limage - xcf/writer.go

     1  package xcf
     2  
     3  import (
     4  	"errors"
     5  	"io"
     6  
     7  	"vimagination.zapto.org/byteio"
     8  )
     9  
    10  type writer struct {
    11  	*byteio.StickyBigEndianWriter
    12  	*writerAtWriter
    13  }
    14  
    15  func newWriter(w io.WriterAt) writer {
    16  	wr := &writerAtWriter{
    17  		WriterAt: w,
    18  	}
    19  	return writer{
    20  		StickyBigEndianWriter: &byteio.StickyBigEndianWriter{Writer: wr},
    21  		writerAtWriter:        wr,
    22  	}
    23  }
    24  
    25  func (w writer) WriteAt(p []byte, off int64) (int, error) {
    26  	if w.Err != nil {
    27  		return 0, w.Err
    28  	}
    29  	var n int
    30  	n, w.Err = w.WriterAt.WriteAt(p, off)
    31  	return n, w.Err
    32  }
    33  
    34  func (w writer) Write(p []byte) {
    35  	w.StickyBigEndianWriter.Write(p)
    36  }
    37  
    38  func (w writer) WriteString(str string) {
    39  	w.WriteUint32(uint32(len(str)) + 1)
    40  	w.Write([]byte(str))
    41  	w.WriteUint8(0)
    42  }
    43  
    44  type pointerWriter struct {
    45  	bw      *byteio.StickyBigEndianWriter
    46  	toWrite uint32
    47  	obw     *byteio.StickyBigEndianWriter
    48  }
    49  
    50  func (p *pointerWriter) WritePointer(ptr uint32) {
    51  	if p.toWrite > 0 {
    52  		p.bw.WriteUint32(ptr)
    53  		p.toWrite--
    54  		if p.bw.Err != nil {
    55  			p.obw.Err = p.bw.Err
    56  		}
    57  	}
    58  }
    59  
    60  func (w writer) ReservePointers(n uint32) *pointerWriter {
    61  	p := &pointerWriter{
    62  		bw: &byteio.StickyBigEndianWriter{
    63  			Writer: &writerAtWriter{
    64  				WriterAt: w.writerAtWriter.WriterAt,
    65  				pos:      w.pos,
    66  			},
    67  		},
    68  		toWrite: n,
    69  		obw:     w.StickyBigEndianWriter,
    70  	}
    71  	w.pos += int64(n) * 4
    72  	return p
    73  }
    74  
    75  func (w writer) ReservePointerList(n uint32) *pointerWriter {
    76  	pw := w.ReservePointers(n)
    77  	w.WriteUint32(0)
    78  	return pw
    79  }
    80  
    81  type writerAtWriter struct {
    82  	io.WriterAt
    83  	pos int64
    84  }
    85  
    86  func (w *writerAtWriter) Write(p []byte) (int, error) {
    87  	n, err := w.WriteAt(p, w.pos)
    88  	w.pos += int64(n)
    89  	return n, err
    90  }
    91  
    92  // Errors
    93  var (
    94  	ErrTooBig = errors.New("write too big")
    95  )
    96