dvb_si/tables/
nit.rs

1//! Network Information Table — ETSI EN 300 468 §5.2.1.
2//!
3//! NIT describes the transport streams belonging to a DVB network, with
4//! network-wide descriptors and per-transport-stream descriptors. The
5//! table is split into two variants by table_id: `0x40` for the actual
6//! TS the receiver is tuned to, `0x41` for other TSes in the same network.
7
8use crate::descriptors::DescriptorLoop;
9use crate::error::{Error, Result};
10use crate::traits::Table;
11use dvb_common::{Parse, Serialize};
12
13/// table_id value for NIT actual (current TS).
14pub const TABLE_ID_ACTUAL: u8 = 0x40;
15/// table_id value for NIT other (other TSes in the network).
16pub const TABLE_ID_OTHER: u8 = 0x41;
17/// Well-known PID on which NIT is carried.
18pub const PID: u16 = 0x0010;
19
20const MIN_HEADER_LEN: usize = 3;
21const EXTENSION_HEADER_LEN: usize = 5;
22/// Bytes after the extension header: reserved_future_use (4 bits) + network_descriptors_length (12 bits) = 2 bytes.
23/// (Previously incorrectly defined as 4 — the parser assumed `network_id`
24/// was duplicated *after* the extension header; spec says it lives IN
25/// the extension header at bytes 3-4 as `table_id_extension`.)
26const POST_EXTENSION_LEN: usize = 2;
27const CRC_LEN: usize = 4;
28/// Per-transport-stream header: ts_id (2) + original_network_id (2) + reserved_future_use (4 bits) + transport_descriptors_length (12 bits).
29const TS_HEADER_LEN: usize = 6;
30
31/// NIT kind — distinguishes `0x40` (actual) from `0x41` (other).
32#[derive(Debug, Clone, Copy, PartialEq, Eq)]
33#[cfg_attr(feature = "serde", derive(serde::Serialize))]
34pub enum NitKind {
35    /// NIT for the transport stream the receiver is tuned to.
36    Actual,
37    /// NIT describing other transport streams in the same network.
38    Other,
39}
40
41/// One transport-stream entry inside the NIT transport_stream_loop.
42#[derive(Debug, Clone, PartialEq, Eq)]
43#[cfg_attr(feature = "serde", derive(serde::Serialize))]
44#[cfg_attr(feature = "yoke", derive(yoke::Yokeable))]
45pub struct NitTransportStream<'a> {
46    /// transport_stream_id of the described TS.
47    pub transport_stream_id: u16,
48    /// original_network_id of the described TS.
49    pub original_network_id: u16,
50    /// Raw descriptor bytes for this transport stream.
51    /// Per-TS descriptor loop. Serializes as the typed descriptor sequence;
52    /// `.raw()` yields the wire bytes.
53    pub descriptors: DescriptorLoop<'a>,
54}
55
56/// Network Information Table.
57#[derive(Debug, Clone, PartialEq, Eq)]
58#[cfg_attr(feature = "serde", derive(serde::Serialize))]
59#[cfg_attr(feature = "yoke", derive(yoke::Yokeable))]
60pub struct Nit<'a> {
61    /// Variant discriminator (table_id 0x40 vs 0x41).
62    pub kind: NitKind,
63    /// Network identifier.
64    pub network_id: u16,
65    /// 5-bit version_number.
66    pub version_number: u8,
67    /// current_next_indicator bit.
68    pub current_next_indicator: bool,
69    /// section_number in the sub-table sequence.
70    pub section_number: u8,
71    /// last_section_number in the sub-table sequence.
72    pub last_section_number: u8,
73    /// Raw network-wide descriptor bytes.
74    /// Network descriptor loop. Serializes as the typed descriptor sequence;
75    /// `.raw()` yields the wire bytes.
76    pub network_descriptors: DescriptorLoop<'a>,
77    /// Transport-stream loop entries in wire order.
78    pub transport_streams: Vec<NitTransportStream<'a>>,
79}
80
81impl<'a> Parse<'a> for Nit<'a> {
82    type Error = crate::error::Error;
83    fn parse(bytes: &'a [u8]) -> Result<Self> {
84        let min_len = MIN_HEADER_LEN + EXTENSION_HEADER_LEN + POST_EXTENSION_LEN + CRC_LEN;
85        if bytes.len() < min_len {
86            return Err(Error::BufferTooShort {
87                need: min_len,
88                have: bytes.len(),
89                what: "Nit",
90            });
91        }
92        let kind = match bytes[0] {
93            TABLE_ID_ACTUAL => NitKind::Actual,
94            TABLE_ID_OTHER => NitKind::Other,
95            other => {
96                return Err(Error::UnexpectedTableId {
97                    table_id: other,
98                    what: "Nit",
99                    expected: &[TABLE_ID_ACTUAL, TABLE_ID_OTHER],
100                });
101            }
102        };
103
104        let section_length = ((bytes[1] & 0x0F) as u16) << 8 | bytes[2] as u16;
105        let total = MIN_HEADER_LEN + section_length as usize;
106        if bytes.len() < total {
107            return Err(Error::SectionLengthOverflow {
108                declared: section_length as usize,
109                available: bytes.len() - MIN_HEADER_LEN,
110            });
111        }
112
113        // Extension header bytes [3..8] per ETSI EN 300 468 §5.2.1:
114        //   bytes[3..5] = table_id_extension = network_id (16 bits)
115        //   bytes[5]    = reserved(2) | version_number(5) | current_next_indicator(1)
116        //   bytes[6]    = section_number
117        //   bytes[7]    = last_section_number
118        let network_id = u16::from_be_bytes([bytes[3], bytes[4]]);
119        let version_number = (bytes[5] >> 1) & 0x1F;
120        let current_next_indicator = (bytes[5] & 0x01) != 0;
121        let section_number = bytes[6];
122        let last_section_number = bytes[7];
123
124        // bytes[8..10] = reserved(4) | network_descriptors_length(12)
125        let network_descriptors_length = (((bytes[8] & 0x0F) as usize) << 8) | bytes[9] as usize;
126
127        let network_desc_start = MIN_HEADER_LEN + EXTENSION_HEADER_LEN + POST_EXTENSION_LEN;
128        let network_desc_end = network_desc_start + network_descriptors_length;
129
130        // Verify network descriptors don't overflow
131        if network_desc_end > total - CRC_LEN {
132            return Err(Error::SectionLengthOverflow {
133                declared: network_descriptors_length,
134                available: (total - CRC_LEN) - network_desc_start,
135            });
136        }
137
138        let network_descriptors = DescriptorLoop::new(&bytes[network_desc_start..network_desc_end]);
139
140        // Parse transport stream loop starting after network descriptors
141        let ts_loop_start = network_desc_end;
142        let ts_loop_end = total - CRC_LEN;
143
144        // First 2 bytes of the loop are: reserved_future_use (4 bits) + transport_stream_loop_length (12 bits)
145        if ts_loop_end - ts_loop_start < 2 {
146            return Err(Error::BufferTooShort {
147                need: ts_loop_end - ts_loop_start + 2,
148                have: ts_loop_end - ts_loop_start,
149                what: "Nit transport_stream_loop",
150            });
151        }
152
153        let transport_stream_loop_length =
154            (((bytes[ts_loop_start] & 0x0F) as usize) << 8) | bytes[ts_loop_start + 1] as usize;
155
156        let mut pos = ts_loop_start + 2;
157        let loop_end = ts_loop_start + 2 + transport_stream_loop_length;
158
159        if loop_end > ts_loop_end {
160            return Err(Error::SectionLengthOverflow {
161                declared: transport_stream_loop_length,
162                available: ts_loop_end - (ts_loop_start + 2),
163            });
164        }
165
166        let mut transport_streams = Vec::new();
167
168        while pos < loop_end {
169            if pos + TS_HEADER_LEN > loop_end {
170                return Err(Error::BufferTooShort {
171                    need: pos + TS_HEADER_LEN,
172                    have: loop_end,
173                    what: "Nit transport_stream_entry",
174                });
175            }
176
177            let transport_stream_id = u16::from_be_bytes([bytes[pos], bytes[pos + 1]]);
178            let original_network_id = u16::from_be_bytes([bytes[pos + 2], bytes[pos + 3]]);
179
180            // transport_descriptors_length is 12 bits: high 4 bits reserved, low 12 bits length
181            let transport_descriptors_length =
182                (((bytes[pos + 4] & 0x0F) as usize) << 8) | bytes[pos + 5] as usize;
183
184            let desc_start = pos + TS_HEADER_LEN;
185            let desc_end = desc_start + transport_descriptors_length;
186
187            if desc_end > loop_end {
188                return Err(Error::SectionLengthOverflow {
189                    declared: transport_descriptors_length,
190                    available: loop_end - desc_start,
191                });
192            }
193
194            transport_streams.push(NitTransportStream {
195                transport_stream_id,
196                original_network_id,
197                descriptors: DescriptorLoop::new(&bytes[desc_start..desc_end]),
198            });
199
200            pos = desc_end;
201        }
202
203        Ok(Nit {
204            kind,
205            network_id,
206            version_number,
207            current_next_indicator,
208            section_number,
209            last_section_number,
210            network_descriptors,
211            transport_streams,
212        })
213    }
214}
215
216impl Serialize for Nit<'_> {
217    type Error = crate::error::Error;
218    fn serialized_len(&self) -> usize {
219        let net_desc_len = self.network_descriptors.len();
220        let ts_bytes: usize = self
221            .transport_streams
222            .iter()
223            .map(|ts| TS_HEADER_LEN + ts.descriptors.len())
224            .sum();
225        MIN_HEADER_LEN
226            + EXTENSION_HEADER_LEN
227            + POST_EXTENSION_LEN
228            + net_desc_len
229            + 2 // transport_stream_loop_length header
230            + ts_bytes
231            + CRC_LEN
232    }
233
234    fn serialize_into(&self, buf: &mut [u8]) -> Result<usize> {
235        let len = self.serialized_len();
236        if buf.len() < len {
237            return Err(Error::OutputBufferTooSmall {
238                need: len,
239                have: buf.len(),
240            });
241        }
242
243        let section_length: u16 = (len - MIN_HEADER_LEN) as u16;
244        buf[0] = match self.kind {
245            NitKind::Actual => TABLE_ID_ACTUAL,
246            NitKind::Other => TABLE_ID_OTHER,
247        };
248        buf[1] = 0xB0 | ((section_length >> 8) as u8 & 0x0F);
249        buf[2] = (section_length & 0xFF) as u8;
250
251        // Extension header per ETSI EN 300 468 §5.2.1:
252        //   bytes[3..5] = network_id (table_id_extension)
253        //   bytes[5]    = reserved | version | current_next
254        //   bytes[6..8] = section_number + last_section_number
255        buf[3..5].copy_from_slice(&self.network_id.to_be_bytes());
256        buf[5] = 0xC0 | ((self.version_number & 0x1F) << 1) | u8::from(self.current_next_indicator);
257        buf[6] = self.section_number;
258        buf[7] = self.last_section_number;
259
260        // bytes[8..10] = reserved(4) | network_descriptors_length(12)
261        let net_dll = self.network_descriptors.len() as u16;
262        buf[8] = 0xF0 | ((net_dll >> 8) as u8 & 0x0F);
263        buf[9] = (net_dll & 0xFF) as u8;
264
265        let net_desc_start = MIN_HEADER_LEN + EXTENSION_HEADER_LEN + POST_EXTENSION_LEN;
266        buf[net_desc_start..net_desc_start + self.network_descriptors.len()]
267            .copy_from_slice(self.network_descriptors.raw());
268
269        let ts_loop_start = net_desc_start + self.network_descriptors.len();
270        let ts_loop_length: u16 = (len - ts_loop_start - 2 - CRC_LEN) as u16;
271        buf[ts_loop_start] = 0xF0 | ((ts_loop_length >> 8) as u8 & 0x0F);
272        buf[ts_loop_start + 1] = (ts_loop_length & 0xFF) as u8;
273
274        let mut pos = ts_loop_start + 2;
275        for ts in &self.transport_streams {
276            buf[pos..pos + 2].copy_from_slice(&ts.transport_stream_id.to_be_bytes());
277            buf[pos + 2..pos + 4].copy_from_slice(&ts.original_network_id.to_be_bytes());
278            let ts_dll = ts.descriptors.len() as u16;
279            buf[pos + 4] = 0xF0 | ((ts_dll >> 8) as u8 & 0x0F);
280            buf[pos + 5] = (ts_dll & 0xFF) as u8;
281            let desc_start = pos + TS_HEADER_LEN;
282            buf[desc_start..desc_start + ts.descriptors.len()]
283                .copy_from_slice(ts.descriptors.raw());
284            pos = desc_start + ts.descriptors.len();
285        }
286
287        let crc_pos = len - CRC_LEN;
288        let crc = dvb_common::crc32_mpeg2::compute(&buf[..crc_pos]);
289        buf[crc_pos..len].copy_from_slice(&crc.to_be_bytes());
290        Ok(len)
291    }
292}
293
294impl<'a> Table<'a> for Nit<'a> {
295    const TABLE_ID: u8 = TABLE_ID_ACTUAL;
296    const PID: u16 = PID;
297}
298
299impl<'a> crate::traits::TableDef<'a> for Nit<'a> {
300    const TABLE_ID_RANGES: &'static [(u8, u8)] = &[(TABLE_ID_ACTUAL, TABLE_ID_OTHER)];
301    const NAME: &'static str = "NETWORK_INFORMATION";
302}
303
304#[cfg(test)]
305mod tests {
306    use super::*;
307
308    type TestTs = (u16, u16, Vec<u8>);
309
310    fn build_nit(
311        kind: NitKind,
312        network_id: u16,
313        network_desc: &[u8],
314        transport_streams: &[TestTs],
315    ) -> Vec<u8> {
316        let ts_bytes: usize = transport_streams
317            .iter()
318            .map(|(_, _, d)| TS_HEADER_LEN + d.len())
319            .sum();
320        let loop_length = ts_bytes as u16;
321        let section_length: u16 = (EXTENSION_HEADER_LEN
322            + POST_EXTENSION_LEN
323            + network_desc.len()
324            + 2
325            + ts_bytes
326            + CRC_LEN) as u16;
327        let mut v = Vec::new();
328        v.push(match kind {
329            NitKind::Actual => TABLE_ID_ACTUAL,
330            NitKind::Other => TABLE_ID_OTHER,
331        });
332        v.push(0xB0 | ((section_length >> 8) as u8 & 0x0F));
333        v.push((section_length & 0xFF) as u8);
334        // Extension header (spec layout): bytes[3..5] = network_id
335        v.extend_from_slice(&network_id.to_be_bytes());
336        v.push(0xC0 | 0x01); // version=0, current_next=1
337        v.push(0); // section_number
338        v.push(0); // last_section_number
339                   // bytes[8..10] = reserved(4) | network_descriptors_length(12)
340        let net_dll = network_desc.len() as u16;
341        v.push(0xF0 | ((net_dll >> 8) as u8 & 0x0F));
342        v.push((net_dll & 0xFF) as u8);
343        v.extend_from_slice(network_desc);
344        // reserved(4) | transport_stream_loop_length(12)
345        v.push(0xF0 | ((loop_length >> 8) as u8 & 0x0F));
346        v.push((loop_length & 0xFF) as u8);
347        for (tsid, onid, desc) in transport_streams {
348            v.extend_from_slice(&tsid.to_be_bytes());
349            v.extend_from_slice(&onid.to_be_bytes());
350            let ts_dll = desc.len() as u16;
351            // reserved(4) | transport_descriptors_length(12)
352            v.push(0xF0 | ((ts_dll >> 8) as u8 & 0x0F));
353            v.push((ts_dll & 0xFF) as u8);
354            v.extend_from_slice(desc);
355        }
356        v.extend_from_slice(&[0, 0, 0, 0]); // CRC placeholder
357        v
358    }
359
360    #[test]
361    fn parse_actual_and_other_distinguished_by_table_id() {
362        let a = build_nit(NitKind::Actual, 0x0001, &[], &[]);
363        let o = build_nit(NitKind::Other, 0x0001, &[], &[]);
364        assert!(matches!(Nit::parse(&a).unwrap().kind, NitKind::Actual));
365        assert!(matches!(Nit::parse(&o).unwrap().kind, NitKind::Other));
366    }
367
368    #[test]
369    fn parse_network_id_extracted() {
370        let bytes = build_nit(NitKind::Actual, 0x0020, &[], &[]);
371        let nit = Nit::parse(&bytes).unwrap();
372        assert_eq!(nit.network_id, 0x0020);
373    }
374
375    #[test]
376    fn parse_network_wide_descriptors() {
377        let net_desc: [u8; 4] = [0x40, 0x02, 0x4E, 0x65]; // network_name descriptor
378        let bytes = build_nit(NitKind::Actual, 0x0001, &net_desc, &[]);
379        let nit = Nit::parse(&bytes).unwrap();
380        assert_eq!(nit.network_descriptors.raw(), &net_desc[..]);
381    }
382
383    #[test]
384    fn parse_transport_stream_entries() {
385        let bytes = build_nit(
386            NitKind::Actual,
387            0x0001,
388            &[],
389            &[
390                (
391                    0x1234,
392                    0x0020,
393                    vec![0x43, 0x07, 0x0B, 0xB8, 0x00, 0x02, 0x00, 0x05],
394                ),
395                (0x5678, 0x0020, vec![]),
396            ],
397        );
398        let nit = Nit::parse(&bytes).unwrap();
399        assert_eq!(nit.transport_streams.len(), 2);
400        assert_eq!(nit.transport_streams[0].transport_stream_id, 0x1234);
401        assert_eq!(nit.transport_streams[0].original_network_id, 0x0020);
402        assert_eq!(
403            nit.transport_streams[0].descriptors.raw(),
404            &[0x43, 0x07, 0x0B, 0xB8, 0x00, 0x02, 0x00, 0x05][..]
405        );
406        assert_eq!(nit.transport_streams[1].transport_stream_id, 0x5678);
407        assert_eq!(nit.transport_streams[1].descriptors.len(), 0);
408    }
409
410    #[test]
411    fn parse_version_and_current_next() {
412        let bytes = build_nit(NitKind::Actual, 0x0001, &[], &[]);
413        let nit = Nit::parse(&bytes).unwrap();
414        assert_eq!(nit.version_number, 0);
415        assert!(nit.current_next_indicator);
416    }
417
418    #[test]
419    fn serialize_round_trip() {
420        let net_desc: [u8; 4] = [0x40, 0x02, 0x4E, 0x65];
421        let ts_desc: [u8; 3] = [0x43, 0x01, 0x01];
422        let nit = Nit {
423            kind: NitKind::Actual,
424            network_id: 0x0020,
425            version_number: 3,
426            current_next_indicator: true,
427            section_number: 0,
428            last_section_number: 0,
429            network_descriptors: DescriptorLoop::new(&net_desc),
430            transport_streams: vec![
431                NitTransportStream {
432                    transport_stream_id: 0x1234,
433                    original_network_id: 0x0020,
434                    descriptors: DescriptorLoop::new(&ts_desc),
435                },
436                NitTransportStream {
437                    transport_stream_id: 0x5678,
438                    original_network_id: 0x0020,
439                    descriptors: DescriptorLoop::new(&[]),
440                },
441            ],
442        };
443        let mut buf = vec![0u8; nit.serialized_len()];
444        nit.serialize_into(&mut buf).unwrap();
445        let re = Nit::parse(&buf).unwrap();
446        assert_eq!(nit, re);
447    }
448
449    #[test]
450    fn zero_transport_streams_is_valid() {
451        let bytes = build_nit(NitKind::Actual, 0x0001, &[], &[]);
452        let nit = Nit::parse(&bytes).unwrap();
453        assert_eq!(nit.transport_streams.len(), 0);
454    }
455
456    #[test]
457    fn parse_rejects_short_buffer() {
458        let err = Nit::parse(&[0x40, 0x00]).unwrap_err();
459        assert!(matches!(err, Error::BufferTooShort { .. }));
460    }
461
462    #[test]
463    fn parse_rejects_wrong_table_id() {
464        let mut bytes = build_nit(NitKind::Actual, 0x0001, &[], &[]);
465        bytes[0] = 0x00;
466        let err = Nit::parse(&bytes).unwrap_err();
467        assert!(matches!(
468            err,
469            Error::UnexpectedTableId { table_id: 0x00, .. }
470        ));
471    }
472
473    #[test]
474    fn serialize_too_small_buffer_returns_error() {
475        let nit = Nit {
476            kind: NitKind::Actual,
477            network_id: 0x0001,
478            version_number: 0,
479            current_next_indicator: true,
480            section_number: 0,
481            last_section_number: 0,
482            network_descriptors: DescriptorLoop::new(&[]),
483            transport_streams: vec![],
484        };
485        let mut buf = vec![0u8; 2];
486        let err = nit.serialize_into(&mut buf).unwrap_err();
487        assert!(matches!(err, Error::OutputBufferTooSmall { .. }));
488    }
489}
dvb_si/tables/nit.rs

dvb_si/tables/
nit.rs
