dvb_si/descriptors/
service_list.rs

1//! Service List Descriptor — ETSI EN 300 468 §6.2.36 (tag 0x41).
2//!
3//! Carried inside NIT/BAT transport_stream_loop second descriptor loop.
4//! Enumerates the service_id/service_type pairs available on the TS.
5
6use super::descriptor_body;
7use super::service::ServiceType;
8use crate::error::{Error, Result};
9use alloc::vec::Vec;
10use dvb_common::{Parse, Serialize};
11
12/// Descriptor tag for service_list_descriptor.
13pub const TAG: u8 = 0x41;
14const HEADER_LEN: usize = 2;
15const ENTRY_LEN: usize = 3;
16
17/// One (service_id, service_type) pair.
18#[derive(Debug, Clone, Copy, PartialEq, Eq)]
19#[cfg_attr(feature = "serde", derive(serde::Serialize))]
20pub struct ServiceListEntry {
21    /// DVB service_id (matches program_number in PAT).
22    pub service_id: u16,
23    /// service_type (ETSI Table 89).
24    pub service_type: ServiceType,
25}
26
27/// Service List Descriptor.
28#[derive(Debug, Clone, PartialEq, Eq)]
29#[cfg_attr(feature = "serde", derive(serde::Serialize))]
30pub struct ServiceListDescriptor {
31    /// Entries in wire order.
32    pub entries: Vec<ServiceListEntry>,
33}
34
35impl<'a> Parse<'a> for ServiceListDescriptor {
36    type Error = crate::error::Error;
37    fn parse(bytes: &'a [u8]) -> Result<Self> {
38        let body = descriptor_body(
39            bytes,
40            TAG,
41            "ServiceListDescriptor",
42            "unexpected tag for service_list_descriptor",
43        )?;
44        if body.len() % 3 != 0 {
45            return Err(Error::InvalidDescriptor {
46                tag: TAG,
47                reason: "descriptor_length must be a multiple of 3",
48            });
49        }
50        let mut entries = Vec::with_capacity(body.len() / ENTRY_LEN);
51        let mut offset = 0;
52        while offset < body.len() {
53            let service_id = u16::from_be_bytes([body[offset], body[offset + 1]]);
54            let service_type = ServiceType::from_u8(body[offset + 2]);
55            entries.push(ServiceListEntry {
56                service_id,
57                service_type,
58            });
59            offset += ENTRY_LEN;
60        }
61        Ok(Self { entries })
62    }
63}
64
65impl Serialize for ServiceListDescriptor {
66    type Error = crate::error::Error;
67    fn serialized_len(&self) -> usize {
68        HEADER_LEN + ENTRY_LEN * self.entries.len()
69    }
70
71    fn serialize_into(&self, buf: &mut [u8]) -> Result<usize> {
72        let len = self.serialized_len();
73        if buf.len() < len {
74            return Err(Error::OutputBufferTooSmall {
75                need: len,
76                have: buf.len(),
77            });
78        }
79        buf[0] = TAG;
80        buf[1] = (len - HEADER_LEN) as u8;
81        let mut offset = HEADER_LEN;
82        for entry in &self.entries {
83            buf[offset..offset + 2].copy_from_slice(&entry.service_id.to_be_bytes());
84            buf[offset + 2] = entry.service_type.to_u8();
85            offset += ENTRY_LEN;
86        }
87        Ok(len)
88    }
89}
90impl<'a> crate::traits::DescriptorDef<'a> for ServiceListDescriptor {
91    const TAG: u8 = TAG;
92    const NAME: &'static str = "SERVICE_LIST";
93}
94
95#[cfg(test)]
96mod tests {
97    use super::*;
98
99    #[test]
100    fn parse_single_entry() {
101        let bytes = [TAG, 3, 0x00, 0x01, 0x01];
102        let d = ServiceListDescriptor::parse(&bytes).unwrap();
103        assert_eq!(d.entries.len(), 1);
104        assert_eq!(d.entries[0].service_id, 1);
105        assert_eq!(d.entries[0].service_type, ServiceType::DigitalTelevision);
106    }
107
108    #[test]
109    fn parse_multiple_entries_preserves_order() {
110        let bytes = [TAG, 9, 0x00, 0x01, 0x01, 0x00, 0x02, 0x02, 0x00, 0x03, 0x03];
111        let d = ServiceListDescriptor::parse(&bytes).unwrap();
112        assert_eq!(d.entries.len(), 3);
113        assert_eq!(d.entries[0].service_id, 1);
114        assert_eq!(d.entries[0].service_type, ServiceType::DigitalTelevision);
115        assert_eq!(d.entries[1].service_id, 2);
116        assert_eq!(d.entries[1].service_type, ServiceType::DigitalRadioSound);
117        assert_eq!(d.entries[2].service_id, 3);
118        assert_eq!(d.entries[2].service_type, ServiceType::Teletext);
119    }
120
121    #[test]
122    fn parse_rejects_wrong_tag() {
123        let err = ServiceListDescriptor::parse(&[0x42, 3, 0x00, 0x01, 0x01]).unwrap_err();
124        assert!(matches!(err, Error::InvalidDescriptor { tag: 0x42, .. }));
125    }
126
127    #[test]
128    fn parse_rejects_length_not_multiple_of_3() {
129        let bytes = [TAG, 4, 0x00, 0x01, 0x01, 0xFF];
130        let err = ServiceListDescriptor::parse(&bytes).unwrap_err();
131        assert!(matches!(err, Error::InvalidDescriptor { tag: TAG, .. }));
132    }
133
134    #[test]
135    fn parse_rejects_truncated_body() {
136        let bytes = [TAG, 6, 0x00, 0x01];
137        let err = ServiceListDescriptor::parse(&bytes).unwrap_err();
138        assert!(matches!(err, Error::BufferTooShort { .. }));
139    }
140
141    #[test]
142    fn empty_descriptor_valid() {
143        let bytes = [TAG, 0];
144        let d = ServiceListDescriptor::parse(&bytes).unwrap();
145        assert!(d.entries.is_empty());
146    }
147
148    #[test]
149    fn serialize_round_trip() {
150        let d = ServiceListDescriptor {
151            entries: vec![
152                ServiceListEntry {
153                    service_id: 1,
154                    service_type: ServiceType::DigitalTelevision,
155                },
156                ServiceListEntry {
157                    service_id: 0x0102,
158                    service_type: ServiceType::NvodReference,
159                },
160            ],
161        };
162        let mut buf = vec![0u8; d.serialized_len()];
163        d.serialize_into(&mut buf).unwrap();
164        let re = ServiceListDescriptor::parse(&buf).unwrap();
165        assert_eq!(d, re);
166    }
167}
dvb_si/descriptors/service_list.rs

dvb_si/descriptors/
service_list.rs
