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

dvb_si/tables/
nit.rs
