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 super::descriptor_body;
8use crate::error::{Error, Result};
9use crate::text::{DvbText, LangCode};
10use alloc::vec::Vec;
11use dvb_common::{Parse, Serialize};
12
13/// Descriptor tag for extended_event_descriptor.
14pub const TAG: u8 = 0x4E;
15const HEADER_LEN: usize = 2;
16const NUMBERS_LEN: usize = 1;
17const LANG_LEN: usize = 3;
18const ITEMS_LEN_FIELD: usize = 1;
19const TEXT_LEN_FIELD: usize = 1;
20const FIXED_PREFIX_LEN: usize = NUMBERS_LEN + LANG_LEN + ITEMS_LEN_FIELD + TEXT_LEN_FIELD;
21
22/// One (description, value) item — e.g. "Director" → "Alice Smith".
23#[derive(Debug, Clone, PartialEq, Eq)]
24#[cfg_attr(feature = "serde", derive(serde::Serialize))]
25#[cfg_attr(feature = "yoke", derive(yoke::Yokeable))]
26pub struct ExtendedEventItem<'a> {
27    /// DVB Annex-A encoded item description.
28    pub description: DvbText<'a>,
29    /// DVB Annex-A encoded item value.
30    pub value: DvbText<'a>,
31}
32
33/// Extended Event Descriptor.
34#[derive(Debug, Clone, PartialEq, Eq)]
35#[cfg_attr(feature = "serde", derive(serde::Serialize))]
36#[cfg_attr(feature = "yoke", derive(yoke::Yokeable))]
37pub struct ExtendedEventDescriptor<'a> {
38    /// 0-based fragment index within the extended event series.
39    pub descriptor_number: u8,
40    /// Index of the final fragment in the series (0-based).
41    pub last_descriptor_number: u8,
42    /// ISO 639-2 language code.
43    pub language_code: LangCode,
44    /// Item list.
45    pub items: Vec<ExtendedEventItem<'a>>,
46    /// DVB Annex-A encoded extended text.
47    pub text: DvbText<'a>,
48}
49
50impl<'a> Parse<'a> for ExtendedEventDescriptor<'a> {
51    type Error = crate::error::Error;
52    fn parse(bytes: &'a [u8]) -> Result<Self> {
53        let min_len = HEADER_LEN + NUMBERS_LEN + LANG_LEN + ITEMS_LEN_FIELD + TEXT_LEN_FIELD;
54        if bytes.len() < min_len {
55            return Err(Error::BufferTooShort {
56                need: min_len,
57                have: bytes.len(),
58                what: "ExtendedEventDescriptor header",
59            });
60        }
61        let body = descriptor_body(
62            bytes,
63            TAG,
64            "ExtendedEventDescriptor",
65            "unexpected tag for extended_event_descriptor",
66        )?;
67        if body.len() < FIXED_PREFIX_LEN {
68            return Err(Error::BufferTooShort {
69                need: FIXED_PREFIX_LEN,
70                have: body.len(),
71                what: "ExtendedEventDescriptor body",
72            });
73        }
74        let numbers_byte = body[0];
75        let descriptor_number = numbers_byte >> 4;
76        let last_descriptor_number = numbers_byte & 0x0F;
77        let language_code = LangCode([body[1], body[2], body[3]]);
78
79        let items_len_pos = NUMBERS_LEN + LANG_LEN;
80        let items_length = body[items_len_pos] as usize;
81        let items_start = items_len_pos + ITEMS_LEN_FIELD;
82        let items_end = items_start + items_length;
83        if items_end + TEXT_LEN_FIELD > body.len() {
84            return Err(Error::InvalidDescriptor {
85                tag: TAG,
86                reason: "length_of_items runs past descriptor end",
87            });
88        }
89
90        let mut items = Vec::new();
91        let mut pos = items_start;
92        while pos < items_end {
93            if pos >= items_end {
94                break;
95            }
96            let desc_len = body[pos] as usize;
97            let desc_start = pos + 1;
98            let desc_end = desc_start + desc_len;
99            if desc_end + 1 > items_end {
100                return Err(Error::InvalidDescriptor {
101                    tag: TAG,
102                    reason: "item_description_length runs past items loop",
103                });
104            }
105            let value_len = body[desc_end] as usize;
106            let value_start = desc_end + 1;
107            let value_end = value_start + value_len;
108            if value_end > items_end {
109                return Err(Error::InvalidDescriptor {
110                    tag: TAG,
111                    reason: "item_length runs past items loop",
112                });
113            }
114            items.push(ExtendedEventItem {
115                description: DvbText::new(&body[desc_start..desc_end]),
116                value: DvbText::new(&body[value_start..value_end]),
117            });
118            pos = value_end;
119        }
120
121        let text_len = body[items_end] as usize;
122        let text_start = items_end + TEXT_LEN_FIELD;
123        let text_end = text_start + text_len;
124        if text_end > body.len() {
125            return Err(Error::InvalidDescriptor {
126                tag: TAG,
127                reason: "text_length runs past descriptor end",
128            });
129        }
130        let text = DvbText::new(&body[text_start..text_end]);
131
132        Ok(Self {
133            descriptor_number,
134            last_descriptor_number,
135            language_code,
136            items,
137            text,
138        })
139    }
140}
141
142impl Serialize for ExtendedEventDescriptor<'_> {
143    type Error = crate::error::Error;
144    fn serialized_len(&self) -> usize {
145        let items_bytes: usize = self
146            .items
147            .iter()
148            .map(|i| 1 + i.description.len() + 1 + i.value.len())
149            .sum();
150        HEADER_LEN
151            + NUMBERS_LEN
152            + LANG_LEN
153            + ITEMS_LEN_FIELD
154            + items_bytes
155            + TEXT_LEN_FIELD
156            + self.text.len()
157    }
158
159    fn serialize_into(&self, buf: &mut [u8]) -> Result<usize> {
160        let len = self.serialized_len();
161        if buf.len() < len {
162            return Err(Error::OutputBufferTooSmall {
163                need: len,
164                have: buf.len(),
165            });
166        }
167        buf[0] = TAG;
168        buf[1] = (len - HEADER_LEN) as u8;
169        buf[2] = ((self.descriptor_number & 0x0F) << 4) | (self.last_descriptor_number & 0x0F);
170        buf[3..6].copy_from_slice(&self.language_code.0);
171
172        let items_bytes: usize = self
173            .items
174            .iter()
175            .map(|i| 1 + i.description.len() + 1 + i.value.len())
176            .sum();
177        buf[6] = items_bytes as u8;
178
179        let mut pos = 7;
180        for item in &self.items {
181            buf[pos] = item.description.len() as u8;
182            let d_start = pos + 1;
183            let d_end = d_start + item.description.len();
184            buf[d_start..d_end].copy_from_slice(item.description.raw());
185            buf[d_end] = item.value.len() as u8;
186            let v_start = d_end + 1;
187            let v_end = v_start + item.value.len();
188            buf[v_start..v_end].copy_from_slice(item.value.raw());
189            pos = v_end;
190        }
191        buf[pos] = self.text.len() as u8;
192        buf[pos + 1..pos + 1 + self.text.len()].copy_from_slice(self.text.raw());
193        Ok(len)
194    }
195}
196impl<'a> crate::traits::DescriptorDef<'a> for ExtendedEventDescriptor<'a> {
197    const TAG: u8 = TAG;
198    const NAME: &'static str = "EXTENDED_EVENT";
199}
200
201#[cfg(test)]
202mod tests {
203    use super::*;
204
205    fn build(
206        descriptor_number: u8,
207        last_descriptor_number: u8,
208        lang: [u8; 3],
209        items: &[(&[u8], &[u8])],
210        text: &[u8],
211    ) -> Vec<u8> {
212        let items_bytes: Vec<u8> = items
213            .iter()
214            .flat_map(|(d, v)| {
215                let mut x = Vec::with_capacity(2 + d.len() + v.len());
216                x.push(d.len() as u8);
217                x.extend_from_slice(d);
218                x.push(v.len() as u8);
219                x.extend_from_slice(v);
220                x
221            })
222            .collect();
223        let body_len = NUMBERS_LEN
224            + LANG_LEN
225            + ITEMS_LEN_FIELD
226            + items_bytes.len()
227            + TEXT_LEN_FIELD
228            + text.len();
229        let mut v = Vec::with_capacity(HEADER_LEN + body_len);
230        v.push(TAG);
231        v.push(body_len as u8);
232        v.push(((descriptor_number & 0x0F) << 4) | (last_descriptor_number & 0x0F));
233        v.extend_from_slice(&lang);
234        v.push(items_bytes.len() as u8);
235        v.extend_from_slice(&items_bytes);
236        v.push(text.len() as u8);
237        v.extend_from_slice(text);
238        v
239    }
240
241    #[test]
242    fn parse_extracts_numbers_language_and_text() {
243        let bytes = build(2, 3, *b"fra", &[], b"Hello");
244        let d = ExtendedEventDescriptor::parse(&bytes).unwrap();
245        assert_eq!(d.descriptor_number, 2);
246        assert_eq!(d.last_descriptor_number, 3);
247        assert_eq!(d.language_code, LangCode(*b"fra"));
248        assert_eq!(d.text.raw(), b"Hello");
249        assert_eq!(d.items.len(), 0);
250    }
251
252    #[test]
253    fn parse_extracts_item_list() {
254        let items: [(&[u8], &[u8]); 2] = [(b"Director", b"Alice"), (b"Year", b"2023")];
255        let bytes = build(0, 0, *b"eng", &items, b"");
256        let d = ExtendedEventDescriptor::parse(&bytes).unwrap();
257        assert_eq!(d.items.len(), 2);
258        assert_eq!(d.items[0].description.raw(), b"Director");
259        assert_eq!(d.items[0].value.raw(), b"Alice");
260        assert_eq!(d.items[1].description.raw(), b"Year");
261        assert_eq!(d.items[1].value.raw(), b"2023");
262    }
263
264    #[test]
265    fn parse_rejects_wrong_tag() {
266        // Full 8-byte descriptor with the wrong tag — must fail with tag mismatch.
267        let bytes = [0x4D, 6, 0x00, b'e', b'n', b'g', 0, 0];
268        assert!(matches!(
269            ExtendedEventDescriptor::parse(&bytes).unwrap_err(),
270            Error::InvalidDescriptor { tag: 0x4D, .. }
271        ));
272    }
273
274    #[test]
275    fn parse_rejects_short_header() {
276        assert!(matches!(
277            ExtendedEventDescriptor::parse(&[TAG, 2, 0, 0]).unwrap_err(),
278            Error::BufferTooShort { .. }
279        ));
280    }
281
282    #[test]
283    fn parse_rejects_item_length_overrun() {
284        // items_length=10 but body only 6 bytes after the items_length field.
285        let bytes = [
286            TAG, 11, 0x00, b'e', b'n', b'g', 10, // items_length claims 10 bytes
287            0, 0, 0, 0, 0, // only 5 bytes of items
288            0, // text_length (partially unreachable)
289        ];
290        assert!(matches!(
291            ExtendedEventDescriptor::parse(&bytes).unwrap_err(),
292            Error::InvalidDescriptor { .. }
293        ));
294    }
295
296    #[test]
297    fn parse_rejects_text_length_overrun() {
298        // body=6: numbers + lang + items_length=0 + text_length=5 but no text bytes.
299        let bytes = [TAG, 6, 0x00, b'e', b'n', b'g', 0, 5];
300        assert!(matches!(
301            ExtendedEventDescriptor::parse(&bytes).unwrap_err(),
302            Error::InvalidDescriptor { .. }
303        ));
304    }
305
306    #[test]
307    fn empty_items_and_text_valid() {
308        let bytes = build(0, 0, *b"eng", &[], b"");
309        let d = ExtendedEventDescriptor::parse(&bytes).unwrap();
310        assert_eq!(d.items.len(), 0);
311        assert_eq!(d.text.raw(), b"");
312    }
313
314    #[test]
315    fn serialize_round_trip_with_items_and_text() {
316        let items: [(&[u8], &[u8]); 1] = [(b"Genre", b"Drama")];
317        let bytes = build(1, 2, *b"eng", &items, b"Plot summary.");
318        let parsed = ExtendedEventDescriptor::parse(&bytes).unwrap();
319        let mut buf = vec![0u8; parsed.serialized_len()];
320        parsed.serialize_into(&mut buf).unwrap();
321        assert_eq!(buf, bytes);
322        let re = ExtendedEventDescriptor::parse(&buf).unwrap();
323        assert_eq!(parsed, re);
324    }
325
326    #[test]
327    fn serialize_round_trip_without_items() {
328        let bytes = build(3, 3, *b"fra", &[], b"Plot.");
329        let parsed = ExtendedEventDescriptor::parse(&bytes).unwrap();
330        let mut buf = vec![0u8; parsed.serialized_len()];
331        parsed.serialize_into(&mut buf).unwrap();
332        assert_eq!(buf, bytes);
333    }
334
335    #[test]
336    fn parse_rejects_short_declared_body() {
337        // Declared length byte = 0, body is empty — must reject with
338        // BufferTooShort before indexing into it.
339        let bytes = &[0x4E, 0x00, 0, 0, 0, 0, 0, 0];
340        assert!(matches!(
341            ExtendedEventDescriptor::parse(bytes).unwrap_err(),
342            Error::BufferTooShort {
343                what: "ExtendedEventDescriptor body",
344                ..
345            }
346        ));
347    }
348}
dvb_si/descriptors/extended_event.rs

dvb_si/descriptors/
extended_event.rs
