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mirror of https://github.com/wader/fq.git synced 2024-12-24 22:05:31 +03:00
fq/format/ogg/ogg_page.go
2022-07-19 18:33:50 +02:00

62 lines
2.0 KiB
Go

package ogg
import (
"bytes"
"github.com/wader/fq/format"
"github.com/wader/fq/pkg/bitio"
"github.com/wader/fq/pkg/checksum"
"github.com/wader/fq/pkg/decode"
"github.com/wader/fq/pkg/interp"
"github.com/wader/fq/pkg/scalar"
)
func init() {
interp.RegisterFormat(decode.Format{
Name: format.OGG_PAGE,
Description: "OGG page",
DecodeFn: pageDecode,
})
}
func pageDecode(d *decode.D, _ any) any {
p := format.OggPageOut{}
startPos := d.Pos()
d.Endian = decode.LittleEndian
d.FieldUTF8("capture_pattern", 4, d.AssertStr("OggS"))
d.FieldU8("version", d.AssertU(0))
d.FieldU5("unused_flags")
p.IsLastPage = d.FieldBool("last_page")
p.IsFirstPage = d.FieldBool("first_page")
p.IsContinuedPacket = d.FieldBool("continued_packet")
d.FieldU64("granule_position")
p.StreamSerialNumber = uint32(d.FieldU32("bitstream_serial_number"))
p.SequenceNo = uint32(d.FieldU32("page_sequence_no"))
d.FieldU32("crc", scalar.ActualHex)
pageSegments := d.FieldU8("page_segments")
var segmentTable []uint64
d.FieldArray("segment_table", func(d *decode.D) {
for i := uint64(0); i < pageSegments; i++ {
segmentTable = append(segmentTable, d.FieldU8("segment_size"))
}
})
d.FieldArray("segments", func(d *decode.D) {
for _, ss := range segmentTable {
bs := d.ReadAllBits(d.FieldRawLen("segment", int64(ss)*8))
p.Segments = append(p.Segments, bs)
}
})
endPos := d.Pos()
pageChecksumValue := d.FieldGet("crc")
pageCRC := &checksum.CRC{Bits: 32, Table: checksum.Poly04c11db7Table}
d.Copy(pageCRC, bitio.NewIOReader(d.BitBufRange(startPos, pageChecksumValue.Range.Start-startPos))) // header before checksum
d.Copy(pageCRC, bytes.NewReader([]byte{0, 0, 0, 0})) // zero checksum bits
d.Copy(pageCRC, bitio.NewIOReader(d.BitBufRange(pageChecksumValue.Range.Stop(), endPos-pageChecksumValue.Range.Stop()))) // rest of page
_ = pageChecksumValue.TryScalarFn(d.ValidateUBytes(pageCRC.Sum(nil)))
return p
}