limage - xcf/reader.go

     1  package xcf
     2  
     3  import (
     4  	"errors"
     5  	"io"
     6  	"unicode/utf8"
     7  
     8  	"vimagination.zapto.org/byteio"
     9  )
    10  
    11  type reader struct {
    12  	*byteio.StickyBigEndianReader
    13  	rs *readSeeker
    14  }
    15  
    16  type readSeeker struct {
    17  	io.ReaderAt
    18  	pos int64
    19  }
    20  
    21  func (r *readSeeker) Read(p []byte) (int, error) {
    22  	n, err := r.ReadAt(p, r.pos)
    23  	r.pos += int64(n)
    24  	return n, err
    25  }
    26  
    27  func newReader(r io.ReaderAt) reader {
    28  	nr := reader{
    29  		rs: &readSeeker{ReaderAt: r},
    30  	}
    31  	nr.StickyBigEndianReader = &byteio.StickyBigEndianReader{Reader: nr.rs}
    32  	return nr
    33  }
    34  
    35  const maxString = 16 * 1024 * 1024
    36  
    37  func (r *reader) ReadString() string {
    38  	length := r.ReadUint32()
    39  	if length == 0 {
    40  		return ""
    41  	} else if length > maxString {
    42  		r.SetError(ErrStringTooLong)
    43  		return ""
    44  	}
    45  	b := make([]byte, length)
    46  	_, err := io.ReadFull(r, b)
    47  	if err != nil {
    48  		r.Err = err
    49  		return ""
    50  	}
    51  	if b[length-1] != 0 || !utf8.Valid(b[:length-1]) {
    52  		r.SetError(ErrInvalidString)
    53  		return ""
    54  	}
    55  	return string(b[:length-1])
    56  }
    57  
    58  func (r *reader) ReadByte() byte {
    59  	return r.ReadUint8()
    60  }
    61  
    62  func (r *reader) Goto(n uint64) {
    63  	r.rs.pos = int64(n)
    64  }
    65  
    66  func (r *reader) SetError(err error) {
    67  	if r.Err == nil {
    68  		r.Err = err
    69  	}
    70  }
    71  
    72  // Errors
    73  var (
    74  	ErrInvalidString = errors.New("string is invalid")
    75  	ErrStringTooLong = errors.New("string exceeds maximum length")
    76  	ErrInvalidSeek   = errors.New("invalid seek")
    77  )
    78