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fq/format/ogg/ogg_page.go

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package ogg
import (
"bytes"
"github.com/wader/fq/format"
"github.com/wader/fq/format/registry"
"github.com/wader/fq/pkg/crc"
"github.com/wader/fq/pkg/decode"
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)
func init() {
registry.MustRegister(decode.Format{
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Name: format.OGG_PAGE,
Description: "OGG page",
DecodeFn: pageDecode,
})
}
func pageDecode(d *decode.D, in interface{}) interface{} {
p := format.OggPageOut{}
startPos := d.Pos()
d.Endian = decode.LittleEndian
d.FieldUTF8("capture_pattern", 4, d.AssertStr("OggS"))
d.FieldU8("version", d.AssertU(0))
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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", d.Hex)
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pageSegments := d.FieldU8("page_segments")
var segmentTable []uint64
d.FieldArray("segment_table", func(d *decode.D) {
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for i := uint64(0); i < pageSegments; i++ {
segmentTable = append(segmentTable, d.FieldU8("segment_size"))
}
})
d.FieldArray("segments", func(d *decode.D) {
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for _, ss := range segmentTable {
p.Segments = append(p.Segments, d.FieldRawLen("segment", int64(ss)*8))
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}
})
endPos := d.Pos()
pageChecksumValue := d.FieldGet("crc")
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pageCRC := &crc.CRC{Bits: 32, Table: crc.Poly04c11db7Table}
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d.MustCopy(pageCRC, d.BitBufRange(startPos, pageChecksumValue.Range.Start-startPos)) // header before checksum
d.MustCopy(pageCRC, bytes.NewReader([]byte{0, 0, 0, 0})) // zero checksum bits
d.MustCopy(pageCRC, d.BitBufRange(pageChecksumValue.Range.Stop(), endPos-pageChecksumValue.Range.Stop())) // rest of page
_ = pageChecksumValue.TryScalarFn(d.ValidateUBytes(pageCRC.Sum(nil)))
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return p
}