writer.go

Documentation: archive/zip

     1  // Copyright 2011 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package zip
     6  
     7  import (
     8  	"bufio"
     9  	"encoding/binary"
    10  	"errors"
    11  	"hash"
    12  	"hash/crc32"
    13  	"io"
    14  	"io/fs"
    15  	"strings"
    16  	"unicode/utf8"
    17  )
    18  
    19  var (
    20  	errLongName  = errors.New("zip: FileHeader.Name too long")
    21  	errLongExtra = errors.New("zip: FileHeader.Extra too long")
    22  )
    23  
    24  // Writer implements a zip file writer.
    25  type Writer struct {
    26  	cw          *countWriter
    27  	dir         []*header
    28  	last        *fileWriter
    29  	closed      bool
    30  	compressors map[uint16]Compressor
    31  	comment     string
    32  
    33  	// testHookCloseSizeOffset if non-nil is called with the size
    34  	// of offset of the central directory at Close.
    35  	testHookCloseSizeOffset func(size, offset uint64)
    36  }
    37  
    38  type header struct {
    39  	*FileHeader
    40  	offset uint64
    41  	raw    bool
    42  }
    43  
    44  // NewWriter returns a new [Writer] writing a zip file to w.
    45  func NewWriter(w io.Writer) *Writer {
    46  	return &Writer{cw: &countWriter{w: bufio.NewWriter(w)}}
    47  }
    48  
    49  // SetOffset sets the offset of the beginning of the zip data within the
    50  // underlying writer. It should be used when the zip data is appended to an
    51  // existing file, such as a binary executable.
    52  // It must be called before any data is written.
    53  func (w *Writer) SetOffset(n int64) {
    54  	if w.cw.count != 0 {
    55  		panic("zip: SetOffset called after data was written")
    56  	}
    57  	w.cw.count = n
    58  }
    59  
    60  // Flush flushes any buffered data to the underlying writer.
    61  // Calling Flush is not normally necessary; calling Close is sufficient.
    62  func (w *Writer) Flush() error {
    63  	return w.cw.w.(*bufio.Writer).Flush()
    64  }
    65  
    66  // SetComment sets the end-of-central-directory comment field.
    67  // It can only be called before [Writer.Close].
    68  func (w *Writer) SetComment(comment string) error {
    69  	if len(comment) > uint16max {
    70  		return errors.New("zip: Writer.Comment too long")
    71  	}
    72  	w.comment = comment
    73  	return nil
    74  }
    75  
    76  // Close finishes writing the zip file by writing the central directory.
    77  // It does not close the underlying writer.
    78  func (w *Writer) Close() error {
    79  	if w.last != nil && !w.last.closed {
    80  		if err := w.last.close(); err != nil {
    81  			return err
    82  		}
    83  		w.last = nil
    84  	}
    85  	if w.closed {
    86  		return errors.New("zip: writer closed twice")
    87  	}
    88  	w.closed = true
    89  
    90  	// write central directory
    91  	start := w.cw.count
    92  	for _, h := range w.dir {
    93  		var buf [directoryHeaderLen]byte
    94  		b := writeBuf(buf[:])
    95  		b.uint32(uint32(directoryHeaderSignature))
    96  		b.uint16(h.CreatorVersion)
    97  		b.uint16(h.ReaderVersion)
    98  		b.uint16(h.Flags)
    99  		b.uint16(h.Method)
   100  		b.uint16(h.ModifiedTime)
   101  		b.uint16(h.ModifiedDate)
   102  		b.uint32(h.CRC32)
   103  		if h.isZip64() || h.offset >= uint32max {
   104  			// the file needs a zip64 header. store maxint in both
   105  			// 32 bit size fields (and offset later) to signal that the
   106  			// zip64 extra header should be used.
   107  			b.uint32(uint32max) // compressed size
   108  			b.uint32(uint32max) // uncompressed size
   109  
   110  			// append a zip64 extra block to Extra
   111  			var buf [28]byte // 2x uint16 + 3x uint64
   112  			eb := writeBuf(buf[:])
   113  			eb.uint16(zip64ExtraID)
   114  			eb.uint16(24) // size = 3x uint64
   115  			eb.uint64(h.UncompressedSize64)
   116  			eb.uint64(h.CompressedSize64)
   117  			eb.uint64(h.offset)
   118  			h.Extra = append(h.Extra, buf[:]...)
   119  		} else {
   120  			b.uint32(h.CompressedSize)
   121  			b.uint32(h.UncompressedSize)
   122  		}
   123  
   124  		b.uint16(uint16(len(h.Name)))
   125  		b.uint16(uint16(len(h.Extra)))
   126  		b.uint16(uint16(len(h.Comment)))
   127  		b = b[4:] // skip disk number start and internal file attr (2x uint16)
   128  		b.uint32(h.ExternalAttrs)
   129  		if h.offset > uint32max {
   130  			b.uint32(uint32max)
   131  		} else {
   132  			b.uint32(uint32(h.offset))
   133  		}
   134  		if _, err := w.cw.Write(buf[:]); err != nil {
   135  			return err
   136  		}
   137  		if _, err := io.WriteString(w.cw, h.Name); err != nil {
   138  			return err
   139  		}
   140  		if _, err := w.cw.Write(h.Extra); err != nil {
   141  			return err
   142  		}
   143  		if _, err := io.WriteString(w.cw, h.Comment); err != nil {
   144  			return err
   145  		}
   146  	}
   147  	end := w.cw.count
   148  
   149  	records := uint64(len(w.dir))
   150  	size := uint64(end - start)
   151  	offset := uint64(start)
   152  
   153  	if f := w.testHookCloseSizeOffset; f != nil {
   154  		f(size, offset)
   155  	}
   156  
   157  	if records >= uint16max || size >= uint32max || offset >= uint32max {
   158  		var buf [directory64EndLen + directory64LocLen]byte
   159  		b := writeBuf(buf[:])
   160  
   161  		// zip64 end of central directory record
   162  		b.uint32(directory64EndSignature)
   163  		b.uint64(directory64EndLen - 12) // length minus signature (uint32) and length fields (uint64)
   164  		b.uint16(zipVersion45)           // version made by
   165  		b.uint16(zipVersion45)           // version needed to extract
   166  		b.uint32(0)                      // number of this disk
   167  		b.uint32(0)                      // number of the disk with the start of the central directory
   168  		b.uint64(records)                // total number of entries in the central directory on this disk
   169  		b.uint64(records)                // total number of entries in the central directory
   170  		b.uint64(size)                   // size of the central directory
   171  		b.uint64(offset)                 // offset of start of central directory with respect to the starting disk number
   172  
   173  		// zip64 end of central directory locator
   174  		b.uint32(directory64LocSignature)
   175  		b.uint32(0)           // number of the disk with the start of the zip64 end of central directory
   176  		b.uint64(uint64(end)) // relative offset of the zip64 end of central directory record
   177  		b.uint32(1)           // total number of disks
   178  
   179  		if _, err := w.cw.Write(buf[:]); err != nil {
   180  			return err
   181  		}
   182  
   183  		// store max values in the regular end record to signal
   184  		// that the zip64 values should be used instead
   185  		records = uint16max
   186  		size = uint32max
   187  		offset = uint32max
   188  	}
   189  
   190  	// write end record
   191  	var buf [directoryEndLen]byte
   192  	b := writeBuf(buf[:])
   193  	b.uint32(uint32(directoryEndSignature))
   194  	b = b[4:]                        // skip over disk number and first disk number (2x uint16)
   195  	b.uint16(uint16(records))        // number of entries this disk
   196  	b.uint16(uint16(records))        // number of entries total
   197  	b.uint32(uint32(size))           // size of directory
   198  	b.uint32(uint32(offset))         // start of directory
   199  	b.uint16(uint16(len(w.comment))) // byte size of EOCD comment
   200  	if _, err := w.cw.Write(buf[:]); err != nil {
   201  		return err
   202  	}
   203  	if _, err := io.WriteString(w.cw, w.comment); err != nil {
   204  		return err
   205  	}
   206  
   207  	return w.cw.w.(*bufio.Writer).Flush()
   208  }
   209  
   210  // Create adds a file to the zip file using the provided name.
   211  // It returns a [Writer] to which the file contents should be written.
   212  // The file contents will be compressed using the [Deflate] method.
   213  // The name must be a relative path: it must not start with a drive
   214  // letter (e.g. C:) or leading slash, and only forward slashes are
   215  // allowed. To create a directory instead of a file, add a trailing
   216  // slash to the name.
   217  // The file's contents must be written to the [io.Writer] before the next
   218  // call to [Writer.Create], [Writer.CreateHeader], or [Writer.Close].
   219  func (w *Writer) Create(name string) (io.Writer, error) {
   220  	header := &FileHeader{
   221  		Name:   name,
   222  		Method: Deflate,
   223  	}
   224  	return w.CreateHeader(header)
   225  }
   226  
   227  // detectUTF8 reports whether s is a valid UTF-8 string, and whether the string
   228  // must be considered UTF-8 encoding (i.e., not compatible with CP-437, ASCII,
   229  // or any other common encoding).
   230  func detectUTF8(s string) (valid, require bool) {
   231  	for i := 0; i < len(s); {
   232  		r, size := utf8.DecodeRuneInString(s[i:])
   233  		i += size
   234  		// Officially, ZIP uses CP-437, but many readers use the system's
   235  		// local character encoding. Most encoding are compatible with a large
   236  		// subset of CP-437, which itself is ASCII-like.
   237  		//
   238  		// Forbid 0x7e and 0x5c since EUC-KR and Shift-JIS replace those
   239  		// characters with localized currency and overline characters.
   240  		if r < 0x20 || r > 0x7d || r == 0x5c {
   241  			if !utf8.ValidRune(r) || (r == utf8.RuneError && size == 1) {
   242  				return false, false
   243  			}
   244  			require = true
   245  		}
   246  	}
   247  	return true, require
   248  }
   249  
   250  // prepare performs the bookkeeping operations required at the start of
   251  // CreateHeader and CreateRaw.
   252  func (w *Writer) prepare(fh *FileHeader) error {
   253  	if w.last != nil && !w.last.closed {
   254  		if err := w.last.close(); err != nil {
   255  			return err
   256  		}
   257  	}
   258  	if len(w.dir) > 0 && w.dir[len(w.dir)-1].FileHeader == fh {
   259  		// See https://golang.org/issue/11144 confusion.
   260  		return errors.New("archive/zip: invalid duplicate FileHeader")
   261  	}
   262  	return nil
   263  }
   264  
   265  // CreateHeader adds a file to the zip archive using the provided [FileHeader]
   266  // for the file metadata. [Writer] takes ownership of fh and may mutate
   267  // its fields. The caller must not modify fh after calling [Writer.CreateHeader].
   268  //
   269  // This returns a [Writer] to which the file contents should be written.
   270  // The file's contents must be written to the io.Writer before the next
   271  // call to [Writer.Create], [Writer.CreateHeader], [Writer.CreateRaw], or [Writer.Close].
   272  func (w *Writer) CreateHeader(fh *FileHeader) (io.Writer, error) {
   273  	if err := w.prepare(fh); err != nil {
   274  		return nil, err
   275  	}
   276  
   277  	// The ZIP format has a sad state of affairs regarding character encoding.
   278  	// Officially, the name and comment fields are supposed to be encoded
   279  	// in CP-437 (which is mostly compatible with ASCII), unless the UTF-8
   280  	// flag bit is set. However, there are several problems:
   281  	//
   282  	//	* Many ZIP readers still do not support UTF-8.
   283  	//	* If the UTF-8 flag is cleared, several readers simply interpret the
   284  	//	name and comment fields as whatever the local system encoding is.
   285  	//
   286  	// In order to avoid breaking readers without UTF-8 support,
   287  	// we avoid setting the UTF-8 flag if the strings are CP-437 compatible.
   288  	// However, if the strings require multibyte UTF-8 encoding and is a
   289  	// valid UTF-8 string, then we set the UTF-8 bit.
   290  	//
   291  	// For the case, where the user explicitly wants to specify the encoding
   292  	// as UTF-8, they will need to set the flag bit themselves.
   293  	utf8Valid1, utf8Require1 := detectUTF8(fh.Name)
   294  	utf8Valid2, utf8Require2 := detectUTF8(fh.Comment)
   295  	switch {
   296  	case fh.NonUTF8:
   297  		fh.Flags &^= 0x800
   298  	case (utf8Require1 || utf8Require2) && (utf8Valid1 && utf8Valid2):
   299  		fh.Flags |= 0x800
   300  	}
   301  
   302  	fh.CreatorVersion = fh.CreatorVersion&0xff00 | zipVersion20 // preserve compatibility byte
   303  	fh.ReaderVersion = zipVersion20
   304  
   305  	// If Modified is set, this takes precedence over MS-DOS timestamp fields.
   306  	if !fh.Modified.IsZero() {
   307  		// Contrary to the FileHeader.SetModTime method, we intentionally
   308  		// do not convert to UTC, because we assume the user intends to encode
   309  		// the date using the specified timezone. A user may want this control
   310  		// because many legacy ZIP readers interpret the timestamp according
   311  		// to the local timezone.
   312  		//
   313  		// The timezone is only non-UTC if a user directly sets the Modified
   314  		// field directly themselves. All other approaches sets UTC.
   315  		fh.ModifiedDate, fh.ModifiedTime = timeToMsDosTime(fh.Modified)
   316  
   317  		// Use "extended timestamp" format since this is what Info-ZIP uses.
   318  		// Nearly every major ZIP implementation uses a different format,
   319  		// but at least most seem to be able to understand the other formats.
   320  		//
   321  		// This format happens to be identical for both local and central header
   322  		// if modification time is the only timestamp being encoded.
   323  		var mbuf [9]byte // 2*SizeOf(uint16) + SizeOf(uint8) + SizeOf(uint32)
   324  		mt := uint32(fh.Modified.Unix())
   325  		eb := writeBuf(mbuf[:])
   326  		eb.uint16(extTimeExtraID)
   327  		eb.uint16(5)  // Size: SizeOf(uint8) + SizeOf(uint32)
   328  		eb.uint8(1)   // Flags: ModTime
   329  		eb.uint32(mt) // ModTime
   330  		fh.Extra = append(fh.Extra, mbuf[:]...)
   331  	}
   332  
   333  	var (
   334  		ow io.Writer
   335  		fw *fileWriter
   336  	)
   337  	h := &header{
   338  		FileHeader: fh,
   339  		offset:     uint64(w.cw.count),
   340  	}
   341  
   342  	if strings.HasSuffix(fh.Name, "/") {
   343  		// Set the compression method to Store to ensure data length is truly zero,
   344  		// which the writeHeader method always encodes for the size fields.
   345  		// This is necessary as most compression formats have non-zero lengths
   346  		// even when compressing an empty string.
   347  		fh.Method = Store
   348  		fh.Flags &^= 0x8 // we will not write a data descriptor
   349  
   350  		// Explicitly clear sizes as they have no meaning for directories.
   351  		fh.CompressedSize = 0
   352  		fh.CompressedSize64 = 0
   353  		fh.UncompressedSize = 0
   354  		fh.UncompressedSize64 = 0
   355  
   356  		ow = dirWriter{}
   357  	} else {
   358  		fh.Flags |= 0x8 // we will write a data descriptor
   359  
   360  		fw = &fileWriter{
   361  			zipw:      w.cw,
   362  			compCount: &countWriter{w: w.cw},
   363  			crc32:     crc32.NewIEEE(),
   364  		}
   365  		comp := w.compressor(fh.Method)
   366  		if comp == nil {
   367  			return nil, ErrAlgorithm
   368  		}
   369  		var err error
   370  		fw.comp, err = comp(fw.compCount)
   371  		if err != nil {
   372  			return nil, err
   373  		}
   374  		fw.rawCount = &countWriter{w: fw.comp}
   375  		fw.header = h
   376  		ow = fw
   377  	}
   378  	w.dir = append(w.dir, h)
   379  	if err := writeHeader(w.cw, h); err != nil {
   380  		return nil, err
   381  	}
   382  	// If we're creating a directory, fw is nil.
   383  	w.last = fw
   384  	return ow, nil
   385  }
   386  
   387  func writeHeader(w io.Writer, h *header) error {
   388  	const maxUint16 = 1<<16 - 1
   389  	if len(h.Name) > maxUint16 {
   390  		return errLongName
   391  	}
   392  	if len(h.Extra) > maxUint16 {
   393  		return errLongExtra
   394  	}
   395  
   396  	var buf [fileHeaderLen]byte
   397  	b := writeBuf(buf[:])
   398  	b.uint32(uint32(fileHeaderSignature))
   399  	b.uint16(h.ReaderVersion)
   400  	b.uint16(h.Flags)
   401  	b.uint16(h.Method)
   402  	b.uint16(h.ModifiedTime)
   403  	b.uint16(h.ModifiedDate)
   404  	// In raw mode (caller does the compression), the values are either
   405  	// written here or in the trailing data descriptor based on the header
   406  	// flags.
   407  	if h.raw && !h.hasDataDescriptor() {
   408  		b.uint32(h.CRC32)
   409  		b.uint32(uint32(min(h.CompressedSize64, uint32max)))
   410  		b.uint32(uint32(min(h.UncompressedSize64, uint32max)))
   411  	} else {
   412  		// When this package handle the compression, these values are
   413  		// always written to the trailing data descriptor.
   414  		b.uint32(0) // crc32
   415  		b.uint32(0) // compressed size
   416  		b.uint32(0) // uncompressed size
   417  	}
   418  	b.uint16(uint16(len(h.Name)))
   419  	b.uint16(uint16(len(h.Extra)))
   420  	if _, err := w.Write(buf[:]); err != nil {
   421  		return err
   422  	}
   423  	if _, err := io.WriteString(w, h.Name); err != nil {
   424  		return err
   425  	}
   426  	_, err := w.Write(h.Extra)
   427  	return err
   428  }
   429  
   430  // CreateRaw adds a file to the zip archive using the provided [FileHeader] and
   431  // returns a [Writer] to which the file contents should be written. The file's
   432  // contents must be written to the io.Writer before the next call to [Writer.Create],
   433  // [Writer.CreateHeader], [Writer.CreateRaw], or [Writer.Close].
   434  //
   435  // In contrast to [Writer.CreateHeader], the bytes passed to Writer are not compressed.
   436  func (w *Writer) CreateRaw(fh *FileHeader) (io.Writer, error) {
   437  	if err := w.prepare(fh); err != nil {
   438  		return nil, err
   439  	}
   440  
   441  	fh.CompressedSize = uint32(min(fh.CompressedSize64, uint32max))
   442  	fh.UncompressedSize = uint32(min(fh.UncompressedSize64, uint32max))
   443  
   444  	h := &header{
   445  		FileHeader: fh,
   446  		offset:     uint64(w.cw.count),
   447  		raw:        true,
   448  	}
   449  	w.dir = append(w.dir, h)
   450  	if err := writeHeader(w.cw, h); err != nil {
   451  		return nil, err
   452  	}
   453  
   454  	if strings.HasSuffix(fh.Name, "/") {
   455  		w.last = nil
   456  		return dirWriter{}, nil
   457  	}
   458  
   459  	fw := &fileWriter{
   460  		header: h,
   461  		zipw:   w.cw,
   462  	}
   463  	w.last = fw
   464  	return fw, nil
   465  }
   466  
   467  // Copy copies the file f (obtained from a [Reader]) into w. It copies the raw
   468  // form directly bypassing decompression, compression, and validation.
   469  func (w *Writer) Copy(f *File) error {
   470  	r, err := f.OpenRaw()
   471  	if err != nil {
   472  		return err
   473  	}
   474  	fw, err := w.CreateRaw(&f.FileHeader)
   475  	if err != nil {
   476  		return err
   477  	}
   478  	_, err = io.Copy(fw, r)
   479  	return err
   480  }
   481  
   482  // RegisterCompressor registers or overrides a custom compressor for a specific
   483  // method ID. If a compressor for a given method is not found, [Writer] will
   484  // default to looking up the compressor at the package level.
   485  func (w *Writer) RegisterCompressor(method uint16, comp Compressor) {
   486  	if w.compressors == nil {
   487  		w.compressors = make(map[uint16]Compressor)
   488  	}
   489  	w.compressors[method] = comp
   490  }
   491  
   492  // AddFS adds the files from fs.FS to the archive.
   493  // It walks the directory tree starting at the root of the filesystem
   494  // adding each file to the zip using deflate while maintaining the directory structure.
   495  func (w *Writer) AddFS(fsys fs.FS) error {
   496  	return fs.WalkDir(fsys, ".", func(name string, d fs.DirEntry, err error) error {
   497  		if err != nil {
   498  			return err
   499  		}
   500  		if d.IsDir() {
   501  			return nil
   502  		}
   503  		info, err := d.Info()
   504  		if err != nil {
   505  			return err
   506  		}
   507  		if !info.Mode().IsRegular() {
   508  			return errors.New("zip: cannot add non-regular file")
   509  		}
   510  		h, err := FileInfoHeader(info)
   511  		if err != nil {
   512  			return err
   513  		}
   514  		h.Name = name
   515  		h.Method = Deflate
   516  		fw, err := w.CreateHeader(h)
   517  		if err != nil {
   518  			return err
   519  		}
   520  		f, err := fsys.Open(name)
   521  		if err != nil {
   522  			return err
   523  		}
   524  		defer f.Close()
   525  		_, err = io.Copy(fw, f)
   526  		return err
   527  	})
   528  }
   529  
   530  func (w *Writer) compressor(method uint16) Compressor {
   531  	comp := w.compressors[method]
   532  	if comp == nil {
   533  		comp = compressor(method)
   534  	}
   535  	return comp
   536  }
   537  
   538  type dirWriter struct{}
   539  
   540  func (dirWriter) Write(b []byte) (int, error) {
   541  	if len(b) == 0 {
   542  		return 0, nil
   543  	}
   544  	return 0, errors.New("zip: write to directory")
   545  }
   546  
   547  type fileWriter struct {
   548  	*header
   549  	zipw      io.Writer
   550  	rawCount  *countWriter
   551  	comp      io.WriteCloser
   552  	compCount *countWriter
   553  	crc32     hash.Hash32
   554  	closed    bool
   555  }
   556  
   557  func (w *fileWriter) Write(p []byte) (int, error) {
   558  	if w.closed {
   559  		return 0, errors.New("zip: write to closed file")
   560  	}
   561  	if w.raw {
   562  		return w.zipw.Write(p)
   563  	}
   564  	w.crc32.Write(p)
   565  	return w.rawCount.Write(p)
   566  }
   567  
   568  func (w *fileWriter) close() error {
   569  	if w.closed {
   570  		return errors.New("zip: file closed twice")
   571  	}
   572  	w.closed = true
   573  	if w.raw {
   574  		return w.writeDataDescriptor()
   575  	}
   576  	if err := w.comp.Close(); err != nil {
   577  		return err
   578  	}
   579  
   580  	// update FileHeader
   581  	fh := w.header.FileHeader
   582  	fh.CRC32 = w.crc32.Sum32()
   583  	fh.CompressedSize64 = uint64(w.compCount.count)
   584  	fh.UncompressedSize64 = uint64(w.rawCount.count)
   585  
   586  	if fh.isZip64() {
   587  		fh.CompressedSize = uint32max
   588  		fh.UncompressedSize = uint32max
   589  		fh.ReaderVersion = zipVersion45 // requires 4.5 - File uses ZIP64 format extensions
   590  	} else {
   591  		fh.CompressedSize = uint32(fh.CompressedSize64)
   592  		fh.UncompressedSize = uint32(fh.UncompressedSize64)
   593  	}
   594  
   595  	return w.writeDataDescriptor()
   596  }
   597  
   598  func (w *fileWriter) writeDataDescriptor() error {
   599  	if !w.hasDataDescriptor() {
   600  		return nil
   601  	}
   602  	// Write data descriptor. This is more complicated than one would
   603  	// think, see e.g. comments in zipfile.c:putextended() and
   604  	// http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=7073588.
   605  	// The approach here is to write 8 byte sizes if needed without
   606  	// adding a zip64 extra in the local header (too late anyway).
   607  	var buf []byte
   608  	if w.isZip64() {
   609  		buf = make([]byte, dataDescriptor64Len)
   610  	} else {
   611  		buf = make([]byte, dataDescriptorLen)
   612  	}
   613  	b := writeBuf(buf)
   614  	b.uint32(dataDescriptorSignature) // de-facto standard, required by OS X
   615  	b.uint32(w.CRC32)
   616  	if w.isZip64() {
   617  		b.uint64(w.CompressedSize64)
   618  		b.uint64(w.UncompressedSize64)
   619  	} else {
   620  		b.uint32(w.CompressedSize)
   621  		b.uint32(w.UncompressedSize)
   622  	}
   623  	_, err := w.zipw.Write(buf)
   624  	return err
   625  }
   626  
   627  type countWriter struct {
   628  	w     io.Writer
   629  	count int64
   630  }
   631  
   632  func (w *countWriter) Write(p []byte) (int, error) {
   633  	n, err := w.w.Write(p)
   634  	w.count += int64(n)
   635  	return n, err
   636  }
   637  
   638  type nopCloser struct {
   639  	io.Writer
   640  }
   641  
   642  func (w nopCloser) Close() error {
   643  	return nil
   644  }
   645  
   646  type writeBuf []byte
   647  
   648  func (b *writeBuf) uint8(v uint8) {
   649  	(*b)[0] = v
   650  	*b = (*b)[1:]
   651  }
   652  
   653  func (b *writeBuf) uint16(v uint16) {
   654  	binary.LittleEndian.PutUint16(*b, v)
   655  	*b = (*b)[2:]
   656  }
   657  
   658  func (b *writeBuf) uint32(v uint32) {
   659  	binary.LittleEndian.PutUint32(*b, v)
   660  	*b = (*b)[4:]
   661  }
   662  
   663  func (b *writeBuf) uint64(v uint64) {
   664  	binary.LittleEndian.PutUint64(*b, v)
   665  	*b = (*b)[8:]
   666  }
   667
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