dvb_si/tables/
dsmcc.rs

1//! DSM-CC section parser — ISO/IEC 13818-6 + ETSI EN 301 192 §9.
2//!
3//! This is intentionally minimal: header framing, table_id dispatch,
4//! length check, and carrying the payload as `Cow<'a, [u8]>`. Full
5//! DSM-CC payload parsing is deliberately out of scope (YAGNI).
6//!
7//! Known limitation: the parser assumes long-form framing (extension header +
8//! trailing CRC_32) regardless of `section_syntax_indicator`. ISO/IEC 13818-6
9//! permits SSI=0 sections whose trailing 4 bytes carry a checksum under a
10//! different rule; those are not distinguished here.
11
12use crate::error::{Error, Result};
13use crate::traits::Table;
14use dvb_common::{Parse, Serialize};
15
16/// First table_id in the DSM-CC section range (inclusive).
17pub const TABLE_ID_FIRST: u8 = 0x3A;
18/// Last table_id in the DSM-CC section range (inclusive).
19pub const TABLE_ID_LAST: u8 = 0x3F;
20/// DSM-CC has no well-known PID.
21pub const PID: u16 = 0x0000;
22
23const MIN_HEADER_LEN: usize = 3;
24const EXTENSION_HEADER_LEN: usize = 5;
25const CRC_LEN: usize = 4;
26
27/// A DSM-CC section — minimal wrapper that validates header framing
28/// and carries the raw payload.
29#[derive(Debug, Clone, PartialEq, Eq)]
30#[cfg_attr(feature = "serde", derive(serde::Serialize))]
31#[cfg_attr(feature = "yoke", derive(yoke::Yokeable))]
32pub struct DsmccSection<'a> {
33    /// The table_id byte (0x3A..=0x3F).
34    pub table_id: u8,
35    /// 16-bit table_id_extension.
36    pub extension_id: u16,
37    /// 5-bit version_number.
38    pub version_number: u8,
39    /// current_next_indicator bit.
40    pub current_next_indicator: bool,
41    /// section_number.
42    pub section_number: u8,
43    /// last_section_number.
44    pub last_section_number: u8,
45    /// Raw payload bytes (everything between the extension header and the CRC).
46    pub payload: &'a [u8],
47}
48
49impl<'a> Parse<'a> for DsmccSection<'a> {
50    type Error = crate::error::Error;
51    fn parse(bytes: &'a [u8]) -> Result<Self> {
52        let min_len = MIN_HEADER_LEN + EXTENSION_HEADER_LEN + CRC_LEN;
53        if bytes.len() < min_len {
54            return Err(Error::BufferTooShort {
55                need: min_len,
56                have: bytes.len(),
57                what: "DsmccSection",
58            });
59        }
60
61        let table_id = bytes[0];
62        if !(TABLE_ID_FIRST..=TABLE_ID_LAST).contains(&table_id) {
63            return Err(Error::UnexpectedTableId {
64                table_id,
65                what: "DsmccSection",
66                expected: &[TABLE_ID_FIRST, TABLE_ID_LAST],
67            });
68        }
69
70        let section_length = ((bytes[1] & 0x0F) as u16) << 8 | bytes[2] as u16;
71        let total = MIN_HEADER_LEN + section_length as usize;
72        if bytes.len() < total {
73            return Err(Error::SectionLengthOverflow {
74                declared: section_length as usize,
75                available: bytes.len() - MIN_HEADER_LEN,
76            });
77        }
78
79        let extension_id = u16::from_be_bytes([bytes[3], bytes[4]]);
80        let version_number = (bytes[5] >> 1) & 0x1F;
81        let current_next_indicator = (bytes[5] & 0x01) != 0;
82        let section_number = bytes[6];
83        let last_section_number = bytes[7];
84
85        let payload_start = MIN_HEADER_LEN + EXTENSION_HEADER_LEN;
86        let payload_end = total - CRC_LEN;
87        let payload = &bytes[payload_start..payload_end];
88
89        Ok(DsmccSection {
90            table_id,
91            extension_id,
92            version_number,
93            current_next_indicator,
94            section_number,
95            last_section_number,
96            payload,
97        })
98    }
99}
100
101impl Serialize for DsmccSection<'_> {
102    type Error = crate::error::Error;
103    fn serialized_len(&self) -> usize {
104        MIN_HEADER_LEN + EXTENSION_HEADER_LEN + self.payload.len() + CRC_LEN
105    }
106
107    fn serialize_into(&self, buf: &mut [u8]) -> Result<usize> {
108        let len = self.serialized_len();
109        if buf.len() < len {
110            return Err(Error::OutputBufferTooSmall {
111                need: len,
112                have: buf.len(),
113            });
114        }
115
116        let section_length: u16 = (len - MIN_HEADER_LEN) as u16;
117        buf[0] = self.table_id;
118        buf[1] = 0xB0 | ((section_length >> 8) as u8 & 0x0F);
119        buf[2] = (section_length & 0xFF) as u8;
120        buf[3..5].copy_from_slice(&self.extension_id.to_be_bytes());
121        buf[5] = 0xC0 | ((self.version_number & 0x1F) << 1) | u8::from(self.current_next_indicator);
122        buf[6] = self.section_number;
123        buf[7] = self.last_section_number;
124
125        let payload_start = MIN_HEADER_LEN + EXTENSION_HEADER_LEN;
126        let payload_end = payload_start + self.payload.len();
127        buf[payload_start..payload_end].copy_from_slice(self.payload);
128
129        let crc_pos = len - CRC_LEN;
130        let crc = dvb_common::crc32_mpeg2::compute(&buf[..crc_pos]);
131        buf[crc_pos..len].copy_from_slice(&crc.to_be_bytes());
132        Ok(len)
133    }
134}
135
136impl<'a> Table<'a> for DsmccSection<'a> {
137    const TABLE_ID: u8 = TABLE_ID_FIRST;
138    const PID: u16 = PID;
139}
140
141impl<'a> crate::traits::TableDef<'a> for DsmccSection<'a> {
142    /// Full DSM-CC range including `0x3E` (MPE datagram_section). The typed
143    /// [`crate::tables::mpe::MpeDatagramSection`] view of `0x3E` is reachable
144    /// type-keyed only (via `AnyTable::parse_as` or
145    /// `MpeDatagramSection::parse`); the default dispatcher routes `0x3E` here.
146    const TABLE_ID_RANGES: &'static [(u8, u8)] = &[(TABLE_ID_FIRST, TABLE_ID_LAST)];
147    const NAME: &'static str = "DSM_CC_SECTION";
148}
149
150#[cfg(test)]
151mod tests {
152    use super::*;
153
154    fn build_dsmcc(table_id: u8, extension_id: u16, version: u8, payload: &[u8]) -> Vec<u8> {
155        let section_length: u16 = (EXTENSION_HEADER_LEN + payload.len() + CRC_LEN) as u16;
156        let mut v = Vec::new();
157        v.push(table_id);
158        v.push(0xB0 | ((section_length >> 8) as u8 & 0x0F));
159        v.push((section_length & 0xFF) as u8);
160        v.extend_from_slice(&extension_id.to_be_bytes());
161        v.push(0xC0 | ((version & 0x1F) << 1) | 0x01);
162        v.push(0);
163        v.push(0);
164        v.extend_from_slice(payload);
165        v.extend_from_slice(&[0, 0, 0, 0]);
166        v
167    }
168
169    #[test]
170    fn parse_rejects_wrong_table_id() {
171        let mut bytes = build_dsmcc(0x3B, 0x0001, 0, &[]);
172        bytes[0] = 0x00;
173        let err = DsmccSection::parse(&bytes).unwrap_err();
174        assert!(matches!(
175            err,
176            Error::UnexpectedTableId { table_id: 0x00, .. }
177        ));
178    }
179
180    #[test]
181    fn parse_rejects_table_id_below_range() {
182        let bytes = build_dsmcc(0x39, 0x0001, 0, &[]);
183        let err = DsmccSection::parse(&bytes).unwrap_err();
184        assert!(matches!(
185            err,
186            Error::UnexpectedTableId { table_id: 0x39, .. }
187        ));
188    }
189
190    #[test]
191    fn parse_rejects_table_id_above_range() {
192        let bytes = build_dsmcc(0x40, 0x0001, 0, &[]);
193        let err = DsmccSection::parse(&bytes).unwrap_err();
194        assert!(matches!(
195            err,
196            Error::UnexpectedTableId { table_id: 0x40, .. }
197        ));
198    }
199
200    #[test]
201    fn parse_rejects_short_buffer() {
202        let err = DsmccSection::parse(&[0x3B, 0x00]).unwrap_err();
203        assert!(matches!(err, Error::BufferTooShort { .. }));
204    }
205
206    #[test]
207    fn parse_empty_payload() {
208        let bytes = build_dsmcc(0x3B, 0x1234, 5, &[]);
209        let sec = DsmccSection::parse(&bytes).expect("parse");
210        assert_eq!(sec.table_id, 0x3B);
211        assert_eq!(sec.extension_id, 0x1234);
212        assert_eq!(sec.version_number, 5);
213        assert!(sec.current_next_indicator);
214        assert_eq!(sec.section_number, 0);
215        assert_eq!(sec.last_section_number, 0);
216        assert_eq!(sec.payload.len(), 0);
217    }
218
219    #[test]
220    fn parse_0x3c_table_id_accepted() {
221        let bytes = build_dsmcc(0x3C, 0x0001, 0, &[0xAA, 0xBB]);
222        let sec = DsmccSection::parse(&bytes).unwrap();
223        assert_eq!(sec.table_id, 0x3C);
224        assert_eq!(sec.payload, &[0xAA, 0xBB]);
225    }
226
227    #[test]
228    fn parse_payload_preserved() {
229        let payload = vec![0x01, 0x02, 0x03, 0x04, 0x05];
230        let bytes = build_dsmcc(0x3B, 0x0001, 0, &payload);
231        let sec = DsmccSection::parse(&bytes).unwrap();
232        assert_eq!(sec.payload, &payload[..]);
233    }
234
235    #[test]
236    fn serialize_round_trip_empty() {
237        let sec = DsmccSection {
238            table_id: 0x3B,
239            extension_id: 0x0001,
240            version_number: 0,
241            current_next_indicator: true,
242            section_number: 0,
243            last_section_number: 0,
244            payload: &[],
245        };
246        let mut buf = vec![0u8; sec.serialized_len()];
247        sec.serialize_into(&mut buf).unwrap();
248        let reparsed = DsmccSection::parse(&buf).unwrap();
249        assert_eq!(sec, reparsed);
250    }
251
252    #[test]
253    fn serialize_round_trip_with_payload() {
254        let payload: [u8; 5] = [0xDE, 0xAD, 0xBE, 0xEF, 0x00];
255        let sec = DsmccSection {
256            table_id: 0x3C,
257            extension_id: 0xABCD,
258            version_number: 3,
259            current_next_indicator: true,
260            section_number: 1,
261            last_section_number: 2,
262            payload: &payload,
263        };
264        let mut buf = vec![0u8; sec.serialized_len()];
265        sec.serialize_into(&mut buf).unwrap();
266        let reparsed = DsmccSection::parse(&buf).unwrap();
267        assert_eq!(sec, reparsed);
268    }
269}
dvb_si/tables/dsmcc.rs

dvb_si/tables/
dsmcc.rs
