When a websocket request is initiated, the response header type is ReadOnlyHttpHeaders

Dependent version

• spring-cloud-dependencies: 2020.0.3
• spring-boot-starter-parent: 2.4.6

1. application.yml

Add one of SetResponseHeader or DedupeResponseHeader under "default-filters"

spring:
  cloud:
    gateway:
      default-filters:
        - SetResponseHeader=Access-Control-Expose-Headers, Content-Disposition
        - DedupeResponseHeader=Access-Control-Allow-Credentials Access-Control-Allow-Origin Vary, RETAIN_UNIQUE

2. a websocket request

ws://localhost:8080/hpfm/websocket?access_token=0d261199-b39e-4424-82f9-9055b92119fd

3. exception

2021-06-04 14:41:48.161 ERROR 20152 --- [ctor-http-nio-7] o.s.w.s.adapter.HttpWebHandlerAdapter    : [ee2db0e7-1] Error [java.lang.UnsupportedOperationException] for HTTP GET "/hpfm/websocket?access_token=0d261199-b39e-4424-82f9-9055b92119fd", but ServerHttpResponse already committed (200 OK)
2021-06-04 14:41:48.164 ERROR 20152 --- [ctor-http-nio-7] r.n.http.server.HttpServerOperations     : [id:ee2db0e7-1, L:/10.215.0.89:8080 - R:bojiangzhou/10.215.0.89:53965] Error finishing response. Closing connection

java.lang.UnsupportedOperationException: null
	at org.springframework.http.ReadOnlyHttpHeaders.put(ReadOnlyHttpHeaders.java:126) ~[spring-web-5.3.7.jar:5.3.7]
	Suppressed: reactor.core.publisher.FluxOnAssembly$OnAssemblyException: 
Error has been observed at the following site(s):
	|_ checkpoint ⇢ org.springframework.boot.actuate.web.trace.reactive.HttpTraceWebFilter [DefaultWebFilterChain]
	|_ checkpoint ⇢ org.springframework.cloud.gateway.filter.WeightCalculatorWebFilter [DefaultWebFilterChain]
	|_ checkpoint ⇢ org.hzero.gateway.filter.GateWayHelperFilter [DefaultWebFilterChain]
	|_ checkpoint ⇢ org.springframework.boot.actuate.metrics.web.reactive.server.MetricsWebFilter [DefaultWebFilterChain]
	|_ checkpoint ⇢ org.springframework.web.cors.reactive.CorsWebFilter [DefaultWebFilterChain]
	|_ checkpoint ⇢ org.hzero.gateway.filter.IpCheckedFilter [DefaultWebFilterChain]
	|_ checkpoint ⇢ HTTP GET "/hpfm/websocket?access_token=0d261199-b39e-4424-82f9-9055b92119fd" [ExceptionHandlingWebHandler]
Stack trace:
		at org.springframework.http.ReadOnlyHttpHeaders.put(ReadOnlyHttpHeaders.java:126) ~[spring-web-5.3.7.jar:5.3.7]
		at org.springframework.cloud.gateway.filter.factory.DedupeResponseHeaderGatewayFilterFactory.dedupe(DedupeResponseHeaderGatewayFilterFactory.java:147) ~[spring-cloud-gateway-server-3.0.3.jar:3.0.3]
		at org.springframework.cloud.gateway.filter.factory.DedupeResponseHeaderGatewayFilterFactory.dedupe(DedupeResponseHeaderGatewayFilterFactory.java:130) ~[spring-cloud-gateway-server-3.0.3.jar:3.0.3]
		at org.springframework.cloud.gateway.filter.factory.DedupeResponseHeaderGatewayFilterFactory$1.lambda$filter$0(DedupeResponseHeaderGatewayFilterFactory.java:93) ~[spring-cloud-gateway-server-3.0.3.jar:3.0.3]
		at reactor.core.publisher.MonoRunnable.call(MonoRunnable.java:73) ~[reactor-core-3.4.6.jar:3.4.6]
		at reactor.core.publisher.MonoRunnable.call(MonoRunnable.java:32) ~[reactor-core-3.4.6.jar:3.4.6]
		at reactor.core.publisher.MonoIgnoreThen$ThenIgnoreMain.subscribeNext(MonoIgnoreThen.java:224) [reactor-core-3.4.6.jar:3.4.6]
..............

4. the reason

When the websocket request is completed, the request will be completed ahead of time.

Then the status of ServerHttpResponse will be changed to COMMITTED.

When finally entering DedupeResponseHeaderGatewayFilterFactory to get HttpHeaders, since the status of ServerHttpResponse is COMMITTED, it returns ReadOnlyHttpHeaders.

Is this a bug, or how to solve it ?

Start with DedupeResponseHeaderGatewayFilterFactory.dedupe, using the reported Spring Cloud Gateway versions and the websocket request with SetResponseHeader or DedupeResponseHeader enabled. Reproduce the ReadOnlyHttpHeaders exception and determine the appropriate handling when the response is already committed; done means the websocket request completes without the filter failing.