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 crate::descriptors::DescriptorLoop;
9use crate::error::{Error, Result};
10use crate::traits::Table;
11use dvb_common::{Parse, Serialize};
12
13/// table_id value for SDT describing services on the actual TS.
14pub const TABLE_ID_ACTUAL: u8 = 0x42;
15/// table_id value for SDT describing services on other TSes.
16pub const TABLE_ID_OTHER: u8 = 0x46;
17/// Well-known PID on which SDT is carried.
18pub const PID: u16 = 0x0011;
19
20const MIN_HEADER_LEN: usize = 3;
21const EXTENSION_HEADER_LEN: usize = 5;
22/// Bytes after the extension header and before the first service entry:
23/// 2 bytes of original_network_id + 1 reserved_future_use byte.
24const POST_EXTENSION_LEN: usize = 3;
25const CRC_LEN: usize = 4;
26const SERVICE_HEADER_LEN: usize = 5;
27
28/// SDT kind — distinguishes `0x42` (actual) from `0x46` (other).
29#[derive(Debug, Clone, Copy, PartialEq, Eq)]
30#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
31pub enum SdtKind {
32    /// Services on the transport stream the receiver is tuned to.
33    Actual,
34    /// Services on other transport streams (cross-TS SDT).
35    Other,
36}
37
38/// One service entry in an SDT.
39#[derive(Debug, Clone, PartialEq, Eq)]
40#[cfg_attr(feature = "serde", derive(serde::Serialize))]
41pub struct SdtService<'a> {
42    /// service_id (matches `program_number` in the PAT).
43    pub service_id: u16,
44    /// EIT schedule flag — present-and-following events are in the EIT/schedule.
45    pub eit_schedule_flag: bool,
46    /// EIT P/F flag — present-and-following events are in the EIT present/following.
47    pub eit_present_following_flag: bool,
48    /// 3-bit running_status (0=undefined .. 4=running).
49    pub running_status: u8,
50    /// free_CA_mode: `true` = at least one elementary stream is scrambled.
51    pub free_ca_mode: bool,
52    /// Descriptor loop for this service (service_descriptor etc.). Serializes
53    /// as the typed descriptor sequence; `.raw()` yields the wire bytes.
54    pub descriptors: DescriptorLoop<'a>,
55}
56
57/// Service Description Table.
58#[derive(Debug, Clone, PartialEq, Eq)]
59#[cfg_attr(feature = "serde", derive(serde::Serialize))]
60pub struct Sdt<'a> {
61    /// Variant discriminator (table_id 0x42 vs 0x46).
62    pub kind: SdtKind,
63    /// transport_stream_id of the described TS.
64    pub transport_stream_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    /// original_network_id of the described TS.
74    pub original_network_id: u16,
75    /// Services in wire order.
76    #[cfg_attr(feature = "serde", serde(borrow))]
77    pub services: Vec<SdtService<'a>>,
78}
79
80impl<'a> Parse<'a> for Sdt<'a> {
81    type Error = crate::error::Error;
82    fn parse(bytes: &'a [u8]) -> Result<Self> {
83        let min_len = MIN_HEADER_LEN + EXTENSION_HEADER_LEN + POST_EXTENSION_LEN + CRC_LEN;
84        if bytes.len() < min_len {
85            return Err(Error::BufferTooShort {
86                need: min_len,
87                have: bytes.len(),
88                what: "Sdt",
89            });
90        }
91        let kind = match bytes[0] {
92            TABLE_ID_ACTUAL => SdtKind::Actual,
93            TABLE_ID_OTHER => SdtKind::Other,
94            other => {
95                return Err(Error::UnexpectedTableId {
96                    table_id: other,
97                    what: "Sdt",
98                    expected: &[TABLE_ID_ACTUAL, TABLE_ID_OTHER],
99                });
100            }
101        };
102
103        let section_length = ((bytes[1] & 0x0F) as u16) << 8 | bytes[2] as u16;
104        let total = MIN_HEADER_LEN + section_length as usize;
105        if bytes.len() < total {
106            return Err(Error::SectionLengthOverflow {
107                declared: section_length as usize,
108                available: bytes.len() - MIN_HEADER_LEN,
109            });
110        }
111
112        let transport_stream_id = u16::from_be_bytes([bytes[3], bytes[4]]);
113        let version_number = (bytes[5] >> 1) & 0x1F;
114        let current_next_indicator = (bytes[5] & 0x01) != 0;
115        let section_number = bytes[6];
116        let last_section_number = bytes[7];
117        let original_network_id = u16::from_be_bytes([bytes[8], bytes[9]]);
118
119        let services_start = MIN_HEADER_LEN + EXTENSION_HEADER_LEN + POST_EXTENSION_LEN;
120        let services_end = total - CRC_LEN;
121        let mut services = Vec::new();
122        let mut pos = services_start;
123        while pos + SERVICE_HEADER_LEN <= services_end {
124            let service_id = u16::from_be_bytes([bytes[pos], bytes[pos + 1]]);
125            let flags = bytes[pos + 2];
126            let eit_schedule_flag = (flags & 0x02) != 0;
127            let eit_present_following_flag = (flags & 0x01) != 0;
128            let status_and_len_hi = bytes[pos + 3];
129            let running_status = (status_and_len_hi >> 5) & 0x07;
130            let free_ca_mode = (status_and_len_hi & 0x10) != 0;
131            let descriptors_loop_length =
132                (((status_and_len_hi & 0x0F) as usize) << 8) | bytes[pos + 4] as usize;
133            let desc_start = pos + SERVICE_HEADER_LEN;
134            let desc_end = desc_start + descriptors_loop_length;
135            if desc_end > services_end {
136                return Err(Error::SectionLengthOverflow {
137                    declared: descriptors_loop_length,
138                    available: services_end - desc_start,
139                });
140            }
141            services.push(SdtService {
142                service_id,
143                eit_schedule_flag,
144                eit_present_following_flag,
145                running_status,
146                free_ca_mode,
147                descriptors: DescriptorLoop::new(&bytes[desc_start..desc_end]),
148            });
149            pos = desc_end;
150        }
151
152        Ok(Sdt {
153            kind,
154            transport_stream_id,
155            version_number,
156            current_next_indicator,
157            section_number,
158            last_section_number,
159            original_network_id,
160            services,
161        })
162    }
163}
164
165impl Serialize for Sdt<'_> {
166    type Error = crate::error::Error;
167    fn serialized_len(&self) -> usize {
168        let svc_bytes: usize = self
169            .services
170            .iter()
171            .map(|s| SERVICE_HEADER_LEN + s.descriptors.len())
172            .sum();
173        MIN_HEADER_LEN + EXTENSION_HEADER_LEN + POST_EXTENSION_LEN + svc_bytes + CRC_LEN
174    }
175
176    fn serialize_into(&self, buf: &mut [u8]) -> Result<usize> {
177        let len = self.serialized_len();
178        if buf.len() < len {
179            return Err(Error::OutputBufferTooSmall {
180                need: len,
181                have: buf.len(),
182            });
183        }
184        let section_length: u16 = (len - MIN_HEADER_LEN) as u16;
185        buf[0] = match self.kind {
186            SdtKind::Actual => TABLE_ID_ACTUAL,
187            SdtKind::Other => TABLE_ID_OTHER,
188        };
189        buf[1] = 0xB0 | ((section_length >> 8) as u8 & 0x0F);
190        buf[2] = (section_length & 0xFF) as u8;
191        buf[3..5].copy_from_slice(&self.transport_stream_id.to_be_bytes());
192        buf[5] = 0xC0 | ((self.version_number & 0x1F) << 1) | u8::from(self.current_next_indicator);
193        buf[6] = self.section_number;
194        buf[7] = self.last_section_number;
195        buf[8..10].copy_from_slice(&self.original_network_id.to_be_bytes());
196        buf[10] = 0xFF; // reserved_future_use
197
198        let mut pos = MIN_HEADER_LEN + EXTENSION_HEADER_LEN + POST_EXTENSION_LEN;
199        for svc in &self.services {
200            buf[pos..pos + 2].copy_from_slice(&svc.service_id.to_be_bytes());
201            let flags = 0xFC
202                | (u8::from(svc.eit_schedule_flag) << 1)
203                | u8::from(svc.eit_present_following_flag);
204            buf[pos + 2] = flags;
205            let dll = svc.descriptors.len() as u16;
206            buf[pos + 3] = ((svc.running_status & 0x07) << 5)
207                | (u8::from(svc.free_ca_mode) << 4)
208                | ((dll >> 8) as u8 & 0x0F);
209            buf[pos + 4] = (dll & 0xFF) as u8;
210            let desc_start = pos + SERVICE_HEADER_LEN;
211            buf[desc_start..desc_start + svc.descriptors.len()]
212                .copy_from_slice(svc.descriptors.raw());
213            pos = desc_start + svc.descriptors.len();
214        }
215
216        let crc_pos = len - CRC_LEN;
217        let crc = dvb_common::crc32_mpeg2::compute(&buf[..crc_pos]);
218        buf[crc_pos..len].copy_from_slice(&crc.to_be_bytes());
219        Ok(len)
220    }
221}
222
223impl<'a> Table<'a> for Sdt<'a> {
224    const TABLE_ID: u8 = TABLE_ID_ACTUAL;
225    const PID: u16 = PID;
226}
227
228impl<'a> crate::traits::TableDef<'a> for Sdt<'a> {
229    const TABLE_ID_RANGES: &'static [(u8, u8)] = &[
230        (TABLE_ID_ACTUAL, TABLE_ID_ACTUAL),
231        (TABLE_ID_OTHER, TABLE_ID_OTHER),
232    ];
233    const NAME: &'static str = "SERVICE_DESCRIPTION";
234}
235
236#[cfg(test)]
237mod tests {
238    use super::*;
239
240    type TestService = (u16, bool, bool, u8, bool, Vec<u8>);
241
242    fn build_sdt(
243        kind: SdtKind,
244        tsid: u16,
245        version: u8,
246        original_network_id: u16,
247        services: &[TestService],
248    ) -> Vec<u8> {
249        let svc_bytes: usize = services
250            .iter()
251            .map(|(_, _, _, _, _, d)| SERVICE_HEADER_LEN + d.len())
252            .sum();
253        let section_length: u16 =
254            (EXTENSION_HEADER_LEN + POST_EXTENSION_LEN + svc_bytes + CRC_LEN) as u16;
255        let mut v = Vec::new();
256        v.push(match kind {
257            SdtKind::Actual => TABLE_ID_ACTUAL,
258            SdtKind::Other => TABLE_ID_OTHER,
259        });
260        v.push(0xB0 | ((section_length >> 8) as u8 & 0x0F));
261        v.push((section_length & 0xFF) as u8);
262        v.extend_from_slice(&tsid.to_be_bytes());
263        v.push(0xC0 | ((version & 0x1F) << 1) | 0x01);
264        v.push(0);
265        v.push(0);
266        v.extend_from_slice(&original_network_id.to_be_bytes());
267        v.push(0xFF);
268        for (sid, eit_s, eit_pf, rs, fca, desc) in services {
269            v.extend_from_slice(&sid.to_be_bytes());
270            let flags = 0xFC | (u8::from(*eit_s) << 1) | u8::from(*eit_pf);
271            v.push(flags);
272            let dll = desc.len() as u16;
273            v.push(((*rs & 0x07) << 5) | (u8::from(*fca) << 4) | ((dll >> 8) as u8 & 0x0F));
274            v.push((dll & 0xFF) as u8);
275            v.extend_from_slice(desc);
276        }
277        v.extend_from_slice(&[0, 0, 0, 0]);
278        v
279    }
280
281    #[test]
282    fn parse_actual_and_other_tables_distinguished_by_table_id() {
283        let a = build_sdt(SdtKind::Actual, 1, 0, 0x20, &[]);
284        let o = build_sdt(SdtKind::Other, 1, 0, 0x20, &[]);
285        assert!(matches!(Sdt::parse(&a).unwrap().kind, SdtKind::Actual));
286        assert!(matches!(Sdt::parse(&o).unwrap().kind, SdtKind::Other));
287    }
288
289    #[test]
290    fn parse_services_with_descriptor_bytes() {
291        let bytes = build_sdt(
292            SdtKind::Actual,
293            1,
294            0,
295            0x20,
296            &[(
297                100,
298                true,
299                true,
300                4,
301                false,
302                vec![0x48, 0x05, 0x01, 0x02, 0x03, 0x04, 0x05],
303            )],
304        );
305        let sdt = Sdt::parse(&bytes).unwrap();
306        assert_eq!(sdt.services.len(), 1);
307        assert_eq!(sdt.services[0].service_id, 100);
308        assert!(sdt.services[0].eit_schedule_flag);
309        assert!(sdt.services[0].eit_present_following_flag);
310        assert_eq!(sdt.services[0].running_status, 4);
311        assert!(!sdt.services[0].free_ca_mode);
312        assert_eq!(
313            sdt.services[0].descriptors.raw(),
314            &[0x48, 0x05, 0x01, 0x02, 0x03, 0x04, 0x05][..]
315        );
316    }
317
318    #[test]
319    fn service_free_ca_mode_flag_extracted() {
320        let bytes = build_sdt(
321            SdtKind::Actual,
322            1,
323            0,
324            0x20,
325            &[(1, false, false, 0, true, vec![])],
326        );
327        let sdt = Sdt::parse(&bytes).unwrap();
328        assert!(sdt.services[0].free_ca_mode);
329    }
330
331    #[test]
332    fn service_running_status_extracted() {
333        let bytes = build_sdt(
334            SdtKind::Actual,
335            1,
336            0,
337            0x20,
338            &[(1, false, false, 2, false, vec![])],
339        );
340        let sdt = Sdt::parse(&bytes).unwrap();
341        assert_eq!(sdt.services[0].running_status, 2);
342    }
343
344    #[test]
345    fn parse_rejects_short_buffer() {
346        let err = Sdt::parse(&[0x42, 0x00]).unwrap_err();
347        assert!(matches!(err, Error::BufferTooShort { .. }));
348    }
349
350    #[test]
351    fn parse_rejects_wrong_table_id() {
352        let mut bytes = build_sdt(SdtKind::Actual, 1, 0, 0x20, &[]);
353        bytes[0] = 0x00;
354        let err = Sdt::parse(&bytes).unwrap_err();
355        assert!(matches!(
356            err,
357            Error::UnexpectedTableId { table_id: 0x00, .. }
358        ));
359    }
360
361    #[test]
362    fn serialize_round_trip() {
363        let desc1: [u8; 4] = [0x48, 0x02, 0xAA, 0xBB];
364        let sdt = Sdt {
365            kind: SdtKind::Actual,
366            transport_stream_id: 0x1234,
367            version_number: 5,
368            current_next_indicator: true,
369            section_number: 0,
370            last_section_number: 0,
371            original_network_id: 0x0020,
372            services: vec![
373                SdtService {
374                    service_id: 100,
375                    eit_schedule_flag: true,
376                    eit_present_following_flag: false,
377                    running_status: 4,
378                    free_ca_mode: false,
379                    descriptors: DescriptorLoop::new(&desc1),
380                },
381                SdtService {
382                    service_id: 101,
383                    eit_schedule_flag: false,
384                    eit_present_following_flag: true,
385                    running_status: 2,
386                    free_ca_mode: true,
387                    descriptors: DescriptorLoop::new(&[]),
388                },
389            ],
390        };
391        let mut buf = vec![0u8; sdt.serialized_len()];
392        sdt.serialize_into(&mut buf).unwrap();
393        let re = Sdt::parse(&buf).unwrap();
394        assert_eq!(sdt, re);
395    }
396
397    #[test]
398    fn zero_services_is_valid() {
399        let bytes = build_sdt(SdtKind::Actual, 1, 0, 0x20, &[]);
400        let sdt = Sdt::parse(&bytes).unwrap();
401        assert_eq!(sdt.services.len(), 0);
402    }
403}
dvb_si/tables/sdt.rs

dvb_si/tables/
sdt.rs
