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::error::{Error, Result};
13use crate::traits::Table;
14use dvb_common::{Parse, Serialize};
15
16/// table_id for Time Offset Table.
17pub const TABLE_ID: u8 = 0x73;
18/// Well-known PID on which TOT is carried (same as TDT).
19pub const PID: u16 = 0x0014;
20
21const HEADER_LEN: usize = 3;
22const UTC_TIME_LEN: usize = 5;
23const DESC_LOOP_LEN_FIELD: usize = 2;
24const CRC_LEN: usize = 4;
25
26/// Time Offset Table.
27#[derive(Debug, Clone, PartialEq, Eq)]
28#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
29pub struct Tot<'a> {
30    /// Raw 5-byte UTC time (16-bit MJD + 24-bit BCD HHMMSS).
31    pub utc_time_raw: [u8; 5],
32    /// Raw descriptor bytes (typically local_time_offset_descriptor tag 0x58).
33    #[cfg_attr(feature = "serde", serde(borrow))]
34    pub descriptors: &'a [u8],
35}
36
37impl<'a> Parse<'a> for Tot<'a> {
38    type Error = crate::error::Error;
39    fn parse(bytes: &'a [u8]) -> Result<Self> {
40        let min_len = HEADER_LEN + UTC_TIME_LEN + DESC_LOOP_LEN_FIELD + CRC_LEN;
41        if bytes.len() < min_len {
42            return Err(Error::BufferTooShort {
43                need: min_len,
44                have: bytes.len(),
45                what: "Tot",
46            });
47        }
48        if bytes[0] != TABLE_ID {
49            return Err(Error::UnexpectedTableId {
50                table_id: bytes[0],
51                what: "Tot",
52                expected: &[TABLE_ID],
53            });
54        }
55        let section_length = ((bytes[1] & 0x0F) as u16) << 8 | bytes[2] as u16;
56        let total = HEADER_LEN + section_length as usize;
57        if bytes.len() < total {
58            return Err(Error::SectionLengthOverflow {
59                declared: section_length as usize,
60                available: bytes.len() - HEADER_LEN,
61            });
62        }
63        let utc_time_raw = [bytes[3], bytes[4], bytes[5], bytes[6], bytes[7]];
64        let dl_pos = HEADER_LEN + UTC_TIME_LEN;
65        let dl = (((bytes[dl_pos] & 0x0F) as usize) << 8) | bytes[dl_pos + 1] as usize;
66        let d_start = dl_pos + DESC_LOOP_LEN_FIELD;
67        let d_end = d_start + dl;
68        if d_end > total - CRC_LEN {
69            return Err(Error::SectionLengthOverflow {
70                declared: dl,
71                available: total - CRC_LEN - d_start,
72            });
73        }
74        Ok(Tot {
75            utc_time_raw,
76            descriptors: &bytes[d_start..d_end],
77        })
78    }
79}
80
81impl Serialize for Tot<'_> {
82    type Error = crate::error::Error;
83    fn serialized_len(&self) -> usize {
84        HEADER_LEN + UTC_TIME_LEN + DESC_LOOP_LEN_FIELD + self.descriptors.len() + CRC_LEN
85    }
86    fn serialize_into(&self, buf: &mut [u8]) -> Result<usize> {
87        let len = self.serialized_len();
88        if buf.len() < len {
89            return Err(Error::OutputBufferTooSmall {
90                need: len,
91                have: buf.len(),
92            });
93        }
94        let section_length = (len - HEADER_LEN) as u16;
95        buf[0] = TABLE_ID;
96        // §5.2.6: section_syntax_indicator SHALL be 0 for the TOT (despite the
97        // trailing CRC_32). 0x70 = SSI(0) | reserved_future_use(1) | reserved(11).
98        buf[1] = 0x70 | ((section_length >> 8) as u8 & 0x0F);
99        buf[2] = (section_length & 0xFF) as u8;
100        buf[3..8].copy_from_slice(&self.utc_time_raw);
101        let dl = self.descriptors.len() as u16;
102        buf[8] = 0xF0 | ((dl >> 8) as u8 & 0x0F);
103        buf[9] = (dl & 0xFF) as u8;
104        let d_end = 10 + self.descriptors.len();
105        buf[10..d_end].copy_from_slice(self.descriptors);
106        let crc_pos = len - CRC_LEN;
107        let crc = dvb_common::crc32_mpeg2::compute(&buf[..crc_pos]);
108        buf[crc_pos..len].copy_from_slice(&crc.to_be_bytes());
109        Ok(len)
110    }
111}
112
113impl<'a> Table<'a> for Tot<'a> {
114    const TABLE_ID: u8 = TABLE_ID;
115    const PID: u16 = PID;
116}
117
118impl<'a> crate::traits::TableDef<'a> for Tot<'a> {
119    const TABLE_ID_RANGES: &'static [(u8, u8)] = &[(TABLE_ID, TABLE_ID)];
120    const NAME: &'static str = "TIME_OFFSET";
121}
122
123#[cfg(test)]
124mod tests {
125    use super::*;
126
127    fn build_tot(desc: &[u8]) -> Vec<u8> {
128        let section_length = (UTC_TIME_LEN + DESC_LOOP_LEN_FIELD + desc.len() + CRC_LEN) as u16;
129        let mut v = Vec::new();
130        v.push(TABLE_ID);
131        // SSI=0 per §5.2.6 (the TOT exception: SSI=0 but CRC present).
132        v.push(0x70 | ((section_length >> 8) as u8 & 0x0F));
133        v.push((section_length & 0xFF) as u8);
134        v.extend_from_slice(&[0xE4, 0x09, 0x12, 0x34, 0x56]);
135        let dl = desc.len() as u16;
136        v.push(0xF0 | ((dl >> 8) as u8 & 0x0F));
137        v.push((dl & 0xFF) as u8);
138        v.extend_from_slice(desc);
139        v.extend_from_slice(&[0, 0, 0, 0]);
140        v
141    }
142
143    #[test]
144    fn parse_with_no_descriptors() {
145        let bytes = build_tot(&[]);
146        let tot = Tot::parse(&bytes).unwrap();
147        assert_eq!(tot.utc_time_raw, [0xE4, 0x09, 0x12, 0x34, 0x56]);
148        assert_eq!(tot.descriptors, &[] as &[u8]);
149    }
150
151    #[test]
152    fn parse_with_local_time_offset_descriptor() {
153        let lto = [
154            0x58u8, 13, b'G', b'B', b'R', 0x02, 0x00, 0x00, 0xE4, 0x09, 0x12, 0x34, 0x56, 0x01,
155            0x00,
156        ];
157        let bytes = build_tot(&lto);
158        let tot = Tot::parse(&bytes).unwrap();
159        assert_eq!(tot.descriptors, &lto[..]);
160    }
161
162    #[test]
163    fn parse_rejects_wrong_tag() {
164        let mut bytes = build_tot(&[]);
165        bytes[0] = 0x70;
166        assert!(matches!(
167            Tot::parse(&bytes).unwrap_err(),
168            Error::UnexpectedTableId { table_id: 0x70, .. }
169        ));
170    }
171
172    #[test]
173    fn serialize_round_trip() {
174        let lto = [0x58u8, 0];
175        let bytes = build_tot(&lto);
176        let tot = Tot::parse(&bytes).unwrap();
177        let mut buf = vec![0u8; tot.serialized_len()];
178        tot.serialize_into(&mut buf).unwrap();
179        let re = Tot::parse(&buf).unwrap();
180        assert_eq!(tot, re);
181    }
182}
dvb_si/tables/tot.rs

dvb_si/tables/
tot.rs
