os: os.DirFS doesn't work with Windows UNC paths #54694
Description
What version of Go are you using (go version)?
$ go version go version go1.19 linux/amd64
Does this issue reproduce with the latest release?
Yes
What operating system and processor architecture are you using (go env)?
I build on Linux and run on Windows (Microsoft Windows [Version 10.0.19044.1889])
go env Output
$ go env GO111MODULE="" GOARCH="amd64" GOBIN="" GOCACHE="/home/patrik/.cache/go-build" GOENV="/home/patrik/.config/go/env" GOEXE="" GOEXPERIMENT="" GOFLAGS="" GOHOSTARCH="amd64" GOHOSTOS="linux" GOINSECURE="" GOMODCACHE="/home/patrik/go/pkg/mod" GONOPROXY="REDCATED" GONOSUMDB="REDCATED" GOOS="linux" GOPATH="/home/patrik/go" GOPRIVATE="REDACTED" GOPROXY="https://proxy.golang.org,direct" GOROOT="/usr/local/go" GOSUMDB="sum.golang.org" GOTMPDIR="" GOTOOLDIR="/usr/local/go/pkg/tool/linux_amd64" GOVCS="" GOVERSION="go1.19" GCCGO="gccgo" GOAMD64="v1" AR="ar" CC="gcc" CXX="g++" CGO_ENABLED="1" GOMOD="/home/patrik/REDACTED/go.mod" GOWORK="" 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 -pthread -Wl,--no-gc-sections -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build4002045871=/tmp/go-build -gno-record-gcc-switches"
What did you do?
I created a test program that tries to walk the root dir. I test it with a normal path and also a UNC path.
The program gives the expected output on Linux using wine, but on a real Windows machine it doesn't work.
I created my own "fixed" implementation of os.DirFS that seems to solve the issue.
package main
import (
"fmt"
"io/fs"
"os"
"path/filepath"
"runtime"
)
func main() {
runTests()
}
func runTests() {
type testT struct {
name string
fs fs.FS
}
tests := []testT{
{name: "Normal path 1", fs: os.DirFS("C:\\")},
{name: "UNC Path 1", fs: os.DirFS("\\\\?\\C:\\")},
{name: "Normal path 2", fs: OSDirFS("C:\\")},
{name: "UNC Path 2", fs: OSDirFS("\\\\?\\C:\\")},
}
for _, t := range tests {
fmt.Println("Testing:", t.name)
err := testFS(t.fs)
if err != nil {
fmt.Println("Error:", err)
} else {
fmt.Println("OK")
}
}
}
func testFS(tfs fs.FS) error {
err := fs.WalkDir(tfs, ".", func(path string, d fs.DirEntry, err error) error {
if err != nil {
return err
}
return fmt.Errorf("dummy")
})
if err != nil && err.Error() != "dummy" {
return err
}
return nil
}
type osDirFS string
func OSDirFS(dir string) fs.FS {
return osDirFS(dir)
}
func containsAny(s, chars string) bool {
for i := 0; i < len(s); i++ {
for j := 0; j < len(chars); j++ {
if s[i] == chars[j] {
return true
}
}
}
return false
}
func (dir osDirFS) Open(name string) (fs.File, error) {
if !fs.ValidPath(name) || runtime.GOOS == "windows" && containsAny(name, `\:`) {
return nil, &fs.PathError{Op: "open", Path: name, Err: fs.ErrInvalid}
}
f, err := os.Open(filepath.Join(string(dir), filepath.FromSlash(name)))
if err != nil {
return nil, err // nil fs.File
}
return f, nil
}
func (dir osDirFS) Stat(name string) (fs.FileInfo, error) {
if !fs.ValidPath(name) || runtime.GOOS == "windows" && containsAny(name, `\:`) {
return nil, &fs.PathError{Op: "stat", Path: name, Err: fs.ErrInvalid}
}
f, err := os.Stat(filepath.Join(string(dir), filepath.FromSlash(name)))
if err != nil {
return nil, err
}
return f, nil
}What did you expect to see?
I expected the UNC path with fs.WalkDir() to work.
What did you see instead?
It gives me an error: CreateFile \\?\C:\/.: The filename, directory name, or volume label syntax is incorrect.
Seems like Windows doesn't like forward slashes in UNC paths.
Testing: Normal path 1
OK
Testing: UNC Path 1
Error: CreateFile \\?\C:\/.: The filename, directory name, or volume label syntax is incorrect.
Testing: Normal path 2
OK
Testing: UNC Path 2
OK
Suggested fix
I think the os.DirFS implementation should convert the forward style slashes of the fs.FS implementation to platform native path separators before sending the function calls off to the os.Open() and os.Stat().