dvb_si/descriptors/
short_event.rs

1//! Short Event Descriptor — ETSI EN 300 468 §6.2.37 (tag 0x4D).
2//!
3//! Carried inside EIT. Gives the event's title and brief description in a
4//! single language.
5
6use super::descriptor_body;
7use crate::error::{Error, Result};
8use crate::text::{DvbText, LangCode};
9use dvb_common::{Parse, Serialize};
10
11/// Descriptor tag for short_event_descriptor.
12pub const TAG: u8 = 0x4D;
13const HEADER_LEN: usize = 2;
14const LANG_LEN: usize = 3;
15
16/// Short Event Descriptor.
17#[derive(Debug, Clone, PartialEq, Eq)]
18#[cfg_attr(feature = "serde", derive(serde::Serialize))]
19#[cfg_attr(feature = "yoke", derive(yoke::Yokeable))]
20pub struct ShortEventDescriptor<'a> {
21    /// ISO 639-2 language code of the event name / text.
22    pub language_code: LangCode,
23    /// DVB Annex-A encoded event name.
24    pub event_name: DvbText<'a>,
25    /// DVB Annex-A encoded brief description.
26    pub text: DvbText<'a>,
27}
28
29impl<'a> Parse<'a> for ShortEventDescriptor<'a> {
30    type Error = crate::error::Error;
31    fn parse(bytes: &'a [u8]) -> Result<Self> {
32        let body = descriptor_body(
33            bytes,
34            TAG,
35            "ShortEventDescriptor",
36            "unexpected tag for short_event_descriptor",
37        )?;
38        if body.len() < LANG_LEN + 2 {
39            return Err(Error::InvalidDescriptor {
40                tag: TAG,
41                reason: "short_event_descriptor body shorter than minimum 5 bytes",
42            });
43        }
44        let language_code = LangCode([body[0], body[1], body[2]]);
45        let name_len = body[LANG_LEN] as usize;
46        let name_start = LANG_LEN + 1;
47        let name_end = name_start + name_len;
48        if name_end + 1 > body.len() {
49            return Err(Error::InvalidDescriptor {
50                tag: TAG,
51                reason: "event_name_length runs past descriptor end",
52            });
53        }
54        let event_name = DvbText::new(&body[name_start..name_end]);
55        let text_len = body[name_end] as usize;
56        let text_start = name_end + 1;
57        let text_end = text_start + text_len;
58        if text_end > body.len() {
59            return Err(Error::InvalidDescriptor {
60                tag: TAG,
61                reason: "text_length runs past descriptor end",
62            });
63        }
64        let text = DvbText::new(&body[text_start..text_end]);
65        Ok(Self {
66            language_code,
67            event_name,
68            text,
69        })
70    }
71}
72
73impl Serialize for ShortEventDescriptor<'_> {
74    type Error = crate::error::Error;
75    fn serialized_len(&self) -> usize {
76        HEADER_LEN + LANG_LEN + 1 + self.event_name.len() + 1 + self.text.len()
77    }
78
79    fn serialize_into(&self, buf: &mut [u8]) -> Result<usize> {
80        let len = self.serialized_len();
81        if buf.len() < len {
82            return Err(Error::OutputBufferTooSmall {
83                need: len,
84                have: buf.len(),
85            });
86        }
87        buf[0] = TAG;
88        buf[1] = (len - HEADER_LEN) as u8;
89        buf[2..5].copy_from_slice(&self.language_code.0);
90        buf[5] = self.event_name.len() as u8;
91        let n_start = 6;
92        let n_end = n_start + self.event_name.len();
93        buf[n_start..n_end].copy_from_slice(self.event_name.raw());
94        buf[n_end] = self.text.len() as u8;
95        let t_start = n_end + 1;
96        buf[t_start..t_start + self.text.len()].copy_from_slice(self.text.raw());
97        Ok(len)
98    }
99}
100impl<'a> crate::traits::DescriptorDef<'a> for ShortEventDescriptor<'a> {
101    const TAG: u8 = TAG;
102    const NAME: &'static str = "SHORT_EVENT";
103}
104
105#[cfg(test)]
106mod tests {
107    use super::*;
108
109    #[test]
110    fn parse_extracts_all_fields() {
111        let bytes = [
112            TAG, 0x0C, b'e', b'n', b'g', 4, b'N', b'e', b'w', b's', 3, b'L', b'i', b'v',
113        ];
114        let d = ShortEventDescriptor::parse(&bytes).unwrap();
115        assert_eq!(d.language_code, LangCode(*b"eng"));
116        assert_eq!(d.event_name.raw(), b"News");
117        assert_eq!(d.text.raw(), b"Liv");
118    }
119
120    #[test]
121    fn parse_rejects_wrong_tag() {
122        let err = ShortEventDescriptor::parse(&[0x4E, 0]).unwrap_err();
123        assert!(matches!(err, Error::InvalidDescriptor { tag: 0x4E, .. }));
124    }
125
126    #[test]
127    fn parse_rejects_short_buffer() {
128        let err = ShortEventDescriptor::parse(&[TAG]).unwrap_err();
129        assert!(matches!(err, Error::BufferTooShort { .. }));
130    }
131
132    #[test]
133    fn parse_rejects_body_too_short_for_minimum() {
134        // Body of length 3 has language code but no event_name length field.
135        let err = ShortEventDescriptor::parse(&[TAG, 3, b'e', b'n', b'g']).unwrap_err();
136        assert!(matches!(err, Error::InvalidDescriptor { .. }));
137    }
138
139    #[test]
140    fn parse_rejects_name_length_overrun() {
141        // body length 5 = lang(3) + name_len(1) + 1 byte of name/text.
142        // Set name_len = 100 — bigger than the remaining body.
143        let bytes = [TAG, 5, b'e', b'n', b'g', 100, 0];
144        let err = ShortEventDescriptor::parse(&bytes).unwrap_err();
145        assert!(matches!(err, Error::InvalidDescriptor { .. }));
146    }
147
148    #[test]
149    fn empty_event_name_and_text_valid() {
150        let bytes = [TAG, 5, b'e', b'n', b'g', 0, 0];
151        let d = ShortEventDescriptor::parse(&bytes).unwrap();
152        assert!(d.event_name.raw().is_empty());
153        assert!(d.text.raw().is_empty());
154    }
155
156    #[test]
157    fn serialize_round_trip() {
158        let d = ShortEventDescriptor {
159            language_code: LangCode(*b"fra"),
160            event_name: DvbText::new(b"Journal"),
161            text: DvbText::new(b"20h"),
162        };
163        let mut buf = vec![0u8; d.serialized_len()];
164        d.serialize_into(&mut buf).unwrap();
165        let re = ShortEventDescriptor::parse(&buf).unwrap();
166        assert_eq!(d, re);
167    }
168
169    #[test]
170    fn descriptor_length_matches_payload() {
171        let d = ShortEventDescriptor {
172            language_code: LangCode(*b"eng"),
173            event_name: DvbText::new(b"ABC"),
174            text: DvbText::new(b"DE"),
175        };
176        // 3 lang + 1 name_len + 3 name + 1 text_len + 2 text = 10
177        assert_eq!(d.serialized_len() - 2, 10);
178    }
179}
dvb_si/descriptors/short_event.rs

dvb_si/descriptors/
short_event.rs
