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))]
30pub struct Tot<'a> {
31    /// Raw 5-byte UTC time (16-bit MJD + 24-bit BCD HHMMSS).
32    pub utc_time_raw: [u8; 5],
33    /// Raw descriptor bytes (typically local_time_offset_descriptor tag 0x58).
34    /// Descriptor loop. Serializes as the typed descriptor sequence;
35    /// `.raw()` yields the wire bytes.
36    pub descriptors: DescriptorLoop<'a>,
37}
38
39impl<'a> Parse<'a> for Tot<'a> {
40    type Error = crate::error::Error;
41    fn parse(bytes: &'a [u8]) -> Result<Self> {
42        let min_len = HEADER_LEN + UTC_TIME_LEN + DESC_LOOP_LEN_FIELD + CRC_LEN;
43        if bytes.len() < min_len {
44            return Err(Error::BufferTooShort {
45                need: min_len,
46                have: bytes.len(),
47                what: "Tot",
48            });
49        }
50        if bytes[0] != TABLE_ID {
51            return Err(Error::UnexpectedTableId {
52                table_id: bytes[0],
53                what: "Tot",
54                expected: &[TABLE_ID],
55            });
56        }
57        let section_length = ((bytes[1] & 0x0F) as u16) << 8 | bytes[2] as u16;
58        let total = HEADER_LEN + section_length as usize;
59        if bytes.len() < total {
60            return Err(Error::SectionLengthOverflow {
61                declared: section_length as usize,
62                available: bytes.len() - HEADER_LEN,
63            });
64        }
65        let utc_time_raw = [bytes[3], bytes[4], bytes[5], bytes[6], bytes[7]];
66        let dl_pos = HEADER_LEN + UTC_TIME_LEN;
67        let dl = (((bytes[dl_pos] & 0x0F) as usize) << 8) | bytes[dl_pos + 1] as usize;
68        let d_start = dl_pos + DESC_LOOP_LEN_FIELD;
69        let d_end = d_start + dl;
70        if d_end > total - CRC_LEN {
71            return Err(Error::SectionLengthOverflow {
72                declared: dl,
73                available: total - CRC_LEN - d_start,
74            });
75        }
76        Ok(Tot {
77            utc_time_raw,
78            descriptors: DescriptorLoop::new(&bytes[d_start..d_end]),
79        })
80    }
81}
82
83impl Serialize for Tot<'_> {
84    type Error = crate::error::Error;
85    fn serialized_len(&self) -> usize {
86        HEADER_LEN + UTC_TIME_LEN + DESC_LOOP_LEN_FIELD + self.descriptors.len() + CRC_LEN
87    }
88    fn serialize_into(&self, buf: &mut [u8]) -> Result<usize> {
89        let len = self.serialized_len();
90        if buf.len() < len {
91            return Err(Error::OutputBufferTooSmall {
92                need: len,
93                have: buf.len(),
94            });
95        }
96        let section_length = (len - HEADER_LEN) as u16;
97        buf[0] = TABLE_ID;
98        // §5.2.6: section_syntax_indicator SHALL be 0 for the TOT (despite the
99        // trailing CRC_32). 0x70 = SSI(0) | reserved_future_use(1) | reserved(11).
100        buf[1] = 0x70 | ((section_length >> 8) as u8 & 0x0F);
101        buf[2] = (section_length & 0xFF) as u8;
102        buf[3..8].copy_from_slice(&self.utc_time_raw);
103        let dl = self.descriptors.len() as u16;
104        buf[8] = 0xF0 | ((dl >> 8) as u8 & 0x0F);
105        buf[9] = (dl & 0xFF) as u8;
106        let d_end = 10 + self.descriptors.len();
107        buf[10..d_end].copy_from_slice(self.descriptors.raw());
108        let crc_pos = len - CRC_LEN;
109        let crc = dvb_common::crc32_mpeg2::compute(&buf[..crc_pos]);
110        buf[crc_pos..len].copy_from_slice(&crc.to_be_bytes());
111        Ok(len)
112    }
113}
114
115impl<'a> Table<'a> for Tot<'a> {
116    const TABLE_ID: u8 = TABLE_ID;
117    const PID: u16 = PID;
118}
119
120impl<'a> crate::traits::TableDef<'a> for Tot<'a> {
121    const TABLE_ID_RANGES: &'static [(u8, u8)] = &[(TABLE_ID, TABLE_ID)];
122    const NAME: &'static str = "TIME_OFFSET";
123}
124
125#[cfg(test)]
126mod tests {
127    use super::*;
128
129    fn build_tot(desc: &[u8]) -> Vec<u8> {
130        let section_length = (UTC_TIME_LEN + DESC_LOOP_LEN_FIELD + desc.len() + CRC_LEN) as u16;
131        let mut v = Vec::new();
132        v.push(TABLE_ID);
133        // SSI=0 per §5.2.6 (the TOT exception: SSI=0 but CRC present).
134        v.push(0x70 | ((section_length >> 8) as u8 & 0x0F));
135        v.push((section_length & 0xFF) as u8);
136        v.extend_from_slice(&[0xE4, 0x09, 0x12, 0x34, 0x56]);
137        let dl = desc.len() as u16;
138        v.push(0xF0 | ((dl >> 8) as u8 & 0x0F));
139        v.push((dl & 0xFF) as u8);
140        v.extend_from_slice(desc);
141        v.extend_from_slice(&[0, 0, 0, 0]);
142        v
143    }
144
145    #[test]
146    fn parse_with_no_descriptors() {
147        let bytes = build_tot(&[]);
148        let tot = Tot::parse(&bytes).unwrap();
149        assert_eq!(tot.utc_time_raw, [0xE4, 0x09, 0x12, 0x34, 0x56]);
150        assert_eq!(tot.descriptors.raw(), &[] as &[u8]);
151    }
152
153    #[test]
154    fn parse_with_local_time_offset_descriptor() {
155        let lto = [
156            0x58u8, 13, b'G', b'B', b'R', 0x02, 0x00, 0x00, 0xE4, 0x09, 0x12, 0x34, 0x56, 0x01,
157            0x00,
158        ];
159        let bytes = build_tot(&lto);
160        let tot = Tot::parse(&bytes).unwrap();
161        assert_eq!(tot.descriptors.raw(), &lto[..]);
162    }
163
164    #[test]
165    fn parse_rejects_wrong_tag() {
166        let mut bytes = build_tot(&[]);
167        bytes[0] = 0x70;
168        assert!(matches!(
169            Tot::parse(&bytes).unwrap_err(),
170            Error::UnexpectedTableId { table_id: 0x70, .. }
171        ));
172    }
173
174    #[test]
175    fn serialize_round_trip() {
176        let lto = [0x58u8, 0];
177        let bytes = build_tot(&lto);
178        let tot = Tot::parse(&bytes).unwrap();
179        let mut buf = vec![0u8; tot.serialized_len()];
180        tot.serialize_into(&mut buf).unwrap();
181        let re = Tot::parse(&buf).unwrap();
182        assert_eq!(tot, re);
183    }
184}
dvb_si/tables/tot.rs

dvb_si/tables/
tot.rs
