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net: OpError(nil).Unwrap() crashes, while .Error() doesn't #36368

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rski opened this issue Jan 2, 2020 · 2 comments
Open

net: OpError(nil).Unwrap() crashes, while .Error() doesn't #36368

rski opened this issue Jan 2, 2020 · 2 comments
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@rski
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@rski rski commented Jan 2, 2020

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

go version
go version devel +ffbc02761a Thu Jan 2 21:41:13 2020 +0000 linux/amd64
and
$ go version
go version go1.13.5 linux/amd64

Does this issue reproduce with the latest release?

yes, with go1.13.5

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

go env Output
$ go env
$ go env
GO111MODULE=""
GOARCH="amd64"
GOBIN=""
GOCACHE="/home/rski/.cache/go-build"
GOENV="/home/rski/.config/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GONOPROXY=""
GONOSUMDB=""
GOOS="linux"
GOPATH="/home/rski/go"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/nix/store/sz7mgf91bxd3xpxgqjzgr2avl9cshlz8-go-1.13.5/share/go"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/nix/store/sz7mgf91bxd3xpxgqjzgr2avl9cshlz8-go-1.13.5/share/go/pkg/tool/linux_amd64"
GCCGO="gccgo"
AR="ar"
CC="/nix/store/47hi526v96skkwgdj7d9c31ccd1xivrx-gcc-wrapper-8.3.0/bin/cc"
CXX="g++"
CGO_ENABLED="0"
GOMOD=""
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -m64 -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build956886521=/tmp/go-build -gno-record-gcc-switches"

What did you do?

As the summary says, this can be verified by code inspection:

func (e *OpError) Unwrap() error { return e.Err }

func (e *OpError) Error() string {
	if e == nil {
		return "<nil>"
	}

and this is the rerpo:

	err := (*net.OpError)(nil)
	err.Error()
	err.Unwrap() // or errors.Unwrap(err), it's just a call to err.Unrwap really

What did you expect to see?

No crash? Unwrap returning nil? I'm not exactly sure what the right behaviour would be here. I'm in favour of just returning nil, since .Error() has set the precedent and a nil is not wrapping anything. Obviously it's not great to have a typed nil floating about. nor would I want to depend on this behaviour, this is more for consistency's sake.

What did you see instead?

go run *.go
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0x46c9dd]

goroutine 1 [running]:
net.(*OpError).Unwrap(...)
	/nix/store/sz7mgf91bxd3xpxgqjzgr2avl9cshlz8-go-1.13.5/share/go/src/net/net.go:458
main.main()
	/home/rski/go/src/playground/at-2020-01-02-212034/snippet.go:18 +0x2d
exit status 2
@ianlancetaylor ianlancetaylor changed the title net.OpError(nil).Unrwap() crashes, while .Error() doesn't net: OpError(nil).Unrwap() crashes, while .Error() doesn't Jan 2, 2020
@ianlancetaylor

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@ianlancetaylor ianlancetaylor commented Jan 2, 2020

@ianlancetaylor ianlancetaylor added this to the Go1.15 milestone Jan 2, 2020
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@jba jba commented Jan 2, 2020

In my opinion, Unwrap is doing the right thing, and Error's behavior is a mistake. So I don't think we should "fix" Unwrap for consistency.

Both the unexported error type of the errors package, and the one in fmt used for %w, will panic on nil.

@smasher164 smasher164 changed the title net: OpError(nil).Unrwap() crashes, while .Error() doesn't net: OpError(nil).Unwrap() crashes, while .Error() doesn't Jan 3, 2020
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