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- // Copyright 2009 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 osutil
- import (
- "os"
- "path/filepath"
- "syscall"
- )
- // DebugSymlinkForTestsOnly is os.Symlink taken from the 1.9.2 stdlib,
- // hacked with the SYMBOLIC_LINK_FLAG_ALLOW_UNPRIVILEGED_CREATE flag to
- // create symlinks when not elevated.
- //
- // This is not and should not be used in Syncthing code, hence the
- // cumbersome name to make it obvious if this ever leaks. Nonetheless it's
- // useful in tests.
- func DebugSymlinkForTestsOnly(oldname, newname string) error {
- // CreateSymbolicLink is not supported before Windows Vista
- if syscall.LoadCreateSymbolicLink() != nil {
- return &os.LinkError{"symlink", oldname, newname, syscall.EWINDOWS}
- }
- // '/' does not work in link's content
- oldname = filepath.FromSlash(oldname)
- // need the exact location of the oldname when its relative to determine if its a directory
- destpath := oldname
- if !filepath.IsAbs(oldname) {
- destpath = filepath.Dir(newname) + `\` + oldname
- }
- fi, err := os.Lstat(destpath)
- isdir := err == nil && fi.IsDir()
- n, err := syscall.UTF16PtrFromString(fixLongPath(newname))
- if err != nil {
- return &os.LinkError{"symlink", oldname, newname, err}
- }
- o, err := syscall.UTF16PtrFromString(fixLongPath(oldname))
- if err != nil {
- return &os.LinkError{"symlink", oldname, newname, err}
- }
- var flags uint32
- if isdir {
- flags |= syscall.SYMBOLIC_LINK_FLAG_DIRECTORY
- }
- flags |= 0x02 // SYMBOLIC_LINK_FLAG_ALLOW_UNPRIVILEGED_CREATE
- err = syscall.CreateSymbolicLink(n, o, flags)
- if err != nil {
- return &os.LinkError{"symlink", oldname, newname, err}
- }
- return nil
- }
- // fixLongPath returns the extended-length (\\?\-prefixed) form of
- // path when needed, in order to avoid the default 260 character file
- // path limit imposed by Windows. If path is not easily converted to
- // the extended-length form (for example, if path is a relative path
- // or contains .. elements), or is short enough, fixLongPath returns
- // path unmodified.
- //
- // See https://msdn.microsoft.com/en-us/library/windows/desktop/aa365247(v=vs.85).aspx#maxpath
- func fixLongPath(path string) string {
- // Do nothing (and don't allocate) if the path is "short".
- // Empirically (at least on the Windows Server 2013 builder),
- // the kernel is arbitrarily okay with < 248 bytes. That
- // matches what the docs above say:
- // "When using an API to create a directory, the specified
- // path cannot be so long that you cannot append an 8.3 file
- // name (that is, the directory name cannot exceed MAX_PATH
- // minus 12)." Since MAX_PATH is 260, 260 - 12 = 248.
- //
- // The MSDN docs appear to say that a normal path that is 248 bytes long
- // will work; empirically the path must be less then 248 bytes long.
- if len(path) < 248 {
- // Don't fix. (This is how Go 1.7 and earlier worked,
- // not automatically generating the \\?\ form)
- return path
- }
- // The extended form begins with \\?\, as in
- // \\?\c:\windows\foo.txt or \\?\UNC\server\share\foo.txt.
- // The extended form disables evaluation of . and .. path
- // elements and disables the interpretation of / as equivalent
- // to \. The conversion here rewrites / to \ and elides
- // . elements as well as trailing or duplicate separators. For
- // simplicity it avoids the conversion entirely for relative
- // paths or paths containing .. elements. For now,
- // \\server\share paths are not converted to
- // \\?\UNC\server\share paths because the rules for doing so
- // are less well-specified.
- if len(path) >= 2 && path[:2] == `\\` {
- // Don't canonicalize UNC paths.
- return path
- }
- if !filepath.IsAbs(path) {
- // Relative path
- return path
- }
- const prefix = `\\?`
- pathbuf := make([]byte, len(prefix)+len(path)+len(`\`))
- copy(pathbuf, prefix)
- n := len(path)
- r, w := 0, len(prefix)
- for r < n {
- switch {
- case os.IsPathSeparator(path[r]):
- // empty block
- r++
- case path[r] == '.' && (r+1 == n || os.IsPathSeparator(path[r+1])):
- // /./
- r++
- case r+1 < n && path[r] == '.' && path[r+1] == '.' && (r+2 == n || os.IsPathSeparator(path[r+2])):
- // /../ is currently unhandled
- return path
- default:
- pathbuf[w] = '\\'
- w++
- for ; r < n && !os.IsPathSeparator(path[r]); r++ {
- pathbuf[w] = path[r]
- w++
- }
- }
- }
- // A drive's root directory needs a trailing \
- if w == len(`\\?\c:`) {
- pathbuf[w] = '\\'
- w++
- }
- return string(pathbuf[:w])
- }
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