dvb_si/tables/
tsdt.rs

1//! Transport Stream Description Table — ISO/IEC 13818-1 §2.4.5.
2//!
3//! TSDT is carried on PID 0x0002 with table_id 0x03. It provides a
4//! means of describing the transport stream using descriptors.
5
6use crate::descriptors::DescriptorLoop;
7use crate::error::{Error, Result};
8use crate::traits::Table;
9use dvb_common::{Parse, Serialize};
10
11/// table_id for Transport Stream Description Table.
12pub const TABLE_ID: u8 = 0x03;
13/// Well-known PID on which TSDT is carried.
14pub const PID: u16 = 0x0002;
15
16const MIN_HEADER_LEN: usize = 3;
17const EXTENSION_HEADER_LEN: usize = 5;
18const CRC_LEN: usize = 4;
19
20/// Transport Stream Description Table.
21#[derive(Debug, Clone, PartialEq, Eq)]
22#[cfg_attr(feature = "serde", derive(serde::Serialize))]
23#[cfg_attr(feature = "yoke", derive(yoke::Yokeable))]
24pub struct Tsdt<'a> {
25    /// 16-bit table_id_extension.
26    pub table_id_extension: u16,
27    /// 5-bit version_number.
28    pub version_number: u8,
29    /// current_next_indicator bit.
30    pub current_next_indicator: bool,
31    /// section_number in the sub-table sequence.
32    pub section_number: u8,
33    /// last_section_number in the sub-table sequence.
34    pub last_section_number: u8,
35    /// Descriptor loop. Serializes as the typed descriptor sequence;
36    /// `.raw()` yields the wire bytes.
37    pub descriptors: DescriptorLoop<'a>,
38}
39
40impl<'a> Parse<'a> for Tsdt<'a> {
41    type Error = crate::error::Error;
42
43    fn parse(bytes: &'a [u8]) -> Result<Self> {
44        let min_len = MIN_HEADER_LEN + EXTENSION_HEADER_LEN + CRC_LEN;
45        if bytes.len() < min_len {
46            return Err(Error::BufferTooShort {
47                need: min_len,
48                have: bytes.len(),
49                what: "Tsdt",
50            });
51        }
52
53        if bytes[0] != TABLE_ID {
54            return Err(Error::UnexpectedTableId {
55                table_id: bytes[0],
56                what: "Tsdt",
57                expected: &[TABLE_ID],
58            });
59        }
60
61        let section_length = ((bytes[1] & 0x0F) as u16) << 8 | bytes[2] as u16;
62        let total = MIN_HEADER_LEN + section_length as usize;
63        if bytes.len() < total {
64            return Err(Error::SectionLengthOverflow {
65                declared: section_length as usize,
66                available: bytes.len() - MIN_HEADER_LEN,
67            });
68        }
69
70        let table_id_extension = u16::from_be_bytes([bytes[3], bytes[4]]);
71        let version_number = (bytes[5] >> 1) & 0x1F;
72        let current_next_indicator = (bytes[5] & 0x01) != 0;
73        let section_number = bytes[6];
74        let last_section_number = bytes[7];
75
76        // §2.4.4.12: descriptors run directly from byte 8 to the CRC; there is
77        // no descriptor_loop_length field. The section_length bounds the loop.
78        let desc_start = MIN_HEADER_LEN + EXTENSION_HEADER_LEN;
79        let desc_end = total - CRC_LEN;
80
81        Ok(Tsdt {
82            table_id_extension,
83            version_number,
84            current_next_indicator,
85            section_number,
86            last_section_number,
87            descriptors: DescriptorLoop::new(&bytes[desc_start..desc_end]),
88        })
89    }
90}
91
92impl Serialize for Tsdt<'_> {
93    type Error = crate::error::Error;
94
95    fn serialized_len(&self) -> usize {
96        MIN_HEADER_LEN + EXTENSION_HEADER_LEN + self.descriptors.len() + CRC_LEN
97    }
98
99    fn serialize_into(&self, buf: &mut [u8]) -> Result<usize> {
100        let len = self.serialized_len();
101        if buf.len() < len {
102            return Err(Error::OutputBufferTooSmall {
103                need: len,
104                have: buf.len(),
105            });
106        }
107
108        let section_length: u16 = (len - MIN_HEADER_LEN) as u16;
109        buf[0] = TABLE_ID;
110        buf[1] = 0xB0 | ((section_length >> 8) as u8 & 0x0F);
111        buf[2] = (section_length & 0xFF) as u8;
112        buf[3..5].copy_from_slice(&self.table_id_extension.to_be_bytes());
113        buf[5] = 0xC0 | ((self.version_number & 0x1F) << 1) | u8::from(self.current_next_indicator);
114        buf[6] = self.section_number;
115        buf[7] = self.last_section_number;
116
117        let desc_start = MIN_HEADER_LEN + EXTENSION_HEADER_LEN;
118        buf[desc_start..desc_start + self.descriptors.len()]
119            .copy_from_slice(self.descriptors.raw());
120
121        let crc_pos = len - CRC_LEN;
122        let crc = dvb_common::crc32_mpeg2::compute(&buf[..crc_pos]);
123        buf[crc_pos..len].copy_from_slice(&crc.to_be_bytes());
124
125        Ok(len)
126    }
127}
128
129impl<'a> Table<'a> for Tsdt<'a> {
130    const TABLE_ID: u8 = TABLE_ID;
131    const PID: u16 = PID;
132}
133
134impl<'a> crate::traits::TableDef<'a> for Tsdt<'a> {
135    const TABLE_ID_RANGES: &'static [(u8, u8)] = &[(TABLE_ID, TABLE_ID)];
136    const NAME: &'static str = "TRANSPORT_STREAM_DESCRIPTION";
137}
138
139#[cfg(test)]
140mod tests {
141    use super::*;
142
143    fn build_tsdt(table_id_extension: u16, version: u8, descriptors: &[u8]) -> Vec<u8> {
144        let section_length: u16 = (EXTENSION_HEADER_LEN + descriptors.len() + CRC_LEN) as u16;
145        let mut v = Vec::new();
146        v.push(TABLE_ID);
147        v.push(0xB0 | ((section_length >> 8) as u8 & 0x0F));
148        v.push((section_length & 0xFF) as u8);
149        v.extend_from_slice(&table_id_extension.to_be_bytes());
150        v.push(0xC0 | ((version & 0x1F) << 1) | 0x01);
151        v.push(0x00);
152        v.push(0x00);
153        v.extend_from_slice(descriptors);
154        v.extend_from_slice(&[0, 0, 0, 0]);
155        v
156    }
157
158    #[test]
159    fn parse_rejects_wrong_tag() {
160        let mut bytes = build_tsdt(0x1234, 5, &[]);
161        bytes[0] = 0x02;
162        assert!(matches!(
163            Tsdt::parse(&bytes).unwrap_err(),
164            Error::UnexpectedTableId { table_id: 0x02, .. }
165        ));
166    }
167
168    #[test]
169    fn parse_rejects_short_buffer() {
170        let err = Tsdt::parse(&[0x03, 0xB0]).unwrap_err();
171        assert!(matches!(err, Error::BufferTooShort { .. }));
172    }
173
174    #[test]
175    fn parse_empty_descriptor_loop() {
176        let bytes = build_tsdt(0x1234, 5, &[]);
177        let tsdt = Tsdt::parse(&bytes).unwrap();
178        assert_eq!(tsdt.table_id_extension, 0x1234);
179        assert_eq!(tsdt.version_number, 5);
180        assert!(tsdt.current_next_indicator);
181        assert_eq!(tsdt.section_number, 0);
182        assert_eq!(tsdt.last_section_number, 0);
183        assert!(tsdt.descriptors.is_empty());
184    }
185
186    #[test]
187    fn parse_with_descriptors() {
188        let descriptors = [0x01, 0x03, 0xAA, 0xBB, 0xCC];
189        let bytes = build_tsdt(0xABCD, 7, &descriptors);
190        let tsdt = Tsdt::parse(&bytes).unwrap();
191        assert_eq!(tsdt.table_id_extension, 0xABCD);
192        assert_eq!(tsdt.version_number, 7);
193        assert_eq!(tsdt.descriptors.raw(), &descriptors[..]);
194    }
195
196    #[test]
197    fn serialize_round_trip() {
198        let descriptors = [0x4D, 0x02, 0x01, 0x02];
199        let bytes = build_tsdt(0xCAFE, 3, &descriptors);
200        let tsdt = Tsdt::parse(&bytes).unwrap();
201        let mut buf = vec![0u8; tsdt.serialized_len()];
202        tsdt.serialize_into(&mut buf).unwrap();
203        let re = Tsdt::parse(&buf).unwrap();
204        assert_eq!(tsdt, re);
205    }
206
207    #[test]
208    fn serialize_round_trip_empty() {
209        let bytes = build_tsdt(0x0001, 0, &[]);
210        let tsdt = Tsdt::parse(&bytes).unwrap();
211        let mut buf = vec![0u8; tsdt.serialized_len()];
212        tsdt.serialize_into(&mut buf).unwrap();
213        let re = Tsdt::parse(&buf).unwrap();
214        assert_eq!(tsdt, re);
215    }
216
217    #[test]
218    fn table_trait_constants() {
219        assert_eq!(<Tsdt<'_> as Table>::TABLE_ID, 0x03);
220        assert_eq!(<Tsdt<'_> as Table>::PID, 0x0002);
221    }
222
223    #[cfg(feature = "serde")]
224    #[test]
225    fn tsdt_serializes_typed_loop() {
226        // TSDT now borrows its descriptor loop (3.0): serialize-only, the loop
227        // emits the typed descriptor sequence (here a short_event, tag 0x4D).
228        let descriptors = [0x4D, 0x02, b'e', b'n']; // valid short_event header bytes
229        let bytes = build_tsdt(0xDEAD, 9, &descriptors);
230        let tsdt = Tsdt::parse(&bytes).unwrap();
231        let v = serde_json::to_value(&tsdt).unwrap();
232        assert!(
233            v["descriptors"].is_array(),
234            "descriptors must serialize as a typed sequence, got {v}"
235        );
236    }
237}
dvb_si/tables/tsdt.rs

dvb_si/tables/
tsdt.rs
