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// Copyright 2012 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package filepath
import (
"errors"
"io/fs"
"os"
"runtime"
"syscall"
)
func walkSymlinks(path string) (string, error) {
volLen := volumeNameLen(path)
pathSeparator := string(os.PathSeparator)
if volLen < len(path) && os.IsPathSeparator(path[volLen]) {
volLen++
}
vol := path[:volLen]
dest := vol
linksWalked := 0
for start, end := volLen, volLen; start < len(path); start = end {
for start < len(path) && os.IsPathSeparator(path[start]) {
start++
}
end = start
for end < len(path) && !os.IsPathSeparator(path[end]) {
end++
}
// On Windows, "." can be a symlink.
// We look it up, and use the value if it is absolute.
// If not, we just return ".".
isWindowsDot := runtime.GOOS == "windows" && path[volumeNameLen(path):] == "."
// The next path component is in path[start:end].
if end == start {
// No more path components.
break
} else if path[start:end] == "." && !isWindowsDot {
// Ignore path component ".".
continue
} else if path[start:end] == ".." {
// Back up to previous component if possible.
// Note that volLen includes any leading slash.
// Set r to the index of the last slash in dest,
// after the volume.
var r int
for r = len(dest) - 1; r >= volLen; r-- {
if os.IsPathSeparator(dest[r]) {
break
}
}
if r < volLen || dest[r+1:] == ".." {
// Either path has no slashes
// (it's empty or just "C:")
// or it ends in a ".." we had to keep.
// Either way, keep this "..".
if len(dest) > volLen {
dest += pathSeparator
}
dest += ".."
} else {
// Discard everything since the last slash.
dest = dest[:r]
}
continue
}
// Ordinary path component. Add it to result.
if len(dest) > volumeNameLen(dest) && !os.IsPathSeparator(dest[len(dest)-1]) {
dest += pathSeparator
}
dest += path[start:end]
// Resolve symlink.
fi, err := os.Lstat(dest)
if err != nil {
return "", err
}
if fi.Mode()&fs.ModeSymlink == 0 {
if !fi.Mode().IsDir() && end < len(path) {
return "", syscall.ENOTDIR
}
continue
}
// Found symlink.
linksWalked++
if linksWalked > 255 {
return "", errors.New("EvalSymlinks: too many links")
}
link, err := os.Readlink(dest)
if err != nil {
return "", err
}
if isWindowsDot && !IsAbs(link) {
// On Windows, if "." is a relative symlink,
// just return ".".
break
}
path = link + path[end:]
v := volumeNameLen(link)
if v > 0 {
// Symlink to drive name is an absolute path.
if v < len(link) && os.IsPathSeparator(link[v]) {
v++
}
vol = link[:v]
dest = vol
end = len(vol)
} else if len(link) > 0 && os.IsPathSeparator(link[0]) {
// Symlink to absolute path.
dest = link[:1]
end = 1
} else {
// Symlink to relative path; replace last
// path component in dest.
var r int
for r = len(dest) - 1; r >= volLen; r-- {
if os.IsPathSeparator(dest[r]) {
break
}
}
if r < volLen {
dest = vol
} else {
dest = dest[:r]
}
end = 0
}
}
return Clean(dest), nil
}
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