1package moxio

2

3import (

4 "fmt"

5 "io"

6 "log/slog"

7 "os"

8

9 "github.com/mjl-/mox/mlog"

10)

11

12// LinkOrCopy attempts to make a hardlink dst. If that fails, it will try to do a

13// regular file copy. If srcReaderOpt is not nil, it will be used for reading. If

14// sync is true and the file is copied, Sync is called on the file after writing to

15// ensure the file is written on disk. Callers should also sync the directory of

16// the destination file, but may want to do that after linking/copying multiple

17// files. If dst was created and an error occurred, it is removed.

18func LinkOrCopy(log mlog.Log, dst, src string, srcReaderOpt io.Reader, sync bool) (rerr error) {

19 // Try hardlink first.

20 err := os.Link(src, dst)

21 if err == nil {

22 return nil

23 } else if os.IsNotExist(err) {

24 // No point in trying with regular copy, we would fail again. Either src doesn't

25 // exist or dst directory doesn't exist.

26 return err

27 }

28

29 // File system may not support hardlinks, or link could be crossing file systems.

30 // Do a regular file copy.

31 if srcReaderOpt == nil {

32 sf, err := os.Open(src)

33 if err != nil {

34 return fmt.Errorf("open source file: %w", err)

35 }

36 defer func() {

37 err := sf.Close()

38 log.Check(err, "closing copied source file")

39 }()

40 srcReaderOpt = sf

41 }

42

43 df, err := os.OpenFile(dst, os.O_CREATE|os.O_EXCL|os.O_WRONLY, 0660)

44 if err != nil {

45 return fmt.Errorf("create destination: %w", err)

46 }

47 defer func() {

48 if df != nil {

49 err := df.Close()

50 log.Check(err, "closing partial destination file")

51 err = os.Remove(dst)

52 log.Check(err, "removing partial destination file", slog.String("path", dst))

53 }

54 }()

55

56 if _, err := io.Copy(df, srcReaderOpt); err != nil {

57 return fmt.Errorf("copy: %w", err)

58 }

59 if sync {

60 if err := df.Sync(); err != nil {

61 return fmt.Errorf("sync destination: %w", err)

62 }

63 }

64 err = df.Close()

65 df = nil

66 if err != nil {

67 err := os.Remove(dst)

68 log.Check(err, "removing partial destination file", slog.String("path", dst))

69 return err

70 }

71 return nil

72}

73