dvb_si/tables/
mpe_fec.rs

1//! MPE-FEC section — ETSI EN 301 192 v1.7.1 §9.9 (table_id 0x78).
2//!
3//! Carries Reed-Solomon FEC data for a MPE-FEC frame in a DVB-H/IP datacast
4//! time-slice burst. Syntax per "Table 45 — MPE-FEC section"
5//! (`dvb-si/docs/en_301_192.md`, §9.9, PDF p. 57):
6//!
7//! ```text
8//! MPE-FEC_section() {
9//!   table_id                  8   (0x78)
10//!   section_syntax_indicator  1
11//!   private_indicator         1
12//!   reserved                  2
13//!   section_length           12
14//!   padding_columns           8
15//!   reserved_for_future_use   8
16//!   reserved                  2
17//!   reserved_for_future_use   5
18//!   current_next_indicator    1
19//!   section_number            8
20//!   last_section_number       8
21//!   real_time_parameters()   32
22//!   for (i=0; i<N; i++) { rs_data_byte 8 }
23//!   CRC_32                   32
24//! }
25//! ```
26//!
27//! Note the byte-3/4 "table_id_extension" slot is NOT a 16-bit identifier here:
28//! it is `padding_columns(8)` followed by an 8-bit `reserved_for_future_use`.
29//! There is no `version_number` field — byte 5 is reserved bits plus the
30//! `current_next_indicator`. `real_time_parameters` is the shared time-slice /
31//! MPE-FEC structure of "Table 46 — real time parameters" (§9.10): a 12-bit
32//! `delta_t`, two boundary flags, and an 18-bit `address`, packed into 4 bytes.
33//!
34//! MPE-FEC is a private section (byte-1 bit 6 = `private_indicator`), handled
35//! with the [`crate::tables::cit`] idiom. `rs_data` is a borrowed raw slice.
36//! No well-known PID — carriage is descriptor-signalled, so `PID = 0x0000`
37//! follows the [`crate::tables::dsmcc`] precedent.
38
39use crate::error::{Error, Result};
40use dvb_common::{Parse, Serialize};
41
42/// table_id for the MPE-FEC section.
43pub const TABLE_ID: u8 = 0x78;
44
45/// MPE-FEC has no well-known PID — its carriage is signalled via the
46/// time_slice_fec_identifier_descriptor. `0x0000` follows the DSM-CC precedent.
47pub const PID: u16 = 0x0000;
48
49/// Bytes 0-2: table_id (1) + flags + section_length (2).
50const HEADER_LEN: usize = 3;
51
52/// Bytes 3-7: padding_columns(1) + reserved_for_future_use(1)
53/// + reserved/rfu/cni byte(1) + section_number(1) + last_section_number(1).
54const EXTENSION_HEADER_LEN: usize = 5;
55
56/// Bytes 8-11: the 32-bit `real_time_parameters()`.
57const RTP_LEN: usize = 4;
58
59/// Bytes occupied by the trailing CRC-32 field.
60const CRC_LEN: usize = 4;
61
62/// Minimum total encoded length: header + extension + RTP + CRC.
63const MIN_LEN: usize = HEADER_LEN + EXTENSION_HEADER_LEN + RTP_LEN + CRC_LEN;
64
65/// Time-slicing / MPE-FEC real-time parameters (EN 301 192 §9.10, Table 46).
66///
67/// 32 bits: `delta_t(12)` | `table_boundary(1)` | `frame_boundary(1)`
68/// | `address(18)`.
69#[derive(Debug, Clone, Copy, PartialEq, Eq)]
70#[cfg_attr(feature = "serde", derive(serde::Serialize))]
71pub struct RealTimeParameters {
72    /// 12-bit `delta_t` — time until the start of the next burst (in units of
73    /// the MPE-FEC frame, see §9.10).
74    pub delta_t: u16,
75    /// `table_boundary` flag.
76    pub table_boundary: bool,
77    /// `frame_boundary` flag.
78    pub frame_boundary: bool,
79    /// 18-bit `address` — byte position of the first payload byte of this
80    /// section within the MPE-FEC frame table.
81    pub address: u32,
82}
83
84impl RealTimeParameters {
85    /// Decode the 4-byte real_time_parameters block.
86    fn from_bytes(b: [u8; RTP_LEN]) -> Self {
87        // delta_t(12) = b[0] | top 4 bits of b[1]
88        let delta_t = ((b[0] as u16) << 4) | ((b[1] >> 4) as u16);
89        let table_boundary = (b[1] & 0x08) != 0;
90        let frame_boundary = (b[1] & 0x04) != 0;
91        // address(18) = bottom 2 bits of b[1] | b[2] | b[3]
92        let address = (((b[1] & 0x03) as u32) << 16) | ((b[2] as u32) << 8) | (b[3] as u32);
93        RealTimeParameters {
94            delta_t,
95            table_boundary,
96            frame_boundary,
97            address,
98        }
99    }
100
101    /// Encode into the 4-byte real_time_parameters block.
102    fn to_bytes(self) -> [u8; RTP_LEN] {
103        let dt = self.delta_t & 0x0FFF;
104        let addr = self.address & 0x0003_FFFF;
105        [
106            (dt >> 4) as u8,
107            (((dt & 0x0F) as u8) << 4)
108                | (u8::from(self.table_boundary) << 3)
109                | (u8::from(self.frame_boundary) << 2)
110                | ((addr >> 16) as u8 & 0x03),
111            ((addr >> 8) & 0xFF) as u8,
112            (addr & 0xFF) as u8,
113        ]
114    }
115}
116
117/// MPE-FEC section (ETSI EN 301 192 v1.7.1 §9.9).
118#[derive(Debug, Clone, PartialEq, Eq)]
119#[cfg_attr(feature = "serde", derive(serde::Serialize))]
120#[cfg_attr(feature = "yoke", derive(yoke::Yokeable))]
121pub struct MpeFecSection<'a> {
122    /// `private_indicator` bit from byte 1 (MPE-FEC is a private section).
123    pub private_indicator: bool,
124    /// `padding_columns` — number of padding RS columns (byte 3).
125    pub padding_columns: u8,
126    /// `current_next_indicator` bit.
127    pub current_next_indicator: bool,
128    /// section_number in the sub-table sequence.
129    pub section_number: u8,
130    /// last_section_number in the sub-table sequence.
131    pub last_section_number: u8,
132    /// The decoded real-time parameters block.
133    pub real_time_parameters: RealTimeParameters,
134    /// Raw Reed-Solomon data bytes (everything between the real_time_parameters
135    /// block and the CRC-32 trailer).
136    pub rs_data: &'a [u8],
137}
138
139impl<'a> Parse<'a> for MpeFecSection<'a> {
140    type Error = crate::error::Error;
141
142    fn parse(bytes: &'a [u8]) -> Result<Self> {
143        if bytes.len() < MIN_LEN {
144            return Err(Error::BufferTooShort {
145                need: MIN_LEN,
146                have: bytes.len(),
147                what: "MpeFecSection",
148            });
149        }
150
151        if bytes[0] != TABLE_ID {
152            return Err(Error::UnexpectedTableId {
153                table_id: bytes[0],
154                what: "MpeFecSection",
155                expected: &[TABLE_ID],
156            });
157        }
158
159        let section_length = (((bytes[1] & 0x0F) as usize) << 8) | bytes[2] as usize;
160        let total = super::check_section_length(bytes.len(), HEADER_LEN, section_length, MIN_LEN)?;
161
162        let private_indicator = (bytes[1] & 0x40) != 0;
163        let padding_columns = bytes[3];
164        // bytes[4] = reserved_for_future_use(8) — ignored on parse.
165        // bytes[5] = reserved(2) | reserved_for_future_use(5) | current_next_indicator(1)
166        let current_next_indicator = (bytes[5] & 0x01) != 0;
167        let section_number = bytes[6];
168        let last_section_number = bytes[7];
169
170        let rtp_start = HEADER_LEN + EXTENSION_HEADER_LEN;
171        let real_time_parameters = RealTimeParameters::from_bytes([
172            bytes[rtp_start],
173            bytes[rtp_start + 1],
174            bytes[rtp_start + 2],
175            bytes[rtp_start + 3],
176        ]);
177
178        let data_start = rtp_start + RTP_LEN;
179        let data_end = total - CRC_LEN;
180        let rs_data = &bytes[data_start..data_end];
181
182        Ok(MpeFecSection {
183            private_indicator,
184            padding_columns,
185            current_next_indicator,
186            section_number,
187            last_section_number,
188            real_time_parameters,
189            rs_data,
190        })
191    }
192}
193
194impl Serialize for MpeFecSection<'_> {
195    type Error = crate::error::Error;
196
197    fn serialized_len(&self) -> usize {
198        HEADER_LEN + EXTENSION_HEADER_LEN + RTP_LEN + self.rs_data.len() + CRC_LEN
199    }
200
201    fn serialize_into(&self, buf: &mut [u8]) -> Result<usize> {
202        let len = self.serialized_len();
203        if buf.len() < len {
204            return Err(Error::OutputBufferTooSmall {
205                need: len,
206                have: buf.len(),
207            });
208        }
209
210        let section_length = (len - HEADER_LEN) as u16;
211        if section_length > 0x0FFF {
212            return Err(Error::SectionLengthOverflow {
213                declared: section_length as usize,
214                available: 0x0FFF,
215            });
216        }
217
218        // Byte 0: table_id.
219        buf[0] = TABLE_ID;
220        // Byte 1: section_syntax_indicator(1)=1 | private_indicator(1)
221        //         | reserved(2)=11 | section_length[11:8](4).
222        buf[1] = 0x80
223            | (u8::from(self.private_indicator) << 6)
224            | 0x30
225            | ((section_length >> 8) as u8 & 0x0F);
226        buf[2] = (section_length & 0xFF) as u8;
227
228        // Extension header.
229        buf[3] = self.padding_columns;
230        buf[4] = 0xFF; // reserved_for_future_use(8) emitted as 1s.
231                       // reserved(2)=11 | reserved_for_future_use(5)=11111 | current_next_indicator(1)
232        buf[5] = 0xFE | u8::from(self.current_next_indicator);
233        buf[6] = self.section_number;
234        buf[7] = self.last_section_number;
235
236        // real_time_parameters.
237        let rtp_start = HEADER_LEN + EXTENSION_HEADER_LEN;
238        buf[rtp_start..rtp_start + RTP_LEN].copy_from_slice(&self.real_time_parameters.to_bytes());
239
240        // rs_data.
241        let data_start = rtp_start + RTP_LEN;
242        let data_end = data_start + self.rs_data.len();
243        buf[data_start..data_end].copy_from_slice(self.rs_data);
244
245        // CRC-32 over everything up to (but not including) the CRC slot.
246        let crc = dvb_common::crc32_mpeg2::compute(&buf[..data_end]);
247        buf[data_end..len].copy_from_slice(&crc.to_be_bytes());
248
249        Ok(len)
250    }
251}
252impl<'a> crate::traits::TableDef<'a> for MpeFecSection<'a> {
253    const TABLE_ID_RANGES: &'static [(u8, u8)] = &[(TABLE_ID, TABLE_ID)];
254    const NAME: &'static str = "MPE_FEC";
255}
256
257#[cfg(test)]
258mod tests {
259    use super::*;
260
261    fn build_mpe_fec(
262        padding_columns: u8,
263        current_next: bool,
264        section_number: u8,
265        last_section_number: u8,
266        rtp: RealTimeParameters,
267        rs_data: &[u8],
268    ) -> Vec<u8> {
269        let s = MpeFecSection {
270            private_indicator: true,
271            padding_columns,
272            current_next_indicator: current_next,
273            section_number,
274            last_section_number,
275            real_time_parameters: rtp,
276            rs_data,
277        };
278        let mut buf = vec![0u8; s.serialized_len()];
279        s.serialize_into(&mut buf).unwrap();
280        buf
281    }
282
283    fn sample_rtp() -> RealTimeParameters {
284        RealTimeParameters {
285            delta_t: 0x0ABC,
286            table_boundary: true,
287            frame_boundary: false,
288            address: 0x0001_2345,
289        }
290    }
291
292    #[test]
293    fn parse_happy_path() {
294        let rs = [0x11u8, 0x22, 0x33, 0x44];
295        let bytes = build_mpe_fec(7, true, 1, 3, sample_rtp(), &rs);
296        let s = MpeFecSection::parse(&bytes).unwrap();
297        assert!(s.private_indicator);
298        assert_eq!(s.padding_columns, 7);
299        assert!(s.current_next_indicator);
300        assert_eq!(s.section_number, 1);
301        assert_eq!(s.last_section_number, 3);
302        assert_eq!(s.real_time_parameters, sample_rtp());
303        assert_eq!(s.rs_data, &rs[..]);
304    }
305
306    #[test]
307    fn parse_empty_rs_data() {
308        let bytes = build_mpe_fec(0, false, 0, 0, sample_rtp(), &[]);
309        let s = MpeFecSection::parse(&bytes).unwrap();
310        assert_eq!(s.padding_columns, 0);
311        assert!(!s.current_next_indicator);
312        assert!(s.rs_data.is_empty());
313        assert_eq!(s.real_time_parameters, sample_rtp());
314    }
315
316    #[test]
317    fn rtp_bit_packing_round_trips_extremes() {
318        // Exercise full-width values to pin the 12/1/1/18 split.
319        let rtp = RealTimeParameters {
320            delta_t: 0x0FFF,
321            table_boundary: false,
322            frame_boundary: true,
323            address: 0x0003_FFFF,
324        };
325        assert_eq!(RealTimeParameters::from_bytes(rtp.to_bytes()), rtp);
326    }
327
328    #[test]
329    fn parse_rejects_wrong_tag() {
330        let mut bytes = build_mpe_fec(0, true, 0, 0, sample_rtp(), &[]);
331        bytes[0] = 0x70; // not 0x78
332        assert!(matches!(
333            MpeFecSection::parse(&bytes).unwrap_err(),
334            Error::UnexpectedTableId { table_id: 0x70, .. }
335        ));
336    }
337
338    #[test]
339    fn parse_rejects_short_buffer() {
340        assert!(matches!(
341            MpeFecSection::parse(&[0x78, 0x80]).unwrap_err(),
342            Error::BufferTooShort { .. }
343        ));
344    }
345
346    #[test]
347    fn parse_rejects_section_length_overflow() {
348        let mut bytes = build_mpe_fec(0, true, 0, 0, sample_rtp(), &[]);
349        let fake_sl: u16 = (bytes.len() as u16) + 100 - HEADER_LEN as u16;
350        bytes[1] = (bytes[1] & 0xF0) | ((fake_sl >> 8) as u8 & 0x0F);
351        bytes[2] = (fake_sl & 0xFF) as u8;
352        assert!(matches!(
353            MpeFecSection::parse(&bytes).unwrap_err(),
354            Error::SectionLengthOverflow { .. }
355        ));
356    }
357
358    #[test]
359    fn serialize_round_trip() {
360        let rs = [0xDEu8, 0xAD, 0xBE, 0xEF, 0x00];
361        let original = MpeFecSection {
362            private_indicator: false,
363            padding_columns: 191,
364            current_next_indicator: false,
365            section_number: 2,
366            last_section_number: 4,
367            real_time_parameters: sample_rtp(),
368            rs_data: &rs,
369        };
370        let mut buf = vec![0u8; original.serialized_len()];
371        original.serialize_into(&mut buf).unwrap();
372        assert_eq!(MpeFecSection::parse(&buf).unwrap(), original);
373    }
374
375    #[test]
376    fn serialize_rejects_output_buffer_too_small() {
377        let s = MpeFecSection {
378            private_indicator: false,
379            padding_columns: 0,
380            current_next_indicator: true,
381            section_number: 0,
382            last_section_number: 0,
383            real_time_parameters: sample_rtp(),
384            rs_data: &[],
385        };
386        let mut buf = vec![0u8; 2];
387        assert!(matches!(
388            s.serialize_into(&mut buf).unwrap_err(),
389            Error::OutputBufferTooSmall { .. }
390        ));
391    }
392
393    #[test]
394    fn table_trait_constants() {
395        assert_eq!(TABLE_ID, 0x78);
396        assert_eq!(PID, 0x0000);
397    }
398
399    #[test]
400    fn parse_rejects_zero_section_length() {
401        let mut buf = vec![0u8; 64];
402        buf[0] = TABLE_ID;
403        buf[1] = 0xF0;
404        buf[2] = 0x00;
405        for b in &mut buf[3..] {
406            *b = 0xFF;
407        }
408        assert!(matches!(
409            MpeFecSection::parse(&buf).unwrap_err(),
410            Error::SectionLengthOverflow { .. }
411        ));
412    }
413
414    #[cfg(feature = "serde")]
415    #[test]
416    fn serde_json_serializes_fields() {
417        // Serialize-only: assert serialization yields valid, field-bearing JSON.
418        let rs = [0x01u8, 0x02];
419        let bytes = build_mpe_fec(12, true, 0, 0, sample_rtp(), &rs);
420        let s = MpeFecSection::parse(&bytes).unwrap();
421        let v: serde_json::Value = serde_json::to_value(&s).unwrap();
422        assert_eq!(v["padding_columns"], 12);
423        assert_eq!(v["current_next_indicator"], true);
424        assert_eq!(v["rs_data"], serde_json::json!([0x01, 0x02]));
425        assert_eq!(v["real_time_parameters"]["delta_t"], 0x0ABC);
426        assert_eq!(v["real_time_parameters"]["table_boundary"], true);
427    }
428}
dvb_si/tables/mpe_fec.rs

dvb_si/tables/
mpe_fec.rs
