src/archive/zip/writer.go - go - Git at Google

 // Copyright 2011 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.

 package zip

 import (
 	"bufio"
 	"encoding/binary"
 	"errors"
 	"hash"
 	"hash/crc32"
 	"io"
 )

 // TODO(adg): support zip file comments

 // Writer implements a zip file writer.
 type Writer struct {
 	cw          *countWriter
 	dir         []*header
 	last        *fileWriter
 	closed      bool
 	compressors map[uint16]Compressor
 }

 type header struct {
 	*FileHeader
 	offset uint64
 }

 // NewWriter returns a new Writer writing a zip file to w.
 func NewWriter(w io.Writer) *Writer {
 	return &Writer{cw: &countWriter{w: bufio.NewWriter(w)}}
 }

 // SetOffset sets the offset of the beginning of the zip data within the
 // underlying writer. It should be used when the zip data is appended to an
 // existing file, such as a binary executable.
 // It must be called before any data is written.
 func (w *Writer) SetOffset(n int64) {
 	if w.cw.count != 0 {
 		panic("zip: SetOffset called after data was written")
 	}
 	w.cw.count = n
 }

 // Flush flushes any buffered data to the underlying writer.
 // Calling Flush is not normally necessary; calling Close is sufficient.
 func (w *Writer) Flush() error {
 	return w.cw.w.(*bufio.Writer).Flush()
 }

 // Close finishes writing the zip file by writing the central directory.
 // It does not (and cannot) close the underlying writer.
 func (w *Writer) Close() error {
 	if w.last != nil && !w.last.closed {
 		if err := w.last.close(); err != nil {
 			return err
 		}
 		w.last = nil
 	}
 	if w.closed {
 		return errors.New("zip: writer closed twice")
 	}
 	w.closed = true

 	// write central directory
 	start := w.cw.count
 	for _, h := range w.dir {
 		var buf [directoryHeaderLen]byte
 		b := writeBuf(buf[:])
 		b.uint32(uint32(directoryHeaderSignature))
 		b.uint16(h.CreatorVersion)
 		b.uint16(h.ReaderVersion)
 		b.uint16(h.Flags)
 		b.uint16(h.Method)
 		b.uint16(h.ModifiedTime)
 		b.uint16(h.ModifiedDate)
 		b.uint32(h.CRC32)
 		if h.isZip64() || h.offset >= uint32max {
 			// the file needs a zip64 header. store maxint in both
 			// 32 bit size fields (and offset later) to signal that the
 			// zip64 extra header should be used.
 			b.uint32(uint32max) // compressed size
 			b.uint32(uint32max) // uncompressed size

 			// append a zip64 extra block to Extra
 			var buf [28]byte // 2x uint16 + 3x uint64
 			eb := writeBuf(buf[:])
 			eb.uint16(zip64ExtraId)
 			eb.uint16(24) // size = 3x uint64
 			eb.uint64(h.UncompressedSize64)
 			eb.uint64(h.CompressedSize64)
 			eb.uint64(h.offset)
 			h.Extra = append(h.Extra, buf[:]...)
 		} else {
 			b.uint32(h.CompressedSize)
 			b.uint32(h.UncompressedSize)
 		}
 		b.uint16(uint16(len(h.Name)))
 		b.uint16(uint16(len(h.Extra)))
 		b.uint16(uint16(len(h.Comment)))
 		b = b[4:] // skip disk number start and internal file attr (2x uint16)
 		b.uint32(h.ExternalAttrs)
 		if h.offset > uint32max {
 			b.uint32(uint32max)
 		} else {
 			b.uint32(uint32(h.offset))
 		}
 		if _, err := w.cw.Write(buf[:]); err != nil {
 			return err
 		}
 		if _, err := io.WriteString(w.cw, h.Name); err != nil {
 			return err
 		}
 		if _, err := w.cw.Write(h.Extra); err != nil {
 			return err
 		}
 		if _, err := io.WriteString(w.cw, h.Comment); err != nil {
 			return err
 		}
 	}
 	end := w.cw.count

 	records := uint64(len(w.dir))
 	size := uint64(end - start)
 	offset := uint64(start)

 	if records > uint16max || size > uint32max || offset > uint32max {
 		var buf [directory64EndLen + directory64LocLen]byte
 		b := writeBuf(buf[:])

 		// zip64 end of central directory record
 		b.uint32(directory64EndSignature)
 		b.uint64(directory64EndLen - 12) // length minus signature (uint32) and length fields (uint64)
 		b.uint16(zipVersion45)           // version made by
 		b.uint16(zipVersion45)           // version needed to extract
 		b.uint32(0)                      // number of this disk
 		b.uint32(0)                      // number of the disk with the start of the central directory
 		b.uint64(records)                // total number of entries in the central directory on this disk
 		b.uint64(records)                // total number of entries in the central directory
 		b.uint64(size)                   // size of the central directory
 		b.uint64(offset)                 // offset of start of central directory with respect to the starting disk number

 		// zip64 end of central directory locator
 		b.uint32(directory64LocSignature)
 		b.uint32(0)           // number of the disk with the start of the zip64 end of central directory
 		b.uint64(uint64(end)) // relative offset of the zip64 end of central directory record
 		b.uint32(1)           // total number of disks

 		if _, err := w.cw.Write(buf[:]); err != nil {
 			return err
 		}

 		// store max values in the regular end record to signal that
 		// that the zip64 values should be used instead
 		records = uint16max
 		size = uint32max
 		offset = uint32max
 	}

 	// write end record
 	var buf [directoryEndLen]byte
 	b := writeBuf(buf[:])
 	b.uint32(uint32(directoryEndSignature))
 	b = b[4:]                 // skip over disk number and first disk number (2x uint16)
 	b.uint16(uint16(records)) // number of entries this disk
 	b.uint16(uint16(records)) // number of entries total
 	b.uint32(uint32(size))    // size of directory
 	b.uint32(uint32(offset))  // start of directory
 	// skipped size of comment (always zero)
 	if _, err := w.cw.Write(buf[:]); err != nil {
 		return err
 	}

 	return w.cw.w.(*bufio.Writer).Flush()
 }

 // Create adds a file to the zip file using the provided name.
 // It returns a Writer to which the file contents should be written.
 // The name must be a relative path: it must not start with a drive
 // letter (e.g. C:) or leading slash, and only forward slashes are
 // allowed.
 // The file's contents must be written to the io.Writer before the next
 // call to Create, CreateHeader, or Close.
 func (w *Writer) Create(name string) (io.Writer, error) {
 	header := &FileHeader{
 		Name:   name,
 		Method: Deflate,
 	}
 	return w.CreateHeader(header)
 }

 // CreateHeader adds a file to the zip file using the provided FileHeader
 // for the file metadata.
 // It returns a Writer to which the file contents should be written.
 //
 // The file's contents must be written to the io.Writer before the next
 // call to Create, CreateHeader, or Close. The provided FileHeader fh
 // must not be modified after a call to CreateHeader.
 func (w *Writer) CreateHeader(fh *FileHeader) (io.Writer, error) {
 	if w.last != nil && !w.last.closed {
 		if err := w.last.close(); err != nil {
 			return nil, err
 		}
 	}
 	if len(w.dir) > 0 && w.dir[len(w.dir)-1].FileHeader == fh {
 		// See https://golang.org/issue/11144 confusion.
 		return nil, errors.New("archive/zip: invalid duplicate FileHeader")
 	}

 	fh.Flags |= 0x8 // we will write a data descriptor

 	fh.CreatorVersion = fh.CreatorVersion&0xff00 | zipVersion20 // preserve compatibility byte
 	fh.ReaderVersion = zipVersion20

 	fw := &fileWriter{
 		zipw:      w.cw,
 		compCount: &countWriter{w: w.cw},
 		crc32:     crc32.NewIEEE(),
 	}
 	comp := w.compressor(fh.Method)
 	if comp == nil {
 		return nil, ErrAlgorithm
 	}
 	var err error
 	fw.comp, err = comp(fw.compCount)
 	if err != nil {
 		return nil, err
 	}
 	fw.rawCount = &countWriter{w: fw.comp}

 	h := &header{
 		FileHeader: fh,
 		offset:     uint64(w.cw.count),
 	}
 	w.dir = append(w.dir, h)
 	fw.header = h

 	if err := writeHeader(w.cw, fh); err != nil {
 		return nil, err
 	}

 	w.last = fw
 	return fw, nil
 }

 func writeHeader(w io.Writer, h *FileHeader) error {
 	var buf [fileHeaderLen]byte
 	b := writeBuf(buf[:])
 	b.uint32(uint32(fileHeaderSignature))
 	b.uint16(h.ReaderVersion)
 	b.uint16(h.Flags)
 	b.uint16(h.Method)
 	b.uint16(h.ModifiedTime)
 	b.uint16(h.ModifiedDate)
 	b.uint32(0) // since we are writing a data descriptor crc32,
 	b.uint32(0) // compressed size,
 	b.uint32(0) // and uncompressed size should be zero
 	b.uint16(uint16(len(h.Name)))
 	b.uint16(uint16(len(h.Extra)))
 	if _, err := w.Write(buf[:]); err != nil {
 		return err
 	}
 	if _, err := io.WriteString(w, h.Name); err != nil {
 		return err
 	}
 	_, err := w.Write(h.Extra)
 	return err
 }

 // RegisterCompressor registers or overrides a custom compressor for a specific
 // method ID. If a compressor for a given method is not found, Writer will
 // default to looking up the compressor at the package level.
 func (w *Writer) RegisterCompressor(method uint16, comp Compressor) {
 	if w.compressors == nil {
 		w.compressors = make(map[uint16]Compressor)
 	}
 	w.compressors[method] = comp
 }

 func (w *Writer) compressor(method uint16) Compressor {
 	comp := w.compressors[method]
 	if comp == nil {
 		comp = compressor(method)
 	}
 	return comp
 }

 type fileWriter struct {
 	*header
 	zipw      io.Writer
 	rawCount  *countWriter
 	comp      io.WriteCloser
 	compCount *countWriter
 	crc32     hash.Hash32
 	closed    bool
 }

 func (w *fileWriter) Write(p []byte) (int, error) {
 	if w.closed {
 		return 0, errors.New("zip: write to closed file")
 	}
 	w.crc32.Write(p)
 	return w.rawCount.Write(p)
 }

 func (w *fileWriter) close() error {
 	if w.closed {
 		return errors.New("zip: file closed twice")
 	}
 	w.closed = true
 	if err := w.comp.Close(); err != nil {
 		return err
 	}

 	// update FileHeader
 	fh := w.header.FileHeader
 	fh.CRC32 = w.crc32.Sum32()
 	fh.CompressedSize64 = uint64(w.compCount.count)
 	fh.UncompressedSize64 = uint64(w.rawCount.count)

 	if fh.isZip64() {
 		fh.CompressedSize = uint32max
 		fh.UncompressedSize = uint32max
 		fh.ReaderVersion = zipVersion45 // requires 4.5 - File uses ZIP64 format extensions
 	} else {
 		fh.CompressedSize = uint32(fh.CompressedSize64)
 		fh.UncompressedSize = uint32(fh.UncompressedSize64)
 	}

 	// Write data descriptor. This is more complicated than one would
 	// think, see e.g. comments in zipfile.c:putextended() and
 	// http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=7073588.
 	// The approach here is to write 8 byte sizes if needed without
 	// adding a zip64 extra in the local header (too late anyway).
 	var buf []byte
 	if fh.isZip64() {
 		buf = make([]byte, dataDescriptor64Len)
 	} else {
 		buf = make([]byte, dataDescriptorLen)
 	}
 	b := writeBuf(buf)
 	b.uint32(dataDescriptorSignature) // de-facto standard, required by OS X
 	b.uint32(fh.CRC32)
 	if fh.isZip64() {
 		b.uint64(fh.CompressedSize64)
 		b.uint64(fh.UncompressedSize64)
 	} else {
 		b.uint32(fh.CompressedSize)
 		b.uint32(fh.UncompressedSize)
 	}
 	_, err := w.zipw.Write(buf)
 	return err
 }

 type countWriter struct {
 	w     io.Writer
 	count int64
 }

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

 type nopCloser struct {
 	io.Writer
 }

 func (w nopCloser) Close() error {
 	return nil
 }

 type writeBuf []byte

 func (b *writeBuf) uint16(v uint16) {
 	binary.LittleEndian.PutUint16(*b, v)
 	*b = (*b)[2:]
 }

 func (b *writeBuf) uint32(v uint32) {
 	binary.LittleEndian.PutUint32(*b, v)
 	*b = (*b)[4:]
 }

 func (b *writeBuf) uint64(v uint64) {
 	binary.LittleEndian.PutUint64(*b, v)
 	*b = (*b)[8:]
 }
	// Copyright 2011 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.

	package zip

	import (
	"bufio"
	"encoding/binary"
	"errors"
	"hash"
	"hash/crc32"
	"io"
	)

	// TODO(adg): support zip file comments

	// Writer implements a zip file writer.
	type Writer struct {
	cw *countWriter
	dir []*header
	last *fileWriter
	closed bool
	compressors map[uint16]Compressor
	}

	type header struct {
	*FileHeader
	offset uint64
	}

	// NewWriter returns a new Writer writing a zip file to w.
	func NewWriter(w io.Writer) *Writer {
	return &Writer{cw: &countWriter{w: bufio.NewWriter(w)}}
	}

	// SetOffset sets the offset of the beginning of the zip data within the
	// underlying writer. It should be used when the zip data is appended to an
	// existing file, such as a binary executable.
	// It must be called before any data is written.
	func (w *Writer) SetOffset(n int64) {
	if w.cw.count != 0 {
	panic("zip: SetOffset called after data was written")
	}
	w.cw.count = n
	}

	// Flush flushes any buffered data to the underlying writer.
	// Calling Flush is not normally necessary; calling Close is sufficient.
	func (w *Writer) Flush() error {
	return w.cw.w.(*bufio.Writer).Flush()
	}

	// Close finishes writing the zip file by writing the central directory.
	// It does not (and cannot) close the underlying writer.
	func (w *Writer) Close() error {
	if w.last != nil && !w.last.closed {
	if err := w.last.close(); err != nil {
	return err
	}
	w.last = nil
	}
	if w.closed {
	return errors.New("zip: writer closed twice")
	}
	w.closed = true

	// write central directory
	start := w.cw.count
	for _, h := range w.dir {
	var buf [directoryHeaderLen]byte
	b := writeBuf(buf[:])
	b.uint32(uint32(directoryHeaderSignature))
	b.uint16(h.CreatorVersion)
	b.uint16(h.ReaderVersion)
	b.uint16(h.Flags)
	b.uint16(h.Method)
	b.uint16(h.ModifiedTime)
	b.uint16(h.ModifiedDate)
	b.uint32(h.CRC32)
	if h.isZip64() \|\| h.offset >= uint32max {
	// the file needs a zip64 header. store maxint in both
	// 32 bit size fields (and offset later) to signal that the
	// zip64 extra header should be used.
	b.uint32(uint32max) // compressed size
	b.uint32(uint32max) // uncompressed size

	// append a zip64 extra block to Extra
	var buf [28]byte // 2x uint16 + 3x uint64
	eb := writeBuf(buf[:])
	eb.uint16(zip64ExtraId)
	eb.uint16(24) // size = 3x uint64
	eb.uint64(h.UncompressedSize64)
	eb.uint64(h.CompressedSize64)
	eb.uint64(h.offset)
	h.Extra = append(h.Extra, buf[:]...)
	} else {
	b.uint32(h.CompressedSize)
	b.uint32(h.UncompressedSize)
	}
	b.uint16(uint16(len(h.Name)))
	b.uint16(uint16(len(h.Extra)))
	b.uint16(uint16(len(h.Comment)))
	b = b[4:] // skip disk number start and internal file attr (2x uint16)
	b.uint32(h.ExternalAttrs)
	if h.offset > uint32max {
	b.uint32(uint32max)
	} else {
	b.uint32(uint32(h.offset))
	}
	if _, err := w.cw.Write(buf[:]); err != nil {
	return err
	}
	if _, err := io.WriteString(w.cw, h.Name); err != nil {
	return err
	}
	if _, err := w.cw.Write(h.Extra); err != nil {
	return err
	}
	if _, err := io.WriteString(w.cw, h.Comment); err != nil {
	return err
	}
	}
	end := w.cw.count

	records := uint64(len(w.dir))
	size := uint64(end - start)
	offset := uint64(start)

	if records > uint16max \|\| size > uint32max \|\| offset > uint32max {
	var buf [directory64EndLen + directory64LocLen]byte
	b := writeBuf(buf[:])

	// zip64 end of central directory record
	b.uint32(directory64EndSignature)
	b.uint64(directory64EndLen - 12) // length minus signature (uint32) and length fields (uint64)
	b.uint16(zipVersion45) // version made by
	b.uint16(zipVersion45) // version needed to extract
	b.uint32(0) // number of this disk
	b.uint32(0) // number of the disk with the start of the central directory
	b.uint64(records) // total number of entries in the central directory on this disk
	b.uint64(records) // total number of entries in the central directory
	b.uint64(size) // size of the central directory
	b.uint64(offset) // offset of start of central directory with respect to the starting disk number

	// zip64 end of central directory locator
	b.uint32(directory64LocSignature)
	b.uint32(0) // number of the disk with the start of the zip64 end of central directory
	b.uint64(uint64(end)) // relative offset of the zip64 end of central directory record
	b.uint32(1) // total number of disks

	if _, err := w.cw.Write(buf[:]); err != nil {
	return err
	}

	// store max values in the regular end record to signal that
	// that the zip64 values should be used instead
	records = uint16max
	size = uint32max
	offset = uint32max
	}

	// write end record
	var buf [directoryEndLen]byte
	b := writeBuf(buf[:])
	b.uint32(uint32(directoryEndSignature))
	b = b[4:] // skip over disk number and first disk number (2x uint16)
	b.uint16(uint16(records)) // number of entries this disk
	b.uint16(uint16(records)) // number of entries total
	b.uint32(uint32(size)) // size of directory
	b.uint32(uint32(offset)) // start of directory
	// skipped size of comment (always zero)
	if _, err := w.cw.Write(buf[:]); err != nil {
	return err
	}

	return w.cw.w.(*bufio.Writer).Flush()
	}

	// Create adds a file to the zip file using the provided name.
	// It returns a Writer to which the file contents should be written.
	// The name must be a relative path: it must not start with a drive
	// letter (e.g. C:) or leading slash, and only forward slashes are
	// allowed.
	// The file's contents must be written to the io.Writer before the next
	// call to Create, CreateHeader, or Close.
	func (w *Writer) Create(name string) (io.Writer, error) {
	header := &FileHeader{
	Name: name,
	Method: Deflate,
	}
	return w.CreateHeader(header)
	}

	// CreateHeader adds a file to the zip file using the provided FileHeader
	// for the file metadata.
	// It returns a Writer to which the file contents should be written.
	//
	// The file's contents must be written to the io.Writer before the next
	// call to Create, CreateHeader, or Close. The provided FileHeader fh
	// must not be modified after a call to CreateHeader.
	func (w Writer) CreateHeader(fh FileHeader) (io.Writer, error) {
	if w.last != nil && !w.last.closed {
	if err := w.last.close(); err != nil {
	return nil, err
	}
	}
	if len(w.dir) > 0 && w.dir[len(w.dir)-1].FileHeader == fh {
	// See https://golang.org/issue/11144 confusion.
	return nil, errors.New("archive/zip: invalid duplicate FileHeader")
	}

	fh.Flags \|= 0x8 // we will write a data descriptor

	fh.CreatorVersion = fh.CreatorVersion&0xff00 \| zipVersion20 // preserve compatibility byte
	fh.ReaderVersion = zipVersion20

	fw := &fileWriter{
	zipw: w.cw,
	compCount: &countWriter{w: w.cw},
	crc32: crc32.NewIEEE(),
	}
	comp := w.compressor(fh.Method)
	if comp == nil {
	return nil, ErrAlgorithm
	}
	var err error
	fw.comp, err = comp(fw.compCount)
	if err != nil {
	return nil, err
	}
	fw.rawCount = &countWriter{w: fw.comp}

	h := &header{
	FileHeader: fh,
	offset: uint64(w.cw.count),
	}
	w.dir = append(w.dir, h)
	fw.header = h

	if err := writeHeader(w.cw, fh); err != nil {
	return nil, err
	}

	w.last = fw
	return fw, nil
	}

	func writeHeader(w io.Writer, h *FileHeader) error {
	var buf [fileHeaderLen]byte
	b := writeBuf(buf[:])
	b.uint32(uint32(fileHeaderSignature))
	b.uint16(h.ReaderVersion)
	b.uint16(h.Flags)
	b.uint16(h.Method)
	b.uint16(h.ModifiedTime)
	b.uint16(h.ModifiedDate)
	b.uint32(0) // since we are writing a data descriptor crc32,
	b.uint32(0) // compressed size,
	b.uint32(0) // and uncompressed size should be zero
	b.uint16(uint16(len(h.Name)))
	b.uint16(uint16(len(h.Extra)))
	if _, err := w.Write(buf[:]); err != nil {
	return err
	}
	if _, err := io.WriteString(w, h.Name); err != nil {
	return err
	}
	_, err := w.Write(h.Extra)
	return err
	}

	// RegisterCompressor registers or overrides a custom compressor for a specific
	// method ID. If a compressor for a given method is not found, Writer will
	// default to looking up the compressor at the package level.
	func (w *Writer) RegisterCompressor(method uint16, comp Compressor) {
	if w.compressors == nil {
	w.compressors = make(map[uint16]Compressor)
	}
	w.compressors[method] = comp
	}

	func (w *Writer) compressor(method uint16) Compressor {
	comp := w.compressors[method]
	if comp == nil {
	comp = compressor(method)
	}
	return comp
	}

	type fileWriter struct {
	*header
	zipw io.Writer
	rawCount *countWriter
	comp io.WriteCloser
	compCount *countWriter
	crc32 hash.Hash32
	closed bool
	}

	func (w *fileWriter) Write(p []byte) (int, error) {
	if w.closed {
	return 0, errors.New("zip: write to closed file")
	}
	w.crc32.Write(p)
	return w.rawCount.Write(p)
	}

	func (w *fileWriter) close() error {
	if w.closed {
	return errors.New("zip: file closed twice")
	}
	w.closed = true
	if err := w.comp.Close(); err != nil {
	return err
	}

	// update FileHeader
	fh := w.header.FileHeader
	fh.CRC32 = w.crc32.Sum32()
	fh.CompressedSize64 = uint64(w.compCount.count)
	fh.UncompressedSize64 = uint64(w.rawCount.count)

	if fh.isZip64() {
	fh.CompressedSize = uint32max
	fh.UncompressedSize = uint32max
	fh.ReaderVersion = zipVersion45 // requires 4.5 - File uses ZIP64 format extensions
	} else {
	fh.CompressedSize = uint32(fh.CompressedSize64)
	fh.UncompressedSize = uint32(fh.UncompressedSize64)
	}

	// Write data descriptor. This is more complicated than one would
	// think, see e.g. comments in zipfile.c:putextended() and
	// http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=7073588.
	// The approach here is to write 8 byte sizes if needed without
	// adding a zip64 extra in the local header (too late anyway).
	var buf []byte
	if fh.isZip64() {
	buf = make([]byte, dataDescriptor64Len)
	} else {
	buf = make([]byte, dataDescriptorLen)
	}
	b := writeBuf(buf)
	b.uint32(dataDescriptorSignature) // de-facto standard, required by OS X
	b.uint32(fh.CRC32)
	if fh.isZip64() {
	b.uint64(fh.CompressedSize64)
	b.uint64(fh.UncompressedSize64)
	} else {
	b.uint32(fh.CompressedSize)
	b.uint32(fh.UncompressedSize)
	}
	_, err := w.zipw.Write(buf)
	return err
	}

	type countWriter struct {
	w io.Writer
	count int64
	}

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

	type nopCloser struct {
	io.Writer
	}

	func (w nopCloser) Close() error {
	return nil
	}

	type writeBuf []byte

	func (b *writeBuf) uint16(v uint16) {
	binary.LittleEndian.PutUint16(*b, v)
	b = (b)[2:]
	}

	func (b *writeBuf) uint32(v uint32) {
	binary.LittleEndian.PutUint32(*b, v)
	b = (b)[4:]
	}

	func (b *writeBuf) uint64(v uint64) {
	binary.LittleEndian.PutUint64(*b, v)
	b = (b)[8:]
	}