os: SameFile should not follow symlinks on windows

[hirochachacha]

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.

package main

import (
	"fmt"
	"os"
)

func main() {
	f, err := os.Create("target")
	if err != nil {
		panic(err)
	}
	err = f.Close()
	if err != nil {
		panic(err)
	}
	defer os.Remove("target")
	err = os.Symlink("target", "symlink")
	if err != nil {
		panic(err)
	}
	defer os.Remove("symlink")
	st1, err := os.Lstat("symlink")
	if err != nil {
		panic(err)
	}
	st2, err := os.Lstat("target")
	if err != nil {
		panic(err)
	}
	fmt.Println(os.SameFile(st1, st2))
}

What did you expect to see?

false

What did you see instead?

true

Does this issue reproduce with the latest release (go1.9)?

I think so.

System details

go version go1.8 windows/amd64
GOARCH="amd64"
GOBIN=""
GOEXE=".exe"
GOHOSTARCH="amd64"
GOHOSTOS="windows"
GOOS="windows"
GOPATH="C:\Users\Hiroshi\gopath"
GORACE=""
GOROOT="C:\Go"
GOTOOLDIR="C:\Go\pkg\tool\windows_amd64"
GCCGO="gccgo"
CC="gcc"
GOGCCFLAGS="-m64 -mthreads -fmessage-length=0 -fdebug-prefix-map=C:\Users\Hiroshi\AppData\Local\Temp\go-build553453167=/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"
GOROOT/bin/go version: go version go1.8 windows/amd64
GOROOT/bin/go tool compile -V: compile version go1.8 X:framepointer
gdb --version: GNU gdb (GDB) 7.12

[ianlancetaylor]

CC @alexbrainman

[alexbrainman]

Why do you think your program should return false?

I read os.SameFile documentation - "... SameFile only applies to results returned by this package's Stat. It returns false in other cases.". Does that mean os.SameFile should return false if it is given result returned by os.Lstat(path) (regardless what path is) ?

Alex

[hirochachacha]

I think that is a documentation bug.
Here is the unix implementation:

func sameFile(fs1, fs2 *fileStat) bool {
	return fs1.sys.Dev == fs2.sys.Dev && fs1.sys.Ino == fs2.sys.Ino
}

[alexbrainman]

Here is the unix implementation:

Unix implementation is irrelevant, because we don't have API that does not follow symlinks.

Also meaning of "symlinks" is different on Windows. We had to include everything that is not file or directory on Windows in that category. For example, I have U:\ drive on my computer that maps to some share on another computer. Should os.SameFile(os.Lstat(U:\a), os.Lstat(\\another_computer\share\a)) return false or true? I think it should return true. But true is discovered by following from U: into \another_computer\share. Do you agree with me that os.SameFile(os.Lstat(U:\a), os.Lstat(\\another_computer\share\a)) should return true? If we agree to that, maybe we should agree that os.SameFile should do the same with symlinks.

Alex

[hirochachacha]

Yes, os.SameFile(os.Lstat(U:\a), os.Lstat(\\another_computer\share\a)) should be true. I agree.
But following symlinks is necessary? I didn't test it yet. I'll try it.

[hirochachacha]

I don't think NTFS is so special. It is based on computer science like other filesystems and share basic concepts.
I think the term 'file' in os.SameFile means a entry of the filesystem.
If two filepaths point the same filesystem entry, os.SameFile should be true, if not should be false.
I don't understand the reason we need to think in more complex ways.

[alexbrainman]

If two filepaths point the same filesystem entry, os.SameFile should be true, if not should be false.

@hirochachacha I do not know what "filesystem entry" is. But if you know how to fix this, go ahead. I won't be working on this.

Alex

[hirochachacha]

Thanks, will do.

[odeke-em]

Gentle ping, how's it going @hirochachacha?

[gopherbot]

Change https://golang.org/cl/134195 mentions this issue: os: use FILE_FLAG_OPEN_REPARSE_POINT in SameFile