func ExampleReader() {
formType, r, err := riff.NewReader(strings.NewReader(data))
if err != nil {
log.Fatal(err)
}
fmt.Printf("RIFF(%s)\n", formType)
if err := dump(r, ".\t"); err != nil {
log.Fatal(err)
}
// Output:
// RIFF(ROOT)
// . ZERO ""
// . ONE "a"
// . LIST(META)
// . . LIST(GOOD)
// . . . ONE "a"
// . . . FIVE "klmno"
// . . ZERO ""
// . . LIST(BAD )
// . . . THRE "def"
// . TWO "bc"
// . LIST(UGLY)
// . . FOUR "ghij"
// . . SIX "pqrstu"
}
func decode(r io.Reader, configOnly bool) (image.Image, image.Config, error) {
formType, riffReader, err := riff.NewReader(r)
if err != nil {
return nil, image.Config{}, err
}
if formType != fccWEBP {
return nil, image.Config{}, errInvalidFormat
}
var (
alpha []byte
alphaStride int
wantAlpha bool
widthMinusOne uint32
heightMinusOne uint32
buf [10]byte
)
for {
chunkID, chunkLen, chunkData, err := riffReader.Next()
if err == io.EOF {
err = errInvalidFormat
}
if err != nil {
return nil, image.Config{}, err
}
switch chunkID {
case fccALPH:
if !wantAlpha {
return nil, image.Config{}, errInvalidFormat
}
wantAlpha = false
// Read the Pre-processing | Filter | Compression byte.
if _, err := io.ReadFull(chunkData, buf[:1]); err != nil {
if err == io.EOF {
err = errInvalidFormat
}
return nil, image.Config{}, err
}
alpha, alphaStride, err = readAlpha(chunkData, widthMinusOne, heightMinusOne, buf[0]&0x03)
if err != nil {
return nil, image.Config{}, err
}
unfilterAlpha(alpha, alphaStride, (buf[0]>>2)&0x03)
case fccVP8:
if wantAlpha {
return nil, image.Config{}, errInvalidFormat
}
d := vp8.NewDecoder()
d.Init(chunkData, int(chunkLen))
fh, err := d.DecodeFrameHeader()
if err != nil {
return nil, image.Config{}, err
}
if configOnly {
return nil, image.Config{
ColorModel: color.YCbCrModel,
Width: fh.Width,
Height: fh.Height,
}, nil
}
m, err := d.DecodeFrame()
if err != nil {
return nil, image.Config{}, err
}
if alpha != nil {
return &nycbcra.Image{
YCbCr: *m,
A: alpha,
AStride: alphaStride,
}, image.Config{}, nil
}
return m, image.Config{}, nil
case fccVP8L:
if wantAlpha || alpha != nil {
return nil, image.Config{}, errInvalidFormat
}
if configOnly {
c, err := vp8l.DecodeConfig(chunkData)
return nil, c, err
}
m, err := vp8l.Decode(chunkData)
return m, image.Config{}, err
case fccVP8X:
if chunkLen != 10 {
return nil, image.Config{}, errInvalidFormat
}
if _, err := io.ReadFull(chunkData, buf[:10]); err != nil {
return nil, image.Config{}, err
}
const (
animationBit = 1 << 1
xmpMetadataBit = 1 << 2
exifMetadataBit = 1 << 3
alphaBit = 1 << 4
iccProfileBit = 1 << 5
)
if buf[0] != alphaBit {
return nil, image.Config{}, errors.New("webp: non-Alpha VP8X is not implemented")
}
widthMinusOne = uint32(buf[4]) | uint32(buf[5])<<8 | uint32(buf[6])<<16
heightMinusOne = uint32(buf[7]) | uint32(buf[8])<<8 | uint32(buf[9])<<16
if configOnly {
return nil, image.Config{
ColorModel: nycbcra.ColorModel,
Width: int(widthMinusOne) + 1,
Height: int(heightMinusOne) + 1,
}, nil
}
wantAlpha = true
}
}
}
func (m Matcher) Identify(na string, b *siegreader.Buffer, exclude ...int) (chan core.Result, error) {
buf, err := b.Slice(0, 8)
if err != nil || buf[0] != 'R' || buf[1] != 'I' || buf[2] != 'F' || buf[3] != 'F' {
res := make(chan core.Result)
close(res)
return res, nil
}
rcc, rrdr, err := riff.NewReader(siegreader.ReaderFrom(b))
if err != nil {
res := make(chan core.Result)
close(res)
return res, nil
}
// now make structures for testing
uniqs := make(map[riff.FourCC]bool)
res := make(chan core.Result)
waitset := m.priorities.WaitSet(exclude...)
// send and report if satisified
send := func(cc riff.FourCC) bool {
if config.Debug() {
fmt.Fprintf(config.Out(), "riff match %s\n", string(cc[:]))
}
if uniqs[cc] {
return false
}
uniqs[cc] = true
for _, hit := range m.riffs[cc] {
if waitset.Check(hit) {
if config.Debug() {
fmt.Fprintf(config.Out(), "sending riff match %s\n", string(cc[:]))
}
res <- result{hit, cc}
if waitset.Put(hit) {
return true
}
}
}
return false
}
// riff walk
var descend func(*riff.Reader) bool
descend = func(r *riff.Reader) bool {
for {
chunkID, chunkLen, chunkData, err := r.Next()
if err != nil || send(chunkID) {
return true
}
if chunkID == riff.LIST {
listType, list, err := riff.NewListReader(chunkLen, chunkData)
if err != nil || send(listType) {
return true
}
if descend(list) {
return true
}
}
}
}
// go time
go func() {
if send(rcc) {
close(res)
return
}
descend(rrdr)
close(res)
}()
return res, nil
}