dvb_si/tables/
tot.rs

1//! Time Offset Table — ETSI EN 300 468 §5.2.6.
2//!
3//! Carried on PID 0x0014 with table_id 0x73. Structure:
4//!   5-byte UTC time + descriptor loop + 4-byte CRC32.
5//!
6//! The TOT is the spec's framing exception: `section_syntax_indicator` SHALL
7//! be `0b0` (§5.2.6: "This 1-bit field shall be set to 0b0") yet the section
8//! still ends with a CRC_32. Do not route TOT bytes through the generic
9//! [`crate::section::Section`] short-form path — it would fold the CRC into
10//! the payload. Parse with [`Tot::parse`] directly.
11
12use crate::descriptors::DescriptorLoop;
13use crate::error::{Error, Result};
14use crate::traits::Table;
15use dvb_common::{Parse, Serialize};
16
17/// table_id for Time Offset Table.
18pub const TABLE_ID: u8 = 0x73;
19/// Well-known PID on which TOT is carried (same as TDT).
20pub const PID: u16 = 0x0014;
21
22const HEADER_LEN: usize = 3;
23const UTC_TIME_LEN: usize = 5;
24const DESC_LOOP_LEN_FIELD: usize = 2;
25const CRC_LEN: usize = 4;
26
27/// Time Offset Table.
28#[derive(Debug, Clone, PartialEq, Eq)]
29#[cfg_attr(feature = "serde", derive(serde::Serialize))]
30#[cfg_attr(feature = "yoke", derive(yoke::Yokeable))]
31pub struct Tot<'a> {
32    /// Raw 5-byte UTC time (16-bit MJD + 24-bit BCD HHMMSS).
33    pub utc_time_raw: [u8; 5],
34    /// Raw descriptor bytes (typically local_time_offset_descriptor tag 0x58).
35    /// Descriptor loop. Serializes as the typed descriptor sequence;
36    /// `.raw()` yields the wire bytes.
37    pub descriptors: DescriptorLoop<'a>,
38}
39
40impl<'a> Parse<'a> for Tot<'a> {
41    type Error = crate::error::Error;
42    fn parse(bytes: &'a [u8]) -> Result<Self> {
43        let min_len = HEADER_LEN + UTC_TIME_LEN + DESC_LOOP_LEN_FIELD + CRC_LEN;
44        if bytes.len() < min_len {
45            return Err(Error::BufferTooShort {
46                need: min_len,
47                have: bytes.len(),
48                what: "Tot",
49            });
50        }
51        if bytes[0] != TABLE_ID {
52            return Err(Error::UnexpectedTableId {
53                table_id: bytes[0],
54                what: "Tot",
55                expected: &[TABLE_ID],
56            });
57        }
58        let section_length = ((bytes[1] & 0x0F) as u16) << 8 | bytes[2] as u16;
59        let total = HEADER_LEN + section_length as usize;
60        if bytes.len() < total {
61            return Err(Error::SectionLengthOverflow {
62                declared: section_length as usize,
63                available: bytes.len() - HEADER_LEN,
64            });
65        }
66        let utc_time_raw = [bytes[3], bytes[4], bytes[5], bytes[6], bytes[7]];
67        let dl_pos = HEADER_LEN + UTC_TIME_LEN;
68        let dl = (((bytes[dl_pos] & 0x0F) as usize) << 8) | bytes[dl_pos + 1] as usize;
69        let d_start = dl_pos + DESC_LOOP_LEN_FIELD;
70        let d_end = d_start + dl;
71        if d_end > total - CRC_LEN {
72            return Err(Error::SectionLengthOverflow {
73                declared: dl,
74                available: total - CRC_LEN - d_start,
75            });
76        }
77        Ok(Tot {
78            utc_time_raw,
79            descriptors: DescriptorLoop::new(&bytes[d_start..d_end]),
80        })
81    }
82}
83
84impl Serialize for Tot<'_> {
85    type Error = crate::error::Error;
86    fn serialized_len(&self) -> usize {
87        HEADER_LEN + UTC_TIME_LEN + DESC_LOOP_LEN_FIELD + self.descriptors.len() + CRC_LEN
88    }
89    fn serialize_into(&self, buf: &mut [u8]) -> Result<usize> {
90        let len = self.serialized_len();
91        if buf.len() < len {
92            return Err(Error::OutputBufferTooSmall {
93                need: len,
94                have: buf.len(),
95            });
96        }
97        let section_length = (len - HEADER_LEN) as u16;
98        buf[0] = TABLE_ID;
99        // §5.2.6: section_syntax_indicator SHALL be 0 for the TOT (despite the
100        // trailing CRC_32). 0x70 = SSI(0) | reserved_future_use(1) | reserved(11).
101        buf[1] = 0x70 | ((section_length >> 8) as u8 & 0x0F);
102        buf[2] = (section_length & 0xFF) as u8;
103        buf[3..8].copy_from_slice(&self.utc_time_raw);
104        let dl = self.descriptors.len() as u16;
105        buf[8] = 0xF0 | ((dl >> 8) as u8 & 0x0F);
106        buf[9] = (dl & 0xFF) as u8;
107        let d_end = 10 + self.descriptors.len();
108        buf[10..d_end].copy_from_slice(self.descriptors.raw());
109        let crc_pos = len - CRC_LEN;
110        let crc = dvb_common::crc32_mpeg2::compute(&buf[..crc_pos]);
111        buf[crc_pos..len].copy_from_slice(&crc.to_be_bytes());
112        Ok(len)
113    }
114}
115
116impl<'a> Table<'a> for Tot<'a> {
117    const TABLE_ID: u8 = TABLE_ID;
118    const PID: u16 = PID;
119}
120
121impl<'a> crate::traits::TableDef<'a> for Tot<'a> {
122    const TABLE_ID_RANGES: &'static [(u8, u8)] = &[(TABLE_ID, TABLE_ID)];
123    const NAME: &'static str = "TIME_OFFSET";
124}
125
126#[cfg(test)]
127mod tests {
128    use super::*;
129
130    fn build_tot(desc: &[u8]) -> Vec<u8> {
131        let section_length = (UTC_TIME_LEN + DESC_LOOP_LEN_FIELD + desc.len() + CRC_LEN) as u16;
132        let mut v = Vec::new();
133        v.push(TABLE_ID);
134        // SSI=0 per §5.2.6 (the TOT exception: SSI=0 but CRC present).
135        v.push(0x70 | ((section_length >> 8) as u8 & 0x0F));
136        v.push((section_length & 0xFF) as u8);
137        v.extend_from_slice(&[0xE4, 0x09, 0x12, 0x34, 0x56]);
138        let dl = desc.len() as u16;
139        v.push(0xF0 | ((dl >> 8) as u8 & 0x0F));
140        v.push((dl & 0xFF) as u8);
141        v.extend_from_slice(desc);
142        v.extend_from_slice(&[0, 0, 0, 0]);
143        v
144    }
145
146    #[test]
147    fn parse_with_no_descriptors() {
148        let bytes = build_tot(&[]);
149        let tot = Tot::parse(&bytes).unwrap();
150        assert_eq!(tot.utc_time_raw, [0xE4, 0x09, 0x12, 0x34, 0x56]);
151        assert_eq!(tot.descriptors.raw(), &[] as &[u8]);
152    }
153
154    #[test]
155    fn parse_with_local_time_offset_descriptor() {
156        let lto = [
157            0x58u8, 13, b'G', b'B', b'R', 0x02, 0x00, 0x00, 0xE4, 0x09, 0x12, 0x34, 0x56, 0x01,
158            0x00,
159        ];
160        let bytes = build_tot(&lto);
161        let tot = Tot::parse(&bytes).unwrap();
162        assert_eq!(tot.descriptors.raw(), &lto[..]);
163    }
164
165    #[test]
166    fn parse_rejects_wrong_tag() {
167        let mut bytes = build_tot(&[]);
168        bytes[0] = 0x70;
169        assert!(matches!(
170            Tot::parse(&bytes).unwrap_err(),
171            Error::UnexpectedTableId { table_id: 0x70, .. }
172        ));
173    }
174
175    #[test]
176    fn serialize_round_trip() {
177        let lto = [0x58u8, 0];
178        let bytes = build_tot(&lto);
179        let tot = Tot::parse(&bytes).unwrap();
180        let mut buf = vec![0u8; tot.serialized_len()];
181        tot.serialize_into(&mut buf).unwrap();
182        let re = Tot::parse(&buf).unwrap();
183        assert_eq!(tot, re);
184    }
185}
dvb_si/tables/tot.rs

dvb_si/tables/
tot.rs
