path/filepath: join function does not allow UNC for pipe

[kayila]

The path has to start with \\.\pipe\ for named pipes on Windows, but filepath.Join() removes the leading \\..

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

1.9.1

Does this issue reproduce with the latest release?

Yes. (1.9.2, as of opening this issue.)

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

GOARCH="amd64"
GOBIN=""
GOEXE=".exe"
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOOS="windows"
GOPATH="/home/kayila/go"
GORACE=""
GOROOT="/usr/lib/go-1.7"
GOTOOLDIR="/usr/lib/go-1.7/pkg/tool/linux_amd64"
CC="gcc"
GOGCCFLAGS="-m64 -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build187455838=/tmp/go-build -gno-record-gcc-switches"
CXX="g++"
CGO_ENABLED="0"

What did you do?

package main

import (
	"fmt"
	"path/filepath"
)

func main() {
	fmt.Println(filepath.Join("\\\\.", "pipe", "blah"))
	fmt.Println(filepath.Join("\\\\.\\pipe", "blah"))
}

What did you expect to see?

\\.\pipe\blah
\\.\pipe\blah

What did you see instead?

\pipe\blah
\pipe\blah

[cznic]

If you know, that a named pipe on Windows has a special prefix that intentionally does comply with filepath.Clean rules, just use

`\\.\` + filepath.Join("pipe", "blah")

ie. don't pass the special prefix to filepath.Join that's documented to Clean the result.

[alexbrainman]

@kayila yes path/filepath package does not support pipe names. But it also does not support paths starting with \\?\ either (which are more common).

https://golang.org/doc/contribute.html if you decide to add missing functionality.

Alex

[qmuntal]

Can't reproduce in go1.20. Probably fixed by CL 444280.