Курнат Андрей
74 lines
2.0 KiB
Go
74 lines
2.0 KiB
Go
package webp
|
|
|
|
import (
|
|
"bytes"
|
|
"errors"
|
|
"io"
|
|
|
|
"golang.org/x/image/riff"
|
|
)
|
|
|
|
var (
|
|
errInvalidHeader = errors.New("could not read an 8 byte header, sub-chunk is not valid")
|
|
)
|
|
|
|
// SubChunkReader helps in reading riff data from an existing chunk which are comprised of sub-chunks.
|
|
// A good example would be ANMF chunks of animated webp files. These chunks can contain headers, ALPH chunks
|
|
// and VP8 or VP8L chunks within the main riff data chunk.
|
|
type SubChunkReader struct {
|
|
r io.Reader
|
|
}
|
|
|
|
// Next will return the FourCC, data, and data length of a subchunk.
|
|
// The io.Reader returned for data will not be the same as the provided reader
|
|
// and is safe to discord without fully reading the contents.
|
|
// Will return an error if the format is invalid or an underlying read operation fails.
|
|
func (c SubChunkReader) Next() (riff.FourCC, io.Reader, uint32, error) {
|
|
header := make([]byte, 8)
|
|
n, err := io.ReadFull(c.r, header)
|
|
if err != nil {
|
|
if err == io.ErrUnexpectedEOF {
|
|
return riff.FourCC{}, nil, 0, errInvalidHeader
|
|
}
|
|
return riff.FourCC{}, nil, 0, err
|
|
}
|
|
if n != 8 {
|
|
return riff.FourCC{}, nil, 0, errInvalidHeader
|
|
}
|
|
|
|
fourCC := riff.FourCC{header[0], header[1], header[2], header[3]}
|
|
chunkLen := u32(header[4:8])
|
|
buf := make([]byte, chunkLen)
|
|
n, err = io.ReadFull(c.r, buf)
|
|
if err != nil {
|
|
if err == io.ErrUnexpectedEOF {
|
|
return riff.FourCC{}, nil, 0, errInvalidFormat
|
|
}
|
|
return riff.FourCC{}, nil, 0, err
|
|
}
|
|
if n != int(chunkLen) {
|
|
return riff.FourCC{}, nil, 0, errInvalidFormat
|
|
}
|
|
|
|
// if chunkLen was odd, we need to maintain a 2-byte boundary per RIFF spec.
|
|
// in this case read off a single byte of padding to re-align with the next
|
|
// fourCC header
|
|
if chunkLen%2 == 1 {
|
|
n, err := c.r.Read([]byte{0})
|
|
if err != nil {
|
|
return riff.FourCC{}, nil, 0, err
|
|
}
|
|
if n != 1 {
|
|
return riff.FourCC{}, nil, 0, errInvalidFormat
|
|
}
|
|
}
|
|
|
|
return fourCC, bytes.NewReader(buf), chunkLen, nil
|
|
}
|
|
|
|
func NewSubChunkReader(r io.Reader) *SubChunkReader {
|
|
return &SubChunkReader{
|
|
r: r,
|
|
}
|
|
}
|