crfs/stargz/stargz.go - build - Git at Google

 // Copyright 2019 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.

 // The stargz package reads & writes tar.gz ("tarball") files in a
 // seekable, indexed format call "stargz". A stargz file is still a
 // valid tarball, but it's slightly bigger with new gzip streams for
 // each new file & throughout large files, and has an index in a magic
 // file at the end.
 package stargz

 import (
 	"archive/tar"
 	"bufio"
 	"bytes"
 	"compress/gzip"
 	"encoding/json"
 	"errors"
 	"fmt"
 	"io"
 	"strconv"
 	"time"
 )

 // TOCTarName is the name of the JSON file in the tar archive in the
 // table of contents gzip stream.
 const TOCTarName = "stargz.index.json"

 // FooterSize is the number of bytes in the stargz footer.
 //
 // The footer is an empty gzip stream with no compression and an Extra
 // header of the form "%016xSTARGZ", where the 64 bit hex-encoded
 // number is the offset to the gzip stream of JSON TOC.
 //
 // 47 comes from:
 //
 //   10 byte gzip header +
 //   2 byte (LE16) length of extra, encoding 22 (16 hex digits + len("STARGZ")) == "\x16\x00" +
 //   22 bytes of extra (fmt.Sprintf("%016xSTARGZ", tocGzipOffset))
 //   5 byte flate header
 //   8 byte gzip footer (two little endian uint32s: digest, size)
 const FooterSize = 47

 // A Reader permits random access reads from a stargz file.
 type Reader struct {
 	sr  *io.SectionReader
 	TOC *TOC
 }

 // Open opens a stargz file for reading.
 func Open(sr *io.SectionReader) (*Reader, error) {
 	if sr.Size() < FooterSize {
 		return nil, fmt.Errorf("stargz size %d is smaller than the stargz footer size", sr.Size())
 	}
 	// TODO: read a bigger chunk (1MB?) at once here to hopefully
 	// get the TOC + footer in one go.
 	var footer [FooterSize]byte
 	if _, err := sr.ReadAt(footer[:], sr.Size()-FooterSize); err != nil {
 		return nil, fmt.Errorf("error reading footer: %v", err)
 	}
 	tocOff, ok := parseFooter(footer[:])
 	if !ok {
 		return nil, fmt.Errorf("error parsing footer")
 	}
 	tocTargz := make([]byte, sr.Size()-tocOff-FooterSize)
 	if _, err := sr.ReadAt(tocTargz, tocOff); err != nil {
 		return nil, fmt.Errorf("error reading %d byte TOC targz: %v", len(tocTargz), err)
 	}
 	zr, err := gzip.NewReader(bytes.NewReader(tocTargz))
 	if err != nil {
 		return nil, fmt.Errorf("malformed TOC gzip header: %v", err)
 	}
 	zr.Multistream(false)
 	tr := tar.NewReader(zr)
 	h, err := tr.Next()
 	if err != nil {
 		return nil, fmt.Errorf("failed to find tar header in TOC gzip stream: %v", err)
 	}
 	if h.Name != TOCTarName {
 		return nil, fmt.Errorf("TOC tar entry had name %q; expected %q", h.Name, TOCTarName)
 	}
 	toc := new(TOC)
 	if err := json.NewDecoder(tr).Decode(&toc); err != nil {
 		return nil, fmt.Errorf("error decoding TOC JSON: %v", err)
 	}
 	return &Reader{sr: sr, TOC: toc}, nil
 }

 // TOCEntry is an entry in the stargz file's TOC (Table of Contents).
 type TOCEntry struct {
 	Offset   int64  `json:"offset,omitempty"` // offset to gzip stream of tar entry (for regular files only)
 	Name     string `json:"name"`
 	Type     string `json:"type"` // "dir", "reg", TODO
 	Size     int64  `json:"size,omitempty"`
 	LinkName string `json:"linkName,omitempty"`  // for symlinks
 	Mode     int64  `json:"mode,omitempty"`      // Permission and mode bits
 	Uid      int    `json:"uid,omitempty"`       // User ID of owner
 	Gid      int    `json:"gid,omitempty"`       // Group ID of owner
 	Uname    string `json:"userName,omitempty"`  // User name of owner
 	Gname    string `json:"groupName,omitempty"` // Group name of owner
 	ModTime  string `json:"modtime,omitempty"`

 	// ChunkOffset is non-zero if this is a chunk of a large,
 	// regular file. If so, the Offset is where the gzip header of
 	// ChunkSize bytes at ChunkOffset in Name begin. If both
 	// ChunkOffset and ChunkSize are zero, the file contents are
 	// completely represented at the tar gzip stream starting at
 	// Offset.
 	ChunkOffset int64 `json:"chunkOffset,omitempty"`
 	ChunkSize   int64 `json:"chunkSize,omitempty"`
 }

 // TOC is the table of contents index of the files in the stargz file.
 type TOC struct {
 	Version int        `json:"version"`
 	Entries []TOCEntry `json:"entries"`
 }

 // A Writer writes stargz files.
 //
 // Use NewWriter to create a new Writer.
 type Writer struct {
 	bw  *bufio.Writer
 	cw  *countWriter
 	toc *TOC

 	closed bool
 	gz     *gzip.Writer
 }

 // NewWriter returns a new stargz writer writing to w.
 //
 // The writer must be closed to write its trailing table of contents.
 func NewWriter(w io.Writer) *Writer {
 	bw := bufio.NewWriter(w)
 	cw := &countWriter{w: bw}
 	return &Writer{
 		bw:  bw,
 		cw:  cw,
 		toc: &TOC{Version: 1},
 	}
 }

 // Close writes the stargz's table of contents and flushes all the
 // buffers, returning any error.
 func (w *Writer) Close() error {
 	if w.closed {
 		return nil
 	}
 	defer func() { w.closed = true }()

 	if err := w.closeGz(); err != nil {
 		return err
 	}

 	// Write the TOC index.
 	tocOff := w.cw.n
 	w.gz, _ = gzip.NewWriterLevel(w.cw, gzip.BestCompression)
 	tw := tar.NewWriter(w.gz)
 	tocJSON, err := json.MarshalIndent(w.toc, "", "\t")
 	if err != nil {
 		return err
 	}
 	if err := tw.WriteHeader(&tar.Header{
 		Typeflag: tar.TypeReg,
 		Name:     TOCTarName,
 		Size:     int64(len(tocJSON)),
 	}); err != nil {
 		return err
 	}
 	if _, err := tw.Write(tocJSON); err != nil {
 		return err
 	}

 	if err := tw.Close(); err != nil {
 		return err
 	}
 	if err := w.closeGz(); err != nil {
 		return err
 	}

 	// And a little footer with pointer to the TOC gzip stream.
 	if _, err := w.bw.Write(footerBytes(tocOff)); err != nil {
 		return err
 	}

 	if err := w.bw.Flush(); err != nil {
 		return err
 	}

 	return nil
 }

 func (w *Writer) closeGz() error {
 	if w.closed {
 		return errors.New("write on closed Writer")
 	}
 	if w.gz != nil {
 		if err := w.gz.Close(); err != nil {
 			return err
 		}
 		w.gz = nil
 	}
 	return nil
 }

 // AppendTar reads the tar or tar.gz file from r and appends
 // each of its contents to w.
 //
 // The input r can optionally be gzip compressed but the output will
 // always be gzip compressed.
 func (w *Writer) AppendTar(r io.Reader) error {
 	br := bufio.NewReader(r)
 	var tr *tar.Reader
 	if isGzip(br) {
 		// NewReader can't fail if isGzip returned true.
 		zr, _ := gzip.NewReader(br)
 		tr = tar.NewReader(zr)
 	} else {
 		tr = tar.NewReader(br)
 	}
 	for {
 		h, err := tr.Next()
 		if err == io.EOF {
 			break
 		}
 		if err != nil {
 			return fmt.Errorf("error reading from source tar: tar.Reader.Next: %v", err)
 		}
 		ent := TOCEntry{
 			Name:    h.Name,
 			Mode:    h.Mode,
 			Uid:     h.Uid,
 			Gid:     h.Gid,
 			Uname:   h.Uname,
 			Gname:   h.Gname,
 			ModTime: formatModtime(h.ModTime),
 		}
 		switch h.Typeflag {
 		case tar.TypeLink:
 			return fmt.Errorf("TODO: unsupported hardlink %q => %q", h.Name, h.Linkname)
 		case tar.TypeSymlink:
 			ent.Type = "symlink"
 			ent.LinkName = h.Linkname
 		case tar.TypeDir:
 			ent.Type = "dir"
 		case tar.TypeReg:
 			ent.Offset = w.cw.n
 			ent.Type = "reg"
 			ent.Size = h.Size

 			// Start a new gzip stream for regular files.
 			if err := w.closeGz(); err != nil {
 				return err
 			}
 		default:
 			return fmt.Errorf("unsupported input tar entry %q", h.Typeflag)
 		}
 		w.toc.Entries = append(w.toc.Entries, ent)
 		if w.gz == nil {
 			w.gz, err = gzip.NewWriterLevel(w.cw, gzip.BestCompression)
 			if err != nil {
 				return err
 			}
 		}
 		tw := tar.NewWriter(w.gz)
 		if err := tw.WriteHeader(h); err != nil {
 			return err
 		}
 		if _, err := io.Copy(tw, tr); err != nil {
 			return err
 		}
 		if err := tw.Flush(); err != nil {
 			return err
 		}
 	}
 	return nil
 }

 // footerBytes the 47 byte footer.
 func footerBytes(tocOff int64) []byte {
 	buf := bytes.NewBuffer(make([]byte, 0, FooterSize))
 	gz, _ := gzip.NewWriterLevel(buf, gzip.NoCompression)
 	gz.Header.Extra = []byte(fmt.Sprintf("%016xSTARGZ", tocOff))
 	gz.Close()
 	if buf.Len() != FooterSize {
 		panic(fmt.Sprintf("footer buffer = %d, not %d", buf.Len(), FooterSize))
 	}
 	return buf.Bytes()
 }

 func parseFooter(p []byte) (tocOffset int64, ok bool) {
 	if len(p) != FooterSize {
 		return 0, false
 	}
 	zr, err := gzip.NewReader(bytes.NewReader(p))
 	if err != nil {
 		return 0, false
 	}
 	extra := zr.Header.Extra
 	if len(extra) != 16+len("STARGZ") {
 		return 0, false
 	}
 	if string(extra[16:]) != "STARGZ" {
 		return 0, false
 	}
 	tocOffset, err = strconv.ParseInt(string(extra[:16]), 16, 64)
 	return tocOffset, err == nil
 }

 func formatModtime(t time.Time) string {
 	if t.IsZero() || t.Unix() == 0 {
 		return ""
 	}
 	t = t.UTC()
 	if t.Equal(t.Round(time.Second)) {
 		return t.UTC().Format(time.RFC3339)
 	}
 	return t.UTC().Format(time.RFC3339Nano)
 }

 // countWriter counts how many bytes have been written to its wrapped
 // io.Writer.
 type countWriter struct {
 	w io.Writer
 	n int64
 }

 func (cw *countWriter) Write(p []byte) (n int, err error) {
 	n, err = cw.w.Write(p)
 	cw.n += int64(n)
 	return
 }

 // isGzip reports whether br is positioned right before an upcoming gzip stream.
 // It does not consume any bytes from br.
 func isGzip(br *bufio.Reader) bool {
 	const (
 		gzipID1     = 0x1f
 		gzipID2     = 0x8b
 		gzipDeflate = 8
 	)
 	peek, _ := br.Peek(3)
 	return len(peek) >= 3 && peek[0] == gzipID1 && peek[1] == gzipID2 && peek[2] == gzipDeflate
 }
	// Copyright 2019 The Go Authors. All rights reserved.
	// Use of this source code is governed by a BSD-style
	// license that can be found in the LICENSE file.

	// The stargz package reads & writes tar.gz ("tarball") files in a
	// seekable, indexed format call "stargz". A stargz file is still a
	// valid tarball, but it's slightly bigger with new gzip streams for
	// each new file & throughout large files, and has an index in a magic
	// file at the end.
	package stargz

	import (
	"archive/tar"
	"bufio"
	"bytes"
	"compress/gzip"
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"strconv"
	"time"
	)

	// TOCTarName is the name of the JSON file in the tar archive in the
	// table of contents gzip stream.
	const TOCTarName = "stargz.index.json"

	// FooterSize is the number of bytes in the stargz footer.
	//
	// The footer is an empty gzip stream with no compression and an Extra
	// header of the form "%016xSTARGZ", where the 64 bit hex-encoded
	// number is the offset to the gzip stream of JSON TOC.
	//
	// 47 comes from:
	//
	// 10 byte gzip header +
	// 2 byte (LE16) length of extra, encoding 22 (16 hex digits + len("STARGZ")) == "\x16\x00" +
	// 22 bytes of extra (fmt.Sprintf("%016xSTARGZ", tocGzipOffset))
	// 5 byte flate header
	// 8 byte gzip footer (two little endian uint32s: digest, size)
	const FooterSize = 47

	// A Reader permits random access reads from a stargz file.
	type Reader struct {
	sr *io.SectionReader
	TOC *TOC
	}

	// Open opens a stargz file for reading.
	func Open(sr io.SectionReader) (Reader, error) {
	if sr.Size() < FooterSize {
	return nil, fmt.Errorf("stargz size %d is smaller than the stargz footer size", sr.Size())
	}
	// TODO: read a bigger chunk (1MB?) at once here to hopefully
	// get the TOC + footer in one go.
	var footer [FooterSize]byte
	if _, err := sr.ReadAt(footer[:], sr.Size()-FooterSize); err != nil {
	return nil, fmt.Errorf("error reading footer: %v", err)
	}
	tocOff, ok := parseFooter(footer[:])
	if !ok {
	return nil, fmt.Errorf("error parsing footer")
	}
	tocTargz := make([]byte, sr.Size()-tocOff-FooterSize)
	if _, err := sr.ReadAt(tocTargz, tocOff); err != nil {
	return nil, fmt.Errorf("error reading %d byte TOC targz: %v", len(tocTargz), err)
	}
	zr, err := gzip.NewReader(bytes.NewReader(tocTargz))
	if err != nil {
	return nil, fmt.Errorf("malformed TOC gzip header: %v", err)
	}
	zr.Multistream(false)
	tr := tar.NewReader(zr)
	h, err := tr.Next()
	if err != nil {
	return nil, fmt.Errorf("failed to find tar header in TOC gzip stream: %v", err)
	}
	if h.Name != TOCTarName {
	return nil, fmt.Errorf("TOC tar entry had name %q; expected %q", h.Name, TOCTarName)
	}
	toc := new(TOC)
	if err := json.NewDecoder(tr).Decode(&toc); err != nil {
	return nil, fmt.Errorf("error decoding TOC JSON: %v", err)
	}
	return &Reader{sr: sr, TOC: toc}, nil
	}

	// TOCEntry is an entry in the stargz file's TOC (Table of Contents).
	type TOCEntry struct {
	Offset int64 `json:"offset,omitempty"` // offset to gzip stream of tar entry (for regular files only)
	Name string `json:"name"`
	Type string `json:"type"` // "dir", "reg", TODO
	Size int64 `json:"size,omitempty"`
	LinkName string `json:"linkName,omitempty"` // for symlinks
	Mode int64 `json:"mode,omitempty"` // Permission and mode bits
	Uid int `json:"uid,omitempty"` // User ID of owner
	Gid int `json:"gid,omitempty"` // Group ID of owner
	Uname string `json:"userName,omitempty"` // User name of owner
	Gname string `json:"groupName,omitempty"` // Group name of owner
	ModTime string `json:"modtime,omitempty"`

	// ChunkOffset is non-zero if this is a chunk of a large,
	// regular file. If so, the Offset is where the gzip header of
	// ChunkSize bytes at ChunkOffset in Name begin. If both
	// ChunkOffset and ChunkSize are zero, the file contents are
	// completely represented at the tar gzip stream starting at
	// Offset.
	ChunkOffset int64 `json:"chunkOffset,omitempty"`
	ChunkSize int64 `json:"chunkSize,omitempty"`
	}

	// TOC is the table of contents index of the files in the stargz file.
	type TOC struct {
	Version int `json:"version"`
	Entries []TOCEntry `json:"entries"`
	}

	// A Writer writes stargz files.
	//
	// Use NewWriter to create a new Writer.
	type Writer struct {
	bw *bufio.Writer
	cw *countWriter
	toc *TOC

	closed bool
	gz *gzip.Writer
	}

	// NewWriter returns a new stargz writer writing to w.
	//
	// The writer must be closed to write its trailing table of contents.
	func NewWriter(w io.Writer) *Writer {
	bw := bufio.NewWriter(w)
	cw := &countWriter{w: bw}
	return &Writer{
	bw: bw,
	cw: cw,
	toc: &TOC{Version: 1},
	}
	}

	// Close writes the stargz's table of contents and flushes all the
	// buffers, returning any error.
	func (w *Writer) Close() error {
	if w.closed {
	return nil
	}
	defer func() { w.closed = true }()

	if err := w.closeGz(); err != nil {
	return err
	}

	// Write the TOC index.
	tocOff := w.cw.n
	w.gz, _ = gzip.NewWriterLevel(w.cw, gzip.BestCompression)
	tw := tar.NewWriter(w.gz)
	tocJSON, err := json.MarshalIndent(w.toc, "", "\t")
	if err != nil {
	return err
	}
	if err := tw.WriteHeader(&tar.Header{
	Typeflag: tar.TypeReg,
	Name: TOCTarName,
	Size: int64(len(tocJSON)),
	}); err != nil {
	return err
	}
	if _, err := tw.Write(tocJSON); err != nil {
	return err
	}

	if err := tw.Close(); err != nil {
	return err
	}
	if err := w.closeGz(); err != nil {
	return err
	}

	// And a little footer with pointer to the TOC gzip stream.
	if _, err := w.bw.Write(footerBytes(tocOff)); err != nil {
	return err
	}

	if err := w.bw.Flush(); err != nil {
	return err
	}

	return nil
	}

	func (w *Writer) closeGz() error {
	if w.closed {
	return errors.New("write on closed Writer")
	}
	if w.gz != nil {
	if err := w.gz.Close(); err != nil {
	return err
	}
	w.gz = nil
	}
	return nil
	}

	// AppendTar reads the tar or tar.gz file from r and appends
	// each of its contents to w.
	//
	// The input r can optionally be gzip compressed but the output will
	// always be gzip compressed.
	func (w *Writer) AppendTar(r io.Reader) error {
	br := bufio.NewReader(r)
	var tr *tar.Reader
	if isGzip(br) {
	// NewReader can't fail if isGzip returned true.
	zr, _ := gzip.NewReader(br)
	tr = tar.NewReader(zr)
	} else {
	tr = tar.NewReader(br)
	}
	for {
	h, err := tr.Next()
	if err == io.EOF {
	break
	}
	if err != nil {
	return fmt.Errorf("error reading from source tar: tar.Reader.Next: %v", err)
	}
	ent := TOCEntry{
	Name: h.Name,
	Mode: h.Mode,
	Uid: h.Uid,
	Gid: h.Gid,
	Uname: h.Uname,
	Gname: h.Gname,
	ModTime: formatModtime(h.ModTime),
	}
	switch h.Typeflag {
	case tar.TypeLink:
	return fmt.Errorf("TODO: unsupported hardlink %q => %q", h.Name, h.Linkname)
	case tar.TypeSymlink:
	ent.Type = "symlink"
	ent.LinkName = h.Linkname
	case tar.TypeDir:
	ent.Type = "dir"
	case tar.TypeReg:
	ent.Offset = w.cw.n
	ent.Type = "reg"
	ent.Size = h.Size

	// Start a new gzip stream for regular files.
	if err := w.closeGz(); err != nil {
	return err
	}
	default:
	return fmt.Errorf("unsupported input tar entry %q", h.Typeflag)
	}
	w.toc.Entries = append(w.toc.Entries, ent)
	if w.gz == nil {
	w.gz, err = gzip.NewWriterLevel(w.cw, gzip.BestCompression)
	if err != nil {
	return err
	}
	}
	tw := tar.NewWriter(w.gz)
	if err := tw.WriteHeader(h); err != nil {
	return err
	}
	if _, err := io.Copy(tw, tr); err != nil {
	return err
	}
	if err := tw.Flush(); err != nil {
	return err
	}
	}
	return nil
	}

	// footerBytes the 47 byte footer.
	func footerBytes(tocOff int64) []byte {
	buf := bytes.NewBuffer(make([]byte, 0, FooterSize))
	gz, _ := gzip.NewWriterLevel(buf, gzip.NoCompression)
	gz.Header.Extra = []byte(fmt.Sprintf("%016xSTARGZ", tocOff))
	gz.Close()
	if buf.Len() != FooterSize {
	panic(fmt.Sprintf("footer buffer = %d, not %d", buf.Len(), FooterSize))
	}
	return buf.Bytes()
	}

	func parseFooter(p []byte) (tocOffset int64, ok bool) {
	if len(p) != FooterSize {
	return 0, false
	}
	zr, err := gzip.NewReader(bytes.NewReader(p))
	if err != nil {
	return 0, false
	}
	extra := zr.Header.Extra
	if len(extra) != 16+len("STARGZ") {
	return 0, false
	}
	if string(extra[16:]) != "STARGZ" {
	return 0, false
	}
	tocOffset, err = strconv.ParseInt(string(extra[:16]), 16, 64)
	return tocOffset, err == nil
	}

	func formatModtime(t time.Time) string {
	if t.IsZero() \|\| t.Unix() == 0 {
	return ""
	}
	t = t.UTC()
	if t.Equal(t.Round(time.Second)) {
	return t.UTC().Format(time.RFC3339)
	}
	return t.UTC().Format(time.RFC3339Nano)
	}

	// countWriter counts how many bytes have been written to its wrapped
	// io.Writer.
	type countWriter struct {
	w io.Writer
	n int64
	}

	func (cw *countWriter) Write(p []byte) (n int, err error) {
	n, err = cw.w.Write(p)
	cw.n += int64(n)
	return
	}

	// isGzip reports whether br is positioned right before an upcoming gzip stream.
	// It does not consume any bytes from br.
	func isGzip(br *bufio.Reader) bool {
	const (
	gzipID1 = 0x1f
	gzipID2 = 0x8b
	gzipDeflate = 8
	)
	peek, _ := br.Peek(3)
	return len(peek) >= 3 && peek[0] == gzipID1 && peek[1] == gzipID2 && peek[2] == gzipDeflate
	}