soft-serve

  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
 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
 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
120	}
121	sum := h.Sum(nil)
122	return Pointer{Oid: hex.EncodeToString(sum), Size: c}, nil
123}