal, in my opinion.

[erizzo]

By the way, I just discovered that using ProxyExchange<> in spring-cloud-gateway-mvc, it does automatically follow redirects. Probably because the underlying Apache HttpClient library has a class, RedirectExec, in the client executor chain that's doing it.
I suspect that "regular" spring-cloud-gateway is using Netty and Reactor which do not use Apache HttpClient and don't have a corresponding auto-redirect handler.

[manisha-shetty]

May be this is helpful-

5.11 here-

https://cloud.spring.io/spring-cloud-static/spring-cloud-gateway/2.1.3.RELEASE/multi/multi__gatewayfilter_factories.html

and

https://github.com/spring-cloud/spring-cloud-gateway/blob/main/spring-cloud-gateway-server/src/main/java/org/springframework/cloud/gateway/filter/factory/RedirectToGatewayFilterFactory.java

[SzaboAdamImre]

Tried to somehow force Cloud Gateway to actually follow redirects

@Bean
   public HttpClientCustomizer httpClientCustomizer() {
       return httpClient -> httpClient.followRedirect(true);
   }

If I specify the above bean in my configuration, it actually tries to follow the 307 received from the upstream, but it fails with below exception.
In the end, I ended up manually implementing the redirect handling in a custom filter.

io.netty.util.IllegalReferenceCountException: refCnt: 0, decrement: 1
	at io.netty.util.internal.ReferenceCountUpdater.toLiveRealRefCnt(ReferenceCountUpdater.java:83)
	at io.netty.util.internal.ReferenceCountUpdater.release(ReferenceCountUpdater.java:147)
	at io.netty.buffer.AbstractReferenceCountedByteBuf.release(AbstractReferenceCountedByteBuf.java:101)
	at reactor.netty.http.client.HttpClientOperations.lambda$send$0(HttpClientOperations.java:444)
	at reactor.core.publisher.MonoFlatMap$FlatMapMain.onNext(MonoFlatMap.java:125)
	at reactor.core.publisher.FluxContextWrite$ContextWriteSubscriber.onNext(FluxContextWrite.java:107)
	at reactor.core.publisher.Operators$MonoSubscriber.complete(Operators.java:1816)
	at reactor.core.publisher.MonoCollectList$MonoCollectListSubscriber.onComplete(MonoCollectList.java:128)
	at reactor.core.publisher.FluxMapFuseable$MapFuseableSubscriber.onComplete(FluxMapFuseable.java:152)
	at reactor.core.publisher.FluxContextWrite$ContextWriteSubscriber.onComplete(FluxContextWrite.java:126)
	at reactor.core.publisher.Operators$ScalarSubscription.request(Operators.java:2400)
	at reactor.core.publisher.FluxContextWrite$ContextWriteSubscriber.request(FluxContextWrite.java:136)
	at reactor.core.publisher.FluxMapFuseable$MapFuseableSubscriber.request(FluxMapFuseable.java:171)
	at reactor.core.publisher.MonoCollectList$MonoCollectListSubscriber.onSubscribe(MonoCollectList.java:79)
	at reactor.core.publisher.FluxMapFuseable$MapFuseableSubscriber.onSubscribe(FluxMapFuseable.java:96)
	at reactor.core.publisher.FluxContextWrite$ContextWriteSubscriber.onSubscribe(FluxContextWrite.java:101)
	at reactor.core.publisher.MonoJust.subscribe(MonoJust.java:55)
	at reactor.core.publisher.Mono.subscribe(Mono.java:4400)
	at reactor.netty.NettyOutbound.subscribe(NettyOutbound.java:336)
	at reactor.core.publisher.MonoSource.subscribe(MonoSource.java:69)
	at reactor.core.publisher.MonoDefer.subscribe(MonoDefer.java:52)
	at reactor.netty.http.client.HttpClientConnect$HttpIOHandlerObserver.onStateChange(HttpClientConnect.java:441)
	at reactor.netty.ReactorNetty$CompositeConnectionObserver.onStateChange(ReactorNetty.java:677)
	at reactor.netty.resources.DefaultPooledConnectionProvider$DisposableAcquire.onStateChange(DefaultPooledConnectionProvider.java:187)
	at reactor.netty.resources.DefaultPooledConnectionProvider$PooledConnection.onStateChange(DefaultPooledConnectionProvider.java:444)
	at reactor.netty.channel.ChannelOperationsHandler.channelActive(ChannelOperationsHandler.java:62)
	at io.netty.channel.AbstractChannelHandlerContext.invokeChannelActive(AbstractChannelHandlerContext.java:230)
	at io.netty.channel.AbstractChannelHandlerContext.invokeChannelActive(AbstractChannelHandlerContext.java:216)
	at io.netty.channel.AbstractChannelHandlerContext.fireChannelActive(AbstractChannelHandlerContext.java:209)
	at io.netty.channel.CombinedChannelDuplexHandler$DelegatingChannelHandlerContext.fireChannelActive(CombinedChannelDuplexHandler.java:412)
	at io.netty.channel.ChannelInboundHandlerAdapter.channelActive(ChannelInboundHandlerAdapter.java:69)
	at io.netty.channel.CombinedChannelDuplexHandler.channelActive(CombinedChannelDuplexHandler.java:211)
	at io.netty.channel.AbstractChannelHandlerContext.invokeChannelActive(AbstractChannelHandlerContext.java:230)
	at io.netty.channel.AbstractChannelHandlerContext.invokeChannelActive(AbstractChannelHandlerContext.java:216)
	at io.netty.channel.AbstractChannelHandlerContext.fireChannelActive(AbstractChannelHandlerContext.java:209)
	at reactor.netty.tcp.SslProvider$SslReadHandler.userEventTriggered(SslProvider.java:847)
	at io.netty.channel.AbstractChannelHandlerContext.invokeUserEventTriggered(AbstractChannelHandlerContext.java:346)
	at io.netty.channel.AbstractChannelHandlerContext.invokeUserEventTriggered(AbstractChannelHandlerContext.java:332)
	at io.netty.channel.AbstractChannelHandlerContext.fireUserEventTriggered(AbstractChannelHandlerContext.java:324)
	at io.netty.handler.ssl.SslHandler.setHandshakeSuccess(SslHandler.java:1837)
	at io.netty.handler.ssl.SslHandler.wrapNonAppData(SslHandler.java:950)
	at io.netty.handler.ssl.SslHandler.unwrap(SslHandler.java:1408)
	at io.netty.handler.ssl.SslHandler.decodeJdkCompatible(SslHandler.java:1235)
	at io.netty.handler.ssl.SslHandler.decode(SslHandler.java:1284)
	at io.netty.handler.codec.ByteToMessageDecoder.decodeRemovalReentryProtection(ByteToMessageDecoder.java:510)
	at io.netty.handler.codec.ByteToMessageDecoder.callDecode(ByteToMessageDecoder.java:449)
	at io.netty.handler.codec.ByteToMessageDecoder.channelRead(ByteToMessageDecoder.java:279)
	at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:379)
	at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:365)
	at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:357)
	at io.netty.channel.DefaultChannelPipeline$HeadContext.channelRead(DefaultChannelPipeline.java:1410)
	at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:379)
	at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:365)
	at io.netty.channel.DefaultChannelPipeline.fireChannelRead(DefaultChannelPipeline.java:919)
	at io.netty.channel.nio.AbstractNioByteChannel$NioByteUnsafe.read(AbstractNioByteChannel.java:166)
	at io.netty.channel.nio.NioEventLoop.processSelectedKey(NioEventLoop.java:722)
	at io.netty.channel.nio.NioEventLoop.processSelectedKeysOptimized(NioEventLoop.java:658)
	at io.netty.channel.nio.NioEventLoop.processSelectedKeys(NioEventLoop.java:584)
	at io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:496)
	at io.netty.util.concurrent.SingleThreadEventExecutor$4.run(SingleThreadEventExecutor.java:995)
	at io.netty.util.internal.ThreadExecutorMap$2.run(ThreadExecutorMap.java:74)
	at io.netty.util.concurrent.FastThreadLocalRunnable.run(FastThreadLocalRunnable.java:30)
	at java.base/java.lang.Thread.run(Thread.java:833)

[ddibernardo]

I have a situation where I'm replacing an existing gateway application with Spring Cloud Gateway, and the older application automatically follows redirects without passing the 30x response back to the client. A way of doing the same in Spring Cloud Gateway would be very useful.