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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.BSD file.
// This code is a modified version of [path/filepath/symlink_windows.go]
// and [path/filepath/symlink.go] from the Go 1.4.2 standard library, and
// added in [docker@9b648df].
//
// [path/filepath/symlink_windows.go]: https://github.com/golang/go/blob/go1.4.2/src/path/filepath/symlink_windows.go
// [path/filepath/symlink.go]: https://github.com/golang/go/blob/go1.4.2/src/path/filepath/symlink.go
// [docker@9b648df]: https://github.com/moby/moby/commit/9b648dfac6453de5944ee4bb749115d85a253a05
package symlink
import (
"bytes"
"errors"
"os"
"path/filepath"
"strings"
"golang.org/x/sys/windows"
)
func toShort(path string) (string, error) {
p, err := windows.UTF16FromString(path)
if err != nil {
return "", err
}
b := p // GetShortPathName says we can reuse buffer
n, err := windows.GetShortPathName(&p[0], &b[0], uint32(len(b)))
if err != nil {
return "", err
}
if n > uint32(len(b)) {
b = make([]uint16, n)
if _, err = windows.GetShortPathName(&p[0], &b[0], uint32(len(b))); err != nil {
return "", err
}
}
return windows.UTF16ToString(b), nil
}
func toLong(path string) (string, error) {
p, err := windows.UTF16FromString(path)
if err != nil {
return "", err
}
b := p // GetLongPathName says we can reuse buffer
n, err := windows.GetLongPathName(&p[0], &b[0], uint32(len(b)))
if err != nil {
return "", err
}
if n > uint32(len(b)) {
b = make([]uint16, n)
n, err = windows.GetLongPathName(&p[0], &b[0], uint32(len(b)))
if err != nil {
return "", err
}
}
b = b[:n]
return windows.UTF16ToString(b), nil
}
func evalSymlinks(path string) (string, error) {
path, err := walkSymlinks(path)
if err != nil {
return "", err
}
p, err := toShort(path)
if err != nil {
return "", err
}
p, err = toLong(p)
if err != nil {
return "", err
}
// windows.GetLongPathName does not change the case of the drive letter,
// but the result of EvalSymlinks must be unique, so we have
// EvalSymlinks(`c:\a`) == EvalSymlinks(`C:\a`).
// Make drive letter upper case.
if len(p) >= 2 && p[1] == ':' && 'a' <= p[0] && p[0] <= 'z' {
p = string(p[0]+'A'-'a') + p[1:]
} else if len(p) >= 6 && p[5] == ':' && 'a' <= p[4] && p[4] <= 'z' {
p = p[:3] + string(p[4]+'A'-'a') + p[5:]
}
return filepath.Clean(p), nil
}
const (
utf8RuneSelf = 0x80
longPathPrefix = `\\?\`
)
func walkSymlinks(path string) (string, error) {
const maxIter = 255
originalPath := path
// consume path by taking each frontmost path element,
// expanding it if it's a symlink, and appending it to b
var b bytes.Buffer
for n := 0; path != ""; n++ {
if n > maxIter {
return "", errors.New("too many links in " + originalPath)
}
// A path beginning with `\\?\` represents the root, so automatically
// skip that part and begin processing the next segment.
if strings.HasPrefix(path, longPathPrefix) {
b.WriteString(longPathPrefix)
path = path[4:]
continue
}
// find next path component, p
i := -1
for j, c := range path {
if c < utf8RuneSelf && os.IsPathSeparator(uint8(c)) {
i = j
break
}
}
var p string
if i == -1 {
p, path = path, ""
} else {
p, path = path[:i], path[i+1:]
}
if p == "" {
if b.Len() == 0 {
// must be absolute path
b.WriteRune(filepath.Separator)
}
continue
}
// If this is the first segment after the long path prefix, accept the
// current segment as a volume root or UNC share and move on to the next.
if b.String() == longPathPrefix {
b.WriteString(p)
b.WriteRune(filepath.Separator)
continue
}
fi, err := os.Lstat(b.String() + p)
if err != nil {
return "", err
}
if fi.Mode()&os.ModeSymlink == 0 {
b.WriteString(p)
if path != "" || (b.Len() == 2 && len(p) == 2 && p[1] == ':') {
b.WriteRune(filepath.Separator)
}
continue
}
// it's a symlink, put it at the front of path
dest, err := os.Readlink(b.String() + p)
if err != nil {
return "", err
}
if isAbs(dest) {
b.Reset()
}
path = dest + string(filepath.Separator) + path
}
return filepath.Clean(b.String()), nil
}
func isDriveOrRoot(p string) bool {
if p == string(filepath.Separator) {
return true
}
length := len(p)
if length >= 2 {
if p[length-1] == ':' && (('a' <= p[length-2] && p[length-2] <= 'z') || ('A' <= p[length-2] && p[length-2] <= 'Z')) {
return true
}
}
return false
}
// isAbs is a platform-specific wrapper for filepath.IsAbs. On Windows,
// golang filepath.IsAbs does not consider a path \windows\system32 as absolute
// as it doesn't start with a drive-letter/colon combination. However, in
// docker we need to verify things such as WORKDIR /windows/system32 in
// a Dockerfile (which gets translated to \windows\system32 when being processed
// by the daemon. This SHOULD be treated as absolute from a docker processing
// perspective.
func isAbs(path string) bool {
if filepath.IsAbs(path) || strings.HasPrefix(path, string(os.PathSeparator)) {
return true
}
return false
}
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