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 crate::error::{Error, Result};
7use crate::text::{DvbText, LangCode};
8use crate::traits::Descriptor;
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        if bytes.len() < HEADER_LEN {
33            return Err(Error::BufferTooShort {
34                need: HEADER_LEN,
35                have: bytes.len(),
36                what: "ShortEventDescriptor header",
37            });
38        }
39        if bytes[0] != TAG {
40            return Err(Error::InvalidDescriptor {
41                tag: bytes[0],
42                reason: "unexpected tag for short_event_descriptor",
43            });
44        }
45        let length = bytes[1] as usize;
46        let end = HEADER_LEN + length;
47        if bytes.len() < end {
48            return Err(Error::BufferTooShort {
49                need: end,
50                have: bytes.len(),
51                what: "ShortEventDescriptor body",
52            });
53        }
54        if length < LANG_LEN + 2 {
55            return Err(Error::InvalidDescriptor {
56                tag: TAG,
57                reason: "short_event_descriptor body shorter than minimum 5 bytes",
58            });
59        }
60        let body_start = HEADER_LEN;
61        let language_code = LangCode([
62            bytes[body_start],
63            bytes[body_start + 1],
64            bytes[body_start + 2],
65        ]);
66        let name_len_pos = body_start + LANG_LEN;
67        let name_len = bytes[name_len_pos] as usize;
68        let name_start = name_len_pos + 1;
69        let name_end = name_start + name_len;
70        if name_end + 1 > end {
71            return Err(Error::InvalidDescriptor {
72                tag: TAG,
73                reason: "event_name_length runs past descriptor end",
74            });
75        }
76        let event_name = DvbText::new(&bytes[name_start..name_end]);
77        let text_len = bytes[name_end] as usize;
78        let text_start = name_end + 1;
79        let text_end = text_start + text_len;
80        if text_end > end {
81            return Err(Error::InvalidDescriptor {
82                tag: TAG,
83                reason: "text_length runs past descriptor end",
84            });
85        }
86        let text = DvbText::new(&bytes[text_start..text_end]);
87        Ok(Self {
88            language_code,
89            event_name,
90            text,
91        })
92    }
93}
94
95impl Serialize for ShortEventDescriptor<'_> {
96    type Error = crate::error::Error;
97    fn serialized_len(&self) -> usize {
98        HEADER_LEN + LANG_LEN + 1 + self.event_name.len() + 1 + self.text.len()
99    }
100
101    fn serialize_into(&self, buf: &mut [u8]) -> Result<usize> {
102        let len = self.serialized_len();
103        if buf.len() < len {
104            return Err(Error::OutputBufferTooSmall {
105                need: len,
106                have: buf.len(),
107            });
108        }
109        buf[0] = TAG;
110        buf[1] = (len - HEADER_LEN) as u8;
111        buf[2..5].copy_from_slice(&self.language_code.0);
112        buf[5] = self.event_name.len() as u8;
113        let n_start = 6;
114        let n_end = n_start + self.event_name.len();
115        buf[n_start..n_end].copy_from_slice(self.event_name.raw());
116        buf[n_end] = self.text.len() as u8;
117        let t_start = n_end + 1;
118        buf[t_start..t_start + self.text.len()].copy_from_slice(self.text.raw());
119        Ok(len)
120    }
121}
122
123impl<'a> Descriptor<'a> for ShortEventDescriptor<'a> {
124    const TAG: u8 = TAG;
125    fn descriptor_length(&self) -> u8 {
126        (self.serialized_len() - HEADER_LEN) as u8
127    }
128}
129
130impl<'a> crate::traits::DescriptorDef<'a> for ShortEventDescriptor<'a> {
131    const TAG: u8 = TAG;
132    const NAME: &'static str = "SHORT_EVENT";
133}
134
135#[cfg(test)]
136mod tests {
137    use super::*;
138
139    #[test]
140    fn parse_extracts_all_fields() {
141        let bytes = [
142            TAG, 0x0C, b'e', b'n', b'g', 4, b'N', b'e', b'w', b's', 3, b'L', b'i', b'v',
143        ];
144        let d = ShortEventDescriptor::parse(&bytes).unwrap();
145        assert_eq!(d.language_code, LangCode(*b"eng"));
146        assert_eq!(d.event_name.raw(), b"News");
147        assert_eq!(d.text.raw(), b"Liv");
148    }
149
150    #[test]
151    fn parse_rejects_wrong_tag() {
152        let err = ShortEventDescriptor::parse(&[0x4E, 0]).unwrap_err();
153        assert!(matches!(err, Error::InvalidDescriptor { tag: 0x4E, .. }));
154    }
155
156    #[test]
157    fn parse_rejects_short_buffer() {
158        let err = ShortEventDescriptor::parse(&[TAG]).unwrap_err();
159        assert!(matches!(err, Error::BufferTooShort { .. }));
160    }
161
162    #[test]
163    fn parse_rejects_body_too_short_for_minimum() {
164        // Body of length 3 has language code but no event_name length field.
165        let err = ShortEventDescriptor::parse(&[TAG, 3, b'e', b'n', b'g']).unwrap_err();
166        assert!(matches!(err, Error::InvalidDescriptor { .. }));
167    }
168
169    #[test]
170    fn parse_rejects_name_length_overrun() {
171        // body length 5 = lang(3) + name_len(1) + 1 byte of name/text.
172        // Set name_len = 100 — bigger than the remaining body.
173        let bytes = [TAG, 5, b'e', b'n', b'g', 100, 0];
174        let err = ShortEventDescriptor::parse(&bytes).unwrap_err();
175        assert!(matches!(err, Error::InvalidDescriptor { .. }));
176    }
177
178    #[test]
179    fn empty_event_name_and_text_valid() {
180        let bytes = [TAG, 5, b'e', b'n', b'g', 0, 0];
181        let d = ShortEventDescriptor::parse(&bytes).unwrap();
182        assert!(d.event_name.raw().is_empty());
183        assert!(d.text.raw().is_empty());
184    }
185
186    #[test]
187    fn serialize_round_trip() {
188        let d = ShortEventDescriptor {
189            language_code: LangCode(*b"fra"),
190            event_name: DvbText::new(b"Journal"),
191            text: DvbText::new(b"20h"),
192        };
193        let mut buf = vec![0u8; d.serialized_len()];
194        d.serialize_into(&mut buf).unwrap();
195        let re = ShortEventDescriptor::parse(&buf).unwrap();
196        assert_eq!(d, re);
197    }
198
199    #[test]
200    fn descriptor_length_matches_payload() {
201        let d = ShortEventDescriptor {
202            language_code: LangCode(*b"eng"),
203            event_name: DvbText::new(b"ABC"),
204            text: DvbText::new(b"DE"),
205        };
206        // 3 lang + 1 name_len + 3 name + 1 text_len + 2 text = 10
207        assert_eq!(d.descriptor_length(), 10);
208    }
209}
dvb_si/descriptors/short_event.rs

dvb_si/descriptors/
short_event.rs
