dvb_si/tables/
tdt.rs

1//! Time and Date Table — ETSI EN 300 468 §5.2.5.
2//!
3//! Short-form section on PID 0x0014 with table_id 0x70. Body is exactly
4//! 5 bytes of UTC time (16-bit MJD + 24-bit BCD HHMMSS). No CRC.
5
6use crate::error::{Error, Result};
7use crate::traits::Table;
8use dvb_common::{Parse, Serialize};
9
10/// table_id for Time and Date Table.
11pub const TABLE_ID: u8 = 0x70;
12/// Well-known PID on which TDT is carried.
13pub const PID: u16 = 0x0014;
14
15const HEADER_LEN: usize = 3;
16const UTC_TIME_LEN: usize = 5;
17
18/// Time and Date Table.
19#[derive(Debug, Clone, Copy, PartialEq, Eq)]
20#[cfg_attr(feature = "serde", derive(serde::Serialize))]
21pub struct Tdt {
22    /// Raw 5-byte UTC time (16-bit MJD + 24-bit BCD HHMMSS) per
23    /// EN 300 468 Annex C.
24    pub utc_time_raw: [u8; 5],
25}
26
27impl Tdt {
28    /// Decode the UTC time to a chrono DateTime when the `chrono` feature is on.
29    #[cfg(feature = "chrono")]
30    #[must_use]
31    pub fn utc_time(&self) -> Option<chrono::DateTime<chrono::Utc>> {
32        use chrono::{NaiveDate, NaiveDateTime, TimeZone};
33        let mjd = u16::from_be_bytes([self.utc_time_raw[0], self.utc_time_raw[1]]);
34        let (y, m, d) = mjd_to_ymd(mjd);
35        let h = bcd(self.utc_time_raw[2])?;
36        let mi = bcd(self.utc_time_raw[3])?;
37        let s = bcd(self.utc_time_raw[4])?;
38        let date = NaiveDate::from_ymd_opt(y, m, d)?;
39        let time = chrono::NaiveTime::from_hms_opt(h.into(), mi.into(), s.into())?;
40        chrono::Utc
41            .from_local_datetime(&NaiveDateTime::new(date, time))
42            .single()
43    }
44}
45
46#[cfg(feature = "chrono")]
47fn bcd(b: u8) -> Option<u8> {
48    let hi = b >> 4;
49    let lo = b & 0x0F;
50    if hi > 9 || lo > 9 {
51        return None;
52    }
53    Some(hi * 10 + lo)
54}
55
56#[cfg(feature = "chrono")]
57fn mjd_to_ymd(mjd: u16) -> (i32, u32, u32) {
58    let mjd = i64::from(mjd);
59    let y_prime = ((mjd as f64 - 15_078.2) / 365.25) as i64;
60    let m_prime = ((mjd as f64 - 14_956.1 - (y_prime as f64 * 365.25).floor()) / 30.6001) as i64;
61    let d = mjd
62        - 14_956
63        - (y_prime as f64 * 365.25).floor() as i64
64        - (m_prime as f64 * 30.6001).floor() as i64;
65    let k = if m_prime == 14 || m_prime == 15 { 1 } else { 0 };
66    let y = y_prime + k + 1900;
67    let m = m_prime - 1 - k * 12;
68    (y as i32, m as u32, d as u32)
69}
70
71impl<'a> Parse<'a> for Tdt {
72    type Error = crate::error::Error;
73    fn parse(bytes: &'a [u8]) -> Result<Self> {
74        let min_len = HEADER_LEN + UTC_TIME_LEN;
75        if bytes.len() < min_len {
76            return Err(Error::BufferTooShort {
77                need: min_len,
78                have: bytes.len(),
79                what: "Tdt",
80            });
81        }
82        if bytes[0] != TABLE_ID {
83            return Err(Error::UnexpectedTableId {
84                table_id: bytes[0],
85                what: "Tdt",
86                expected: &[TABLE_ID],
87            });
88        }
89        let section_length = ((bytes[1] & 0x0F) as u16) << 8 | bytes[2] as u16;
90        if section_length as usize != UTC_TIME_LEN {
91            return Err(Error::SectionLengthOverflow {
92                declared: section_length as usize,
93                available: UTC_TIME_LEN,
94            });
95        }
96        let utc_time_raw = [bytes[3], bytes[4], bytes[5], bytes[6], bytes[7]];
97        Ok(Tdt { utc_time_raw })
98    }
99}
100
101impl Serialize for Tdt {
102    type Error = crate::error::Error;
103    fn serialized_len(&self) -> usize {
104        HEADER_LEN + UTC_TIME_LEN
105    }
106    fn serialize_into(&self, buf: &mut [u8]) -> Result<usize> {
107        let len = self.serialized_len();
108        if buf.len() < len {
109            return Err(Error::OutputBufferTooSmall {
110                need: len,
111                have: buf.len(),
112            });
113        }
114        buf[0] = TABLE_ID;
115        buf[1] = 0x70 | ((UTC_TIME_LEN as u16 >> 8) as u8 & 0x0F);
116        buf[2] = UTC_TIME_LEN as u8;
117        buf[3..8].copy_from_slice(&self.utc_time_raw);
118        Ok(len)
119    }
120}
121
122impl<'a> Table<'a> for Tdt {
123    const TABLE_ID: u8 = TABLE_ID;
124    const PID: u16 = PID;
125}
126
127impl<'a> crate::traits::TableDef<'a> for Tdt {
128    const TABLE_ID_RANGES: &'static [(u8, u8)] = &[(TABLE_ID, TABLE_ID)];
129    const NAME: &'static str = "TIME_AND_DATE";
130}
131
132#[cfg(test)]
133mod tests {
134    use super::*;
135
136    #[test]
137    fn parse_extracts_utc_time_raw() {
138        let bytes = [TABLE_ID, 0x70, 0x05, 0xE4, 0x09, 0x12, 0x34, 0x56];
139        let tdt = Tdt::parse(&bytes).unwrap();
140        assert_eq!(tdt.utc_time_raw, [0xE4, 0x09, 0x12, 0x34, 0x56]);
141    }
142
143    #[test]
144    fn parse_rejects_wrong_tag() {
145        let bytes = [0x71, 0x70, 0x05, 0, 0, 0, 0, 0];
146        assert!(matches!(
147            Tdt::parse(&bytes).unwrap_err(),
148            Error::UnexpectedTableId { table_id: 0x71, .. }
149        ));
150    }
151
152    #[test]
153    fn parse_rejects_wrong_section_length() {
154        let bytes = [TABLE_ID, 0x70, 0x04, 0, 0, 0, 0, 0];
155        assert!(matches!(
156            Tdt::parse(&bytes).unwrap_err(),
157            Error::SectionLengthOverflow { .. }
158        ));
159    }
160
161    #[test]
162    fn serialize_round_trip() {
163        let tdt = Tdt {
164            utc_time_raw: [0xE4, 0x09, 0x12, 0x34, 0x56],
165        };
166        let mut buf = vec![0u8; tdt.serialized_len()];
167        tdt.serialize_into(&mut buf).unwrap();
168        let re = Tdt::parse(&buf).unwrap();
169        assert_eq!(tdt, re);
170    }
171
172    #[test]
173    fn utc_time_decodes_to_chrono() {
174        let tdt = Tdt {
175            utc_time_raw: [0xEA, 0x19, 0x12, 0x34, 0x56],
176        };
177        let dt = tdt.utc_time();
178        assert!(dt.is_some());
179    }
180}
dvb_si/tables/tdt.rs

dvb_si/tables/
tdt.rs
