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

dvb_si/descriptors/
extended_event.rs
