net/http: TimeoutHandler allows wrapped handlers crash server with panics

[artyom]

Please answer these questions before submitting your issue. Thanks!

What did you do?

If possible, provide a recipe for reproducing the error.
A complete runnable program is good.
A link on play.golang.org is best.

https://play.golang.org/p/Ycz0W8a_ff

What did you expect to see?

I expect panics from http.Handlers to be handled by http.Server as documented (recovered), i.e. with the sentinel panic value http.ErrAbortHandler this program outputs something like this:

2017/09/28 22:55:18 Get http://127.0.0.1:52111: EOF

What did you see instead?

Program crashes:

panic: net/http: abort Handler

goroutine 21 [running]:
main.do.func1(0x13eb0e0, 0xc42011a0a0, 0xc420134000)
	/tmp/repro.go:19 +0x42
net/http.HandlerFunc.ServeHTTP(0x12c3438, 0x13eb0e0, 0xc42011a0a0, 0xc420134000)
	/Users/artyom/Library/go/src/net/http/server.go:1918 +0x44
net/http.(*timeoutHandler).ServeHTTP.func1(0xc420076c00, 0xc42011a0a0, 0xc420134000, 0xc420138060)
	/Users/artyom/Library/go/src/net/http/server.go:3043 +0x53
created by net/http.(*timeoutHandler).ServeHTTP
	/Users/artyom/Library/go/src/net/http/server.go:3042 +0x158
exit status 2

System details

go version go1.9 darwin/amd64
GOARCH="amd64"
GOBIN=""
GOEXE=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOOS="darwin"
GOPATH="/tmp/go:/Users/artyom/go"
GORACE=""
GOROOT="/Users/artyom/Library/go"
GOTOOLDIR="/Users/artyom/Library/go/pkg/tool/darwin_amd64"
GCCGO="gccgo"
CC="clang"
GOGCCFLAGS="-fPIC -m64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/lb/3rk8rqs53czgb4v35w_342xc0000gn/T/go-build484141897=/tmp/go-build -gno-record-gcc-switches -fno-common"
CXX="clang++"
CGO_ENABLED="1"
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOROOT/bin/go version: go version go1.9 darwin/amd64
GOROOT/bin/go tool compile -V: compile version go1.9
uname -v: Darwin Kernel Version 17.0.0: Thu Aug 24 21:48:19 PDT 2017; root:xnu-4570.1.46~2/RELEASE_X86_64
ProductName:	Mac OS X
ProductVersion:	10.13
BuildVersion:	17A365
lldb --version: lldb-900.0.45
  Swift-4.0

This happens because TimeoutHandler starts original handler in a separate goroutine:

go/src/net/http/server.go

Lines 3042 to 3045 in 78a0a31

	go func() {
	h.handler.ServeHTTP(tw, r)
	close(done)
	}()

I can work on fixing this by handling panic in this goroutine and re-raising it from the timeoutHandler.ServeHTTP itself, so it's handled by the Server. Please assign this to me if this solution looks ok.

[mvdan]

/cc @tombergan @bradfitz

[gopherbot]

Change https://golang.org/cl/67410 mentions this issue: net/http: make TimeoutHandler recover child handler panics