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, serde::Deserialize))]
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))]
44pub struct NitTransportStream<'a> {
45    /// transport_stream_id of the described TS.
46    pub transport_stream_id: u16,
47    /// original_network_id of the described TS.
48    pub original_network_id: u16,
49    /// Raw descriptor bytes for this transport stream.
50    #[cfg_attr(feature = "serde", serde(borrow))]
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))]
59pub struct Nit<'a> {
60    /// Variant discriminator (table_id 0x40 vs 0x41).
61    pub kind: NitKind,
62    /// Network identifier.
63    pub network_id: u16,
64    /// 5-bit version_number.
65    pub version_number: u8,
66    /// current_next_indicator bit.
67    pub current_next_indicator: bool,
68    /// section_number in the sub-table sequence.
69    pub section_number: u8,
70    /// last_section_number in the sub-table sequence.
71    pub last_section_number: u8,
72    /// Raw network-wide descriptor bytes.
73    #[cfg_attr(feature = "serde", serde(borrow))]
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    #[cfg_attr(feature = "serde", serde(borrow))]
79    pub transport_streams: Vec<NitTransportStream<'a>>,
80}
81
82impl<'a> Parse<'a> for Nit<'a> {
83    type Error = crate::error::Error;
84    fn parse(bytes: &'a [u8]) -> Result<Self> {
85        let min_len = MIN_HEADER_LEN + EXTENSION_HEADER_LEN + POST_EXTENSION_LEN + CRC_LEN;
86        if bytes.len() < min_len {
87            return Err(Error::BufferTooShort {
88                need: min_len,
89                have: bytes.len(),
90                what: "Nit",
91            });
92        }
93        let kind = match bytes[0] {
94            TABLE_ID_ACTUAL => NitKind::Actual,
95            TABLE_ID_OTHER => NitKind::Other,
96            other => {
97                return Err(Error::UnexpectedTableId {
98                    table_id: other,
99                    what: "Nit",
100                    expected: &[TABLE_ID_ACTUAL, TABLE_ID_OTHER],
101                });
102            }
103        };
104
105        let section_length = ((bytes[1] & 0x0F) as u16) << 8 | bytes[2] as u16;
106        let total = MIN_HEADER_LEN + section_length as usize;
107        if bytes.len() < total {
108            return Err(Error::SectionLengthOverflow {
109                declared: section_length as usize,
110                available: bytes.len() - MIN_HEADER_LEN,
111            });
112        }
113
114        // Extension header bytes [3..8] per ETSI EN 300 468 §5.2.1:
115        //   bytes[3..5] = table_id_extension = network_id (16 bits)
116        //   bytes[5]    = reserved(2) | version_number(5) | current_next_indicator(1)
117        //   bytes[6]    = section_number
118        //   bytes[7]    = last_section_number
119        let network_id = u16::from_be_bytes([bytes[3], bytes[4]]);
120        let version_number = (bytes[5] >> 1) & 0x1F;
121        let current_next_indicator = (bytes[5] & 0x01) != 0;
122        let section_number = bytes[6];
123        let last_section_number = bytes[7];
124
125        // bytes[8..10] = reserved(4) | network_descriptors_length(12)
126        let network_descriptors_length = (((bytes[8] & 0x0F) as usize) << 8) | bytes[9] as usize;
127
128        let network_desc_start = MIN_HEADER_LEN + EXTENSION_HEADER_LEN + POST_EXTENSION_LEN;
129        let network_desc_end = network_desc_start + network_descriptors_length;
130
131        // Verify network descriptors don't overflow
132        if network_desc_end > total - CRC_LEN {
133            return Err(Error::SectionLengthOverflow {
134                declared: network_descriptors_length,
135                available: (total - CRC_LEN) - network_desc_start,
136            });
137        }
138
139        let network_descriptors = DescriptorLoop::new(&bytes[network_desc_start..network_desc_end]);
140
141        // Parse transport stream loop starting after network descriptors
142        let ts_loop_start = network_desc_end;
143        let ts_loop_end = total - CRC_LEN;
144
145        // First 2 bytes of the loop are: reserved_future_use (4 bits) + transport_stream_loop_length (12 bits)
146        if ts_loop_end - ts_loop_start < 2 {
147            return Err(Error::BufferTooShort {
148                need: ts_loop_end - ts_loop_start + 2,
149                have: ts_loop_end - ts_loop_start,
150                what: "Nit transport_stream_loop",
151            });
152        }
153
154        let transport_stream_loop_length =
155            (((bytes[ts_loop_start] & 0x0F) as usize) << 8) | bytes[ts_loop_start + 1] as usize;
156
157        let mut pos = ts_loop_start + 2;
158        let loop_end = ts_loop_start + 2 + transport_stream_loop_length;
159
160        if loop_end > ts_loop_end {
161            return Err(Error::SectionLengthOverflow {
162                declared: transport_stream_loop_length,
163                available: ts_loop_end - (ts_loop_start + 2),
164            });
165        }
166
167        let mut transport_streams = Vec::new();
168
169        while pos < loop_end {
170            if pos + TS_HEADER_LEN > loop_end {
171                return Err(Error::BufferTooShort {
172                    need: pos + TS_HEADER_LEN,
173                    have: loop_end,
174                    what: "Nit transport_stream_entry",
175                });
176            }
177
178            let transport_stream_id = u16::from_be_bytes([bytes[pos], bytes[pos + 1]]);
179            let original_network_id = u16::from_be_bytes([bytes[pos + 2], bytes[pos + 3]]);
180
181            // transport_descriptors_length is 12 bits: high 4 bits reserved, low 12 bits length
182            let transport_descriptors_length =
183                (((bytes[pos + 4] & 0x0F) as usize) << 8) | bytes[pos + 5] as usize;
184
185            let desc_start = pos + TS_HEADER_LEN;
186            let desc_end = desc_start + transport_descriptors_length;
187
188            if desc_end > loop_end {
189                return Err(Error::SectionLengthOverflow {
190                    declared: transport_descriptors_length,
191                    available: loop_end - desc_start,
192                });
193            }
194
195            transport_streams.push(NitTransportStream {
196                transport_stream_id,
197                original_network_id,
198                descriptors: DescriptorLoop::new(&bytes[desc_start..desc_end]),
199            });
200
201            pos = desc_end;
202        }
203
204        Ok(Nit {
205            kind,
206            network_id,
207            version_number,
208            current_next_indicator,
209            section_number,
210            last_section_number,
211            network_descriptors,
212            transport_streams,
213        })
214    }
215}
216
217impl Serialize for Nit<'_> {
218    type Error = crate::error::Error;
219    fn serialized_len(&self) -> usize {
220        let net_desc_len = self.network_descriptors.len();
221        let ts_bytes: usize = self
222            .transport_streams
223            .iter()
224            .map(|ts| TS_HEADER_LEN + ts.descriptors.len())
225            .sum();
226        MIN_HEADER_LEN
227            + EXTENSION_HEADER_LEN
228            + POST_EXTENSION_LEN
229            + net_desc_len
230            + 2 // transport_stream_loop_length header
231            + ts_bytes
232            + CRC_LEN
233    }
234
235    fn serialize_into(&self, buf: &mut [u8]) -> Result<usize> {
236        let len = self.serialized_len();
237        if buf.len() < len {
238            return Err(Error::OutputBufferTooSmall {
239                need: len,
240                have: buf.len(),
241            });
242        }
243
244        let section_length: u16 = (len - MIN_HEADER_LEN) as u16;
245        buf[0] = match self.kind {
246            NitKind::Actual => TABLE_ID_ACTUAL,
247            NitKind::Other => TABLE_ID_OTHER,
248        };
249        buf[1] = 0xB0 | ((section_length >> 8) as u8 & 0x0F);
250        buf[2] = (section_length & 0xFF) as u8;
251
252        // Extension header per ETSI EN 300 468 §5.2.1:
253        //   bytes[3..5] = network_id (table_id_extension)
254        //   bytes[5]    = reserved | version | current_next
255        //   bytes[6..8] = section_number + last_section_number
256        buf[3..5].copy_from_slice(&self.network_id.to_be_bytes());
257        buf[5] = 0xC0 | ((self.version_number & 0x1F) << 1) | u8::from(self.current_next_indicator);
258        buf[6] = self.section_number;
259        buf[7] = self.last_section_number;
260
261        // bytes[8..10] = reserved(4) | network_descriptors_length(12)
262        let net_dll = self.network_descriptors.len() as u16;
263        buf[8] = 0xF0 | ((net_dll >> 8) as u8 & 0x0F);
264        buf[9] = (net_dll & 0xFF) as u8;
265
266        let net_desc_start = MIN_HEADER_LEN + EXTENSION_HEADER_LEN + POST_EXTENSION_LEN;
267        buf[net_desc_start..net_desc_start + self.network_descriptors.len()]
268            .copy_from_slice(self.network_descriptors.raw());
269
270        let ts_loop_start = net_desc_start + self.network_descriptors.len();
271        let ts_loop_length: u16 = (len - ts_loop_start - 2 - CRC_LEN) as u16;
272        buf[ts_loop_start] = 0xF0 | ((ts_loop_length >> 8) as u8 & 0x0F);
273        buf[ts_loop_start + 1] = (ts_loop_length & 0xFF) as u8;
274
275        let mut pos = ts_loop_start + 2;
276        for ts in &self.transport_streams {
277            buf[pos..pos + 2].copy_from_slice(&ts.transport_stream_id.to_be_bytes());
278            buf[pos + 2..pos + 4].copy_from_slice(&ts.original_network_id.to_be_bytes());
279            let ts_dll = ts.descriptors.len() as u16;
280            buf[pos + 4] = 0xF0 | ((ts_dll >> 8) as u8 & 0x0F);
281            buf[pos + 5] = (ts_dll & 0xFF) as u8;
282            let desc_start = pos + TS_HEADER_LEN;
283            buf[desc_start..desc_start + ts.descriptors.len()]
284                .copy_from_slice(ts.descriptors.raw());
285            pos = desc_start + ts.descriptors.len();
286        }
287
288        let crc_pos = len - CRC_LEN;
289        let crc = dvb_common::crc32_mpeg2::compute(&buf[..crc_pos]);
290        buf[crc_pos..len].copy_from_slice(&crc.to_be_bytes());
291        Ok(len)
292    }
293}
294
295impl<'a> Table<'a> for Nit<'a> {
296    const TABLE_ID: u8 = TABLE_ID_ACTUAL;
297    const PID: u16 = PID;
298}
299
300impl<'a> crate::traits::TableDef<'a> for Nit<'a> {
301    const TABLE_ID_RANGES: &'static [(u8, u8)] = &[(TABLE_ID_ACTUAL, TABLE_ID_OTHER)];
302    const NAME: &'static str = "NETWORK_INFORMATION";
303}
304
305#[cfg(test)]
306mod tests {
307    use super::*;
308
309    type TestTs = (u16, u16, Vec<u8>);
310
311    fn build_nit(
312        kind: NitKind,
313        network_id: u16,
314        network_desc: &[u8],
315        transport_streams: &[TestTs],
316    ) -> Vec<u8> {
317        let ts_bytes: usize = transport_streams
318            .iter()
319            .map(|(_, _, d)| TS_HEADER_LEN + d.len())
320            .sum();
321        let loop_length = ts_bytes as u16;
322        let section_length: u16 = (EXTENSION_HEADER_LEN
323            + POST_EXTENSION_LEN
324            + network_desc.len()
325            + 2
326            + ts_bytes
327            + CRC_LEN) as u16;
328        let mut v = Vec::new();
329        v.push(match kind {
330            NitKind::Actual => TABLE_ID_ACTUAL,
331            NitKind::Other => TABLE_ID_OTHER,
332        });
333        v.push(0xB0 | ((section_length >> 8) as u8 & 0x0F));
334        v.push((section_length & 0xFF) as u8);
335        // Extension header (spec layout): bytes[3..5] = network_id
336        v.extend_from_slice(&network_id.to_be_bytes());
337        v.push(0xC0 | 0x01); // version=0, current_next=1
338        v.push(0); // section_number
339        v.push(0); // last_section_number
340                   // bytes[8..10] = reserved(4) | network_descriptors_length(12)
341        let net_dll = network_desc.len() as u16;
342        v.push(0xF0 | ((net_dll >> 8) as u8 & 0x0F));
343        v.push((net_dll & 0xFF) as u8);
344        v.extend_from_slice(network_desc);
345        // reserved(4) | transport_stream_loop_length(12)
346        v.push(0xF0 | ((loop_length >> 8) as u8 & 0x0F));
347        v.push((loop_length & 0xFF) as u8);
348        for (tsid, onid, desc) in transport_streams {
349            v.extend_from_slice(&tsid.to_be_bytes());
350            v.extend_from_slice(&onid.to_be_bytes());
351            let ts_dll = desc.len() as u16;
352            // reserved(4) | transport_descriptors_length(12)
353            v.push(0xF0 | ((ts_dll >> 8) as u8 & 0x0F));
354            v.push((ts_dll & 0xFF) as u8);
355            v.extend_from_slice(desc);
356        }
357        v.extend_from_slice(&[0, 0, 0, 0]); // CRC placeholder
358        v
359    }
360
361    #[test]
362    fn parse_actual_and_other_distinguished_by_table_id() {
363        let a = build_nit(NitKind::Actual, 0x0001, &[], &[]);
364        let o = build_nit(NitKind::Other, 0x0001, &[], &[]);
365        assert!(matches!(Nit::parse(&a).unwrap().kind, NitKind::Actual));
366        assert!(matches!(Nit::parse(&o).unwrap().kind, NitKind::Other));
367    }
368
369    #[test]
370    fn parse_network_id_extracted() {
371        let bytes = build_nit(NitKind::Actual, 0x0020, &[], &[]);
372        let nit = Nit::parse(&bytes).unwrap();
373        assert_eq!(nit.network_id, 0x0020);
374    }
375
376    #[test]
377    fn parse_network_wide_descriptors() {
378        let net_desc: [u8; 4] = [0x40, 0x02, 0x4E, 0x65]; // network_name descriptor
379        let bytes = build_nit(NitKind::Actual, 0x0001, &net_desc, &[]);
380        let nit = Nit::parse(&bytes).unwrap();
381        assert_eq!(nit.network_descriptors.raw(), &net_desc[..]);
382    }
383
384    #[test]
385    fn parse_transport_stream_entries() {
386        let bytes = build_nit(
387            NitKind::Actual,
388            0x0001,
389            &[],
390            &[
391                (
392                    0x1234,
393                    0x0020,
394                    vec![0x43, 0x07, 0x0B, 0xB8, 0x00, 0x02, 0x00, 0x05],
395                ),
396                (0x5678, 0x0020, vec![]),
397            ],
398        );
399        let nit = Nit::parse(&bytes).unwrap();
400        assert_eq!(nit.transport_streams.len(), 2);
401        assert_eq!(nit.transport_streams[0].transport_stream_id, 0x1234);
402        assert_eq!(nit.transport_streams[0].original_network_id, 0x0020);
403        assert_eq!(
404            nit.transport_streams[0].descriptors.raw(),
405            &[0x43, 0x07, 0x0B, 0xB8, 0x00, 0x02, 0x00, 0x05][..]
406        );
407        assert_eq!(nit.transport_streams[1].transport_stream_id, 0x5678);
408        assert_eq!(nit.transport_streams[1].descriptors.len(), 0);
409    }
410
411    #[test]
412    fn parse_version_and_current_next() {
413        let bytes = build_nit(NitKind::Actual, 0x0001, &[], &[]);
414        let nit = Nit::parse(&bytes).unwrap();
415        assert_eq!(nit.version_number, 0);
416        assert!(nit.current_next_indicator);
417    }
418
419    #[test]
420    fn serialize_round_trip() {
421        let net_desc: [u8; 4] = [0x40, 0x02, 0x4E, 0x65];
422        let ts_desc: [u8; 3] = [0x43, 0x01, 0x01];
423        let nit = Nit {
424            kind: NitKind::Actual,
425            network_id: 0x0020,
426            version_number: 3,
427            current_next_indicator: true,
428            section_number: 0,
429            last_section_number: 0,
430            network_descriptors: DescriptorLoop::new(&net_desc),
431            transport_streams: vec![
432                NitTransportStream {
433                    transport_stream_id: 0x1234,
434                    original_network_id: 0x0020,
435                    descriptors: DescriptorLoop::new(&ts_desc),
436                },
437                NitTransportStream {
438                    transport_stream_id: 0x5678,
439                    original_network_id: 0x0020,
440                    descriptors: DescriptorLoop::new(&[]),
441                },
442            ],
443        };
444        let mut buf = vec![0u8; nit.serialized_len()];
445        nit.serialize_into(&mut buf).unwrap();
446        let re = Nit::parse(&buf).unwrap();
447        assert_eq!(nit, re);
448    }
449
450    #[test]
451    fn zero_transport_streams_is_valid() {
452        let bytes = build_nit(NitKind::Actual, 0x0001, &[], &[]);
453        let nit = Nit::parse(&bytes).unwrap();
454        assert_eq!(nit.transport_streams.len(), 0);
455    }
456
457    #[test]
458    fn parse_rejects_short_buffer() {
459        let err = Nit::parse(&[0x40, 0x00]).unwrap_err();
460        assert!(matches!(err, Error::BufferTooShort { .. }));
461    }
462
463    #[test]
464    fn parse_rejects_wrong_table_id() {
465        let mut bytes = build_nit(NitKind::Actual, 0x0001, &[], &[]);
466        bytes[0] = 0x00;
467        let err = Nit::parse(&bytes).unwrap_err();
468        assert!(matches!(
469            err,
470            Error::UnexpectedTableId { table_id: 0x00, .. }
471        ));
472    }
473
474    #[test]
475    fn serialize_too_small_buffer_returns_error() {
476        let nit = Nit {
477            kind: NitKind::Actual,
478            network_id: 0x0001,
479            version_number: 0,
480            current_next_indicator: true,
481            section_number: 0,
482            last_section_number: 0,
483            network_descriptors: DescriptorLoop::new(&[]),
484            transport_streams: vec![],
485        };
486        let mut buf = vec![0u8; 2];
487        let err = nit.serialize_into(&mut buf).unwrap_err();
488        assert!(matches!(err, Error::OutputBufferTooSmall { .. }));
489    }
490}
dvb_si/tables/nit.rs

dvb_si/tables/
nit.rs
