dvb_si/descriptors/
ecm_repetition_rate.rs

1//! ECM Repetition Rate Descriptor — ETSI EN 301 192 §9.9, Table 44 (tag 0x78).
2//!
3//! Carried in the PMT to advertise the maximum interval between ECMs for a
4//! given CA system. Per en_301_192.md "Table 44 — ECM repetition rate
5//! descriptor" (PDF p. 56) the body is: CA_system_ID(16) +
6//! ECM_repetition_rate(16) + trailing private_data_byte run.
7
8pub use super::ca::ca_system_name;
9use super::descriptor_body;
10use crate::error::{Error, Result};
11use dvb_common::{Parse, Serialize};
12
13/// Descriptor tag for ECM_repetition_rate_descriptor.
14pub const TAG: u8 = 0x78;
15const HEADER_LEN: usize = 2;
16const FIXED_LEN: usize = 4;
17
18/// ECM Repetition Rate Descriptor.
19#[derive(Debug, Clone, PartialEq, Eq)]
20#[cfg_attr(feature = "serde", derive(serde::Serialize))]
21#[cfg_attr(feature = "yoke", derive(yoke::Yokeable))]
22pub struct EcmRepetitionRateDescriptor<'a> {
23    /// 16-bit CA_system_ID this rate applies to.
24    pub ca_system_id: u16,
25    /// 16-bit ECM_repetition_rate (max ms between successive ECMs).
26    pub ecm_repetition_rate: u16,
27    /// Trailing private_data bytes.
28    pub private_data: &'a [u8],
29}
30
31impl<'a> Parse<'a> for EcmRepetitionRateDescriptor<'a> {
32    type Error = crate::error::Error;
33    fn parse(bytes: &'a [u8]) -> Result<Self> {
34        let body = descriptor_body(
35            bytes,
36            TAG,
37            "EcmRepetitionRateDescriptor",
38            "unexpected tag for ECM_repetition_rate_descriptor",
39        )?;
40        if body.len() < FIXED_LEN {
41            return Err(Error::InvalidDescriptor {
42                tag: TAG,
43                reason: "ECM_repetition_rate_descriptor body shorter than 4 bytes",
44            });
45        }
46        let ca_system_id = u16::from_be_bytes([body[0], body[1]]);
47        let ecm_repetition_rate = u16::from_be_bytes([body[2], body[3]]);
48        let private_data = &body[FIXED_LEN..];
49        Ok(Self {
50            ca_system_id,
51            ecm_repetition_rate,
52            private_data,
53        })
54    }
55}
56
57impl Serialize for EcmRepetitionRateDescriptor<'_> {
58    type Error = crate::error::Error;
59    fn serialized_len(&self) -> usize {
60        HEADER_LEN + FIXED_LEN + self.private_data.len()
61    }
62
63    fn serialize_into(&self, buf: &mut [u8]) -> Result<usize> {
64        if FIXED_LEN + self.private_data.len() > u8::MAX as usize {
65            return Err(Error::InvalidDescriptor {
66                tag: TAG,
67                reason: "ECM_repetition_rate_descriptor body exceeds 255 bytes",
68            });
69        }
70        let len = self.serialized_len();
71        if buf.len() < len {
72            return Err(Error::OutputBufferTooSmall {
73                need: len,
74                have: buf.len(),
75            });
76        }
77        buf[0] = TAG;
78        buf[1] = (FIXED_LEN + self.private_data.len()) as u8;
79        buf[2..4].copy_from_slice(&self.ca_system_id.to_be_bytes());
80        buf[4..6].copy_from_slice(&self.ecm_repetition_rate.to_be_bytes());
81        buf[HEADER_LEN + FIXED_LEN..len].copy_from_slice(self.private_data);
82        Ok(len)
83    }
84}
85impl<'a> crate::traits::DescriptorDef<'a> for EcmRepetitionRateDescriptor<'a> {
86    const TAG: u8 = TAG;
87    const NAME: &'static str = "ECM_REPETITION_RATE";
88}
89
90#[cfg(test)]
91mod tests {
92    use super::*;
93
94    #[test]
95    fn parse_no_private_data() {
96        let bytes = [TAG, 4, 0x06, 0x48, 0x01, 0xF4];
97        let d = EcmRepetitionRateDescriptor::parse(&bytes).unwrap();
98        assert_eq!(d.ca_system_id, 0x0648);
99        assert_eq!(d.ecm_repetition_rate, 500);
100        assert!(d.private_data.is_empty());
101    }
102
103    #[test]
104    fn parse_with_private_data() {
105        let bytes = [TAG, 6, 0x05, 0x00, 0x00, 0xC8, 0xAA, 0xBB];
106        let d = EcmRepetitionRateDescriptor::parse(&bytes).unwrap();
107        assert_eq!(d.ca_system_id, 0x0500);
108        assert_eq!(d.ecm_repetition_rate, 200);
109        assert_eq!(d.private_data, &[0xAA, 0xBB]);
110    }
111
112    #[test]
113    fn parse_rejects_wrong_tag() {
114        assert!(matches!(
115            EcmRepetitionRateDescriptor::parse(&[0x77, 4, 0, 0, 0, 0]).unwrap_err(),
116            Error::InvalidDescriptor { tag: 0x77, .. }
117        ));
118    }
119
120    #[test]
121    fn parse_rejects_body_too_short() {
122        let bytes = [TAG, 3, 0, 0, 0];
123        assert!(matches!(
124            EcmRepetitionRateDescriptor::parse(&bytes).unwrap_err(),
125            Error::InvalidDescriptor { .. }
126        ));
127    }
128
129    #[test]
130    fn parse_rejects_length_overrunning_buffer() {
131        let bytes = [TAG, 6, 0, 0, 0, 0];
132        assert!(matches!(
133            EcmRepetitionRateDescriptor::parse(&bytes).unwrap_err(),
134            Error::BufferTooShort { .. }
135        ));
136    }
137
138    #[test]
139    fn serialize_round_trip() {
140        let d = EcmRepetitionRateDescriptor {
141            ca_system_id: 0x0B00,
142            ecm_repetition_rate: 1000,
143            private_data: &[0x01, 0x02],
144        };
145        let mut buf = vec![0u8; d.serialized_len()];
146        d.serialize_into(&mut buf).unwrap();
147        assert_eq!(EcmRepetitionRateDescriptor::parse(&buf).unwrap(), d);
148    }
149
150    #[test]
151    fn serialize_rejects_too_small_buffer() {
152        let d = EcmRepetitionRateDescriptor {
153            ca_system_id: 0,
154            ecm_repetition_rate: 0,
155            private_data: &[],
156        };
157        let mut buf = vec![0u8; 3];
158        assert!(matches!(
159            d.serialize_into(&mut buf).unwrap_err(),
160            Error::OutputBufferTooSmall { .. }
161        ));
162    }
163
164    #[cfg(feature = "serde")]
165    #[test]
166    fn serde_serializes_to_stable_json() {
167        // Borrowed `&[u8]` cannot deserialize from a JSON number array, so we
168        // assert the Serialize impl is wired and emits stable JSON.
169        let d = EcmRepetitionRateDescriptor {
170            ca_system_id: 0x0648,
171            ecm_repetition_rate: 480,
172            private_data: &[0xFE],
173        };
174        let j = serde_json::to_string(&d).unwrap();
175        // Valid, re-parseable JSON (key order is map-defined, so we do not
176        // assert byte-for-byte string stability).
177        let _v: serde_json::Value = serde_json::from_str(&j).unwrap();
178        assert!(j.contains("ca_system_id"));
179    }
180}
dvb_si/descriptors/ecm_repetition_rate.rs

dvb_si/descriptors/
ecm_repetition_rate.rs
