net/http: hijack deadlock bug

[septs]

Please answer these questions before submitting your issue. Thanks!

What version of Go are you using (go version)?

go version go1.8beta2 linux/amd64

What operating system and processor architecture are you using (go env)?

GOARCH="amd64"
GOBIN=""
GOEXE=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOOS="linux"
GOPATH="/home/septs/.goenv"
GORACE=""
GOROOT="/usr/local/go"
GOTOOLDIR="/usr/local/go/pkg/tool/linux_amd64"
GCCGO="gccgo"
CC="gcc"
GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build373922980=/tmp/go-build -gno-record-gcc-switches"
CXX="g++"
CGO_ENABLED="1"
PKG_CONFIG="pkg-config"
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"

What did you do?

PoC
see https://play.golang.org/p/23AuanjGHM

What did you expect to see?

fix it

What did you see instead?

[septs]

I think that might be relevant to the code snippet
see https://github.com/golang/go/blob/release-branch.go1.8/src/net/pipe.go#L57-L67
see https://github.com/golang/go/blob/release-branch.go1.8/src/net/http/server.go#L288-L306
see https://github.com/golang/go/blob/release-branch.go1.8/src/net/http/server.go#L677-L689

[bradfitz]

For questions about Go, see https://golang.org/wiki/Questions.

This just looks like a bug in your program. Your channel is unbuffered, so your dial never completes.

[Icenowy]

icenowy@x220i [ tmp ] $ go-gnu run poc.go 
hijack start
hijack done
fatal error: all goroutines are asleep - deadlock!

runtime stack:

	:0

	:0

	:0

	:0

	:0

	:0
main
	/var/lib/abbs/build/tmp.krByaGDdEY/gcc-6.2.0/libgo/runtime/go-main.c:55

	:0

	:0

	:0

goroutine 16 [select]:

	:0

	:0

	:0

	:0

	:0

	:0
main.main
	/tmp/poc.go:29

	:0

	:0

	:0

	:0
created by main
	/var/lib/abbs/build/tmp.krByaGDdEY/gcc-6.2.0/libgo/runtime/go-main.c:54

goroutine 17 [syscall]:
	goroutine in C code; stack unavailable

goroutine 18 [finalizer wait]:

	:0

	:0

	:0

	:0

goroutine 19 [GC sweep wait]:

	:0

	:0

	:0

	:0

goroutine 20 [chan receive]:

	:0
main.Accept.pN21_main.listenerWithPipe
	/tmp/poc.go:34

	:0

	:0

	:0

	:0

	:0
created by main.main
	/tmp/poc.go:19

goroutine 22 [semacquire]:

	:0

	:0

	:0

	:0

	:0

	:0

	:0

	:0

	:0

	:0

	:0

	:0

	:0

goroutine 23 [select]:

	:0

	:0

	:0

	:0

	:0

	:0
exit status 2
icenowy@x220i [ tmp ] ! go-gnu env
GOARCH="amd64"
GOBIN=""
GOEXE=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOOS="linux"
GOPATH=""
GORACE=""
GOROOT="/usr"
GOTOOLDIR="/usr/lib/gcc/x86_64-aosc-linux-gnu/6.2.0"
GO15VENDOREXPERIMENT="1"
CC="/usr/bin/gcc"
GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0"
CXX="/usr/bin/g++"
CGO_ENABLED="1"

Results on GCC Go.

[septs]

Hijack is not used and does not cause problems
@bradfitz see https://play.golang.org/p/XgZwSOs6W3

[bradfitz]

The bug in your code I mentioned above still remains in your code.

Please take this to a forum. This isn't a bug in Go.

[septs]

Your channel is unbuffered, so your dial never completes.

https://play.golang.org/p/vUcIHQ9Lyu
@bradfitz not is channel issue

[bradfitz]

Well you hijack the connection and then never do anything with it, ignoring the return result, so of course nothing happens. The client is deadlocked waiting for a result that will never come.

Please take this to a mailing list.

This is a bug in your program.

[septs]

package main

import (
	"net"
	"net/http"
)

func main() {
	mux := http.NewServeMux()
	mux.HandleFunc("/hijack", func(rw http.ResponseWriter, r *http.Request) {
		println("hijack start")
		conn, buf, err := rw.(http.Hijacker).Hijack()
		println(conn, buf, err)
		println("hijack done")
	})
	go http.ListenAndServe("127.0.0.1:9999", mux)
	client := &http.Client{
		Transport: &http.Transport{Dial: net.Dial},
	}
	client.Get("http://127.0.0.1:9999/hijack")
}

do not use net.Pipe()

➜  poc git:(master) ✗ go run poc2.go
hijack start
(0x7a6700,0xc4200fe000) 0xc4200ee090 (0x0,0x0)
hijack done

[septs]

through net.Pipe() can not run to println("hijack done")

[septs]

@bradfitz ??

[bradfitz]

You don't understand how Hijack works. Please use a forum.

I don't provide technical support in the bug tracker.

Again, for questions about Go, see https://golang.org/wiki/Questions.