dvb_si/tables/
pat.rs

1//! Program Association Table — MPEG-2 ISO/IEC 13818-1 §2.4.4.3.
2//!
3//! PAT is carried on PID 0x0000 with table_id 0x00. It maps
4//! program_number values to the PID on which their PMT is carried.
5//! program_number 0x0000 is special — its PID is the NIT PID.
6
7use crate::error::{Error, Result};
8use dvb_common::{Parse, Serialize};
9
10/// PAT table_id (ISO/IEC 13818-1 Table 2-30).
11pub const TABLE_ID: u8 = 0x00;
12/// PAT well-known PID.
13pub const PID: u16 = 0x0000;
14/// program_number value that carries the NIT PID rather than a PMT PID.
15pub const PROGRAM_NUMBER_NIT: u16 = 0x0000;
16
17const MIN_HEADER_LEN: usize = 3;
18const EXTENSION_HEADER_LEN: usize = 5;
19const CRC_LEN: usize = 4;
20const MIN_SECTION_LEN: usize = MIN_HEADER_LEN + EXTENSION_HEADER_LEN + CRC_LEN;
21const ENTRY_LEN: usize = 4;
22
23/// One entry in the PAT program loop.
24#[derive(Debug, Clone, PartialEq, Eq)]
25#[cfg_attr(feature = "serde", derive(serde::Serialize))]
26pub struct PatEntry {
27    /// program_number. 0x0000 means "next PID is the NIT PID".
28    pub program_number: u16,
29    /// PMT PID (or NIT PID when program_number == 0).
30    pub pid: u16,
31}
32
33/// Program Association Table.
34#[derive(Debug, Clone, Default, PartialEq, Eq)]
35#[cfg_attr(feature = "serde", derive(serde::Serialize))]
36pub struct PatSection {
37    /// transport_stream_id from the section header.
38    pub transport_stream_id: u16,
39    /// 5-bit version_number from the section header.
40    pub version_number: u8,
41    /// current_next_indicator bit.
42    pub current_next_indicator: bool,
43    /// section_number in the sub-table sequence.
44    pub section_number: u8,
45    /// last_section_number in the sub-table sequence.
46    pub last_section_number: u8,
47    /// Program entries in wire order.
48    pub entries: Vec<PatEntry>,
49}
50
51impl<'a> Parse<'a> for PatSection {
52    type Error = crate::error::Error;
53    fn parse(bytes: &'a [u8]) -> Result<Self> {
54        if bytes.len() < MIN_HEADER_LEN + EXTENSION_HEADER_LEN + CRC_LEN {
55            return Err(Error::BufferTooShort {
56                need: MIN_HEADER_LEN + EXTENSION_HEADER_LEN + CRC_LEN,
57                have: bytes.len(),
58                what: "PatSection",
59            });
60        }
61
62        if bytes[0] != TABLE_ID {
63            return Err(Error::UnexpectedTableId {
64                table_id: bytes[0],
65                what: "PatSection",
66                expected: &[TABLE_ID],
67            });
68        }
69
70        let section_length = ((bytes[1] & 0x0F) as u16) << 8 | bytes[2] as u16;
71        let total = super::check_section_length(
72            bytes.len(),
73            MIN_HEADER_LEN,
74            section_length as usize,
75            MIN_SECTION_LEN,
76        )?;
77
78        let transport_stream_id = u16::from_be_bytes([bytes[3], bytes[4]]);
79        let version_number = (bytes[5] >> 1) & 0x1F;
80        let current_next_indicator = (bytes[5] & 0x01) != 0;
81        let section_number = bytes[6];
82        let last_section_number = bytes[7];
83
84        let end = total - CRC_LEN;
85        let mut entries = Vec::new();
86        let mut pos = 8;
87        while pos < end {
88            if pos + ENTRY_LEN > end {
89                return Err(Error::BufferTooShort {
90                    need: ENTRY_LEN,
91                    have: end - pos,
92                    what: "PatSection trailing entry bytes",
93                });
94            }
95            let chunk = &bytes[pos..pos + ENTRY_LEN];
96            let program_number = u16::from_be_bytes([chunk[0], chunk[1]]);
97            let pid = (((chunk[2] & 0x1F) as u16) << 8) | chunk[3] as u16;
98            entries.push(PatEntry {
99                program_number,
100                pid,
101            });
102            pos += ENTRY_LEN;
103        }
104
105        Ok(PatSection {
106            transport_stream_id,
107            version_number,
108            current_next_indicator,
109            section_number,
110            last_section_number,
111            entries,
112        })
113    }
114}
115
116impl Serialize for PatSection {
117    type Error = crate::error::Error;
118    fn serialized_len(&self) -> usize {
119        MIN_HEADER_LEN + EXTENSION_HEADER_LEN + self.entries.len() * ENTRY_LEN + CRC_LEN
120    }
121
122    fn serialize_into(&self, buf: &mut [u8]) -> Result<usize> {
123        let len = self.serialized_len();
124        if buf.len() < len {
125            return Err(Error::OutputBufferTooSmall {
126                need: len,
127                have: buf.len(),
128            });
129        }
130
131        let section_length: u16 =
132            (EXTENSION_HEADER_LEN + self.entries.len() * ENTRY_LEN + CRC_LEN) as u16;
133
134        buf[0] = TABLE_ID;
135        buf[1] = super::SECTION_B1_FLAGS_PSI | ((section_length >> 8) as u8 & 0x0F);
136        buf[2] = (section_length & 0xFF) as u8;
137        buf[3..5].copy_from_slice(&self.transport_stream_id.to_be_bytes());
138        buf[5] = 0xC0 | ((self.version_number & 0x1F) << 1) | u8::from(self.current_next_indicator);
139        buf[6] = self.section_number;
140        buf[7] = self.last_section_number;
141
142        let mut pos = 8;
143        for entry in &self.entries {
144            buf[pos..pos + 2].copy_from_slice(&entry.program_number.to_be_bytes());
145            buf[pos + 2] = 0xE0 | ((entry.pid >> 8) as u8 & 0x1F);
146            buf[pos + 3] = (entry.pid & 0xFF) as u8;
147            pos += ENTRY_LEN;
148        }
149
150        let crc_pos = len - CRC_LEN;
151        let crc = dvb_common::crc32_mpeg2::compute(&buf[..crc_pos]);
152        buf[crc_pos..len].copy_from_slice(&crc.to_be_bytes());
153
154        Ok(len)
155    }
156}
157impl<'a> crate::traits::TableDef<'a> for PatSection {
158    const TABLE_ID_RANGES: &'static [(u8, u8)] = &[(TABLE_ID, TABLE_ID)];
159    const NAME: &'static str = "PROGRAM_ASSOCIATION";
160}
161
162impl PatSection {
163    /// Program entries excluding the NIT entry.
164    pub fn programmes(&self) -> impl Iterator<Item = &PatEntry> {
165        self.entries
166            .iter()
167            .filter(|e| e.program_number != PROGRAM_NUMBER_NIT)
168    }
169
170    /// NIT PID if this PAT carries an entry with program_number == 0.
171    pub fn nit_pid(&self) -> Option<u16> {
172        self.entries
173            .iter()
174            .find(|e| e.program_number == PROGRAM_NUMBER_NIT)
175            .map(|e| e.pid)
176    }
177}
178
179#[cfg(test)]
180mod tests {
181    use super::*;
182
183    /// Build a PAT section with the given entries and a placeholder CRC.
184    fn build_pat(tsid: u16, version: u8, entries: &[(u16, u16)]) -> Vec<u8> {
185        let section_length: u16 =
186            (EXTENSION_HEADER_LEN + entries.len() * ENTRY_LEN + CRC_LEN) as u16;
187        let mut v = Vec::new();
188        v.push(TABLE_ID);
189        v.push(super::super::SECTION_B1_FLAGS_PSI | ((section_length >> 8) as u8 & 0x0F));
190        v.push((section_length & 0xFF) as u8);
191        v.extend_from_slice(&tsid.to_be_bytes());
192        v.push(0xC0 | ((version & 0x1F) << 1) | 0x01); // version, cni=1
193        v.push(0x00); // section_number
194        v.push(0x00); // last_section_number
195        for &(pn, pid) in entries {
196            v.extend_from_slice(&pn.to_be_bytes());
197            v.push(0xE0 | ((pid >> 8) as u8 & 0x1F));
198            v.push((pid & 0xFF) as u8);
199        }
200        v.extend_from_slice(&[0, 0, 0, 0]); // placeholder CRC
201        v
202    }
203
204    #[test]
205    fn parse_empty_pat_zero_programs() {
206        let bytes = build_pat(0x1234, 5, &[]);
207        let pat = PatSection::parse(&bytes).expect("parse");
208        assert_eq!(pat.transport_stream_id, 0x1234);
209        assert_eq!(pat.version_number, 5);
210        assert!(pat.current_next_indicator);
211        assert_eq!(pat.section_number, 0);
212        assert_eq!(pat.last_section_number, 0);
213        assert_eq!(pat.entries.len(), 0);
214    }
215
216    #[test]
217    fn parse_single_program_extracts_pmt_pid() {
218        let bytes = build_pat(1, 0, &[(42, 0x1234)]);
219        let pat = PatSection::parse(&bytes).unwrap();
220        assert_eq!(pat.entries.len(), 1);
221        assert_eq!(pat.entries[0].program_number, 42);
222        assert_eq!(pat.entries[0].pid, 0x1234);
223    }
224
225    #[test]
226    fn parse_many_programs_preserves_order() {
227        let entries: Vec<(u16, u16)> = (1..=10).map(|i| (i, 0x1000 + i)).collect();
228        let bytes = build_pat(1, 0, &entries);
229        let pat = PatSection::parse(&bytes).unwrap();
230        assert_eq!(pat.entries.len(), 10);
231        for (i, e) in pat.entries.iter().enumerate() {
232            assert_eq!(e.program_number, (i + 1) as u16);
233            assert_eq!(e.pid, 0x1000 + (i + 1) as u16);
234        }
235    }
236
237    #[test]
238    fn parse_rejects_wrong_table_id() {
239        let mut bytes = build_pat(1, 0, &[]);
240        bytes[0] = 0x02; // PMT table_id
241        let err = PatSection::parse(&bytes).unwrap_err();
242        assert!(matches!(
243            err,
244            Error::UnexpectedTableId { table_id: 0x02, .. }
245        ));
246    }
247
248    #[test]
249    fn parse_rejects_short_buffer() {
250        let err = PatSection::parse(&[0x00, 0x00]).unwrap_err();
251        assert!(matches!(err, Error::BufferTooShort { .. }));
252    }
253
254    #[test]
255    fn serialize_round_trip_empty() {
256        let pat = PatSection {
257            transport_stream_id: 0x0001,
258            version_number: 0,
259            current_next_indicator: true,
260            section_number: 0,
261            last_section_number: 0,
262            entries: vec![],
263        };
264        let mut buf = vec![0u8; pat.serialized_len()];
265        pat.serialize_into(&mut buf).expect("serialize");
266        let reparsed = PatSection::parse(&buf).expect("reparse");
267        assert_eq!(pat, reparsed);
268    }
269
270    #[test]
271    fn serialize_round_trip_many_programs() {
272        let entries: Vec<PatEntry> = (1..=5)
273            .map(|i| PatEntry {
274                program_number: i,
275                pid: 0x1000 + i,
276            })
277            .collect();
278        let pat = PatSection {
279            transport_stream_id: 0xABCD,
280            version_number: 3,
281            current_next_indicator: true,
282            section_number: 0,
283            last_section_number: 0,
284            entries,
285        };
286        let mut buf = vec![0u8; pat.serialized_len()];
287        pat.serialize_into(&mut buf).unwrap();
288        let reparsed = PatSection::parse(&buf).unwrap();
289        assert_eq!(pat, reparsed);
290    }
291
292    #[test]
293    fn parse_rejects_zero_section_length() {
294        let mut buf = vec![0u8; 64];
295        buf[0] = TABLE_ID;
296        buf[1] = 0xB0;
297        buf[2] = 0x00;
298        for b in &mut buf[3..] {
299            *b = 0xFF;
300        }
301        assert!(matches!(
302            PatSection::parse(&buf).unwrap_err(),
303            Error::SectionLengthOverflow { .. }
304        ));
305    }
306
307    #[test]
308    fn network_pid_entry_identified_by_program_number_0() {
309        let bytes = build_pat(1, 0, &[(0, 0x0010), (1, 0x0100)]);
310        let pat = PatSection::parse(&bytes).unwrap();
311        assert_eq!(pat.nit_pid(), Some(0x0010));
312        assert_eq!(pat.programmes().count(), 1);
313        assert_eq!(pat.programmes().next().unwrap().program_number, 1);
314    }
315
316    #[test]
317    fn parse_rejects_trailing_slack_bytes() {
318        let mut bytes = build_pat(1, 0, &[(1, 0x100)]);
319        let sl = (bytes.len() - MIN_HEADER_LEN) as u16;
320        bytes[1] = (bytes[1] & 0xF0) | (((sl + 2) >> 8) as u8 & 0x0F);
321        bytes[2] = ((sl + 2) & 0xFF) as u8;
322        bytes.extend_from_slice(&[0xFF, 0xFF]);
323        let crc_pos = bytes.len();
324        let crc = dvb_common::crc32_mpeg2::compute(&bytes[..crc_pos - CRC_LEN]);
325        bytes[crc_pos - CRC_LEN..crc_pos].copy_from_slice(&crc.to_be_bytes());
326        assert!(matches!(
327            PatSection::parse(&bytes).unwrap_err(),
328            Error::BufferTooShort {
329                what: "PatSection trailing entry bytes",
330                ..
331            }
332        ));
333    }
334}
dvb_si/tables/pat.rs

dvb_si/tables/
pat.rs
