libgo/go/archive/zip/writer.go - gofrontend - 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"
 	"unicode/utf8"
 )

 var (
 	errLongName  = errors.New("zip: FileHeader.Name too long")
 	errLongExtra = errors.New("zip: FileHeader.Extra too long")
 )

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

 	// testHookCloseSizeOffset if non-nil is called with the size
 	// of offset of the central directory at Close.
 	testHookCloseSizeOffset func(size, offset uint64)
 }

 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()
 }

 // SetComment sets the end-of-central-directory comment field.
 // It can only be called before Close.
 func (w *Writer) SetComment(comment string) error {
 	if len(comment) > uint16max {
 		return errors.New("zip: Writer.Comment too long")
 	}
 	w.comment = comment
 	return nil
 }

 // 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 f := w.testHookCloseSizeOffset; f != nil {
 		f(size, offset)
 	}

 	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
 	b.uint16(uint16(len(w.comment))) // byte size of EOCD comment
 	if _, err := w.cw.Write(buf[:]); err != nil {
 		return err
 	}
 	if _, err := io.WriteString(w.cw, w.comment); 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 file contents will be compressed using the Deflate method.
 // 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)
 }

 // detectUTF8 reports whether s is a valid UTF-8 string, and whether the string
 // must be considered UTF-8 encoding (i.e., not compatible with CP-437, ASCII,
 // or any other common encoding).
 func detectUTF8(s string) (valid, require bool) {
 	for i := 0; i < len(s); {
 		r, size := utf8.DecodeRuneInString(s[i:])
 		i += size
 		// Officially, ZIP uses CP-437, but many readers use the system's
 		// local character encoding. Most encoding are compatible with a large
 		// subset of CP-437, which itself is ASCII-like.
 		//
 		// Forbid 0x7e and 0x5c since EUC-KR and Shift-JIS replace those
 		// characters with localized currency and overline characters.
 		if r < 0x20 || r > 0x7d || r == 0x5c {
 			if !utf8.ValidRune(r) || (r == utf8.RuneError && size == 1) {
 				return false, false
 			}
 			require = true
 		}
 	}
 	return true, require
 }

 // CreateHeader adds a file to the zip archive using the provided FileHeader
 // for the file metadata. Writer takes ownership of fh and may mutate
 // its fields. The caller must not modify fh after calling CreateHeader.
 //
 // This 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.
 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

 	// The ZIP format has a sad state of affairs regarding character encoding.
 	// Officially, the name and comment fields are supposed to be encoded
 	// in CP-437 (which is mostly compatible with ASCII), unless the UTF-8
 	// flag bit is set. However, there are several problems:
 	//
 	//	* Many ZIP readers still do not support UTF-8.
 	//	* If the UTF-8 flag is cleared, several readers simply interpret the
 	//	name and comment fields as whatever the local system encoding is.
 	//
 	// In order to avoid breaking readers without UTF-8 support,
 	// we avoid setting the UTF-8 flag if the strings are CP-437 compatible.
 	// However, if the strings require multibyte UTF-8 encoding and is a
 	// valid UTF-8 string, then we set the UTF-8 bit.
 	//
 	// For the case, where the user explicitly wants to specify the encoding
 	// as UTF-8, they will need to set the flag bit themselves.
 	utf8Valid1, utf8Require1 := detectUTF8(fh.Name)
 	utf8Valid2, utf8Require2 := detectUTF8(fh.Comment)
 	switch {
 	case fh.NonUTF8:
 		fh.Flags &^= 0x800
 	case (utf8Require1 || utf8Require2) && (utf8Valid1 && utf8Valid2):
 		fh.Flags |= 0x800
 	}

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

 	// If Modified is set, this takes precedence over MS-DOS timestamp fields.
 	if !fh.Modified.IsZero() {
 		// Contrary to the FileHeader.SetModTime method, we intentionally
 		// do not convert to UTC, because we assume the user intends to encode
 		// the date using the specified timezone. A user may want this control
 		// because many legacy ZIP readers interpret the timestamp according
 		// to the local timezone.
 		//
 		// The timezone is only non-UTC if a user directly sets the Modified
 		// field directly themselves. All other approaches sets UTC.
 		fh.ModifiedDate, fh.ModifiedTime = timeToMsDosTime(fh.Modified)

 		// Use "extended timestamp" format since this is what Info-ZIP uses.
 		// Nearly every major ZIP implementation uses a different format,
 		// but at least most seem to be able to understand the other formats.
 		//
 		// This format happens to be identical for both local and central header
 		// if modification time is the only timestamp being encoded.
 		var mbuf [9]byte // 2*SizeOf(uint16) + SizeOf(uint8) + SizeOf(uint32)
 		mt := uint32(fh.Modified.Unix())
 		eb := writeBuf(mbuf[:])
 		eb.uint16(extTimeExtraID)
 		eb.uint16(5)  // Size: SizeOf(uint8) + SizeOf(uint32)
 		eb.uint8(1)   // Flags: ModTime
 		eb.uint32(mt) // ModTime
 		fh.Extra = append(fh.Extra, mbuf[:]...)
 	}

 	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 {
 	const maxUint16 = 1<<16 - 1
 	if len(h.Name) > maxUint16 {
 		return errLongName
 	}
 	if len(h.Extra) > maxUint16 {
 		return errLongExtra
 	}

 	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) uint8(v uint8) {
 	(*b)[0] = v
 	*b = (*b)[1:]
 }

 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"
	"unicode/utf8"
	)

	var (
	errLongName = errors.New("zip: FileHeader.Name too long")
	errLongExtra = errors.New("zip: FileHeader.Extra too long")
	)

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

	// testHookCloseSizeOffset if non-nil is called with the size
	// of offset of the central directory at Close.
	testHookCloseSizeOffset func(size, offset uint64)
	}

	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()
	}

	// SetComment sets the end-of-central-directory comment field.
	// It can only be called before Close.
	func (w *Writer) SetComment(comment string) error {
	if len(comment) > uint16max {
	return errors.New("zip: Writer.Comment too long")
	}
	w.comment = comment
	return nil
	}

	// 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 f := w.testHookCloseSizeOffset; f != nil {
	f(size, offset)
	}

	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
	b.uint16(uint16(len(w.comment))) // byte size of EOCD comment
	if _, err := w.cw.Write(buf[:]); err != nil {
	return err
	}
	if _, err := io.WriteString(w.cw, w.comment); 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 file contents will be compressed using the Deflate method.
	// 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)
	}

	// detectUTF8 reports whether s is a valid UTF-8 string, and whether the string
	// must be considered UTF-8 encoding (i.e., not compatible with CP-437, ASCII,
	// or any other common encoding).
	func detectUTF8(s string) (valid, require bool) {
	for i := 0; i < len(s); {
	r, size := utf8.DecodeRuneInString(s[i:])
	i += size
	// Officially, ZIP uses CP-437, but many readers use the system's
	// local character encoding. Most encoding are compatible with a large
	// subset of CP-437, which itself is ASCII-like.
	//
	// Forbid 0x7e and 0x5c since EUC-KR and Shift-JIS replace those
	// characters with localized currency and overline characters.
	if r < 0x20 \|\| r > 0x7d \|\| r == 0x5c {
	if !utf8.ValidRune(r) \|\| (r == utf8.RuneError && size == 1) {
	return false, false
	}
	require = true
	}
	}
	return true, require
	}

	// CreateHeader adds a file to the zip archive using the provided FileHeader
	// for the file metadata. Writer takes ownership of fh and may mutate
	// its fields. The caller must not modify fh after calling CreateHeader.
	//
	// This 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.
	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

	// The ZIP format has a sad state of affairs regarding character encoding.
	// Officially, the name and comment fields are supposed to be encoded
	// in CP-437 (which is mostly compatible with ASCII), unless the UTF-8
	// flag bit is set. However, there are several problems:
	//
	// * Many ZIP readers still do not support UTF-8.
	// * If the UTF-8 flag is cleared, several readers simply interpret the
	// name and comment fields as whatever the local system encoding is.
	//
	// In order to avoid breaking readers without UTF-8 support,
	// we avoid setting the UTF-8 flag if the strings are CP-437 compatible.
	// However, if the strings require multibyte UTF-8 encoding and is a
	// valid UTF-8 string, then we set the UTF-8 bit.
	//
	// For the case, where the user explicitly wants to specify the encoding
	// as UTF-8, they will need to set the flag bit themselves.
	utf8Valid1, utf8Require1 := detectUTF8(fh.Name)
	utf8Valid2, utf8Require2 := detectUTF8(fh.Comment)
	switch {
	case fh.NonUTF8:
	fh.Flags &^= 0x800
	case (utf8Require1 \|\| utf8Require2) && (utf8Valid1 && utf8Valid2):
	fh.Flags \|= 0x800
	}

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

	// If Modified is set, this takes precedence over MS-DOS timestamp fields.
	if !fh.Modified.IsZero() {
	// Contrary to the FileHeader.SetModTime method, we intentionally
	// do not convert to UTC, because we assume the user intends to encode
	// the date using the specified timezone. A user may want this control
	// because many legacy ZIP readers interpret the timestamp according
	// to the local timezone.
	//
	// The timezone is only non-UTC if a user directly sets the Modified
	// field directly themselves. All other approaches sets UTC.
	fh.ModifiedDate, fh.ModifiedTime = timeToMsDosTime(fh.Modified)

	// Use "extended timestamp" format since this is what Info-ZIP uses.
	// Nearly every major ZIP implementation uses a different format,
	// but at least most seem to be able to understand the other formats.
	//
	// This format happens to be identical for both local and central header
	// if modification time is the only timestamp being encoded.
	var mbuf [9]byte // 2*SizeOf(uint16) + SizeOf(uint8) + SizeOf(uint32)
	mt := uint32(fh.Modified.Unix())
	eb := writeBuf(mbuf[:])
	eb.uint16(extTimeExtraID)
	eb.uint16(5) // Size: SizeOf(uint8) + SizeOf(uint32)
	eb.uint8(1) // Flags: ModTime
	eb.uint32(mt) // ModTime
	fh.Extra = append(fh.Extra, mbuf[:]...)
	}

	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 {
	const maxUint16 = 1<<16 - 1
	if len(h.Name) > maxUint16 {
	return errLongName
	}
	if len(h.Extra) > maxUint16 {
	return errLongExtra
	}

	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) uint8(v uint8) {
	(*b)[0] = v
	b = (b)[1:]
	}

	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:]
	}