Add allocation-free API for routing RTCP

application_defined.go

@@ -110,6 +110,17 @@ func (a *ApplicationDefined) Unmarshal(rawPacket []byte) error {
 	return nil
 }
 
+func appendApplicationDefinedSSRCs(dst []uint32, header Header, pkt []byte) ([]uint32, error) {
+	if header.Type != TypeApplicationDefined {
+		return dst, errWrongType
+	}
+	if len(pkt) < 12 {
+		return dst, errPacketTooShort
+	}
+
+	return append(dst, binary.BigEndian.Uint32(pkt[4:8])), nil
+}
+
 // MarshalSize returns the size of the packet once marshaled.
 func (a *ApplicationDefined) MarshalSize() int {
 	dataLength := len(a.Data)

extended_report.go

@@ -4,6 +4,7 @@
 package rtcp
 
 import (
+	"encoding/binary"
 	"fmt"
 )
 
@@ -661,6 +662,51 @@ func (x *ExtendedReport) Unmarshal(b []byte) error {
 	return nil
 }
 
+const (
+	xrHeaderLength   = 4
+	dlrrReportLength = 12
+)
+
+func appendXRSSRCs(dst []uint32, header Header, pkt []byte) ([]uint32, error) {
+	if header.Type != TypeExtendedReport {
+		return dst, errWrongType
+	}
+	if len(pkt) < headerLength+ssrcLength {
+		return dst, errPacketTooShort
+	}
+	// The sender's SSRC, then one SSRC per report block that refers to a
+	// source (the receiver reference time block does not); see
+	// ExtendedReport for the packet layout.
+	dst = append(dst, binary.BigEndian.Uint32(pkt[headerLength:]))
+	for offset := headerLength + ssrcLength; offset < len(pkt); {
+		if offset+xrHeaderLength > len(pkt) {
+			return dst, errPacketTooShort
+		}
+		// Each block begins with an XRHeader.
+		blockLen := (int(binary.BigEndian.Uint16(pkt[offset+2:])) + 1) * 4
+		// A block whose declared length overruns the packet is truncated at
+		// the packet end, mirroring packetBuffer.split.
+		if offset+blockLen > len(pkt) {
+			blockLen = len(pkt) - offset
+		}
+		switch pkt[offset] {
+		case LossRLEReportBlockType, DuplicateRLEReportBlockType, PacketReceiptTimesReportBlockType,
+			StatisticsSummaryReportBlockType, VoIPMetricsReportBlockType:
+			if blockLen < xrHeaderLength+ssrcLength {
+				return dst, errPacketTooShort
+			}
+			dst = append(dst, binary.BigEndian.Uint32(pkt[offset+xrHeaderLength:]))
+		case DLRRReportBlockType:
+			for sub := offset + xrHeaderLength; sub+dlrrReportLength <= offset+blockLen; sub += dlrrReportLength {
+				dst = append(dst, binary.BigEndian.Uint32(pkt[sub:]))
+			}
+		}
+		offset += blockLen
+	}
+
+	return dst, nil
+}
+
 // DestinationSSRC returns an array of SSRC values that this packet refers to.
 func (x *ExtendedReport) DestinationSSRC() []uint32 {
 	ssrc := make([]uint32, 0, len(x.Reports)+1)

full_intra_request.go

@@ -86,6 +86,21 @@ func (p *FullIntraRequest) Unmarshal(rawPacket []byte) error {
 	return nil
 }
 
+func appendFIRSSRCs(dst []uint32, header Header, pkt []byte) ([]uint32, error) {
+	if header.Type != TypePayloadSpecificFeedback || header.Count != FormatFIR {
+		return dst, errWrongType
+	}
+	if 4*int(header.Length)-firOffset <= 0 || (4*int(header.Length))%8 != 0 {
+		return dst, errBadLength
+	}
+	for i := headerLength + firOffset; i < (headerLength + 4*int(header.Length)); i += 8 {
+		entry := pkt[i : i+8]
+		dst = append(dst, binary.BigEndian.Uint32(entry))
+	}
+
+	return dst, nil
+}
+
 // Header returns the Header associated with this packet.
 func (p *FullIntraRequest) Header() Header {
 	return Header{

goodbye.go

@@ -121,6 +121,23 @@ func (g *Goodbye) Unmarshal(rawPacket []byte) error {
 	return nil
 }
 
+func appendGoodbyeSSRCs(dst []uint32, header Header, pkt []byte) ([]uint32, error) {
+	if header.Type != TypeGoodbye {
+		return dst, errWrongType
+	}
+	reasonOffset := int(headerLength + header.Count*ssrcLength)
+	if reasonOffset > len(pkt) {
+		return dst, errPacketTooShort
+	}
+	for i := 0; i < int(header.Count); i++ {
+		offset := headerLength + i*ssrcLength
+
+		dst = append(dst, binary.BigEndian.Uint32(pkt[offset:]))
+	}
+
+	return dst, nil
+}
+
 // Header returns the Header associated with this packet.
 func (g *Goodbye) Header() Header {
 	return Header{

raw_packet.go

@@ -3,7 +3,10 @@
 
 package rtcp
 
-import "fmt"
+import (
+	"encoding/binary"
+	"fmt"
+)
 
 // RawPacket represents an unparsed RTCP packet. It's returned by Unmarshal when
 // a packet with an unknown type is encountered.
@@ -51,3 +54,136 @@ func (r RawPacket) String() string {
 func (r RawPacket) MarshalSize() int {
 	return len(r)
 }
+
+// UnmarshalRaw takes an entire udp datagram (which may consist of multiple
+// RTCP packets) and returns the raw packets it contains, without unmarshaling
+// their contents.
+//
+// The returned packets are subslices of data, not copies.
+func UnmarshalRaw(data []byte) ([]RawPacket, error) {
+	return AppendRawPackets(nil, data)
+}
+
+// AppendRawPackets appends the raw packets of the datagram data, as produced
+// by UnmarshalRaw, to dst and returns the extended slice. On error dst is
+// returned unchanged.
+func AppendRawPackets(dst []RawPacket, data []byte) ([]RawPacket, error) {
+	orig := dst
+	found := 0
+	for rest := data; len(rest) > 0; {
+		var header Header
+		if err := header.Unmarshal(rest); err != nil {
+			return orig, err
+		}
+		size := (int(header.Length) + 1) * 4
+		if size > len(rest) {
+			return orig, errPacketTooShort
+		}
+		dst = append(dst, RawPacket(rest[:size:size]))
+		rest = rest[size:]
+		found++
+	}
+	if found == 0 {
+		return orig, errInvalidHeader
+	}
+
+	return dst, nil
+}
+
+// ParseDestinationSSRC parses the destination SSRCs of the packet out of its
+// raw bytes, appends them to dst, and returns the extended slice. It reports
+// the SSRCs that Unmarshal followed by Packet.DestinationSSRC would for every
+// packet type known to this package; unknown packet types have none. r must
+// be a single RTCP packet, as produced by UnmarshalRaw.
+//
+// Only the structure needed to locate the SSRCs is validated; a packet
+// accepted by this method may still fail a full Unmarshal.
+//
+// ParseDestinationSSRC will only allocate in order to resize dst as needed;
+// the parsing itself is allocation-free.
+//
+//nolint:cyclop
+func (r RawPacket) ParseDestinationSSRC(dst []uint32) ([]uint32, error) {
+	pkt := []byte(r)
+	var header Header
+	if err := header.Unmarshal(pkt); err != nil {
+		return dst, err
+	}
+	if size := (int(header.Length) + 1) * 4; size != len(pkt) {
+		return dst, errBadLength
+	}
+
+	switch header.Type {
+	case TypeSenderReport:
+		return appendSenderReportSSRCs(dst, header, pkt)
+	case TypeReceiverReport:
+		return appendReceiverReportSSRCs(dst, header, pkt)
+	case TypeSourceDescription:
+		return appendSourceDescriptionSSRCs(dst, header, pkt)
+	case TypeGoodbye:
+		return appendGoodbyeSSRCs(dst, header, pkt)
+	case TypeApplicationDefined:
+		return appendApplicationDefinedSSRCs(dst, header, pkt)
+	case TypeTransportSpecificFeedback:
+		switch header.Count {
+		case FormatRRR:
+			var rrr RapidResynchronizationRequest
+			if err := rrr.Unmarshal(pkt); err != nil {
+				return dst, err
+			}
+
+			return append(dst, rrr.MediaSSRC), nil
+		case FormatTLN, FormatTCC:
+			return appendMediaSSRC(dst, header, pkt)
+		case FormatCCFB:
+			return appendCCFBSSRCs(dst, header, pkt)
+		}
+	case TypePayloadSpecificFeedback:
+		switch header.Count {
+		case FormatPLI:
+			var pli PictureLossIndication
+			if err := pli.Unmarshal(pkt); err != nil {
+				return dst, err
+			}
+
+			return append(dst, pli.MediaSSRC), nil
+		case FormatSLI:
+			return appendMediaSSRC(dst, header, pkt)
+		case FormatFIR:
+			return appendFIRSSRCs(dst, header, pkt)
+		case FormatREMB:
+			return appendREMBSSRCs(dst, header, pkt)
+		}
+	case TypeExtendedReport:
+		return appendXRSSRCs(dst, header, pkt)
+	}
+
+	return dst, nil
+}
+
+// appendMediaSSRC handles the feedback packets whose only destination is the
+// media SSRC in the fixed part of the packet and whose full Unmarshal
+// allocates (SLI, NACK, TWCC). They share the common packet format for
+// feedback messages:
+//
+// https://tools.ietf.org/html/rfc4585#section-6.1
+//
+//	 0                   1                   2                   3
+//	 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+//	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+//	|V=2|P|   FMT   |       PT      |          length               |
+//	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+//	|                  SSRC of packet sender                        |
+//	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+//	|                  SSRC of media source                         |
+//	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+//	:            Feedback Control Information (FCI)                 :
+//	:                                                               :
+//	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+func appendMediaSSRC(dst []uint32, _ Header, pkt []byte) ([]uint32, error) {
+	if len(pkt) < (headerLength + (ssrcLength * 2)) {
+		return dst, errPacketTooShort
+	}
+
+	return append(dst, binary.BigEndian.Uint32(pkt[headerLength+ssrcLength:])), nil
+}