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// fileSync is true and the file is copied instead of hardlinked, fsync is called

15// on the file after writing to ensure the file is flushed to disk. Callers should

16// also sync the directory of the destination file, but may want to do that after

17// linking/copying multiple files. If dst was created and an error occurred, it is

18// removed.

19func LinkOrCopy(log mlog.Log, dst, src string, srcReaderOpt io.Reader, fileSync bool) (rerr error) {

20

21 // Try hardlink first.

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

23 if err == nil {

24 return nil

25 } else if os.IsNotExist(err) {

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

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

28 return err

29 }

30

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

32 // Do a regular file copy.

33 if srcReaderOpt == nil {

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

35 if err != nil {

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

37 }

38 defer func() {

39 err := sf.Close()

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

41 }()

42 srcReaderOpt = sf

43 }

44

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

46 if err != nil {

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

48 }

49 defer func() {

50 if df != nil {

51 err := df.Close()

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

53 }

54 if rerr != nil {

55 err = os.Remove(dst)

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

57 }

58 }()

59

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

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

62 }

63 if fileSync {

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

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

66 }

67 }

68 if err := df.Close(); err != nil {

69 return fmt.Errorf("flush and close destination file: %w", err)

70 }

71 df = nil

72 return nil

73}

74