Initial QSfera import

Server/vendor/github.com/kovidgoyal/imaging/webp/subchunkreader.go

@@ -0,0 +1,73 @@
+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,
+	}
+}