os: executable FileMode bit is not set on Windows

[gochist]

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

$ go version
go version go1.13.8 windows/amd64

Does this issue reproduce with the latest release?

Yes

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

go env Output

$ go env
set GO111MODULE=
set GOARCH=amd64
set GOBIN=
set GOCACHE=C:\Users\june.yi\AppData\Local\go-build
set GOENV=C:\Users\june.yi\AppData\Roaming\go\env
set GOEXE=.exe
set GOFLAGS=
set GOHOSTARCH=amd64
set GOHOSTOS=windows
set GONOPROXY=
set GONOSUMDB=
set GOOS=windows
set GOPATH=C:\Users\june.yi\go
set GOPRIVATE=
set GOPROXY=https://proxy.golang.org,direct
set GOROOT=C:\Go
set GOSUMDB=sum.golang.org
set GOTMPDIR=
set GOTOOLDIR=C:\Go\pkg\tool\windows_amd64
set GCCGO=gccgo
set AR=ar
set CC=gcc
set CXX=g++
set CGO_ENABLED=1
set GOMOD=
set CGO_CFLAGS=-g -O2
set CGO_CPPFLAGS=
set CGO_CXXFLAGS=-g -O2
set CGO_FFLAGS=-g -O2
set CGO_LDFLAGS=-g -O2
set PKG_CONFIG=pkg-config
set GOGCCFLAGS=-m64 -mthreads -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=C:\Users\june.yi\Aset GOGCCFLAGS=-m64 -mthreads -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=C:\Users\june.yi\A
ppData\Local\Temp\go-build564788466=/tmp/go-build -gno-record-gcc-switches

What did you do?

I ran the code to check if a file is executable on Windows.

package main

import "os"

func main() {
	f, err := os.Stat("C:\\Users\\june.yi\\Downloads\\SopsSecretGenerator_1.3.1_windows_amd64.exe")

	if err == nil {
		println(f.Mode())
		println(f.Mode() & 0111 == 0000)
	}
}

What did you expect to see?

Bit operation was performed to implement a function that checks whether a file is executable. However, it seems that the executable bit is not set even though it is an executable file on Windows.

493
false

(493==0755)

What did you see instead?

438
true

(438==0644)

[ianlancetaylor]

How do you suggest we decide whether a file is executable on Windows?

[gochist]

I'm sorry I don't have a solid idea. But wouldn't the following quote help?

Checking access is discouraged since it's race-prone, but if you have to do it in POSIX, you should use faccessat with X_OK and AT_EACCESS in order to evaluate the file's mode and ACL permissions against the effective user and group IDs and supplementary groups of the process. -- from https://stackoverflow.com/questions/63911706/how-to-check-if-a-file-is-executable-on-windows-with-golang#comment113020583_63911706

[davecheney]

Can I ask, if go were changed to return the mode bits you propose, what problem would that allow you to solve?

Perhaps there is another way to accomplish what you need without wading into the depths of Unix file permissions on a platform that isn’t Unix. Do you think that is possible?

[networkimprov]

cc @alexbrainman @mattn @iwdgo

[gochist]

@davecheney

Can I ask, if go were changed to return the mode bits you propose, what problem would that allow you to solve?

There is a plugin system in a cli-based tool called kustomize, which supports exec type and go library type. FileMode is used to determine whether a plug-in is available when loading a plug-in and to classify the type, but in Windows, it is getting different results than the intended one. (related with kubernetes-sigs/kustomize#3027)

Perhaps there is another way to accomplish what you need without wading into the depths of Unix file permissions on a platform that isn’t Unix. Do you think that is possible?

I think it is possible. However, from the kustomize project's point of view(although I am not an active contributor), it also seems necessary to check whether the standard library will support this feature in the future in any way.

[mattn]

I do not agree with this. File permissions and ACLs need to be distinguished. Whereas the file's permissions indicate whether the file itself is executable or not, the ACL indicates whether the file is accessible or not for the user. Also, File permissions must be persistent when copied to another file system. Windows file system has no executable bits for executables. Also we can't determine file extension. For example, we can execute script files using PATHEXT enviroment variable.

One more thing I have to mention about this. Windows can execute without .exe, .bat, .com or file extensions contains in PATHEXT.

C:\temp>type test.go
package main

func main() {
        println("Hello!")
}

C:\temp>go build test.go

C:\temp>ren test.exe test.gopher

C:\temp>test.gopher
Hello!

Probably cmd.exe is looking magick-word MZ in the file. So we can't check the file extension for determine that the file is executable. i.e. we should not have a way to determine the file is executable, I think.

[jgrieger]

What about the GetBinaryTypeW function?

I have a POC using the golang.org/x/sys/windows package, passing the path of an executable file with arbitrary file extension, receiving the value 6 (SCS_64BIT_BINARY) = "A 64-bit Windows-based application.".