dvb_si/tables/
sit.rs

1//! Selection Information Table — ETSI EN 300 468 §7.1.2.
2//!
3//! Carried on PID 0x001F with table_id 0x7F, only in partial transport streams
4//! (e.g. a recording). After the section header it has two loops:
5//!   1. `transmission_info_descriptors` — descriptors describing the whole
6//!      partial stream, prefixed by a 12-bit length;
7//!   2. a per-service loop: `service_id(16) + reserved(1) + running_status(3) +
8//!      service_descriptors_length(12) + descriptors`.
9//!
10//! Both loops are exposed as raw bytes for the caller to walk with the
11//! descriptor parsers.
12
13use crate::error::{Error, Result};
14use crate::traits::Table;
15use dvb_common::{Parse, Serialize};
16
17/// table_id for the Selection Information Table.
18pub const TABLE_ID: u8 = 0x7F;
19/// Well-known PID on which the SIT is carried.
20pub const PID: u16 = 0x001F;
21
22const MIN_HEADER_LEN: usize = 3;
23const EXTENSION_HEADER_LEN: usize = 5;
24const DESC_LOOP_LEN_FIELD: usize = 2;
25const CRC_LEN: usize = 4;
26
27/// Selection Information Table (§7.1.2, Table 164).
28#[derive(Debug, Clone, PartialEq, Eq)]
29#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
30pub struct Sit {
31    /// 16-bit field after section_length — reserved_future_use for the SIT
32    /// (conventionally 0xFFFF); retained verbatim.
33    pub table_id_extension: u16,
34    /// 5-bit version_number.
35    pub version_number: u8,
36    /// current_next_indicator bit.
37    pub current_next_indicator: bool,
38    /// section_number in the sub-table sequence.
39    pub section_number: u8,
40    /// last_section_number in the sub-table sequence.
41    pub last_section_number: u8,
42    /// Transmission-info descriptor loop bytes (the first loop).
43    pub transmission_info_descriptors: Vec<u8>,
44    /// Per-service loop bytes (service_id + running_status + descriptors), raw.
45    pub service_loop: Vec<u8>,
46}
47
48impl<'a> Parse<'a> for Sit {
49    type Error = crate::error::Error;
50
51    fn parse(bytes: &'a [u8]) -> Result<Self> {
52        let min_len = MIN_HEADER_LEN + EXTENSION_HEADER_LEN + DESC_LOOP_LEN_FIELD + CRC_LEN;
53        if bytes.len() < min_len {
54            return Err(Error::BufferTooShort {
55                need: min_len,
56                have: bytes.len(),
57                what: "Sit",
58            });
59        }
60        if bytes[0] != TABLE_ID {
61            return Err(Error::UnexpectedTableId {
62                table_id: bytes[0],
63                what: "Sit",
64                expected: &[TABLE_ID],
65            });
66        }
67        let section_length = ((bytes[1] & 0x0F) as usize) << 8 | bytes[2] as usize;
68        let total = MIN_HEADER_LEN + section_length;
69        if bytes.len() < total {
70            return Err(Error::SectionLengthOverflow {
71                declared: section_length,
72                available: bytes.len() - MIN_HEADER_LEN,
73            });
74        }
75
76        let table_id_extension = u16::from_be_bytes([bytes[3], bytes[4]]);
77        let version_number = (bytes[5] >> 1) & 0x1F;
78        let current_next_indicator = (bytes[5] & 0x01) != 0;
79        let section_number = bytes[6];
80        let last_section_number = bytes[7];
81
82        let dl_pos = MIN_HEADER_LEN + EXTENSION_HEADER_LEN;
83        let ti_len = (((bytes[dl_pos] & 0x0F) as usize) << 8) | bytes[dl_pos + 1] as usize;
84        let ti_start = dl_pos + DESC_LOOP_LEN_FIELD;
85        let ti_end = ti_start + ti_len;
86        let crc_start = total - CRC_LEN;
87        if ti_end > crc_start {
88            return Err(Error::SectionLengthOverflow {
89                declared: ti_len,
90                available: crc_start.saturating_sub(ti_start),
91            });
92        }
93
94        Ok(Sit {
95            table_id_extension,
96            version_number,
97            current_next_indicator,
98            section_number,
99            last_section_number,
100            transmission_info_descriptors: bytes[ti_start..ti_end].to_vec(),
101            // Everything between the transmission-info loop and the CRC is the
102            // per-service loop, kept raw.
103            service_loop: bytes[ti_end..crc_start].to_vec(),
104        })
105    }
106}
107
108impl Serialize for Sit {
109    type Error = crate::error::Error;
110
111    fn serialized_len(&self) -> usize {
112        MIN_HEADER_LEN
113            + EXTENSION_HEADER_LEN
114            + DESC_LOOP_LEN_FIELD
115            + self.transmission_info_descriptors.len()
116            + self.service_loop.len()
117            + CRC_LEN
118    }
119
120    fn serialize_into(&self, buf: &mut [u8]) -> Result<usize> {
121        let len = self.serialized_len();
122        if buf.len() < len {
123            return Err(Error::OutputBufferTooSmall {
124                need: len,
125                have: buf.len(),
126            });
127        }
128        let section_length = (len - MIN_HEADER_LEN) as u16;
129        buf[0] = TABLE_ID;
130        buf[1] = 0xB0 | ((section_length >> 8) as u8 & 0x0F);
131        buf[2] = (section_length & 0xFF) as u8;
132        buf[3..5].copy_from_slice(&self.table_id_extension.to_be_bytes());
133        buf[5] = 0xC0 | ((self.version_number & 0x1F) << 1) | u8::from(self.current_next_indicator);
134        buf[6] = self.section_number;
135        buf[7] = self.last_section_number;
136
137        let dl_pos = MIN_HEADER_LEN + EXTENSION_HEADER_LEN;
138        let ti_len = self.transmission_info_descriptors.len() as u16;
139        buf[dl_pos] = 0xF0 | ((ti_len >> 8) as u8 & 0x0F);
140        buf[dl_pos + 1] = (ti_len & 0xFF) as u8;
141        let ti_start = dl_pos + DESC_LOOP_LEN_FIELD;
142        let ti_end = ti_start + self.transmission_info_descriptors.len();
143        buf[ti_start..ti_end].copy_from_slice(&self.transmission_info_descriptors);
144        let sl_end = ti_end + self.service_loop.len();
145        buf[ti_end..sl_end].copy_from_slice(&self.service_loop);
146
147        let crc_pos = len - CRC_LEN;
148        let crc = dvb_common::crc32_mpeg2::compute(&buf[..crc_pos]);
149        buf[crc_pos..len].copy_from_slice(&crc.to_be_bytes());
150        Ok(len)
151    }
152}
153
154impl<'a> Table<'a> for Sit {
155    const TABLE_ID: u8 = TABLE_ID;
156    const PID: u16 = PID;
157}
158
159impl<'a> crate::traits::TableDef<'a> for Sit {
160    const TABLE_ID_RANGES: &'static [(u8, u8)] = &[(TABLE_ID, TABLE_ID)];
161    const NAME: &'static str = "SELECTION_INFORMATION";
162}
163
164#[cfg(test)]
165mod tests {
166    use super::*;
167
168    fn build_sit(
169        table_id_extension: u16,
170        version: u8,
171        ti_desc: &[u8],
172        service_loop: &[u8],
173    ) -> Vec<u8> {
174        let section_length = (EXTENSION_HEADER_LEN
175            + DESC_LOOP_LEN_FIELD
176            + ti_desc.len()
177            + service_loop.len()
178            + CRC_LEN) as u16;
179        let mut v = vec![
180            TABLE_ID,
181            0xB0 | ((section_length >> 8) as u8 & 0x0F),
182            (section_length & 0xFF) as u8,
183        ];
184        v.extend_from_slice(&table_id_extension.to_be_bytes());
185        v.push(0xC0 | ((version & 0x1F) << 1) | 0x01);
186        v.push(0x00);
187        v.push(0x00);
188        let dl = ti_desc.len() as u16;
189        v.push(0xF0 | ((dl >> 8) as u8 & 0x0F));
190        v.push((dl & 0xFF) as u8);
191        v.extend_from_slice(ti_desc);
192        v.extend_from_slice(service_loop);
193        v.extend_from_slice(&[0, 0, 0, 0]);
194        v
195    }
196
197    #[test]
198    fn parse_rejects_wrong_tag() {
199        let mut bytes = build_sit(0x1234, 5, &[], &[]);
200        bytes[0] = 0x7E;
201        assert!(matches!(
202            Sit::parse(&bytes).unwrap_err(),
203            Error::UnexpectedTableId { table_id: 0x7E, .. }
204        ));
205    }
206
207    #[test]
208    fn parse_rejects_short_buffer() {
209        assert!(matches!(
210            Sit::parse(&[0x7F, 0xB0]).unwrap_err(),
211            Error::BufferTooShort { .. }
212        ));
213    }
214
215    #[test]
216    fn parse_empty() {
217        let sit = Sit::parse(&build_sit(0x1234, 5, &[], &[])).unwrap();
218        assert_eq!(sit.table_id_extension, 0x1234);
219        assert_eq!(sit.version_number, 5);
220        assert!(sit.current_next_indicator);
221        assert!(sit.transmission_info_descriptors.is_empty());
222        assert!(sit.service_loop.is_empty());
223    }
224
225    #[test]
226    fn parse_separates_both_loops() {
227        let ti = [0x4D, 0x02, 0x01, 0x02]; // a transmission-info descriptor
228                                           // one service entry: service_id=0x0001, running_status=4, svc_desc_len=0
229        let service = [0x00, 0x01, 0x80 | (4 << 4), 0x00];
230        let sit = Sit::parse(&build_sit(0xABCD, 7, &ti, &service)).unwrap();
231        assert_eq!(sit.transmission_info_descriptors, &ti[..]);
232        assert_eq!(sit.service_loop, &service[..]);
233    }
234
235    #[test]
236    fn serialize_round_trip() {
237        let ti = [0x4D, 0x02, 0x01, 0x02];
238        let service = [0x00, 0x01, 0xC0, 0x00];
239        let sit = Sit::parse(&build_sit(0xCAFE, 3, &ti, &service)).unwrap();
240        let mut buf = vec![0u8; sit.serialized_len()];
241        sit.serialize_into(&mut buf).unwrap();
242        assert_eq!(Sit::parse(&buf).unwrap(), sit);
243    }
244
245    #[test]
246    fn serialize_round_trip_empty() {
247        let sit = Sit::parse(&build_sit(0x0001, 0, &[], &[])).unwrap();
248        let mut buf = vec![0u8; sit.serialized_len()];
249        sit.serialize_into(&mut buf).unwrap();
250        assert_eq!(Sit::parse(&buf).unwrap(), sit);
251    }
252
253    #[test]
254    fn table_trait_constants() {
255        assert_eq!(<Sit as Table>::TABLE_ID, 0x7F);
256        assert_eq!(<Sit as Table>::PID, 0x001F);
257    }
258
259    #[test]
260    fn sit_round_trips_via_json() {
261        let sit = Sit::parse(&build_sit(
262            0xDEAD,
263            9,
264            &[0x4D, 0x00],
265            &[0x00, 0x01, 0xC0, 0x00],
266        ))
267        .unwrap();
268        let j = serde_json::to_string(&sit).unwrap();
269        assert_eq!(serde_json::from_str::<Sit>(&j).unwrap(), sit);
270    }
271}
dvb_si/tables/sit.rs

dvb_si/tables/
sit.rs
