// 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 readerfunc 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-pointerfunc (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 pointerfunc (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 contentfunc 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}