dvb_si/descriptors/
vbi_teletext.rs

1//! VBI Teletext Descriptor — ETSI EN 300 468 §6.2.48 (tag 0x46).
2//!
3//! Table 108 (PDF p. 111). Identical wire layout to the teletext_descriptor
4//! (Table 101): a loop of 5-byte entries, each a 3-char ISO 639 language code
5//! plus teletext_type (5 bits) / magazine_number (3 bits) / page_number
6//! (8 bits). Signals teletext also carried in the analogue VBI lines.
7
8use crate::error::{Error, Result};
9use crate::text::LangCode;
10use crate::traits::Descriptor;
11use dvb_common::{Parse, Serialize};
12
13/// Descriptor tag for VBI_teletext_descriptor.
14pub const TAG: u8 = 0x46;
15const HEADER_LEN: usize = 2;
16const ENTRY_LEN: usize = 5;
17const LANG_LEN: usize = 3;
18/// Maximum body length expressible in the 8-bit `descriptor_length` field.
19const MAX_BODY_LEN: usize = u8::MAX as usize;
20
21/// One VBI teletext component.
22#[derive(Debug, Clone, Copy, PartialEq, Eq)]
23#[cfg_attr(feature = "serde", derive(serde::Serialize))]
24pub struct VbiTeletextEntry {
25    /// ISO 639-2 language code of this teletext service.
26    pub language_code: LangCode,
27    /// 5-bit teletext_type (EN 300 468 Table 102).
28    pub teletext_type: u8,
29    /// 3-bit teletext_magazine_number.
30    pub magazine_number: u8,
31    /// 8-bit BCD teletext_page_number.
32    pub page_number: u8,
33}
34
35/// VBI Teletext Descriptor.
36#[derive(Debug, Clone, PartialEq, Eq)]
37#[cfg_attr(feature = "serde", derive(serde::Serialize))]
38pub struct VbiTeletextDescriptor {
39    /// Teletext components in wire order.
40    pub entries: Vec<VbiTeletextEntry>,
41}
42
43impl<'a> Parse<'a> for VbiTeletextDescriptor {
44    type Error = crate::error::Error;
45    fn parse(bytes: &'a [u8]) -> Result<Self> {
46        if bytes.len() < HEADER_LEN {
47            return Err(Error::BufferTooShort {
48                need: HEADER_LEN,
49                have: bytes.len(),
50                what: "VbiTeletextDescriptor header",
51            });
52        }
53        if bytes[0] != TAG {
54            return Err(Error::InvalidDescriptor {
55                tag: bytes[0],
56                reason: "unexpected tag for VBI_teletext_descriptor",
57            });
58        }
59        let length = bytes[1] as usize;
60        if length % ENTRY_LEN != 0 {
61            return Err(Error::InvalidDescriptor {
62                tag: TAG,
63                reason: "descriptor_length must be a multiple of 5",
64            });
65        }
66        let end = HEADER_LEN + length;
67        if bytes.len() < end {
68            return Err(Error::BufferTooShort {
69                need: end,
70                have: bytes.len(),
71                what: "VbiTeletextDescriptor body",
72            });
73        }
74        let body = &bytes[HEADER_LEN..end];
75        let mut entries = Vec::with_capacity(length / ENTRY_LEN);
76        for chunk in body.chunks_exact(ENTRY_LEN) {
77            let language_code = LangCode([chunk[0], chunk[1], chunk[2]]);
78            let type_and_mag = chunk[LANG_LEN];
79            entries.push(VbiTeletextEntry {
80                language_code,
81                teletext_type: (type_and_mag >> 3) & 0x1F,
82                magazine_number: type_and_mag & 0x07,
83                page_number: chunk[LANG_LEN + 1],
84            });
85        }
86        Ok(Self { entries })
87    }
88}
89
90impl Serialize for VbiTeletextDescriptor {
91    type Error = crate::error::Error;
92    fn serialized_len(&self) -> usize {
93        HEADER_LEN + ENTRY_LEN * self.entries.len()
94    }
95
96    fn serialize_into(&self, buf: &mut [u8]) -> Result<usize> {
97        let len = self.serialized_len();
98        if buf.len() < len {
99            return Err(Error::OutputBufferTooSmall {
100                need: len,
101                have: buf.len(),
102            });
103        }
104        let body_len = ENTRY_LEN * self.entries.len();
105        // 8-bit descriptor_length field: error rather than silently truncate.
106        if body_len > MAX_BODY_LEN {
107            return Err(Error::SectionLengthOverflow {
108                declared: body_len,
109                available: MAX_BODY_LEN,
110            });
111        }
112        buf[0] = TAG;
113        buf[1] = body_len as u8;
114        let mut pos = HEADER_LEN;
115        for e in &self.entries {
116            buf[pos..pos + LANG_LEN].copy_from_slice(&e.language_code.0);
117            buf[pos + LANG_LEN] = ((e.teletext_type & 0x1F) << 3) | (e.magazine_number & 0x07);
118            buf[pos + LANG_LEN + 1] = e.page_number;
119            pos += ENTRY_LEN;
120        }
121        Ok(len)
122    }
123}
124
125impl<'a> Descriptor<'a> for VbiTeletextDescriptor {
126    const TAG: u8 = TAG;
127    fn descriptor_length(&self) -> u8 {
128        (ENTRY_LEN * self.entries.len()) as u8
129    }
130}
131
132impl<'a> crate::traits::DescriptorDef<'a> for VbiTeletextDescriptor {
133    const TAG: u8 = TAG;
134    const NAME: &'static str = "VBI_TELETEXT";
135}
136
137#[cfg(test)]
138mod tests {
139    use super::*;
140
141    #[test]
142    fn parse_single_entry() {
143        let bytes = [TAG, 5, b'e', b'n', b'g', (1 << 3) | 2, 0x10];
144        let d = VbiTeletextDescriptor::parse(&bytes).unwrap();
145        assert_eq!(d.entries.len(), 1);
146        assert_eq!(d.entries[0].language_code, LangCode(*b"eng"));
147        assert_eq!(d.entries[0].teletext_type, 1);
148        assert_eq!(d.entries[0].magazine_number, 2);
149        assert_eq!(d.entries[0].page_number, 0x10);
150    }
151
152    #[test]
153    fn parse_multiple_entries() {
154        let bytes = [
155            TAG,
156            10,
157            b'e',
158            b'n',
159            b'g',
160            (1 << 3) | 1,
161            0x10,
162            b'f',
163            b'r',
164            b'a',
165            (2 << 3) | 1,
166            0x20,
167        ];
168        let d = VbiTeletextDescriptor::parse(&bytes).unwrap();
169        assert_eq!(d.entries.len(), 2);
170        assert_eq!(d.entries[1].teletext_type, 2);
171        assert_eq!(d.entries[1].language_code, LangCode(*b"fra"));
172    }
173
174    #[test]
175    fn parse_rejects_wrong_tag() {
176        assert!(matches!(
177            VbiTeletextDescriptor::parse(&[0x47, 0]).unwrap_err(),
178            Error::InvalidDescriptor { tag: 0x47, .. }
179        ));
180    }
181
182    #[test]
183    fn parse_rejects_short_buffer() {
184        let bytes = [TAG, 5, b'e', b'n'];
185        assert!(matches!(
186            VbiTeletextDescriptor::parse(&bytes).unwrap_err(),
187            Error::BufferTooShort { .. }
188        ));
189    }
190
191    #[test]
192    fn parse_rejects_length_not_multiple_of_5() {
193        let bytes = [TAG, 4, 0, 0, 0, 0];
194        assert!(matches!(
195            VbiTeletextDescriptor::parse(&bytes).unwrap_err(),
196            Error::InvalidDescriptor { tag: TAG, .. }
197        ));
198    }
199
200    #[test]
201    fn empty_descriptor_valid() {
202        let d = VbiTeletextDescriptor::parse(&[TAG, 0]).unwrap();
203        assert!(d.entries.is_empty());
204    }
205
206    #[test]
207    fn serialize_round_trip() {
208        let d = VbiTeletextDescriptor {
209            entries: vec![VbiTeletextEntry {
210                language_code: LangCode(*b"fra"),
211                teletext_type: 2,
212                magazine_number: 8 & 0x07,
213                page_number: 0x88,
214            }],
215        };
216        let mut buf = vec![0u8; d.serialized_len()];
217        d.serialize_into(&mut buf).unwrap();
218        assert_eq!(VbiTeletextDescriptor::parse(&buf).unwrap(), d);
219    }
220
221    #[test]
222    fn serialize_rejects_over_range_body() {
223        // 52 entries = 260 body bytes, past the u8 length field.
224        let d = VbiTeletextDescriptor {
225            entries: vec![
226                VbiTeletextEntry {
227                    language_code: LangCode(*b"eng"),
228                    teletext_type: 1,
229                    magazine_number: 1,
230                    page_number: 0,
231                };
232                52
233            ],
234        };
235        let mut buf = vec![0u8; d.serialized_len()];
236        assert!(matches!(
237            d.serialize_into(&mut buf).unwrap_err(),
238            Error::SectionLengthOverflow { .. }
239        ));
240    }
241
242    #[cfg(feature = "serde")]
243    #[test]
244    fn serde_round_trip() {
245        let d = VbiTeletextDescriptor {
246            entries: vec![VbiTeletextEntry {
247                language_code: LangCode(*b"eng"),
248                teletext_type: 2,
249                magazine_number: 1,
250                page_number: 0x10,
251            }],
252        };
253        let json = serde_json::to_string(&d).unwrap();
254        // Serialize-only: assert the emitted JSON re-parses (serialize-stable).
255        let _v: serde_json::Value = serde_json::from_str(&json).unwrap();
256    }
257}
dvb_si/descriptors/vbi_teletext.rs

dvb_si/descriptors/
vbi_teletext.rs
