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package twcc
import (
"sync/atomic"
"github.com/pion/interceptor"
"github.com/pion/rtp"
)
// HeaderExtensionInterceptorFactory is a interceptor.Factory for a HeaderExtensionInterceptor
type HeaderExtensionInterceptorFactory struct{}
// NewInterceptor constructs a new HeaderExtensionInterceptor
func (h *HeaderExtensionInterceptorFactory) NewInterceptor(id string) (interceptor.Interceptor, error) {
return &HeaderExtensionInterceptor{}, nil
}
// NewHeaderExtensionInterceptor returns a HeaderExtensionInterceptorFactory
func NewHeaderExtensionInterceptor() (*HeaderExtensionInterceptorFactory, error) {
return &HeaderExtensionInterceptorFactory{}, nil
}
// HeaderExtensionInterceptor adds transport wide sequence numbers as header extension to each RTP packet
type HeaderExtensionInterceptor struct {
interceptor.NoOp
nextSequenceNr uint32
}
const transportCCURI = "http://www.ietf.org/id/draft-holmer-rmcat-transport-wide-cc-extensions-01"
// BindLocalStream returns a writer that adds a rtp.TransportCCExtension
// header with increasing sequence numbers to each outgoing packet.
func (h *HeaderExtensionInterceptor) BindLocalStream(info *interceptor.StreamInfo, writer interceptor.RTPWriter) interceptor.RTPWriter {
var hdrExtID uint8
for _, e := range info.RTPHeaderExtensions {
if e.URI == transportCCURI {
hdrExtID = uint8(e.ID)
break
}
}
if hdrExtID == 0 { // Don't add header extension if ID is 0, because 0 is an invalid extension ID
return writer
}
return interceptor.RTPWriterFunc(func(header *rtp.Header, payload []byte, attributes interceptor.Attributes) (int, error) {
sequenceNumber := atomic.AddUint32(&h.nextSequenceNr, 1) - 1
tcc, err := (&rtp.TransportCCExtension{TransportSequence: uint16(sequenceNumber)}).Marshal()
if err != nil {
return 0, err
}
err = header.SetExtension(hdrExtID, tcc)
if err != nil {
return 0, err
}
return writer.Write(header, payload, attributes)
})
}
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