1 files changed, 808 insertions, 0 deletions
diff --git a/storage/filesystem/dotgit/dotgit.go b/storage/filesystem/dotgit/dotgit.go
new file mode 100644
index 0000000..52b621c
--- /dev/null
+++ b/storage/filesystem/dotgit/dotgit.go
@@ -0,0 +1,808 @@
+// https://github.com/git/git/blob/master/Documentation/gitrepository-layout.txt
+package dotgit
+
+import (
+	"bufio"
+	"errors"
+	"fmt"
+	"io"
+	stdioutil "io/ioutil"
+	"os"
+	"path/filepath"
+	"strings"
+	"time"
+
+	"gopkg.in/src-d/go-billy.v4/osfs"
+	"gopkg.in/src-d/go-git.v4/plumbing"
+	"gopkg.in/src-d/go-git.v4/utils/ioutil"
+
+	"gopkg.in/src-d/go-billy.v4"
+)
+
+const (
+	suffix         = ".git"
+	packedRefsPath = "packed-refs"
+	configPath     = "config"
+	indexPath      = "index"
+	shallowPath    = "shallow"
+	modulePath     = "modules"
+	objectsPath    = "objects"
+	packPath       = "pack"
+	refsPath       = "refs"
+
+	tmpPackedRefsPrefix = "._packed-refs"
+
+	packExt = ".pack"
+	idxExt  = ".idx"
+)
+
+var (
+	// ErrNotFound is returned by New when the path is not found.
+	ErrNotFound = errors.New("path not found")
+	// ErrIdxNotFound is returned by Idxfile when the idx file is not found
+	ErrIdxNotFound = errors.New("idx file not found")
+	// ErrPackfileNotFound is returned by Packfile when the packfile is not found
+	ErrPackfileNotFound = errors.New("packfile not found")
+	// ErrConfigNotFound is returned by Config when the config is not found
+	ErrConfigNotFound = errors.New("config file not found")
+	// ErrPackedRefsDuplicatedRef is returned when a duplicated reference is
+	// found in the packed-ref file. This is usually the case for corrupted git
+	// repositories.
+	ErrPackedRefsDuplicatedRef = errors.New("duplicated ref found in packed-ref file")
+	// ErrPackedRefsBadFormat is returned when the packed-ref file corrupt.
+	ErrPackedRefsBadFormat = errors.New("malformed packed-ref")
+	// ErrSymRefTargetNotFound is returned when a symbolic reference is
+	// targeting a non-existing object. This usually means the repository
+	// is corrupt.
+	ErrSymRefTargetNotFound = errors.New("symbolic reference target not found")
+)
+
+// The DotGit type represents a local git repository on disk. This
+// type is not zero-value-safe, use the New function to initialize it.
+type DotGit struct {
+	fs billy.Filesystem
+}
+
+// New returns a DotGit value ready to be used. The path argument must
+// be the absolute path of a git repository directory (e.g.
+// "/foo/bar/.git").
+func New(fs billy.Filesystem) *DotGit {
+	return &DotGit{fs: fs}
+}
+
+// Initialize creates all the folder scaffolding.
+func (d *DotGit) Initialize() error {
+	mustExists := []string{
+		d.fs.Join("objects", "info"),
+		d.fs.Join("objects", "pack"),
+		d.fs.Join("refs", "heads"),
+		d.fs.Join("refs", "tags"),
+	}
+
+	for _, path := range mustExists {
+		_, err := d.fs.Stat(path)
+		if err == nil {
+			continue
+		}
+
+		if !os.IsNotExist(err) {
+			return err
+		}
+
+		if err := d.fs.MkdirAll(path, os.ModeDir|os.ModePerm); err != nil {
+			return err
+		}
+	}
+
+	return nil
+}
+
+// ConfigWriter returns a file pointer for write to the config file
+func (d *DotGit) ConfigWriter() (billy.File, error) {
+	return d.fs.Create(configPath)
+}
+
+// Config returns a file pointer for read to the config file
+func (d *DotGit) Config() (billy.File, error) {
+	return d.fs.Open(configPath)
+}
+
+// IndexWriter returns a file pointer for write to the index file
+func (d *DotGit) IndexWriter() (billy.File, error) {
+	return d.fs.Create(indexPath)
+}
+
+// Index returns a file pointer for read to the index file
+func (d *DotGit) Index() (billy.File, error) {
+	return d.fs.Open(indexPath)
+}
+
+// ShallowWriter returns a file pointer for write to the shallow file
+func (d *DotGit) ShallowWriter() (billy.File, error) {
+	return d.fs.Create(shallowPath)
+}
+
+// Shallow returns a file pointer for read to the shallow file
+func (d *DotGit) Shallow() (billy.File, error) {
+	f, err := d.fs.Open(shallowPath)
+	if err != nil {
+		if os.IsNotExist(err) {
+			return nil, nil
+		}
+
+		return nil, err
+	}
+
+	return f, nil
+}
+
+// NewObjectPack return a writer for a new packfile, it saves the packfile to
+// disk and also generates and save the index for the given packfile.
+func (d *DotGit) NewObjectPack() (*PackWriter, error) {
+	return newPackWrite(d.fs)
+}
+
+// ObjectPacks returns the list of availables packfiles
+func (d *DotGit) ObjectPacks() ([]plumbing.Hash, error) {
+	packDir := d.fs.Join(objectsPath, packPath)
+	files, err := d.fs.ReadDir(packDir)
+	if err != nil {
+		if os.IsNotExist(err) {
+			return nil, nil
+		}
+
+		return nil, err
+	}
+
+	var packs []plumbing.Hash
+	for _, f := range files {
+		if !strings.HasSuffix(f.Name(), packExt) {
+			continue
+		}
+
+		n := f.Name()
+		h := plumbing.NewHash(n[5 : len(n)-5]) //pack-(hash).pack
+		if h.IsZero() {
+			// Ignore files with badly-formatted names.
+			continue
+		}
+		packs = append(packs, h)
+	}
+
+	return packs, nil
+}
+
+func (d *DotGit) objectPackPath(hash plumbing.Hash, extension string) string {
+	return d.fs.Join(objectsPath, packPath, fmt.Sprintf("pack-%s.%s", hash.String(), extension))
+}
+
+func (d *DotGit) objectPackOpen(hash plumbing.Hash, extension string) (billy.File, error) {
+	pack, err := d.fs.Open(d.objectPackPath(hash, extension))
+	if err != nil {
+		if os.IsNotExist(err) {
+			return nil, ErrPackfileNotFound
+		}
+
+		return nil, err
+	}
+
+	return pack, nil
+}
+
+// ObjectPack returns a fs.File of the given packfile
+func (d *DotGit) ObjectPack(hash plumbing.Hash) (billy.File, error) {
+	return d.objectPackOpen(hash, `pack`)
+}
+
+// ObjectPackIdx returns a fs.File of the index file for a given packfile
+func (d *DotGit) ObjectPackIdx(hash plumbing.Hash) (billy.File, error) {
+	return d.objectPackOpen(hash, `idx`)
+}
+
+func (d *DotGit) DeleteOldObjectPackAndIndex(hash plumbing.Hash, t time.Time) error {
+	path := d.objectPackPath(hash, `pack`)
+	if !t.IsZero() {
+		fi, err := d.fs.Stat(path)
+		if err != nil {
+			return err
+		}
+		// too new, skip deletion.
+		if !fi.ModTime().Before(t) {
+			return nil
+		}
+	}
+	err := d.fs.Remove(path)
+	if err != nil {
+		return err
+	}
+	return d.fs.Remove(d.objectPackPath(hash, `idx`))
+}
+
+// NewObject return a writer for a new object file.
+func (d *DotGit) NewObject() (*ObjectWriter, error) {
+	return newObjectWriter(d.fs)
+}
+
+// Objects returns a slice with the hashes of objects found under the
+// .git/objects/ directory.
+func (d *DotGit) Objects() ([]plumbing.Hash, error) {
+	var objects []plumbing.Hash
+	err := d.ForEachObjectHash(func(hash plumbing.Hash) error {
+		objects = append(objects, hash)
+		return nil
+	})
+	if err != nil {
+		return nil, err
+	}
+	return objects, nil
+}
+
+// Objects returns a slice with the hashes of objects found under the
+// .git/objects/ directory.
+func (d *DotGit) ForEachObjectHash(fun func(plumbing.Hash) error) error {
+	files, err := d.fs.ReadDir(objectsPath)
+	if err != nil {
+		if os.IsNotExist(err) {
+			return nil
+		}
+
+		return err
+	}
+
+	for _, f := range files {
+		if f.IsDir() && len(f.Name()) == 2 && isHex(f.Name()) {
+			base := f.Name()
+			d, err := d.fs.ReadDir(d.fs.Join(objectsPath, base))
+			if err != nil {
+				return err
+			}
+
+			for _, o := range d {
+				h := plumbing.NewHash(base + o.Name())
+				if h.IsZero() {
+					// Ignore files with badly-formatted names.
+					continue
+				}
+				err = fun(h)
+				if err != nil {
+					return err
+				}
+			}
+		}
+	}
+
+	return nil
+}
+
+func (d *DotGit) objectPath(h plumbing.Hash) string {
+	hash := h.String()
+	return d.fs.Join(objectsPath, hash[0:2], hash[2:40])
+}
+
+// Object returns a fs.File pointing the object file, if exists
+func (d *DotGit) Object(h plumbing.Hash) (billy.File, error) {
+	return d.fs.Open(d.objectPath(h))
+}
+
+// ObjectStat returns a os.FileInfo pointing the object file, if exists
+func (d *DotGit) ObjectStat(h plumbing.Hash) (os.FileInfo, error) {
+	return d.fs.Stat(d.objectPath(h))
+}
+
+// ObjectDelete removes the object file, if exists
+func (d *DotGit) ObjectDelete(h plumbing.Hash) error {
+	return d.fs.Remove(d.objectPath(h))
+}
+
+func (d *DotGit) readReferenceFrom(rd io.Reader, name string) (ref *plumbing.Reference, err error) {
+	b, err := stdioutil.ReadAll(rd)
+	if err != nil {
+		return nil, err
+	}
+
+	line := strings.TrimSpace(string(b))
+	return plumbing.NewReferenceFromStrings(name, line), nil
+}
+
+func (d *DotGit) checkReferenceAndTruncate(f billy.File, old *plumbing.Reference) error {
+	if old == nil {
+		return nil
+	}
+	ref, err := d.readReferenceFrom(f, old.Name().String())
+	if err != nil {
+		return err
+	}
+	if ref.Hash() != old.Hash() {
+		return fmt.Errorf("reference has changed concurrently")
+	}
+	_, err = f.Seek(0, io.SeekStart)
+	if err != nil {
+		return err
+	}
+	return f.Truncate(0)
+}
+
+func (d *DotGit) SetRef(r, old *plumbing.Reference) error {
+	var content string
+	switch r.Type() {
+	case plumbing.SymbolicReference:
+		content = fmt.Sprintf("ref: %s\n", r.Target())
+	case plumbing.HashReference:
+		content = fmt.Sprintln(r.Hash().String())
+	}
+
+	fileName := r.Name().String()
+
+	return d.setRef(fileName, content, old)
+}
+
+// Refs scans the git directory collecting references, which it returns.
+// Symbolic references are resolved and included in the output.
+func (d *DotGit) Refs() ([]*plumbing.Reference, error) {
+	var refs []*plumbing.Reference
+	var seen = make(map[plumbing.ReferenceName]bool)
+	if err := d.addRefsFromRefDir(&refs, seen); err != nil {
+		return nil, err
+	}
+
+	if err := d.addRefsFromPackedRefs(&refs, seen); err != nil {
+		return nil, err
+	}
+
+	if err := d.addRefFromHEAD(&refs); err != nil {
+		return nil, err
+	}
+
+	return refs, nil
+}
+
+// Ref returns the reference for a given reference name.
+func (d *DotGit) Ref(name plumbing.ReferenceName) (*plumbing.Reference, error) {
+	ref, err := d.readReferenceFile(".", name.String())
+	if err == nil {
+		return ref, nil
+	}
+
+	return d.packedRef(name)
+}
+
+func (d *DotGit) findPackedRefsInFile(f billy.File) ([]*plumbing.Reference, error) {
+	s := bufio.NewScanner(f)
+	var refs []*plumbing.Reference
+	for s.Scan() {
+		ref, err := d.processLine(s.Text())
+		if err != nil {
+			return nil, err
+		}
+
+		if ref != nil {
+			refs = append(refs, ref)
+		}
+	}
+
+	return refs, s.Err()
+}
+
+func (d *DotGit) findPackedRefs() (r []*plumbing.Reference, err error) {
+	f, err := d.fs.Open(packedRefsPath)
+	if err != nil {
+		if os.IsNotExist(err) {
+			return nil, nil
+		}
+		return nil, err
+	}
+
+	defer ioutil.CheckClose(f, &err)
+	return d.findPackedRefsInFile(f)
+}
+
+func (d *DotGit) packedRef(name plumbing.ReferenceName) (*plumbing.Reference, error) {
+	refs, err := d.findPackedRefs()
+	if err != nil {
+		return nil, err
+	}
+
+	for _, ref := range refs {
+		if ref.Name() == name {
+			return ref, nil
+		}
+	}
+
+	return nil, plumbing.ErrReferenceNotFound
+}
+
+// RemoveRef removes a reference by name.
+func (d *DotGit) RemoveRef(name plumbing.ReferenceName) error {
+	path := d.fs.Join(".", name.String())
+	_, err := d.fs.Stat(path)
+	if err == nil {
+		err = d.fs.Remove(path)
+		// Drop down to remove it from the packed refs file, too.
+	}
+
+	if err != nil && !os.IsNotExist(err) {
+		return err
+	}
+
+	return d.rewritePackedRefsWithoutRef(name)
+}
+
+func (d *DotGit) addRefsFromPackedRefs(refs *[]*plumbing.Reference, seen map[plumbing.ReferenceName]bool) (err error) {
+	packedRefs, err := d.findPackedRefs()
+	if err != nil {
+		return err
+	}
+
+	for _, ref := range packedRefs {
+		if !seen[ref.Name()] {
+			*refs = append(*refs, ref)
+			seen[ref.Name()] = true
+		}
+	}
+	return nil
+}
+
+func (d *DotGit) addRefsFromPackedRefsFile(refs *[]*plumbing.Reference, f billy.File, seen map[plumbing.ReferenceName]bool) (err error) {
+	packedRefs, err := d.findPackedRefsInFile(f)
+	if err != nil {
+		return err
+	}
+
+	for _, ref := range packedRefs {
+		if !seen[ref.Name()] {
+			*refs = append(*refs, ref)
+			seen[ref.Name()] = true
+		}
+	}
+	return nil
+}
+
+func (d *DotGit) openAndLockPackedRefs(doCreate bool) (
+	pr billy.File, err error) {
+	var f billy.File
+	defer func() {
+		if err != nil && f != nil {
+			ioutil.CheckClose(f, &err)
+		}
+	}()
+
+	// File mode is retrieved from a constant defined in the target specific
+	// files (dotgit_rewrite_packed_refs_*). Some modes are not available
+	// in all filesystems.
+	openFlags := openAndLockPackedRefsMode
+	if doCreate {
+		openFlags |= os.O_CREATE
+	}
+
+	// Keep trying to open and lock the file until we're sure the file
+	// didn't change between the open and the lock.
+	for {
+		f, err = d.fs.OpenFile(packedRefsPath, openFlags, 0600)
+		if err != nil {
+			if os.IsNotExist(err) && !doCreate {
+				return nil, nil
+			}
+
+			return nil, err
+		}
+		fi, err := d.fs.Stat(packedRefsPath)
+		if err != nil {
+			return nil, err
+		}
+		mtime := fi.ModTime()
+
+		err = f.Lock()
+		if err != nil {
+			return nil, err
+		}
+
+		fi, err = d.fs.Stat(packedRefsPath)
+		if err != nil {
+			return nil, err
+		}
+		if mtime.Equal(fi.ModTime()) {
+			break
+		}
+		// The file has changed since we opened it.  Close and retry.
+		err = f.Close()
+		if err != nil {
+			return nil, err
+		}
+	}
+	return f, nil
+}
+
+func (d *DotGit) rewritePackedRefsWithoutRef(name plumbing.ReferenceName) (err error) {
+	pr, err := d.openAndLockPackedRefs(false)
+	if err != nil {
+		return err
+	}
+	if pr == nil {
+		return nil
+	}
+	defer ioutil.CheckClose(pr, &err)
+
+	// Creating the temp file in the same directory as the target file
+	// improves our chances for rename operation to be atomic.
+	tmp, err := d.fs.TempFile("", tmpPackedRefsPrefix)
+	if err != nil {
+		return err
+	}
+	tmpName := tmp.Name()
+	defer func() {
+		ioutil.CheckClose(tmp, &err)
+		_ = d.fs.Remove(tmpName) // don't check err, we might have renamed it
+	}()
+
+	s := bufio.NewScanner(pr)
+	found := false
+	for s.Scan() {
+		line := s.Text()
+		ref, err := d.processLine(line)
+		if err != nil {
+			return err
+		}
+
+		if ref != nil && ref.Name() == name {
+			found = true
+			continue
+		}
+
+		if _, err := fmt.Fprintln(tmp, line); err != nil {
+			return err
+		}
+	}
+
+	if err := s.Err(); err != nil {
+		return err
+	}
+
+	if !found {
+		return nil
+	}
+
+	return d.rewritePackedRefsWhileLocked(tmp, pr)
+}
+
+// process lines from a packed-refs file
+func (d *DotGit) processLine(line string) (*plumbing.Reference, error) {
+	if len(line) == 0 {
+		return nil, nil
+	}
+
+	switch line[0] {
+	case '#': // comment - ignore
+		return nil, nil
+	case '^': // annotated tag commit of the previous line - ignore
+		return nil, nil
+	default:
+		ws := strings.Split(line, " ") // hash then ref
+		if len(ws) != 2 {
+			return nil, ErrPackedRefsBadFormat
+		}
+
+		return plumbing.NewReferenceFromStrings(ws[1], ws[0]), nil
+	}
+}
+
+func (d *DotGit) addRefsFromRefDir(refs *[]*plumbing.Reference, seen map[plumbing.ReferenceName]bool) error {
+	return d.walkReferencesTree(refs, []string{refsPath}, seen)
+}
+
+func (d *DotGit) walkReferencesTree(refs *[]*plumbing.Reference, relPath []string, seen map[plumbing.ReferenceName]bool) error {
+	files, err := d.fs.ReadDir(d.fs.Join(relPath...))
+	if err != nil {
+		if os.IsNotExist(err) {
+			return nil
+		}
+
+		return err
+	}
+
+	for _, f := range files {
+		newRelPath := append(append([]string(nil), relPath...), f.Name())
+		if f.IsDir() {
+			if err = d.walkReferencesTree(refs, newRelPath, seen); err != nil {
+				return err
+			}
+
+			continue
+		}
+
+		ref, err := d.readReferenceFile(".", strings.Join(newRelPath, "/"))
+		if err != nil {
+			return err
+		}
+
+		if ref != nil && !seen[ref.Name()] {
+			*refs = append(*refs, ref)
+			seen[ref.Name()] = true
+		}
+	}
+
+	return nil
+}
+
+func (d *DotGit) addRefFromHEAD(refs *[]*plumbing.Reference) error {
+	ref, err := d.readReferenceFile(".", "HEAD")
+	if err != nil {
+		if os.IsNotExist(err) {
+			return nil
+		}
+
+		return err
+	}
+
+	*refs = append(*refs, ref)
+	return nil
+}
+
+func (d *DotGit) readReferenceFile(path, name string) (ref *plumbing.Reference, err error) {
+	path = d.fs.Join(path, d.fs.Join(strings.Split(name, "/")...))
+	f, err := d.fs.Open(path)
+	if err != nil {
+		return nil, err
+	}
+	defer ioutil.CheckClose(f, &err)
+
+	return d.readReferenceFrom(f, name)
+}
+
+func (d *DotGit) CountLooseRefs() (int, error) {
+	var refs []*plumbing.Reference
+	var seen = make(map[plumbing.ReferenceName]bool)
+	if err := d.addRefsFromRefDir(&refs, seen); err != nil {
+		return 0, err
+	}
+
+	return len(refs), nil
+}
+
+// PackRefs packs all loose refs into the packed-refs file.
+//
+// This implementation only works under the assumption that the view
+// of the file system won't be updated during this operation.  This
+// strategy would not work on a general file system though, without
+// locking each loose reference and checking it again before deleting
+// the file, because otherwise an updated reference could sneak in and
+// then be deleted by the packed-refs process.  Alternatively, every
+// ref update could also lock packed-refs, so only one lock is
+// required during ref-packing.  But that would worsen performance in
+// the common case.
+//
+// TODO: add an "all" boolean like the `git pack-refs --all` flag.
+// When `all` is false, it would only pack refs that have already been
+// packed, plus all tags.
+func (d *DotGit) PackRefs() (err error) {
+	// Lock packed-refs, and create it if it doesn't exist yet.
+	f, err := d.openAndLockPackedRefs(true)
+	if err != nil {
+		return err
+	}
+	defer ioutil.CheckClose(f, &err)
+
+	// Gather all refs using addRefsFromRefDir and addRefsFromPackedRefs.
+	var refs []*plumbing.Reference
+	seen := make(map[plumbing.ReferenceName]bool)
+	if err = d.addRefsFromRefDir(&refs, seen); err != nil {
+		return err
+	}
+	if len(refs) == 0 {
+		// Nothing to do!
+		return nil
+	}
+	numLooseRefs := len(refs)
+	if err = d.addRefsFromPackedRefsFile(&refs, f, seen); err != nil {
+		return err
+	}
+
+	// Write them all to a new temp packed-refs file.
+	tmp, err := d.fs.TempFile("", tmpPackedRefsPrefix)
+	if err != nil {
+		return err
+	}
+	tmpName := tmp.Name()
+	defer func() {
+		ioutil.CheckClose(tmp, &err)
+		_ = d.fs.Remove(tmpName) // don't check err, we might have renamed it
+	}()
+
+	w := bufio.NewWriter(tmp)
+	for _, ref := range refs {
+		_, err = w.WriteString(ref.String() + "\n")
+		if err != nil {
+			return err
+		}
+	}
+	err = w.Flush()
+	if err != nil {
+		return err
+	}
+
+	// Rename the temp packed-refs file.
+	err = d.rewritePackedRefsWhileLocked(tmp, f)
+	if err != nil {
+		return err
+	}
+
+	// Delete all the loose refs, while still holding the packed-refs
+	// lock.
+	for _, ref := range refs[:numLooseRefs] {
+		path := d.fs.Join(".", ref.Name().String())
+		err = d.fs.Remove(path)
+		if err != nil && !os.IsNotExist(err) {
+			return err
+		}
+	}
+
+	return nil
+}
+
+// Module return a billy.Filesystem pointing to the module folder
+func (d *DotGit) Module(name string) (billy.Filesystem, error) {
+	return d.fs.Chroot(d.fs.Join(modulePath, name))
+}
+
+// Alternates returns DotGit(s) based off paths in objects/info/alternates if
+// available. This can be used to checks if it's a shared repository.
+func (d *DotGit) Alternates() ([]*DotGit, error) {
+	altpath := d.fs.Join("objects", "info", "alternates")
+	f, err := d.fs.Open(altpath)
+	if err != nil {
+		return nil, err
+	}
+	defer f.Close()
+
+	var alternates []*DotGit
+
+	// Read alternate paths line-by-line and create DotGit objects.
+	scanner := bufio.NewScanner(f)
+	for scanner.Scan() {
+		path := scanner.Text()
+		if !filepath.IsAbs(path) {
+			// For relative paths, we can perform an internal conversion to
+			// slash so that they work cross-platform.
+			slashPath := filepath.ToSlash(path)
+			// If the path is not absolute, it must be relative to object
+			// database (.git/objects/info).
+			// https://www.kernel.org/pub/software/scm/git/docs/gitrepository-layout.html
+			// Hence, derive a path relative to DotGit's root.
+			// "../../../reponame/.git/" -> "../../reponame/.git"
+			// Remove the first ../
+			relpath := filepath.Join(strings.Split(slashPath, "/")[1:]...)
+			normalPath := filepath.FromSlash(relpath)
+			path = filepath.Join(d.fs.Root(), normalPath)
+		}
+		fs := osfs.New(filepath.Dir(path))
+		alternates = append(alternates, New(fs))
+	}
+
+	if err = scanner.Err(); err != nil {
+		return nil, err
+	}
+
+	return alternates, nil
+}
+
+func isHex(s string) bool {
+	for _, b := range []byte(s) {
+		if isNum(b) {
+			continue
+		}
+		if isHexAlpha(b) {
+			continue
+		}
+
+		return false
+	}
+
+	return true
+}
+
+func isNum(b byte) bool {
+	return b >= '0' && b <= '9'
+}
+
+func isHexAlpha(b byte) bool {
+	return b >= 'a' && b <= 'f' || b >= 'A' && b <= 'F'
+}