rtc_rtcp/

header.rs

//! The RTCP header.
//!
//! Four bytes on every packet: version and padding flags, a 5-bit count whose meaning depends on
//! the packet type, the [`PacketType`](crate::header::PacketType) itself, and a length in 32-bit words. The `*_SHIFT` and
//! `*_MASK` constants describe how the flags pack into the first octet.
//!
//! The length field is why RTCP is compound: several packets can be concatenated in one
//! datagram and walked by stepping over each header's length.
use shared::{
    error::{Error, Result},
    marshal::{Marshal, MarshalSize, Unmarshal},
};

use bytes::{Buf, BufMut};

/// PacketType specifies the type of an RTCP packet
/// RTCP packet types registered with IANA. See: <https://www.iana.org/assignments/rtp-parameters/rtp-parameters.xhtml#rtp-parameters-4>
#[derive(Default, Debug, Copy, Clone, PartialEq, Eq)]
#[repr(u8)]
pub enum PacketType {
    #[default]
    /// A packet type this crate does not model.
    Unsupported = 0,
    /// Sender Report ([RFC 3550] §6.4.1): a sender's timing and packet counts.
    SenderReport = 200, // RFC 3550, 6.4.1
    /// Receiver Report ([RFC 3550] §6.4.2): reception quality from a receiver.
    ReceiverReport = 201, // RFC 3550, 6.4.2
    /// Source Description ([RFC 3550] §6.5): CNAME and other source metadata.
    SourceDescription = 202, // RFC 3550, 6.5
    /// BYE ([RFC 3550] §6.6): the source is leaving the session.
    Goodbye = 203, // RFC 3550, 6.6
    /// APP ([RFC 3550] §6.7): application-defined data. Not modelled by this crate.
    ApplicationDefined = 204, // RFC 3550, 6.7 (unimplemented)
    /// Transport-layer feedback ([RFC 4585]): NACK and transport-wide CC.
    TransportSpecificFeedback = 205, // RFC 4585, 6051
    /// Payload-specific feedback ([RFC 4585] §6.3): PLI, FIR, SLI, REMB.
    PayloadSpecificFeedback = 206, // RFC 4585, 6.3
    /// Extended Report ([RFC 3611]).
    ExtendedReport = 207, // RFC 3611
}

/// Transport and Payload specific feedback messages overload the count field to act as a message type. those are listed here
pub const FORMAT_SLI: u8 = 2;
/// Transport and Payload specific feedback messages overload the count field to act as a message type. those are listed here
pub const FORMAT_PLI: u8 = 1;
/// Transport and Payload specific feedback messages overload the count field to act as a message type. those are listed here
pub const FORMAT_FIR: u8 = 4;
/// Transport and Payload specific feedback messages overload the count field to act as a message type. those are listed here
pub const FORMAT_TLN: u8 = 1;
/// Transport and Payload specific feedback messages overload the count field to act as a message type. those are listed here
pub const FORMAT_RRR: u8 = 5;
/// Transport and Payload specific feedback messages overload the count field to act as a message type. those are listed here
pub const FORMAT_REMB: u8 = 15;
/// Transport and Payload specific feedback messages overload the count field to act as a message type. those are listed here.
/// <https://tools.ietf.org/html/draft-holmer-rmcat-transport-wide-cc-extensions-01#page-5>
pub const FORMAT_TCC: u8 = 15;
/// FMT value for CCFB (Congestion Control Feedback) per RFC 8888
pub const FORMAT_CCFB: u8 = 11;

impl std::fmt::Display for PacketType {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        let s = match self {
            PacketType::Unsupported => "Unsupported",
            PacketType::SenderReport => "SR",
            PacketType::ReceiverReport => "RR",
            PacketType::SourceDescription => "SDES",
            PacketType::Goodbye => "BYE",
            PacketType::ApplicationDefined => "APP",
            PacketType::TransportSpecificFeedback => "TSFB",
            PacketType::PayloadSpecificFeedback => "PSFB",
            PacketType::ExtendedReport => "XR",
        };
        write!(f, "{s}")
    }
}

impl From<u8> for PacketType {
    fn from(b: u8) -> Self {
        match b {
            200 => PacketType::SenderReport,              // RFC 3550, 6.4.1
            201 => PacketType::ReceiverReport,            // RFC 3550, 6.4.2
            202 => PacketType::SourceDescription,         // RFC 3550, 6.5
            203 => PacketType::Goodbye,                   // RFC 3550, 6.6
            204 => PacketType::ApplicationDefined,        // RFC 3550, 6.7 (unimplemented)
            205 => PacketType::TransportSpecificFeedback, // RFC 4585, 6051
            206 => PacketType::PayloadSpecificFeedback,   // RFC 4585, 6.3
            207 => PacketType::ExtendedReport,            // RFC 3611
            _ => PacketType::Unsupported,
        }
    }
}

/// The RTP/RTCP version this crate speaks.
pub const RTP_VERSION: u8 = 2;
/// Bit offset of the version field in the first header octet.
pub const VERSION_SHIFT: u8 = 6;
/// Bit mask of the version field once shifted.
pub const VERSION_MASK: u8 = 0x3;
/// Bit offset of the padding flag.
pub const PADDING_SHIFT: u8 = 5;
/// Bit mask of the padding flag once shifted.
pub const PADDING_MASK: u8 = 0x1;
/// Bit offset of the report/source count field.
pub const COUNT_SHIFT: u8 = 0;
/// Bit mask of the report/source count field.
pub const COUNT_MASK: u8 = 0x1f;

/// Length of the RTCP header in bytes.
pub const HEADER_LENGTH: usize = 4;
/// The largest report count the 5-bit field can hold.
pub const COUNT_MAX: usize = (1 << 5) - 1;
/// Length of an SSRC in bytes.
pub const SSRC_LENGTH: usize = 4;
/// The longest SDES item value, bounded by its one-byte length field.
pub const SDES_MAX_OCTET_COUNT: usize = (1 << 8) - 1;

// https://datatracker.ietf.org/doc/html/rfc5104#section-4.3.1
//
// The FCI field MUST contain one or more FIR entries.
//
// https://datatracker.ietf.org/doc/html/rfc5104#section-4.3.1.1
//
// The length of the FIR feedback message MUST be set to
//    2+2*N, where N is the number of FCI entries.
/// The smallest valid FIR packet, in bytes.
pub const FIR_MIN_OCTET_COUNT: usize = 20;

/// A Header is the common header shared by all RTCP packets
#[derive(Debug, PartialEq, Eq, Default, Clone)]
pub struct Header {
    /// If the padding bit is set, this individual RTCP packet contains
    /// some additional padding octets at the end which are not part of
    /// the control information but are included in the length field.
    pub padding: bool,
    /// The number of reception reports, sources contained or FMT in this packet (depending on the Type)
    pub count: u8,
    /// The RTCP packet type for this packet
    pub packet_type: PacketType,
    /// The length of this RTCP packet in 32-bit words minus one,
    /// including the header and any padding.
    pub length: u16,
}

/// Marshal encodes the Header in binary
impl MarshalSize for Header {
    fn marshal_size(&self) -> usize {
        HEADER_LENGTH
    }
}

impl Marshal for Header {
    fn marshal_to(&self, mut buf: &mut [u8]) -> Result<usize> {
        if self.count > 31 {
            return Err(Error::InvalidHeader);
        }
        if buf.remaining_mut() < HEADER_LENGTH {
            return Err(Error::BufferTooShort);
        }

        /*
         *  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|    RC   |   PT=SR=200   |             length            |
         * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
         */
        let b0 = (RTP_VERSION << VERSION_SHIFT)
            | ((self.padding as u8) << PADDING_SHIFT)
            | (self.count << COUNT_SHIFT);

        buf.put_u8(b0);
        buf.put_u8(self.packet_type as u8);
        buf.put_u16(self.length);

        Ok(HEADER_LENGTH)
    }
}

impl Unmarshal for Header {
    /// Unmarshal decodes the Header from binary
    fn unmarshal<B>(raw_packet: &mut B) -> Result<Self>
    where
        Self: Sized,
        B: Buf,
    {
        if raw_packet.remaining() < HEADER_LENGTH {
            return Err(Error::PacketTooShort);
        }

        /*
         *  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|    RC   |      PT       |             length            |
         * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
         */
        let b0 = raw_packet.get_u8();
        let version = (b0 >> VERSION_SHIFT) & VERSION_MASK;
        if version != RTP_VERSION {
            return Err(Error::BadVersion);
        }

        let padding = ((b0 >> PADDING_SHIFT) & PADDING_MASK) > 0;
        let count = (b0 >> COUNT_SHIFT) & COUNT_MASK;
        let packet_type = PacketType::from(raw_packet.get_u8());
        let length = raw_packet.get_u16();

        Ok(Header {
            padding,
            count,
            packet_type,
            length,
        })
    }
}

#[cfg(test)]
mod test {
    use super::*;
    use bytes::Bytes;

    #[test]
    fn test_header_unmarshal() {
        let tests = vec![
            (
                "valid",
                Bytes::from_static(&[
                    // v=2, p=0, count=1, RR, len=7
                    0x81u8, 0xc9, 0x00, 0x07,
                ]),
                Header {
                    padding: false,
                    count: 1,
                    packet_type: PacketType::ReceiverReport,
                    length: 7,
                },
                None,
            ),
            (
                "also valid",
                Bytes::from_static(&[
                    // v=2, p=1, count=1, BYE, len=7
                    0xa1, 0xcc, 0x00, 0x07,
                ]),
                Header {
                    padding: true,
                    count: 1,
                    packet_type: PacketType::ApplicationDefined,
                    length: 7,
                },
                None,
            ),
            (
                "bad version",
                Bytes::from_static(&[
                    // v=0, p=0, count=0, RR, len=4
                    0x00, 0xc9, 0x00, 0x04,
                ]),
                Header {
                    padding: false,
                    count: 0,
                    packet_type: PacketType::Unsupported,
                    length: 0,
                },
                Some(Error::BadVersion),
            ),
        ];

        for (name, data, want, want_error) in tests {
            let buf = &mut data.clone();
            let got = Header::unmarshal(buf);

            assert_eq!(
                got.is_err(),
                want_error.is_some(),
                "Unmarshal {name}: err = {got:?}, want {want_error:?}"
            );

            if let Some(want_error) = want_error {
                let got_err = got.err().unwrap();
                assert_eq!(
                    want_error, got_err,
                    "Unmarshal {name}: err = {got_err:?}, want {want_error:?}",
                );
            } else {
                let actual = got.unwrap();
                assert_eq!(
                    actual, want,
                    "Unmarshal {name}: got {actual:?}, want {want:?}"
                );
            }
        }
    }

    #[test]
    fn test_header_roundtrip() {
        let tests = vec![
            (
                "valid",
                Header {
                    padding: true,
                    count: 31,
                    packet_type: PacketType::SenderReport,
                    length: 4,
                },
                None,
            ),
            (
                "also valid",
                Header {
                    padding: false,
                    count: 28,
                    packet_type: PacketType::ReceiverReport,
                    length: 65535,
                },
                None,
            ),
            (
                "invalid count",
                Header {
                    padding: false,
                    count: 40,
                    packet_type: PacketType::Unsupported,
                    length: 0,
                },
                Some(Error::InvalidHeader),
            ),
        ];

        for (name, want, want_error) in tests {
            let got = want.marshal();

            assert_eq!(
                got.is_ok(),
                want_error.is_none(),
                "Marshal {name}: err = {got:?}, want {want_error:?}"
            );

            if let Some(err) = want_error {
                let got_err = got.err().unwrap();
                assert_eq!(
                    err, got_err,
                    "Unmarshal {name} rr: err = {got_err:?}, want {err:?}",
                );
            } else {
                let data = got.ok().unwrap();
                let buf = &mut data.clone();
                let actual = Header::unmarshal(buf).unwrap_or_else(|_| panic!("Unmarshal {name}"));

                assert_eq!(
                    actual, want,
                    "{name} round trip: got {actual:?}, want {want:?}"
                )
            }
        }
    }
}