1package lfs
2
3import (
4 "crypto/sha256"
5 "encoding/hex"
6 "errors"
7 "fmt"
8 "io"
9 "path"
10 "regexp"
11 "strconv"
12 "strings"
13)
14
15const (
16 blobSizeCutoff = 1024
17
18 // HashAlgorithmSHA256 is the hash algorithm used for Git LFS.
19 HashAlgorithmSHA256 = "sha256"
20
21 // MetaFileIdentifier is the string appearing at the first line of LFS pointer files.
22 // https://github.com/git-lfs/git-lfs/blob/master/docs/spec.md
23 MetaFileIdentifier = "version https://git-lfs.github.com/spec/v1"
24
25 // MetaFileOidPrefix appears in LFS pointer files on a line before the sha256 hash.
26 MetaFileOidPrefix = "oid " + HashAlgorithmSHA256 + ":"
27)
28
29var (
30 // ErrMissingPrefix occurs if the content lacks the LFS prefix.
31 ErrMissingPrefix = errors.New("content lacks the LFS prefix")
32
33 // ErrInvalidStructure occurs if the content has an invalid structure.
34 ErrInvalidStructure = errors.New("content has an invalid structure")
35
36 // ErrInvalidOIDFormat occurs if the oid has an invalid format.
37 ErrInvalidOIDFormat = errors.New("OID has an invalid format")
38)
39
40// ReadPointer tries to read LFS pointer data from the reader.
41func ReadPointer(reader io.Reader) (Pointer, error) {
42 buf := make([]byte, blobSizeCutoff)
43 n, err := io.ReadFull(reader, buf)
44 if err != nil && err != io.ErrUnexpectedEOF {
45 return Pointer{}, err //nolint:wrapcheck
46 }
47 buf = buf[:n]
48
49 return ReadPointerFromBuffer(buf)
50}
51
52var oidPattern = regexp.MustCompile(`^[a-f\d]{64}$`)
53
54// ReadPointerFromBuffer will return a pointer if the provided byte slice is a pointer file or an error otherwise.
55func ReadPointerFromBuffer(buf []byte) (Pointer, error) {
56 var p Pointer
57
58 headString := string(buf)
59 if !strings.HasPrefix(headString, MetaFileIdentifier) {
60 return p, ErrMissingPrefix
61 }
62
63 splitLines := strings.Split(headString, "\n")
64 if len(splitLines) < 3 {
65 return p, ErrInvalidStructure
66 }
67
68 oid := strings.TrimPrefix(splitLines[1], MetaFileOidPrefix)
69 if len(oid) != 64 || !oidPattern.MatchString(oid) {
70 return p, ErrInvalidOIDFormat
71 }
72 size, err := strconv.ParseInt(strings.TrimPrefix(splitLines[2], "size "), 10, 64)
73 if err != nil {
74 return p, err //nolint:wrapcheck
75 }
76
77 p.Oid = oid
78 p.Size = size
79
80 return p, nil
81}
82
83// IsValid checks if the pointer has a valid structure.
84// It doesn't check if the pointed-to-content exists.
85func (p Pointer) IsValid() bool {
86 if len(p.Oid) != 64 {
87 return false
88 }
89 if !oidPattern.MatchString(p.Oid) {
90 return false
91 }
92 if p.Size < 0 {
93 return false
94 }
95 return true
96}
97
98// String returns the string representation of the pointer
99// https://github.com/git-lfs/git-lfs/blob/main/docs/spec.md#the-pointer
100func (p Pointer) String() string {
101 return fmt.Sprintf("%s\n%s%s\nsize %d\n", MetaFileIdentifier, MetaFileOidPrefix, p.Oid, p.Size)
102}
103
104// RelativePath returns the relative storage path of the pointer
105// https://github.com/git-lfs/git-lfs/blob/main/docs/spec.md#intercepting-git
106func (p Pointer) RelativePath() string {
107 if len(p.Oid) < 5 {
108 return p.Oid
109 }
110
111 return path.Join(p.Oid[0:2], p.Oid[2:4], p.Oid)
112}
113
114// GeneratePointer generates a pointer for arbitrary content.
115func GeneratePointer(content io.Reader) (Pointer, error) {
116 h := sha256.New()
117 c, err := io.Copy(h, content)
118 if err != nil {
119 return Pointer{}, err //nolint:wrapcheck
120 }
121 sum := h.Sum(nil)
122 return Pointer{Oid: hex.EncodeToString(sum), Size: c}, nil
123}