Forwarding route produces error at the first request.

[onacit]

Describe the bug

First request of a forwarding route fails.

I have a cached-enabled route and a forwarding route.

        - id: some
          uri: http://...
          predicates:
            - Method=GET
            - Path=/some
          filters:
            - AddResponseHeader=Vary, Accept
            - LocalResponseCache=..., ...
        - id: other
          uri: forward:/some
          predicates:
            - Method=GET
            - Header=Accept, application/hal\+json
          filters:
            - SetRequestHeader=Accept, application/xml

The other route fails at first time after the application launched. Subsequent requests work.

Seems like some class tries to clear a read-only thing.

12:22:34.080 [http-nio-8080-exec-3] ERROR o.a.c.c.C.[.[.[.[httpHandlerServlet] -- Servlet.service() for servlet [httpHandlerServlet] threw exception
java.lang.UnsupportedOperationException: null
	at org.springframework.http.ReadOnlyHttpHeaders.clear(ReadOnlyHttpHeaders.java:145)
	Suppressed: reactor.core.publisher.FluxOnAssembly$OnAssemblyException: 
Assembly trace from producer [reactor.core.publisher.MonoDefer] :
	reactor.core.publisher.Mono.defer(Mono.java:219)
	org.springframework.cloud.gateway.filter.NettyWriteResponseFilter.filter(NettyWriteResponseFilter.java:69)
Error has been observed at the following site(s):
	*__________Mono.defer ⇢ at org.springframework.cloud.gateway.filter.NettyWriteResponseFilter.filter(NettyWriteResponseFilter.java:69)
	*___________Mono.then ⇢ at org.springframework.cloud.gateway.filter.NettyWriteResponseFilter.filter(NettyWriteResponseFilter.java:69)
	|_    Mono.doOnCancel ⇢ at org.springframework.cloud.gateway.filter.NettyWriteResponseFilter.filter(NettyWriteResponseFilter.java:101)
	|_     Mono.doOnError ⇢ at org.springframework.cloud.gateway.filter.NettyWriteResponseFilter.filter(NettyWriteResponseFilter.java:102)
	*__________Mono.defer ⇢ at org.springframework.cloud.gateway.handler.FilteringWebHandler$DefaultGatewayFilterChain.filter(FilteringWebHandler.java:123)
	*__________Mono.defer ⇢ at org.springframework.cloud.gateway.handler.FilteringWebHandler$DefaultGatewayFilterChain.filter(FilteringWebHandler.java:123)
	*__________Mono.defer ⇢ at org.springframework.cloud.gateway.handler.FilteringWebHandler$DefaultGatewayFilterChain.filter(FilteringWebHandler.java:123)
	|_     Mono.doFinally ⇢ at org.springframework.cloud.gateway.filter.RemoveCachedBodyFilter.filter(RemoveCachedBodyFilter.java:35)

Sample

You can run my Application and invoke the following command.

curl --location 'http://localhost:8080/api/retrieveEngAddressService/states' \
--header 'Accept: application/hal+json'

[onacit]

public class SetResponseHeadersAfterCacheExchangeMutator implements AfterCacheExchangeMutator {

	@Override
	public void accept(ServerWebExchange exchange, CachedResponse cachedResponse) {
		ServerHttpResponse response = exchange.getResponse();
		response.getHeaders().clear(); // <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
		response.getHeaders().addAll(cachedResponse.headers());
	}

}