1 files changed, 129 insertions, 0 deletions
diff --git a/modules/lfs/pointer.go b/modules/lfs/pointer.go
new file mode 100644
index 00000000..ebde20f8
--- /dev/null
+++ b/modules/lfs/pointer.go
@@ -0,0 +1,129 @@
+// Copyright 2021 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package lfs
+
+import (
+	"crypto/sha256"
+	"encoding/hex"
+	"errors"
+	"fmt"
+	"io"
+	"path"
+	"regexp"
+	"strconv"
+	"strings"
+)
+
+const (
+	blobSizeCutoff = 1024
+
+	// MetaFileIdentifier is the string appearing at the first line of LFS pointer files.
+	// https://github.com/git-lfs/git-lfs/blob/master/docs/spec.md
+	MetaFileIdentifier = "version https://git-lfs.github.com/spec/v1"
+
+	// MetaFileOidPrefix appears in LFS pointer files on a line before the sha256 hash.
+	MetaFileOidPrefix = "oid sha256:"
+)
+
+var (
+	// ErrMissingPrefix occurs if the content lacks the LFS prefix
+	ErrMissingPrefix = errors.New("content lacks the LFS prefix")
+
+	// ErrInvalidStructure occurs if the content has an invalid structure
+	ErrInvalidStructure = errors.New("content has an invalid structure")
+
+	// ErrInvalidOIDFormat occurs if the oid has an invalid format
+	ErrInvalidOIDFormat = errors.New("OID has an invalid format")
+)
+
+// ReadPointer tries to read LFS pointer data from the reader
+func ReadPointer(reader io.Reader) (Pointer, error) {
+	buf := make([]byte, blobSizeCutoff)
+	n, err := io.ReadFull(reader, buf)
+	if err != nil && err != io.ErrUnexpectedEOF {
+		return Pointer{}, err
+	}
+	buf = buf[:n]
+
+	return ReadPointerFromBuffer(buf)
+}
+
+var oidPattern = regexp.MustCompile(`^[a-f\d]{64}$`)
+
+// ReadPointerFromBuffer will return a pointer if the provided byte slice is a pointer file or an error otherwise.
+func ReadPointerFromBuffer(buf []byte) (Pointer, error) {
+	var p Pointer
+
+	headString := string(buf)
+	if !strings.HasPrefix(headString, MetaFileIdentifier) {
+		return p, ErrMissingPrefix
+	}
+
+	splitLines := strings.Split(headString, "\n")
+	if len(splitLines) < 3 {
+		return p, ErrInvalidStructure
+	}
+
+	oid := strings.TrimPrefix(splitLines[1], MetaFileOidPrefix)
+	if len(oid) != 64 || !oidPattern.MatchString(oid) {
+		return p, ErrInvalidOIDFormat
+	}
+	size, err := strconv.ParseInt(strings.TrimPrefix(splitLines[2], "size "), 10, 64)
+	if err != nil {
+		return p, err
+	}
+
+	p.Oid = oid
+	p.Size = size
+
+	return p, nil
+}
+
+// IsValid checks if the pointer has a valid structure.
+// It doesn't check if the pointed-to-content exists.
+func (p Pointer) IsValid() bool {
+	if len(p.Oid) != 64 {
+		return false
+	}
+	if !oidPattern.MatchString(p.Oid) {
+		return false
+	}
+	if p.Size < 0 {
+		return false
+	}
+	return true
+}
+
+// StringContent returns the string representation of the pointer
+// https://github.com/git-lfs/git-lfs/blob/main/docs/spec.md#the-pointer
+func (p Pointer) StringContent() string {
+	return fmt.Sprintf("%s\n%s%s\nsize %d\n", MetaFileIdentifier, MetaFileOidPrefix, p.Oid, p.Size)
+}
+
+// RelativePath returns the relative storage path of the pointer
+func (p Pointer) RelativePath() string {
+	if len(p.Oid) < 5 {
+		return p.Oid
+	}
+
+	return path.Join(p.Oid[0:2], p.Oid[2:4], p.Oid[4:])
+}
+
+func (p Pointer) LogString() string {
+	if p.Oid == "" && p.Size == 0 {
+		return "<LFSPointer empty>"
+	}
+	return fmt.Sprintf("<LFSPointer %s:%d>", p.Oid, p.Size)
+}
+
+// GeneratePointer generates a pointer for arbitrary content
+func GeneratePointer(content io.Reader) (Pointer, error) {
+	h := sha256.New()
+	c, err := io.Copy(h, content)
+	if err != nil {
+		return Pointer{}, err
+	}
+	sum := h.Sum(nil)
+	return Pointer{Oid: hex.EncodeToString(sum), Size: c}, nil
+}