dvb_si/descriptors/
extended_event.rs

1//! Extended Event Descriptor — ETSI EN 300 468 §6.2.16 (tag 0x4E).
2//!
3//! Carried inside EIT. Provides the full event description split across
4//! descriptor_number / last_descriptor_number fragments. Each fragment
5//! contributes text plus an optional list of (item_description, item) pairs.
6
7use crate::error::{Error, Result};
8use crate::text::{DvbText, LangCode};
9use crate::traits::Descriptor;
10use dvb_common::{Parse, Serialize};
11
12/// Descriptor tag for extended_event_descriptor.
13pub const TAG: u8 = 0x4E;
14const HEADER_LEN: usize = 2;
15const NUMBERS_LEN: usize = 1;
16const LANG_LEN: usize = 3;
17const ITEMS_LEN_FIELD: usize = 1;
18const TEXT_LEN_FIELD: usize = 1;
19
20/// One (description, value) item — e.g. "Director" → "Alice Smith".
21#[derive(Debug, Clone, PartialEq, Eq)]
22#[cfg_attr(feature = "serde", derive(serde::Serialize))]
23pub struct ExtendedEventItem<'a> {
24    /// DVB Annex-A encoded item description.
25    pub description: DvbText<'a>,
26    /// DVB Annex-A encoded item value.
27    pub value: DvbText<'a>,
28}
29
30/// Extended Event Descriptor.
31#[derive(Debug, Clone, PartialEq, Eq)]
32#[cfg_attr(feature = "serde", derive(serde::Serialize))]
33pub struct ExtendedEventDescriptor<'a> {
34    /// 0-based fragment index within the extended event series.
35    pub descriptor_number: u8,
36    /// Index of the final fragment in the series (0-based).
37    pub last_descriptor_number: u8,
38    /// ISO 639-2 language code.
39    pub language_code: LangCode,
40    /// Item list.
41    pub items: Vec<ExtendedEventItem<'a>>,
42    /// DVB Annex-A encoded extended text.
43    pub text: DvbText<'a>,
44}
45
46impl<'a> Parse<'a> for ExtendedEventDescriptor<'a> {
47    type Error = crate::error::Error;
48    fn parse(bytes: &'a [u8]) -> Result<Self> {
49        let min_len = HEADER_LEN + NUMBERS_LEN + LANG_LEN + ITEMS_LEN_FIELD + TEXT_LEN_FIELD;
50        if bytes.len() < min_len {
51            return Err(Error::BufferTooShort {
52                need: min_len,
53                have: bytes.len(),
54                what: "ExtendedEventDescriptor header",
55            });
56        }
57        if bytes[0] != TAG {
58            return Err(Error::InvalidDescriptor {
59                tag: bytes[0],
60                reason: "unexpected tag for extended_event_descriptor",
61            });
62        }
63        let length = bytes[1] as usize;
64        let end = HEADER_LEN + length;
65        if bytes.len() < end {
66            return Err(Error::BufferTooShort {
67                need: end,
68                have: bytes.len(),
69                what: "ExtendedEventDescriptor body",
70            });
71        }
72        let numbers_byte = bytes[2];
73        let descriptor_number = numbers_byte >> 4;
74        let last_descriptor_number = numbers_byte & 0x0F;
75        let language_code = LangCode([bytes[3], bytes[4], bytes[5]]);
76
77        let items_len_pos = HEADER_LEN + NUMBERS_LEN + LANG_LEN;
78        let items_length = bytes[items_len_pos] as usize;
79        let items_start = items_len_pos + ITEMS_LEN_FIELD;
80        let items_end = items_start + items_length;
81        if items_end + TEXT_LEN_FIELD > end {
82            return Err(Error::InvalidDescriptor {
83                tag: TAG,
84                reason: "length_of_items runs past descriptor end",
85            });
86        }
87
88        let mut items = Vec::new();
89        let mut pos = items_start;
90        while pos < items_end {
91            if pos >= items_end {
92                break;
93            }
94            let desc_len = bytes[pos] as usize;
95            let desc_start = pos + 1;
96            let desc_end = desc_start + desc_len;
97            if desc_end + 1 > items_end {
98                return Err(Error::InvalidDescriptor {
99                    tag: TAG,
100                    reason: "item_description_length runs past items loop",
101                });
102            }
103            let value_len = bytes[desc_end] as usize;
104            let value_start = desc_end + 1;
105            let value_end = value_start + value_len;
106            if value_end > items_end {
107                return Err(Error::InvalidDescriptor {
108                    tag: TAG,
109                    reason: "item_length runs past items loop",
110                });
111            }
112            items.push(ExtendedEventItem {
113                description: DvbText::new(&bytes[desc_start..desc_end]),
114                value: DvbText::new(&bytes[value_start..value_end]),
115            });
116            pos = value_end;
117        }
118
119        let text_len = bytes[items_end] as usize;
120        let text_start = items_end + TEXT_LEN_FIELD;
121        let text_end = text_start + text_len;
122        if text_end > end {
123            return Err(Error::InvalidDescriptor {
124                tag: TAG,
125                reason: "text_length runs past descriptor end",
126            });
127        }
128        let text = DvbText::new(&bytes[text_start..text_end]);
129
130        Ok(Self {
131            descriptor_number,
132            last_descriptor_number,
133            language_code,
134            items,
135            text,
136        })
137    }
138}
139
140impl Serialize for ExtendedEventDescriptor<'_> {
141    type Error = crate::error::Error;
142    fn serialized_len(&self) -> usize {
143        let items_bytes: usize = self
144            .items
145            .iter()
146            .map(|i| 1 + i.description.len() + 1 + i.value.len())
147            .sum();
148        HEADER_LEN
149            + NUMBERS_LEN
150            + LANG_LEN
151            + ITEMS_LEN_FIELD
152            + items_bytes
153            + TEXT_LEN_FIELD
154            + self.text.len()
155    }
156
157    fn serialize_into(&self, buf: &mut [u8]) -> Result<usize> {
158        let len = self.serialized_len();
159        if buf.len() < len {
160            return Err(Error::OutputBufferTooSmall {
161                need: len,
162                have: buf.len(),
163            });
164        }
165        buf[0] = TAG;
166        buf[1] = (len - HEADER_LEN) as u8;
167        buf[2] = ((self.descriptor_number & 0x0F) << 4) | (self.last_descriptor_number & 0x0F);
168        buf[3..6].copy_from_slice(&self.language_code.0);
169
170        let items_bytes: usize = self
171            .items
172            .iter()
173            .map(|i| 1 + i.description.len() + 1 + i.value.len())
174            .sum();
175        buf[6] = items_bytes as u8;
176
177        let mut pos = 7;
178        for item in &self.items {
179            buf[pos] = item.description.len() as u8;
180            let d_start = pos + 1;
181            let d_end = d_start + item.description.len();
182            buf[d_start..d_end].copy_from_slice(item.description.raw());
183            buf[d_end] = item.value.len() as u8;
184            let v_start = d_end + 1;
185            let v_end = v_start + item.value.len();
186            buf[v_start..v_end].copy_from_slice(item.value.raw());
187            pos = v_end;
188        }
189        buf[pos] = self.text.len() as u8;
190        buf[pos + 1..pos + 1 + self.text.len()].copy_from_slice(self.text.raw());
191        Ok(len)
192    }
193}
194
195impl<'a> Descriptor<'a> for ExtendedEventDescriptor<'a> {
196    const TAG: u8 = TAG;
197    fn descriptor_length(&self) -> u8 {
198        (self.serialized_len() - HEADER_LEN) as u8
199    }
200}
201
202impl<'a> crate::traits::DescriptorDef<'a> for ExtendedEventDescriptor<'a> {
203    const TAG: u8 = TAG;
204    const NAME: &'static str = "EXTENDED_EVENT";
205}
206
207#[cfg(test)]
208mod tests {
209    use super::*;
210
211    fn build(
212        descriptor_number: u8,
213        last_descriptor_number: u8,
214        lang: [u8; 3],
215        items: &[(&[u8], &[u8])],
216        text: &[u8],
217    ) -> Vec<u8> {
218        let items_bytes: Vec<u8> = items
219            .iter()
220            .flat_map(|(d, v)| {
221                let mut x = Vec::with_capacity(2 + d.len() + v.len());
222                x.push(d.len() as u8);
223                x.extend_from_slice(d);
224                x.push(v.len() as u8);
225                x.extend_from_slice(v);
226                x
227            })
228            .collect();
229        let body_len = NUMBERS_LEN
230            + LANG_LEN
231            + ITEMS_LEN_FIELD
232            + items_bytes.len()
233            + TEXT_LEN_FIELD
234            + text.len();
235        let mut v = Vec::with_capacity(HEADER_LEN + body_len);
236        v.push(TAG);
237        v.push(body_len as u8);
238        v.push(((descriptor_number & 0x0F) << 4) | (last_descriptor_number & 0x0F));
239        v.extend_from_slice(&lang);
240        v.push(items_bytes.len() as u8);
241        v.extend_from_slice(&items_bytes);
242        v.push(text.len() as u8);
243        v.extend_from_slice(text);
244        v
245    }
246
247    #[test]
248    fn parse_extracts_numbers_language_and_text() {
249        let bytes = build(2, 3, *b"fra", &[], b"Hello");
250        let d = ExtendedEventDescriptor::parse(&bytes).unwrap();
251        assert_eq!(d.descriptor_number, 2);
252        assert_eq!(d.last_descriptor_number, 3);
253        assert_eq!(d.language_code, LangCode(*b"fra"));
254        assert_eq!(d.text.raw(), b"Hello");
255        assert_eq!(d.items.len(), 0);
256    }
257
258    #[test]
259    fn parse_extracts_item_list() {
260        let items: [(&[u8], &[u8]); 2] = [(b"Director", b"Alice"), (b"Year", b"2023")];
261        let bytes = build(0, 0, *b"eng", &items, b"");
262        let d = ExtendedEventDescriptor::parse(&bytes).unwrap();
263        assert_eq!(d.items.len(), 2);
264        assert_eq!(d.items[0].description.raw(), b"Director");
265        assert_eq!(d.items[0].value.raw(), b"Alice");
266        assert_eq!(d.items[1].description.raw(), b"Year");
267        assert_eq!(d.items[1].value.raw(), b"2023");
268    }
269
270    #[test]
271    fn parse_rejects_wrong_tag() {
272        // Full 8-byte descriptor with the wrong tag — must fail with tag mismatch.
273        let bytes = [0x4D, 6, 0x00, b'e', b'n', b'g', 0, 0];
274        assert!(matches!(
275            ExtendedEventDescriptor::parse(&bytes).unwrap_err(),
276            Error::InvalidDescriptor { tag: 0x4D, .. }
277        ));
278    }
279
280    #[test]
281    fn parse_rejects_short_header() {
282        assert!(matches!(
283            ExtendedEventDescriptor::parse(&[TAG, 2, 0, 0]).unwrap_err(),
284            Error::BufferTooShort { .. }
285        ));
286    }
287
288    #[test]
289    fn parse_rejects_item_length_overrun() {
290        // items_length=10 but body only 6 bytes after the items_length field.
291        let bytes = [
292            TAG, 11, 0x00, b'e', b'n', b'g', 10, // items_length claims 10 bytes
293            0, 0, 0, 0, 0, // only 5 bytes of items
294            0, // text_length (partially unreachable)
295        ];
296        assert!(matches!(
297            ExtendedEventDescriptor::parse(&bytes).unwrap_err(),
298            Error::InvalidDescriptor { .. }
299        ));
300    }
301
302    #[test]
303    fn parse_rejects_text_length_overrun() {
304        // body=6: numbers + lang + items_length=0 + text_length=5 but no text bytes.
305        let bytes = [TAG, 6, 0x00, b'e', b'n', b'g', 0, 5];
306        assert!(matches!(
307            ExtendedEventDescriptor::parse(&bytes).unwrap_err(),
308            Error::InvalidDescriptor { .. }
309        ));
310    }
311
312    #[test]
313    fn empty_items_and_text_valid() {
314        let bytes = build(0, 0, *b"eng", &[], b"");
315        let d = ExtendedEventDescriptor::parse(&bytes).unwrap();
316        assert_eq!(d.items.len(), 0);
317        assert_eq!(d.text.raw(), b"");
318    }
319
320    #[test]
321    fn serialize_round_trip_with_items_and_text() {
322        let items: [(&[u8], &[u8]); 1] = [(b"Genre", b"Drama")];
323        let bytes = build(1, 2, *b"eng", &items, b"Plot summary.");
324        let parsed = ExtendedEventDescriptor::parse(&bytes).unwrap();
325        let mut buf = vec![0u8; parsed.serialized_len()];
326        parsed.serialize_into(&mut buf).unwrap();
327        assert_eq!(buf, bytes);
328        let re = ExtendedEventDescriptor::parse(&buf).unwrap();
329        assert_eq!(parsed, re);
330    }
331
332    #[test]
333    fn serialize_round_trip_without_items() {
334        let bytes = build(3, 3, *b"fra", &[], b"Plot.");
335        let parsed = ExtendedEventDescriptor::parse(&bytes).unwrap();
336        let mut buf = vec![0u8; parsed.serialized_len()];
337        parsed.serialize_into(&mut buf).unwrap();
338        assert_eq!(buf, bytes);
339    }
340}
dvb_si/descriptors/extended_event.rs

dvb_si/descriptors/
extended_event.rs
