dvb_si/tables/
sdt.rs

1//! Service Description Table — ETSI EN 300 468 §5.2.3.
2//!
3//! SDT lists the services available in a transport stream, with a
4//! descriptor loop per service (service_descriptor etc.). The table is
5//! split into two variants by table_id: `0x42` for the actual TS the
6//! receiver is tuned to, `0x46` for services on other TSes.
7
8use super::RunningStatus;
9use crate::descriptors::DescriptorLoop;
10use crate::error::{Error, Result};
11use alloc::vec::Vec;
12use dvb_common::{Parse, Serialize};
13
14/// table_id value for SDT describing services on the actual TS.
15pub const TABLE_ID_ACTUAL: u8 = 0x42;
16/// table_id value for SDT describing services on other TSes.
17pub const TABLE_ID_OTHER: u8 = 0x46;
18/// Well-known PID on which SDT is carried.
19pub const PID: u16 = 0x0011;
20
21const MIN_HEADER_LEN: usize = 3;
22const EXTENSION_HEADER_LEN: usize = 5;
23/// Bytes after the extension header and before the first service entry:
24/// 2 bytes of original_network_id + 1 reserved_future_use byte.
25const POST_EXTENSION_LEN: usize = 3;
26const CRC_LEN: usize = 4;
27const MIN_SECTION_LEN: usize = MIN_HEADER_LEN + EXTENSION_HEADER_LEN + POST_EXTENSION_LEN + CRC_LEN;
28const SERVICE_HEADER_LEN: usize = 5;
29
30/// SDT kind — distinguishes `0x42` (actual) from `0x46` (other).
31#[derive(Debug, Clone, Copy, PartialEq, Eq)]
32#[cfg_attr(feature = "serde", derive(serde::Serialize))]
33#[non_exhaustive]
34pub enum SdtKind {
35    /// Services on the transport stream the receiver is tuned to.
36    Actual,
37    /// Services on other transport streams (cross-TS SDT).
38    Other,
39}
40
41/// One service entry in an SDT.
42#[derive(Debug, Clone, PartialEq, Eq)]
43#[cfg_attr(feature = "serde", derive(serde::Serialize))]
44#[cfg_attr(feature = "yoke", derive(yoke::Yokeable))]
45pub struct SdtService<'a> {
46    /// service_id (matches `program_number` in the PAT).
47    pub service_id: u16,
48    /// EIT schedule flag — present-and-following events are in the EIT/schedule.
49    pub eit_schedule_flag: bool,
50    /// EIT P/F flag — present-and-following events are in the EIT present/following.
51    pub eit_present_following_flag: bool,
52    /// 3-bit running_status (EN 300 468 Table 6).
53    pub running_status: RunningStatus,
54    /// free_CA_mode: `true` = at least one elementary stream is scrambled.
55    pub free_ca_mode: bool,
56    /// Descriptor loop for this service (service_descriptor etc.). Serializes
57    /// as the typed descriptor sequence; `.raw()` yields the wire bytes.
58    pub descriptors: DescriptorLoop<'a>,
59}
60
61/// Service Description Table.
62#[derive(Debug, Clone, PartialEq, Eq)]
63#[cfg_attr(feature = "serde", derive(serde::Serialize))]
64#[cfg_attr(feature = "yoke", derive(yoke::Yokeable))]
65pub struct SdtSection<'a> {
66    /// Variant discriminator (table_id 0x42 vs 0x46).
67    pub kind: SdtKind,
68    /// transport_stream_id of the described TS.
69    pub transport_stream_id: u16,
70    /// 5-bit version_number.
71    pub version_number: u8,
72    /// current_next_indicator bit.
73    pub current_next_indicator: bool,
74    /// section_number in the sub-table sequence.
75    pub section_number: u8,
76    /// last_section_number in the sub-table sequence.
77    pub last_section_number: u8,
78    /// original_network_id of the described TS.
79    pub original_network_id: u16,
80    /// Services in wire order.
81    pub services: Vec<SdtService<'a>>,
82}
83
84impl<'a> Parse<'a> for SdtSection<'a> {
85    type Error = crate::error::Error;
86    fn parse(bytes: &'a [u8]) -> Result<Self> {
87        let min_len = MIN_HEADER_LEN + EXTENSION_HEADER_LEN + POST_EXTENSION_LEN + CRC_LEN;
88        if bytes.len() < min_len {
89            return Err(Error::BufferTooShort {
90                need: min_len,
91                have: bytes.len(),
92                what: "SdtSection",
93            });
94        }
95        let kind = match bytes[0] {
96            TABLE_ID_ACTUAL => SdtKind::Actual,
97            TABLE_ID_OTHER => SdtKind::Other,
98            other => {
99                return Err(Error::UnexpectedTableId {
100                    table_id: other,
101                    what: "SdtSection",
102                    expected: &[TABLE_ID_ACTUAL, TABLE_ID_OTHER],
103                });
104            }
105        };
106
107        let section_length = ((bytes[1] & 0x0F) as u16) << 8 | bytes[2] as u16;
108        let total = super::check_section_length(
109            bytes.len(),
110            MIN_HEADER_LEN,
111            section_length as usize,
112            MIN_SECTION_LEN,
113        )?;
114
115        let transport_stream_id = u16::from_be_bytes([bytes[3], bytes[4]]);
116        let version_number = (bytes[5] >> 1) & 0x1F;
117        let current_next_indicator = (bytes[5] & 0x01) != 0;
118        let section_number = bytes[6];
119        let last_section_number = bytes[7];
120        let original_network_id = u16::from_be_bytes([bytes[8], bytes[9]]);
121
122        let services_start = MIN_HEADER_LEN + EXTENSION_HEADER_LEN + POST_EXTENSION_LEN;
123        let services_end = total - CRC_LEN;
124        let mut services = Vec::new();
125        let mut pos = services_start;
126        while pos + SERVICE_HEADER_LEN <= services_end {
127            let service_id = u16::from_be_bytes([bytes[pos], bytes[pos + 1]]);
128            let flags = bytes[pos + 2];
129            let eit_schedule_flag = (flags & 0x02) != 0;
130            let eit_present_following_flag = (flags & 0x01) != 0;
131            let status_and_len_hi = bytes[pos + 3];
132            let running_status = RunningStatus::from_u8((status_and_len_hi >> 5) & 0x07);
133            let free_ca_mode = (status_and_len_hi & 0x10) != 0;
134            let descriptors_loop_length =
135                (((status_and_len_hi & 0x0F) as usize) << 8) | bytes[pos + 4] as usize;
136            let desc_start = pos + SERVICE_HEADER_LEN;
137            let desc_end = desc_start + descriptors_loop_length;
138            if desc_end > services_end {
139                return Err(Error::SectionLengthOverflow {
140                    declared: descriptors_loop_length,
141                    available: services_end.saturating_sub(desc_start),
142                });
143            }
144            services.push(SdtService {
145                service_id,
146                eit_schedule_flag,
147                eit_present_following_flag,
148                running_status,
149                free_ca_mode,
150                descriptors: DescriptorLoop::new(&bytes[desc_start..desc_end]),
151            });
152            pos = desc_end;
153        }
154
155        Ok(SdtSection {
156            kind,
157            transport_stream_id,
158            version_number,
159            current_next_indicator,
160            section_number,
161            last_section_number,
162            original_network_id,
163            services,
164        })
165    }
166}
167
168impl Serialize for SdtSection<'_> {
169    type Error = crate::error::Error;
170    fn serialized_len(&self) -> usize {
171        let svc_bytes: usize = self
172            .services
173            .iter()
174            .map(|s| SERVICE_HEADER_LEN + s.descriptors.len())
175            .sum();
176        MIN_HEADER_LEN + EXTENSION_HEADER_LEN + POST_EXTENSION_LEN + svc_bytes + CRC_LEN
177    }
178
179    fn serialize_into(&self, buf: &mut [u8]) -> Result<usize> {
180        let len = self.serialized_len();
181        if buf.len() < len {
182            return Err(Error::OutputBufferTooSmall {
183                need: len,
184                have: buf.len(),
185            });
186        }
187        let section_length: u16 = (len - MIN_HEADER_LEN) as u16;
188        buf[0] = match self.kind {
189            SdtKind::Actual => TABLE_ID_ACTUAL,
190            SdtKind::Other => TABLE_ID_OTHER,
191        };
192        buf[1] = super::SECTION_B1_FLAGS_DVB | ((section_length >> 8) as u8 & 0x0F);
193        buf[2] = (section_length & 0xFF) as u8;
194        buf[3..5].copy_from_slice(&self.transport_stream_id.to_be_bytes());
195        buf[5] = 0xC0 | ((self.version_number & 0x1F) << 1) | u8::from(self.current_next_indicator);
196        buf[6] = self.section_number;
197        buf[7] = self.last_section_number;
198        buf[8..10].copy_from_slice(&self.original_network_id.to_be_bytes());
199        buf[10] = 0xFF; // reserved_future_use
200
201        let mut pos = MIN_HEADER_LEN + EXTENSION_HEADER_LEN + POST_EXTENSION_LEN;
202        for svc in &self.services {
203            buf[pos..pos + 2].copy_from_slice(&svc.service_id.to_be_bytes());
204            let flags = 0xFC
205                | (u8::from(svc.eit_schedule_flag) << 1)
206                | u8::from(svc.eit_present_following_flag);
207            buf[pos + 2] = flags;
208            let dll = svc.descriptors.len() as u16;
209            buf[pos + 3] = (svc.running_status.to_u8() << 5)
210                | (u8::from(svc.free_ca_mode) << 4)
211                | ((dll >> 8) as u8 & 0x0F);
212            buf[pos + 4] = (dll & 0xFF) as u8;
213            let desc_start = pos + SERVICE_HEADER_LEN;
214            buf[desc_start..desc_start + svc.descriptors.len()]
215                .copy_from_slice(svc.descriptors.raw());
216            pos = desc_start + svc.descriptors.len();
217        }
218
219        let crc_pos = len - CRC_LEN;
220        let crc = dvb_common::crc32_mpeg2::compute(&buf[..crc_pos]);
221        buf[crc_pos..len].copy_from_slice(&crc.to_be_bytes());
222        Ok(len)
223    }
224}
225impl<'a> crate::traits::TableDef<'a> for SdtSection<'a> {
226    const TABLE_ID_RANGES: &'static [(u8, u8)] = &[
227        (TABLE_ID_ACTUAL, TABLE_ID_ACTUAL),
228        (TABLE_ID_OTHER, TABLE_ID_OTHER),
229    ];
230    const NAME: &'static str = "SERVICE_DESCRIPTION";
231}
232
233#[cfg(test)]
234mod tests {
235    use super::*;
236
237    type TestService = (u16, bool, bool, u8, bool, Vec<u8>);
238
239    fn build_sdt(
240        kind: SdtKind,
241        tsid: u16,
242        version: u8,
243        original_network_id: u16,
244        services: &[TestService],
245    ) -> Vec<u8> {
246        let svc_bytes: usize = services
247            .iter()
248            .map(|(_, _, _, _, _, d)| SERVICE_HEADER_LEN + d.len())
249            .sum();
250        let section_length: u16 =
251            (EXTENSION_HEADER_LEN + POST_EXTENSION_LEN + svc_bytes + CRC_LEN) as u16;
252        let mut v = Vec::new();
253        v.push(match kind {
254            SdtKind::Actual => TABLE_ID_ACTUAL,
255            SdtKind::Other => TABLE_ID_OTHER,
256        });
257        v.push(super::super::SECTION_B1_FLAGS_DVB | ((section_length >> 8) as u8 & 0x0F));
258        v.push((section_length & 0xFF) as u8);
259        v.extend_from_slice(&tsid.to_be_bytes());
260        v.push(0xC0 | ((version & 0x1F) << 1) | 0x01);
261        v.push(0);
262        v.push(0);
263        v.extend_from_slice(&original_network_id.to_be_bytes());
264        v.push(0xFF);
265        for (sid, eit_s, eit_pf, rs, fca, desc) in services {
266            v.extend_from_slice(&sid.to_be_bytes());
267            let flags = 0xFC | (u8::from(*eit_s) << 1) | u8::from(*eit_pf);
268            v.push(flags);
269            let dll = desc.len() as u16;
270            v.push(((*rs & 0x07) << 5) | (u8::from(*fca) << 4) | ((dll >> 8) as u8 & 0x0F));
271            v.push((dll & 0xFF) as u8);
272            v.extend_from_slice(desc);
273        }
274        v.extend_from_slice(&[0, 0, 0, 0]);
275        v
276    }
277
278    #[test]
279    fn parse_actual_and_other_tables_distinguished_by_table_id() {
280        let a = build_sdt(SdtKind::Actual, 1, 0, 0x20, &[]);
281        let o = build_sdt(SdtKind::Other, 1, 0, 0x20, &[]);
282        assert!(matches!(
283            SdtSection::parse(&a).unwrap().kind,
284            SdtKind::Actual
285        ));
286        assert!(matches!(
287            SdtSection::parse(&o).unwrap().kind,
288            SdtKind::Other
289        ));
290    }
291
292    #[test]
293    fn parse_services_with_descriptor_bytes() {
294        let bytes = build_sdt(
295            SdtKind::Actual,
296            1,
297            0,
298            0x20,
299            &[(
300                100,
301                true,
302                true,
303                4,
304                false,
305                vec![0x48, 0x05, 0x01, 0x02, 0x03, 0x04, 0x05],
306            )],
307        );
308        let sdt = SdtSection::parse(&bytes).unwrap();
309        assert_eq!(sdt.services.len(), 1);
310        assert_eq!(sdt.services[0].service_id, 100);
311        assert!(sdt.services[0].eit_schedule_flag);
312        assert!(sdt.services[0].eit_present_following_flag);
313        assert_eq!(sdt.services[0].running_status, RunningStatus::Running);
314        assert!(!sdt.services[0].free_ca_mode);
315        assert_eq!(
316            sdt.services[0].descriptors.raw(),
317            &[0x48, 0x05, 0x01, 0x02, 0x03, 0x04, 0x05][..]
318        );
319    }
320
321    #[test]
322    fn service_free_ca_mode_flag_extracted() {
323        let bytes = build_sdt(
324            SdtKind::Actual,
325            1,
326            0,
327            0x20,
328            &[(1, false, false, 0, true, vec![])],
329        );
330        let sdt = SdtSection::parse(&bytes).unwrap();
331        assert!(sdt.services[0].free_ca_mode);
332    }
333
334    #[test]
335    fn service_running_status_extracted() {
336        let bytes = build_sdt(
337            SdtKind::Actual,
338            1,
339            0,
340            0x20,
341            &[(1, false, false, 2, false, vec![])],
342        );
343        let sdt = SdtSection::parse(&bytes).unwrap();
344        assert_eq!(
345            sdt.services[0].running_status,
346            RunningStatus::StartsInAFewSeconds
347        );
348    }
349
350    #[test]
351    fn parse_rejects_short_buffer() {
352        let err = SdtSection::parse(&[0x42, 0x00]).unwrap_err();
353        assert!(matches!(err, Error::BufferTooShort { .. }));
354    }
355
356    #[test]
357    fn parse_rejects_wrong_table_id() {
358        let mut bytes = build_sdt(SdtKind::Actual, 1, 0, 0x20, &[]);
359        bytes[0] = 0x00;
360        let err = SdtSection::parse(&bytes).unwrap_err();
361        assert!(matches!(
362            err,
363            Error::UnexpectedTableId { table_id: 0x00, .. }
364        ));
365    }
366
367    #[test]
368    fn serialize_round_trip() {
369        let desc1: [u8; 4] = [0x48, 0x02, 0xAA, 0xBB];
370        let sdt = SdtSection {
371            kind: SdtKind::Actual,
372            transport_stream_id: 0x1234,
373            version_number: 5,
374            current_next_indicator: true,
375            section_number: 0,
376            last_section_number: 0,
377            original_network_id: 0x0020,
378            services: vec![
379                SdtService {
380                    service_id: 100,
381                    eit_schedule_flag: true,
382                    eit_present_following_flag: false,
383                    running_status: RunningStatus::Running,
384                    free_ca_mode: false,
385                    descriptors: DescriptorLoop::new(&desc1),
386                },
387                SdtService {
388                    service_id: 101,
389                    eit_schedule_flag: false,
390                    eit_present_following_flag: true,
391                    running_status: RunningStatus::StartsInAFewSeconds,
392                    free_ca_mode: true,
393                    descriptors: DescriptorLoop::new(&[]),
394                },
395            ],
396        };
397        let mut buf = vec![0u8; sdt.serialized_len()];
398        sdt.serialize_into(&mut buf).unwrap();
399        let re = SdtSection::parse(&buf).unwrap();
400        assert_eq!(sdt, re);
401    }
402
403    #[test]
404    fn zero_services_is_valid() {
405        let bytes = build_sdt(SdtKind::Actual, 1, 0, 0x20, &[]);
406        let sdt = SdtSection::parse(&bytes).unwrap();
407        assert_eq!(sdt.services.len(), 0);
408    }
409
410    #[test]
411    fn parse_rejects_zero_section_length() {
412        let mut buf = vec![0u8; 64];
413        buf[0] = TABLE_ID_ACTUAL;
414        buf[1] = 0xF0;
415        buf[2] = 0x00;
416        for b in &mut buf[3..] {
417            *b = 0xFF;
418        }
419        assert!(matches!(
420            SdtSection::parse(&buf).unwrap_err(),
421            Error::SectionLengthOverflow { .. }
422        ));
423    }
424}
dvb_si/tables/sdt.rs

dvb_si/tables/
sdt.rs
