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package osutil
import (
"io/fs"
"os"
. "syscall"
"unsafe"
)
// OpenFile behaves the same as [os.OpenFile],
// except on Windows it sets [syscall.FILE_SHARE_DELETE].
//
// See: https://go.dev/issue/32088#issuecomment-502850674
func OpenFile(name string, flag int, perm fs.FileMode) (*os.File, error) {
if name == "" {
return nil, &os.PathError{Op: "open", Path: name, Err: ENOENT}
}
r, e := syscallOpen(name, flag, uint32(perm.Perm()))
if e != nil {
return nil, &os.PathError{Op: "open", Path: name, Err: e}
}
return os.NewFile(uintptr(r), name), nil
}
// syscallOpen is a copy of [syscall.Open]
// that uses [syscall.FILE_SHARE_DELETE].
//
// https://go.dev/src/syscall/syscall_windows.go
func syscallOpen(path string, mode int, perm uint32) (fd Handle, err error) {
if len(path) == 0 {
return InvalidHandle, ERROR_FILE_NOT_FOUND
}
pathp, err := UTF16PtrFromString(path)
if err != nil {
return InvalidHandle, err
}
var access uint32
switch mode & (O_RDONLY | O_WRONLY | O_RDWR) {
case O_RDONLY:
access = GENERIC_READ
case O_WRONLY:
access = GENERIC_WRITE
case O_RDWR:
access = GENERIC_READ | GENERIC_WRITE
}
if mode&O_CREAT != 0 {
access |= GENERIC_WRITE
}
if mode&O_APPEND != 0 {
access &^= GENERIC_WRITE
access |= FILE_APPEND_DATA
}
sharemode := uint32(FILE_SHARE_READ | FILE_SHARE_WRITE | FILE_SHARE_DELETE)
var sa *SecurityAttributes
if mode&O_CLOEXEC == 0 {
sa = makeInheritSa()
}
var createmode uint32
switch {
case mode&(O_CREAT|O_EXCL) == (O_CREAT | O_EXCL):
createmode = CREATE_NEW
case mode&(O_CREAT|O_TRUNC) == (O_CREAT | O_TRUNC):
createmode = CREATE_ALWAYS
case mode&O_CREAT == O_CREAT:
createmode = OPEN_ALWAYS
case mode&O_TRUNC == O_TRUNC:
createmode = TRUNCATE_EXISTING
default:
createmode = OPEN_EXISTING
}
var attrs uint32 = FILE_ATTRIBUTE_NORMAL
if perm&S_IWRITE == 0 {
attrs = FILE_ATTRIBUTE_READONLY
if createmode == CREATE_ALWAYS {
const _ERROR_BAD_NETPATH = Errno(53)
// We have been asked to create a read-only file.
// If the file already exists, the semantics of
// the Unix open system call is to preserve the
// existing permissions. If we pass CREATE_ALWAYS
// and FILE_ATTRIBUTE_READONLY to CreateFile,
// and the file already exists, CreateFile will
// change the file permissions.
// Avoid that to preserve the Unix semantics.
h, e := CreateFile(pathp, access, sharemode, sa, TRUNCATE_EXISTING, FILE_ATTRIBUTE_NORMAL, 0)
switch e {
case ERROR_FILE_NOT_FOUND, _ERROR_BAD_NETPATH, ERROR_PATH_NOT_FOUND:
// File does not exist. These are the same
// errors as Errno.Is checks for ErrNotExist.
// Carry on to create the file.
default:
// Success or some different error.
return h, e
}
}
}
if createmode == OPEN_EXISTING && access == GENERIC_READ {
// Necessary for opening directory handles.
attrs |= FILE_FLAG_BACKUP_SEMANTICS
}
if mode&O_SYNC != 0 {
const _FILE_FLAG_WRITE_THROUGH = 0x80000000
attrs |= _FILE_FLAG_WRITE_THROUGH
}
return CreateFile(pathp, access, sharemode, sa, createmode, attrs, 0)
}
func makeInheritSa() *SecurityAttributes {
var sa SecurityAttributes
sa.Length = uint32(unsafe.Sizeof(sa))
sa.InheritHandle = 1
return &sa
}
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