1
use super::extend_u16;
2
use super::{FeedbackMessageType, ReportList, RtcpHeader, RtcpPacket, SeqNo};
3
use super::{RtcpType, Ssrc, TransportType};
4
 
5
use super::list::private::WordSized;
6
 
7
/// A NACK entry indiciating packets missing.
8
#[derive(Debug, Clone, PartialEq, Eq)]
9
pub struct Nack {
10
    /// Sender of this feedback. Mostly irrelevant, but part of RTCP packets.
11
    pub sender_ssrc: Ssrc,
12
    /// The SSRC this nack reports missing packets for.
13
    pub ssrc: Ssrc,
14
    /// The missing nack. This can be multiple segments.
15
    pub reports: ReportList<NackEntry>,
16
}
17
 
18
/// A range of sequence numbers missing.
19
#[allow(missing_docs)]
20
#[derive(Debug, PartialEq, Eq, Default, Clone, Copy)]
21
pub struct NackEntry {
22
    pub pid: u16,
23
    pub blp: u16,
24
}
25
 
26
impl RtcpPacket for Nack {
27
    fn header(&self) -> RtcpHeader {
28
        RtcpHeader {
29
            rtcp_type: RtcpType::TransportLayerFeedback,
30
            feedback_message_type: FeedbackMessageType::TransportFeedback(TransportType::Nack),
31
            words_less_one: (self.length_words() - 1) as u16,
32
        }
33
    }
34
 
35
    fn length_words(&self) -> usize {
36
        // header
37
        // sender SSRC
38
        // media SSRC
39
        // 1 word per NackPair
40
        1 + 2 + self.reports.len()
41
    }
42
 
43
    fn write_to(&self, buf: &mut [u8]) -> usize {
44
        self.header().write_to(&mut buf[..4]);
45
        buf[4..8].copy_from_slice(&self.sender_ssrc.to_be_bytes());
46
        buf[8..12].copy_from_slice(&self.ssrc.to_be_bytes());
47
        let mut buf = &mut buf[12..];
48
        for r in &self.reports {
49
            buf[0..2].copy_from_slice(&r.pid.to_be_bytes());
50
            buf[2..4].copy_from_slice(&r.blp.to_be_bytes());
51
            buf = &mut buf[4..];
52
        }
53
        self.length_words() * 4
54
    }
55
}
56
 
57
impl WordSized for NackEntry {
58
    fn word_size(&self) -> usize {
59
        1
60
    }
61
}
62
 
63
impl<'a> TryFrom<&'a [u8]> for Nack {
64
    type Error = &'static str;
65
 
66
    fn try_from(buf: &'a [u8]) -> Result<Self, Self::Error> {
67
        if buf.len() < 12 {
68
            return Err("Nack less than 12 bytes");
69
        }
70
 
71
        let sender_ssrc = u32::from_be_bytes([buf[0], buf[1], buf[2], buf[3]]).into();
72
        let ssrc = u32::from_be_bytes([buf[4], buf[5], buf[6], buf[7]]).into();
73
 
74
        let mut reports = ReportList::new();
75
 
76
        let mut buf = &buf[8..];
77
        let count = buf.len() / 4;
78
        let max = count.min(31);
79
 
80
        for _ in 0..max {
81
            let pid = u16::from_be_bytes([buf[0], buf[1]]);
82
            let blp = u16::from_be_bytes([buf[2], buf[3]]);
83
            reports.push(NackEntry { pid, blp });
84
            buf = &buf[4..];
85
        }
86
 
87
        Ok(Nack {
88
            sender_ssrc,
89
            ssrc,
90
            reports,
91
        })
92
    }
93
}
94
 
95
impl NackEntry {
96
    /// Iterator over sequence numbers missing.
97
    ///
98
    /// The given sequence number is used to interpret ROC.
99
    pub fn into_iter(self, seq_no: SeqNo) -> impl Iterator<Item = SeqNo> {
100
        NackEntryIterator(self, 0, seq_no)
101
    }
102
}
103
 
104
pub struct NackEntryIterator(NackEntry, u16, SeqNo);
105
 
106
impl Iterator for NackEntryIterator {
107
    type Item = SeqNo;
108
 
109
    fn next(&mut self) -> Option<Self::Item> {
110
        let seq_16 = if self.1 == 0 {
111
            self.1 += 1;
112
            self.0.pid
113
        } else {
114
            loop {
115
                if self.1 >= 17 {
116
                    return None;
117
                }
118
                let i = self.1 - 1;
119
                self.1 += 1;
120
                if 1 << i & self.0.blp > 0 {
121
                    break self.0.pid.wrapping_add(self.1 - 1);
122
                }
123
            }
124
        };
125
        let l = extend_u16(Some(*self.2), seq_16);
126
        Some(l.into())
127
    }
128
}
129
 
130
#[cfg(test)]
131
mod test {
132
    use super::*;
133
 
134
    #[test]
135
    fn nack_entry_iter() {
136
        // 196_618
137
        let seq_no: SeqNo = (65_536_u64 * 3 + 10).into();
138
 
139
        // 196_508
140
        let pid = (65_536_u32 - 100) as u16;
141
 
142
        println!("{seq_no:?} {pid:?}");
143
 
144
        // 196_509, 196_512, 196_524
145
        let blp = 0b1000_0000_0000_1001;
146
 
147
        let entry = NackEntry { pid, blp };
148
 
149
        let nacks: Vec<_> = entry.into_iter(seq_no).collect();
150
 
151
        assert_eq!(
152
            nacks,
153
            vec![196508.into(), 196509.into(), 196512.into(), 196524.into()]
154
        );
155
    }
156
}