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Voice: Add packet correction for RTCP per RFC3350

This commit is contained in:
diamondburned 2021-02-22 12:32:55 -08:00
parent a939a26cab
commit 3b5a4ed94d
1 changed files with 59 additions and 8 deletions
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67
voice/udp/udp.go
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@ -230,8 +230,8 @@ func (c *Connection) write(b []byte) (int, error) {
}
// ReadPacket reads the UDP connection and returns a packet if successful. This
// packet is not thread-safe to use, as it shares recvBuf's buffer. Byte slices inside
// it must be copied or used before the next call to ReadPacket happens.
// packet is not thread-safe to use, as it shares recvBuf's buffer. Byte slices
// inside it must be copied or used before the next call to ReadPacket happens.
func (c *Connection) ReadPacket() (*Packet, error) {
for {
rlen, err := c.conn.Read(c.recvBuf)
@ -254,17 +254,68 @@ func (c *Connection) ReadPacket() (*Packet, error) {
var ok bool
c.recvPacket.Opus, ok = secretbox.Open(c.recvOpus[:0], c.recvBuf[packetHeaderSize:rlen], &c.recvNonce, &c.secret)
c.recvPacket.Opus, ok = secretbox.Open(
c.recvOpus[:0], c.recvBuf[packetHeaderSize:rlen], &c.recvNonce, &c.secret)
if !ok {
return nil, ErrDecryptionFailed
}
ext := binary.BigEndian.Uint16(c.recvPacket.Opus[0:2])
// Partial structure of the RTP header for reference
//
// 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|X| CC |M| PT | sequence number |
// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// | timestamp |
// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
//
// References
//
// https://tools.ietf.org/html/rfc3550#section-5.1
//
if c.recvPacket.VersionFlags&0x10 != 0 && ext == 0xBEDE {
// TODO: Implement RFC 5285
c.recvPacket.Opus = c.recvPacket.Opus[8:]
// We first check VersionFlags (8-bit) for whether or not the 4th bit
// (extension) is set. The value of 0x10 is 0b00010000. RFC3550 section
// 5.1 explains the extension bit as:
//
// If the extension bit is set, the fixed header MUST be followed by
// exactly one header extension, with a format defined in Section
// 5.3.1.
//
isExtension := c.recvPacket.VersionFlags&0x10 == 0x10
// We then check for whether or not the marker bit (9th bit) is set. The
// 9th bit is carried over to the second byte (Type), so we check its
// presence with 0x80, or 0b10000000. RFC3550 section 5.1 explains the
// marker bit as:
//
// The interpretation of the marker is defined by a profile. It is
// intended to allow significant events such as frame boundaries to
// be marked in the packet stream. A profile MAY define additional
// marker bits or specify that there is no marker bit by changing
// the number of bits in the payload type field (see Section 5.3).
//
// RFC3350 section 12.1 also writes:
//
// When the RTCP packet type field is compared to the corresponding
// octet of the RTP header, this range corresponds to the marker bit
// being 1 (which it usually is not in data packets) and to the high
// bit of the standard payload type field being 1 (since the static
// payload types are typically defined in the low half).
//
// This implies that, when the marker bit is 1, the received packet is
// an RTCP packet and NOT an RTP packet; therefore, we must ignore the
// unknown sections, so we do a (NOT isMarker) check below.
isMarker := c.recvPacket.Type&0x80 != 0x0
if isExtension && !isMarker {
extLen := binary.BigEndian.Uint16(c.recvPacket.Opus[2:4])
shift := 4 + 4*int(extLen)
if len(c.recvPacket.Opus) > shift {
c.recvPacket.Opus = c.recvPacket.Opus[shift:]
}
}
return c.recvPacket, nil