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 [`TotSection::parse`] directly.
11
12use crate::descriptors::DescriptorLoop;
13use crate::error::{Error, Result};
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;
25const MIN_SECTION_LEN: usize = HEADER_LEN + UTC_TIME_LEN + DESC_LOOP_LEN_FIELD + CRC_LEN;
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 TotSection<'a> {
32    /// Raw 5-byte UTC time (16-bit MJD + 24-bit BCD HHMMSS).
33    /// Private — use [`utc_time_decoded`](Self::utc_time_decoded) for
34    /// decoded access.
35    pub(crate) utc_time_raw: [u8; 5],
36    /// Raw descriptor bytes (typically local_time_offset_descriptor tag 0x58).
37    /// Descriptor loop. Serializes as the typed descriptor sequence;
38    /// `.raw()` yields the wire bytes.
39    pub descriptors: DescriptorLoop<'a>,
40}
41
42impl<'a> TotSection<'a> {
43    /// Decode the UTC time to a plain date-time struct (no `chrono` feature
44    /// required).
45    ///
46    /// Returns `None` if the date/time fields are out of range. MJD→calendar
47    /// conversion per ETSI EN 300 468 Annex C.
48    #[must_use]
49    pub fn utc_time_decoded(&self) -> Option<dvb_common::time::MjdBcdDateTime> {
50        dvb_common::time::decode_mjd_bcd(self.utc_time_raw)
51    }
52
53    /// Set the UTC time, encoding it from a [`dvb_common::time::MjdBcdDateTime`].
54    ///
55    /// # Errors
56    /// [`ValueOutOfRange`](crate::Error::ValueOutOfRange) if the date is
57    /// outside the representable 16-bit MJD range.
58    pub fn set_utc_time_decoded(&mut self, dt: dvb_common::time::MjdBcdDateTime) -> Result<()> {
59        self.utc_time_raw = dvb_common::time::encode_mjd_bcd(dt).ok_or(Error::ValueOutOfRange {
60            field: "TotSection::utc_time",
61            reason: "date not representable in 16-bit MJD",
62        })?;
63        Ok(())
64    }
65
66    /// Raw 5-byte UTC time field (for round-trip / serialization).
67    #[must_use]
68    pub fn utc_time_raw(&self) -> [u8; 5] {
69        self.utc_time_raw
70    }
71
72    /// Construct a `TotSection` from raw wire fields.
73    #[must_use]
74    pub fn new(utc_time_raw: [u8; 5], descriptors: DescriptorLoop<'a>) -> Self {
75        Self {
76            utc_time_raw,
77            descriptors,
78        }
79    }
80}
81
82#[cfg(feature = "chrono")]
83impl TotSection<'_> {
84    /// Decode `utc_time_raw` (16-bit MJD + 24-bit BCD UTC) to a UTC datetime.
85    ///
86    /// Returns `None` if the date/time fields are out of range. MJD→calendar
87    /// conversion per ETSI EN 300 468 Annex C.
88    #[must_use]
89    pub fn utc_time(&self) -> Option<chrono::DateTime<chrono::Utc>> {
90        dvb_common::time::decode_mjd_bcd_utc(self.utc_time_raw)
91    }
92
93    /// Set the UTC time, encoding it into the 40-bit `utc_time` field.
94    ///
95    /// # Errors
96    /// [`ValueOutOfRange`](crate::Error::ValueOutOfRange) if the date is
97    /// outside the representable 16-bit MJD range.
98    pub fn set_utc_time(&mut self, utc_time: chrono::DateTime<chrono::Utc>) -> Result<()> {
99        self.utc_time_raw =
100            dvb_common::time::encode_mjd_bcd_utc(utc_time).ok_or(Error::ValueOutOfRange {
101                field: "TotSection::utc_time",
102                reason: "date not representable in 16-bit MJD",
103            })?;
104        Ok(())
105    }
106}
107
108impl<'a> Parse<'a> for TotSection<'a> {
109    type Error = crate::error::Error;
110    fn parse(bytes: &'a [u8]) -> Result<Self> {
111        let min_len = HEADER_LEN + UTC_TIME_LEN + DESC_LOOP_LEN_FIELD + CRC_LEN;
112        if bytes.len() < min_len {
113            return Err(Error::BufferTooShort {
114                need: min_len,
115                have: bytes.len(),
116                what: "TotSection",
117            });
118        }
119        if bytes[0] != TABLE_ID {
120            return Err(Error::UnexpectedTableId {
121                table_id: bytes[0],
122                what: "TotSection",
123                expected: &[TABLE_ID],
124            });
125        }
126        let section_length = ((bytes[1] & 0x0F) as u16) << 8 | bytes[2] as u16;
127        let total = super::check_section_length(
128            bytes.len(),
129            HEADER_LEN,
130            section_length as usize,
131            MIN_SECTION_LEN,
132        )?;
133        let utc_time_raw = [bytes[3], bytes[4], bytes[5], bytes[6], bytes[7]];
134        let dl_pos = HEADER_LEN + UTC_TIME_LEN;
135        let dl = (((bytes[dl_pos] & 0x0F) as usize) << 8) | bytes[dl_pos + 1] as usize;
136        let d_start = dl_pos + DESC_LOOP_LEN_FIELD;
137        let d_end = d_start + dl;
138        if d_end > total - CRC_LEN {
139            return Err(Error::SectionLengthOverflow {
140                declared: dl,
141                available: (total - CRC_LEN).saturating_sub(d_start),
142            });
143        }
144        Ok(TotSection {
145            utc_time_raw,
146            descriptors: DescriptorLoop::new(&bytes[d_start..d_end]),
147        })
148    }
149}
150
151impl Serialize for TotSection<'_> {
152    type Error = crate::error::Error;
153    fn serialized_len(&self) -> usize {
154        HEADER_LEN + UTC_TIME_LEN + DESC_LOOP_LEN_FIELD + self.descriptors.len() + CRC_LEN
155    }
156    fn serialize_into(&self, buf: &mut [u8]) -> Result<usize> {
157        let len = self.serialized_len();
158        if buf.len() < len {
159            return Err(Error::OutputBufferTooSmall {
160                need: len,
161                have: buf.len(),
162            });
163        }
164        let section_length = (len - HEADER_LEN) as u16;
165        if section_length > 0x0FFF {
166            return Err(Error::SectionLengthOverflow {
167                declared: section_length as usize,
168                available: 0x0FFF,
169            });
170        }
171        buf[0] = TABLE_ID;
172        // §5.2.6: section_syntax_indicator SHALL be 0 for the TOT (despite the
173        // trailing CRC_32). 0x70 = SSI(0) | reserved_future_use(1) | reserved(11).
174        buf[1] = super::SECTION_B1_FLAGS_SHORT | ((section_length >> 8) as u8 & 0x0F);
175        buf[2] = (section_length & 0xFF) as u8;
176        buf[3..8].copy_from_slice(&self.utc_time_raw);
177        let dl = self.descriptors.len() as u16;
178        buf[8] = 0xF0 | ((dl >> 8) as u8 & 0x0F);
179        buf[9] = (dl & 0xFF) as u8;
180        let d_end = 10 + self.descriptors.len();
181        buf[10..d_end].copy_from_slice(self.descriptors.raw());
182        let crc_pos = len - CRC_LEN;
183        let crc = dvb_common::crc32_mpeg2::compute(&buf[..crc_pos]);
184        buf[crc_pos..len].copy_from_slice(&crc.to_be_bytes());
185        Ok(len)
186    }
187}
188impl<'a> crate::traits::TableDef<'a> for TotSection<'a> {
189    const TABLE_ID_RANGES: &'static [(u8, u8)] = &[(TABLE_ID, TABLE_ID)];
190    const NAME: &'static str = "TIME_OFFSET";
191}
192
193#[cfg(test)]
194mod tests {
195    use super::*;
196
197    fn build_tot(desc: &[u8]) -> Vec<u8> {
198        let section_length = (UTC_TIME_LEN + DESC_LOOP_LEN_FIELD + desc.len() + CRC_LEN) as u16;
199        let mut v = Vec::new();
200        v.push(TABLE_ID);
201        // SSI=0 per §5.2.6 (the TOT exception: SSI=0 but CRC present).
202        v.push(0x70 | ((section_length >> 8) as u8 & 0x0F));
203        v.push((section_length & 0xFF) as u8);
204        v.extend_from_slice(&[0xE4, 0x09, 0x12, 0x34, 0x56]);
205        let dl = desc.len() as u16;
206        v.push(0xF0 | ((dl >> 8) as u8 & 0x0F));
207        v.push((dl & 0xFF) as u8);
208        v.extend_from_slice(desc);
209        let crc = dvb_common::crc32_mpeg2::compute(&v);
210        v.extend_from_slice(&crc.to_be_bytes());
211        v
212    }
213
214    #[test]
215    fn parse_with_no_descriptors() {
216        let bytes = build_tot(&[]);
217        let tot = TotSection::parse(&bytes).unwrap();
218        assert_eq!(tot.utc_time_raw(), [0xE4, 0x09, 0x12, 0x34, 0x56]);
219        assert_eq!(tot.descriptors.raw(), &[] as &[u8]);
220    }
221
222    #[test]
223    fn parse_with_local_time_offset_descriptor() {
224        let lto = [
225            0x58u8, 13, b'G', b'B', b'R', 0x02, 0x00, 0x00, 0xE4, 0x09, 0x12, 0x34, 0x56, 0x01,
226            0x00,
227        ];
228        let bytes = build_tot(&lto);
229        let tot = TotSection::parse(&bytes).unwrap();
230        assert_eq!(tot.descriptors.raw(), &lto[..]);
231    }
232
233    #[test]
234    fn parse_rejects_wrong_tag() {
235        let mut bytes = build_tot(&[]);
236        bytes[0] = 0x70;
237        assert!(matches!(
238            TotSection::parse(&bytes).unwrap_err(),
239            Error::UnexpectedTableId { table_id: 0x70, .. }
240        ));
241    }
242
243    #[test]
244    fn serialize_round_trip() {
245        let lto = [0x58u8, 0];
246        let bytes = build_tot(&lto);
247        let tot = TotSection::parse(&bytes).unwrap();
248        let mut buf = vec![0u8; tot.serialized_len()];
249        tot.serialize_into(&mut buf).unwrap();
250        assert_eq!(buf, bytes, "TOT byte-identity against hand-built input");
251        let re = TotSection::parse(&buf).unwrap();
252        assert_eq!(tot, re);
253    }
254
255    #[test]
256    fn parse_rejects_zero_section_length() {
257        let mut buf = vec![0u8; 64];
258        buf[0] = TABLE_ID;
259        buf[1] = 0xF0;
260        buf[2] = 0x00;
261        for b in &mut buf[3..] {
262            *b = 0xFF;
263        }
264        assert!(matches!(
265            TotSection::parse(&buf).unwrap_err(),
266            Error::SectionLengthOverflow { .. }
267        ));
268    }
269}
dvb_si/tables/tot.rs

dvb_si/tables/
tot.rs
