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

dvb_si/tables/
tsdt.rs
