1package sys
 2
 3import (
 4	"io"
 5	"io/fs"
 6	"os"
 7)
 8
 9// UnwrapOSError returns an Errno or zero if the input is nil.
10func UnwrapOSError(err error) Errno {
11	if err == nil {
12		return 0
13	}
14	err = underlyingError(err)
15	switch err {
16	case nil, io.EOF:
17		return 0 // EOF is not a Errno
18	case fs.ErrInvalid:
19		return EINVAL
20	case fs.ErrPermission:
21		return EPERM
22	case fs.ErrExist:
23		return EEXIST
24	case fs.ErrNotExist:
25		return ENOENT
26	case fs.ErrClosed:
27		return EBADF
28	}
29	return errorToErrno(err)
30}
31
32// underlyingError returns the underlying error if a well-known OS error type.
33//
34// This impl is basically the same as os.underlyingError in os/error.go
35func underlyingError(err error) error {
36	switch err := err.(type) {
37	case *os.PathError:
38		return err.Err
39	case *os.LinkError:
40		return err.Err
41	case *os.SyscallError:
42		return err.Err
43	}
44	return err
45}