net/http: TimeoutHandler does not support Pusher interface

[inliquid]

When used as a middleware http.TimeoutHandler breaks HTTP/2.0 Server Push mechanism, as its own writer does not support http.Pusher interface.

[cuonglm]

@inliquid can you give an example code?

[inliquid]

1. Set up middleware

func setupHandler(r *mux.Router) {
	if cfg.ServerUseGzip {
		server.Handler = alice.New(
			loggerMiddleware,
			throttleMiddleware,
			//timeoutMiddleware,  // <-- breaks Push
			compressMiddleWare,
			recoverMiddleware,
			sessionMiddleware,
			authMiddleware,
		).Then(r)
	} else {
		server.Handler = alice.New(
			loggerMiddleware,
			throttleMiddleware,
			//timeoutMiddleware,   // <-- breaks Push
			recoverMiddleware,
			sessionMiddleware,
			authMiddleware,
		).Then(r)
	}
}

2. timeoutMiddleware returns http.TimeoutHandler and is quite simple

func timeoutMiddleware(next http.Handler) http.Handler {
	return http.TimeoutHandler(next, time.Duration(cfg.ServerHandlerTimeout)*time.Second, http.StatusText(http.StatusServiceUnavailable))
}

3. Push something

	p, ok := w.(http.Pusher)
	if ok {
		if err := p.Push("/assets/css/pure/pure.css", &http.PushOptions{
			//Method: "GET",
			Header: http.Header{
				"Accept-Encoding": []string{"gzip"},
			},
		}); err != nil {
			logger.Error.Println("Error pushing pure.css!")
		}
	}

When timeoutMiddleware uncommented ok == false and p == nil

[gopherbot]

Change https://golang.org/cl/154383 mentions this issue: net/http: TimeoutHandler supports server Push

[cuonglm]

@inliquid Ah sorry, the example can be more simple by using code from blog. I mis-interpreted the response when trying it.

Can you try above commit if it's fixed for you.

[inliquid]

Ok, is there any instruction how to patch and test stdlib with these changes applied?

[cuonglm]

@inliquid I think there's no way unless you re-build your go binary from source.

[odeke-em]

Thank you for filing this bug @inliquid and @Gnouc for the preliminary questions.

@Gnouc in regards to your question in #29193 (comment)
here is a minimal repro to demonstrate this problem https://play.golang.org/p/e6Pr0U_pMCp or inlined below

package main

import (
	"log"
	"net/http"
	"time"
)

func main() {
	hf := http.HandlerFunc(func(rw http.ResponseWriter, req *http.Request) {
		rw.Write([]byte("OK"))
	})
	handler := http.TimeoutHandler(hf, 55*time.Second, "Timed out!")
	_, ok := handler.(http.Pusher)
	if !ok {
		log.Fatal("TimeoutHandler does not implement http.Pusher")
	}
	log.Print("TimeoutHandler implements http.Pusher")
}

which will print out

TimeoutHandler does not implement http.Pusher

Thanks @Gnouc for the CL, we shall review it for Go1.13.

@bradfitz might you have a wishlist for interfaces that many of these helpers should implement? If so, let's review collaborate on this.

[cuonglm]

@odeke-em In case we have the wishlist, shall we implement in this issue or raise another one?

[odeke-em]

@Gnouc great question! So I think we should spin off another issue after we get the wishlist. That way if any rollback needs to be performed, it'll be piecemeal and this CL will stay in solid :)

[cuonglm]

@bradfitz can you please take a look?