Ilia Denisov
95 lines
2.1 KiB
Go
95 lines
2.1 KiB
Go
package fs
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import (
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"errors"
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"os"
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"path/filepath"
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"syscall"
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)
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// writable reports whether path is writable on Windows.
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//
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// Semantics:
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// - for an existing regular file, it tries to open it for writing;
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// - for an existing directory, it tries to create and remove a temp file inside it;
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// - for other file types, it returns false with no error.
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//
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// This is intentionally an operational check, not a mode-bit check, because
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// on Windows effective writability is determined by ACLs and file attributes,
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// not by POSIX-like permission bits from os.FileMode.
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func writable(path string) (bool, error) {
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info, err := os.Stat(path)
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if err != nil {
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return false, err
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}
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if info.IsDir() {
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return writableDir(path)
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}
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if !info.Mode().IsRegular() {
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return false, nil
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}
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return writableFile(path)
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}
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// writableFile checks whether an existing regular file can be opened for writing.
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func writableFile(path string) (bool, error) {
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f, err := os.OpenFile(path, os.O_WRONLY|os.O_APPEND, 0)
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if err == nil {
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_ = f.Close()
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return true, nil
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}
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if isPermissionLikeError(err) {
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return false, nil
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}
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return false, err
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}
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// writableDir checks whether a directory allows creating a child file.
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// That is usually the most useful definition of "directory is writable".
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func writableDir(path string) (bool, error) {
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pattern := filepath.Join(path, ".writable-check-*")
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f, err := os.CreateTemp(path, filepath.Base(pattern))
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if err == nil {
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name := f.Name()
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_ = f.Close()
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_ = os.Remove(name)
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return true, nil
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}
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if isPermissionLikeError(err) {
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return false, nil
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}
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return false, err
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}
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// isPermissionLikeError normalizes the common Windows "access denied" style
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// failures to a simple false result instead of surfacing them as hard errors.
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func isPermissionLikeError(err error) bool {
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if err == nil {
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return false
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}
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if errors.Is(err, os.ErrPermission) {
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return true
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}
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var errno syscall.Errno
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if errors.As(err, &errno) {
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// ERROR_ACCESS_DENIED
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if errno == syscall.ERROR_ACCESS_DENIED {
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return true
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}
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}
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var pathErr *os.PathError
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if errors.As(err, &pathErr) && errors.Is(pathErr.Err, os.ErrPermission) {
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return true
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}
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return false
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}
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