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 super::descriptor_body;
9use crate::error::{Error, Result};
10use crate::text::LangCode;
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        let body = descriptor_body(
47            bytes,
48            TAG,
49            "VbiTeletextDescriptor",
50            "unexpected tag for VBI_teletext_descriptor",
51        )?;
52        if body.len() % ENTRY_LEN != 0 {
53            return Err(Error::InvalidDescriptor {
54                tag: TAG,
55                reason: "descriptor_length must be a multiple of 5",
56            });
57        }
58        let mut entries = Vec::with_capacity(body.len() / ENTRY_LEN);
59        for chunk in body.chunks_exact(ENTRY_LEN) {
60            let language_code = LangCode([chunk[0], chunk[1], chunk[2]]);
61            let type_and_mag = chunk[LANG_LEN];
62            entries.push(VbiTeletextEntry {
63                language_code,
64                teletext_type: (type_and_mag >> 3) & 0x1F,
65                magazine_number: type_and_mag & 0x07,
66                page_number: chunk[LANG_LEN + 1],
67            });
68        }
69        Ok(Self { entries })
70    }
71}
72
73impl Serialize for VbiTeletextDescriptor {
74    type Error = crate::error::Error;
75    fn serialized_len(&self) -> usize {
76        HEADER_LEN + ENTRY_LEN * self.entries.len()
77    }
78
79    fn serialize_into(&self, buf: &mut [u8]) -> Result<usize> {
80        let len = self.serialized_len();
81        if buf.len() < len {
82            return Err(Error::OutputBufferTooSmall {
83                need: len,
84                have: buf.len(),
85            });
86        }
87        let body_len = ENTRY_LEN * self.entries.len();
88        // 8-bit descriptor_length field: error rather than silently truncate.
89        if body_len > MAX_BODY_LEN {
90            return Err(Error::InvalidDescriptor {
91                tag: TAG,
92                reason: "VBI_teletext_descriptor body exceeds 255 bytes",
93            });
94        }
95        buf[0] = TAG;
96        buf[1] = body_len as u8;
97        let mut pos = HEADER_LEN;
98        for e in &self.entries {
99            buf[pos..pos + LANG_LEN].copy_from_slice(&e.language_code.0);
100            buf[pos + LANG_LEN] = ((e.teletext_type & 0x1F) << 3) | (e.magazine_number & 0x07);
101            buf[pos + LANG_LEN + 1] = e.page_number;
102            pos += ENTRY_LEN;
103        }
104        Ok(len)
105    }
106}
107impl<'a> crate::traits::DescriptorDef<'a> for VbiTeletextDescriptor {
108    const TAG: u8 = TAG;
109    const NAME: &'static str = "VBI_TELETEXT";
110}
111
112#[cfg(test)]
113mod tests {
114    use super::*;
115
116    #[test]
117    fn parse_single_entry() {
118        let bytes = [TAG, 5, b'e', b'n', b'g', (1 << 3) | 2, 0x10];
119        let d = VbiTeletextDescriptor::parse(&bytes).unwrap();
120        assert_eq!(d.entries.len(), 1);
121        assert_eq!(d.entries[0].language_code, LangCode(*b"eng"));
122        assert_eq!(d.entries[0].teletext_type, 1);
123        assert_eq!(d.entries[0].magazine_number, 2);
124        assert_eq!(d.entries[0].page_number, 0x10);
125    }
126
127    #[test]
128    fn parse_multiple_entries() {
129        let bytes = [
130            TAG,
131            10,
132            b'e',
133            b'n',
134            b'g',
135            (1 << 3) | 1,
136            0x10,
137            b'f',
138            b'r',
139            b'a',
140            (2 << 3) | 1,
141            0x20,
142        ];
143        let d = VbiTeletextDescriptor::parse(&bytes).unwrap();
144        assert_eq!(d.entries.len(), 2);
145        assert_eq!(d.entries[1].teletext_type, 2);
146        assert_eq!(d.entries[1].language_code, LangCode(*b"fra"));
147    }
148
149    #[test]
150    fn parse_rejects_wrong_tag() {
151        assert!(matches!(
152            VbiTeletextDescriptor::parse(&[0x47, 0]).unwrap_err(),
153            Error::InvalidDescriptor { tag: 0x47, .. }
154        ));
155    }
156
157    #[test]
158    fn parse_rejects_short_buffer() {
159        let bytes = [TAG, 5, b'e', b'n'];
160        assert!(matches!(
161            VbiTeletextDescriptor::parse(&bytes).unwrap_err(),
162            Error::BufferTooShort { .. }
163        ));
164    }
165
166    #[test]
167    fn parse_rejects_length_not_multiple_of_5() {
168        let bytes = [TAG, 4, 0, 0, 0, 0];
169        assert!(matches!(
170            VbiTeletextDescriptor::parse(&bytes).unwrap_err(),
171            Error::InvalidDescriptor { tag: TAG, .. }
172        ));
173    }
174
175    #[test]
176    fn empty_descriptor_valid() {
177        let d = VbiTeletextDescriptor::parse(&[TAG, 0]).unwrap();
178        assert!(d.entries.is_empty());
179    }
180
181    #[test]
182    fn serialize_round_trip() {
183        let d = VbiTeletextDescriptor {
184            entries: vec![VbiTeletextEntry {
185                language_code: LangCode(*b"fra"),
186                teletext_type: 2,
187                magazine_number: 8 & 0x07,
188                page_number: 0x88,
189            }],
190        };
191        let mut buf = vec![0u8; d.serialized_len()];
192        d.serialize_into(&mut buf).unwrap();
193        assert_eq!(VbiTeletextDescriptor::parse(&buf).unwrap(), d);
194    }
195
196    #[test]
197    fn serialize_rejects_over_range_body() {
198        // 52 entries = 260 body bytes, past the u8 length field.
199        let d = VbiTeletextDescriptor {
200            entries: vec![
201                VbiTeletextEntry {
202                    language_code: LangCode(*b"eng"),
203                    teletext_type: 1,
204                    magazine_number: 1,
205                    page_number: 0,
206                };
207                52
208            ],
209        };
210        let mut buf = vec![0u8; d.serialized_len()];
211        assert!(matches!(
212            d.serialize_into(&mut buf).unwrap_err(),
213            Error::InvalidDescriptor { tag: TAG, .. }
214        ));
215    }
216
217    #[cfg(feature = "serde")]
218    #[test]
219    fn serde_round_trip() {
220        let d = VbiTeletextDescriptor {
221            entries: vec![VbiTeletextEntry {
222                language_code: LangCode(*b"eng"),
223                teletext_type: 2,
224                magazine_number: 1,
225                page_number: 0x10,
226            }],
227        };
228        let json = serde_json::to_string(&d).unwrap();
229        // Serialize-only: assert the emitted JSON re-parses (serialize-stable).
230        let _v: serde_json::Value = serde_json::from_str(&json).unwrap();
231    }
232}
dvb_si/descriptors/vbi_teletext.rs

dvb_si/descriptors/
vbi_teletext.rs
