[Bug] met a interface conversion panic of skywalking.http.flush problem

[akilichen]

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• I had searched in the issues and found no similar issues.

Apache SkyWalking Component

Go Agent (apache/skywalking-go)

What happened

I am using the standard package named httputil with its NewSingleHostReverseProxy function, here is the error messages encountered.

panic: interface conversion: *mux.skywalking_operatorTypeMuxwriterWrapper is not http.Flusher: missing method Flush

goroutine 62 [running]:
github.com/gin-gonic/gin.(*responseWriter).Flush(0xc0001a2500?)
        /app/go-project/ms-gateway/vendor/github.com/gin-gonic/gin/response_writer.go:118 +0x59
net/http/httputil.(*maxLatencyWriter).delayedFlush(0xc0006939b0)
        /usr/local/go/src/net/http/httputil/reverseproxy.go:546 +0x95
created by time.goFunc
        /usr/local/go/src/time/sleep.go:176 +0x32

here is my code.

        proxy := httputil.NewSingleHostReverseProxy(remote) // remote mean target host.
	//Define the director func
	urlPath := c.Param("proxyPath")
	proxy.Director = func(req *orginHttp.Request) {
		req.Header = c.Request.Header
		req.Host = remote.Host
		req.URL.Scheme = remote.Scheme
		req.URL.Host = remote.Host
		req.URL.Path = c.Request.URL.Path
		// some code operation here
		......
	}
	proxy.ServeHTTP(c.Writer, c.Request)

something else:
the sw-agent version is v0.3.0 with go1.19.

What you expected to happen

fix the bug!
Is the httputil reverse proxy not supported by SW, or something I did wrong? What should I do?

How to reproduce

see What happened

Anything else

If anything I do not explain clearly, leave me a message. Thanks!

Are you willing to submit a pull request to fix on your own?

• Yes I am willing to submit a pull request on my own!

Code of Conduct

• I agree to follow this project's Code of Conduct

[wu-sheng]

Please at least use the latest go-agent release. 0.3 is months ago.

[akilichen]

We originally planned not to use the latest go-agent release, because it needs to upgrade most of the package's dependencies, which may lead to some unexpected error. So it's nothing to do but use the latest go-agent release?

[wu-sheng]

Please read the change log. Many changes are included from 0.3 to the latest.

We originally planned not to use the latest go-agent release

That is your call, but for the community, we only maintain the latest.

[akilichen]

Thanks for your answers, I will use the latest release first!

[akilichen]

I tried the latest release v0.5.0, but the bug is still. Here is the new error messages:

panic: interface conversion: *mux.skywalking_operatorTypeMuxwriterWrapperWithHijacker is not http.Flusher: missing method Flush

goroutine 60 [running]:
github.com/gin-gonic/gin.(*responseWriter).Flush(0xc0005be700?)
        /app/go-project/ms-gateway/vendor/github.com/gin-gonic/gin/response_writer.go:118 +0x59
net/http/httputil.(*maxLatencyWriter).delayedFlush(0xc0002059e0)
        /usr/local/go/src/net/http/httputil/reverseproxy.go:546 +0x95
created by time.goFunc
        /usr/local/go/src/time/sleep.go:176 +0x32

[wu-sheng]

fyi @mrproliu

[akilichen]

@mrproliu Following this, please help me find the reasons so I can solve the bug. Thanks!

[mrproliu]

Sorry, I forget this discussion. Looks like we do not support this scenario.
If there is dependency the mux plugin, for getting the response status code, the agent will wrap the response write in there: https://github.com/apache/skywalking-go/blob/main/plugins/mux/serve_interceptor.go#L64-L74. So I think if you want to resolver this bug, you can enhance in there to let response writer support the http.Flusher.

[akilichen]

Thanks for your reply. I will try to fix it.