dvb_si/descriptors/
teletext.rs

1//! Teletext Descriptor — ETSI EN 300 468 §6.2.44 (tag 0x56).
2//!
3//! Carried inside PMT's ES_info loop. Enumerates teletext components: one
4//! entry per 3-char language code + type/magazine/page triple (5 bytes).
5
6use super::descriptor_body;
7use crate::error::{Error, Result};
8use crate::text::LangCode;
9use dvb_common::{Parse, Serialize};
10
11/// Descriptor tag for teletext_descriptor.
12pub const TAG: u8 = 0x56;
13const HEADER_LEN: usize = 2;
14const ENTRY_LEN: usize = 5;
15const LANG_LEN: usize = 3;
16
17/// Teletext type — ETSI EN 300 468 Table 102.
18#[derive(Debug, Clone, Copy, PartialEq, Eq)]
19#[cfg_attr(feature = "serde", derive(serde::Serialize))]
20#[non_exhaustive]
21pub enum TeletextType {
22    /// 0x01 — initial teletext page.
23    InitialPage,
24    /// 0x02 — teletext subtitle page.
25    SubtitlePage,
26    /// 0x03 — additional information page.
27    AdditionalInformationPage,
28    /// 0x04 — programme schedule page.
29    ProgrammeSchedulePage,
30    /// 0x05 — teletext subtitle page for hearing impaired people.
31    HearingImpairedSubtitlePage,
32    /// Reserved/unallocated wire value, preserved verbatim for round-trip.
33    Reserved(u8),
34}
35
36impl TeletextType {
37    #[must_use]
38    /// Creates a value from a wire byte, preserving every possible
39    /// byte value for lossless round-trip.
40    pub fn from_u8(v: u8) -> Self {
41        match v {
42            0x01 => Self::InitialPage,
43            0x02 => Self::SubtitlePage,
44            0x03 => Self::AdditionalInformationPage,
45            0x04 => Self::ProgrammeSchedulePage,
46            0x05 => Self::HearingImpairedSubtitlePage,
47            v => Self::Reserved(v),
48        }
49    }
50
51    #[must_use]
52    /// Returns the wire byte for this value.
53    pub fn to_u8(self) -> u8 {
54        match self {
55            Self::InitialPage => 0x01,
56            Self::SubtitlePage => 0x02,
57            Self::AdditionalInformationPage => 0x03,
58            Self::ProgrammeSchedulePage => 0x04,
59            Self::HearingImpairedSubtitlePage => 0x05,
60            Self::Reserved(v) => v,
61        }
62    }
63
64    #[must_use]
65    /// Returns a human-readable spec name for this value.
66    pub fn name(self) -> &'static str {
67        match self {
68            Self::InitialPage => "initial teletext page",
69            Self::SubtitlePage => "teletext subtitle page",
70            Self::AdditionalInformationPage => "additional information page",
71            Self::ProgrammeSchedulePage => "programme schedule page",
72            Self::HearingImpairedSubtitlePage => {
73                "teletext subtitle page for hearing impaired people"
74            }
75            Self::Reserved(_) => "reserved",
76        }
77    }
78}
79dvb_common::impl_spec_display!(TeletextType, Reserved);
80
81/// One teletext component.
82#[derive(Debug, Clone, PartialEq, Eq)]
83#[cfg_attr(feature = "serde", derive(serde::Serialize))]
84pub struct TeletextEntry {
85    /// ISO 639-2 language code of this teletext service.
86    pub language_code: LangCode,
87    /// 5-bit teletext_type (ETSI Table 102).
88    pub teletext_type: TeletextType,
89    /// 3-bit teletext_magazine_number.
90    pub magazine_number: u8,
91    /// 8-bit BCD teletext_page_number.
92    pub page_number: u8,
93}
94
95/// Teletext Descriptor.
96#[derive(Debug, Clone, PartialEq, Eq)]
97#[cfg_attr(feature = "serde", derive(serde::Serialize))]
98pub struct TeletextDescriptor {
99    /// Teletext components listed in wire order.
100    pub entries: Vec<TeletextEntry>,
101}
102
103impl<'a> Parse<'a> for TeletextDescriptor {
104    type Error = crate::error::Error;
105    fn parse(bytes: &'a [u8]) -> Result<Self> {
106        let body = descriptor_body(
107            bytes,
108            TAG,
109            "TeletextDescriptor",
110            "unexpected tag for teletext_descriptor",
111        )?;
112        if body.len() % ENTRY_LEN != 0 {
113            return Err(Error::InvalidDescriptor {
114                tag: TAG,
115                reason: "teletext_descriptor length must be a multiple of 5",
116            });
117        }
118        let mut entries = Vec::with_capacity(body.len() / ENTRY_LEN);
119        for chunk in body.chunks_exact(ENTRY_LEN) {
120            let language_code = LangCode([chunk[0], chunk[1], chunk[2]]);
121            let type_and_mag = chunk[LANG_LEN];
122            let teletext_type = TeletextType::from_u8((type_and_mag >> 3) & 0x1F);
123            let magazine_number = type_and_mag & 0x07;
124            let page_number = chunk[LANG_LEN + 1];
125            entries.push(TeletextEntry {
126                language_code,
127                teletext_type,
128                magazine_number,
129                page_number,
130            });
131        }
132        Ok(Self { entries })
133    }
134}
135
136impl Serialize for TeletextDescriptor {
137    type Error = crate::error::Error;
138    fn serialized_len(&self) -> usize {
139        HEADER_LEN + self.entries.len() * ENTRY_LEN
140    }
141
142    fn serialize_into(&self, buf: &mut [u8]) -> Result<usize> {
143        let len = self.serialized_len();
144        if buf.len() < len {
145            return Err(Error::OutputBufferTooSmall {
146                need: len,
147                have: buf.len(),
148            });
149        }
150        buf[0] = TAG;
151        buf[1] = (self.entries.len() * ENTRY_LEN) as u8;
152        let mut pos = HEADER_LEN;
153        for e in &self.entries {
154            buf[pos..pos + LANG_LEN].copy_from_slice(&e.language_code.0);
155            buf[pos + LANG_LEN] =
156                ((e.teletext_type.to_u8() & 0x1F) << 3) | (e.magazine_number & 0x07);
157            buf[pos + LANG_LEN + 1] = e.page_number;
158            pos += ENTRY_LEN;
159        }
160        Ok(len)
161    }
162}
163impl<'a> crate::traits::DescriptorDef<'a> for TeletextDescriptor {
164    const TAG: u8 = TAG;
165    const NAME: &'static str = "TELETEXT";
166}
167
168#[cfg(test)]
169mod tests {
170    use super::*;
171
172    #[test]
173    fn parse_single_entry() {
174        // lang=eng, type=1, mag=2, page=0x10
175        let bytes = [TAG, 5, b'e', b'n', b'g', (1 << 3) | 2, 0x10];
176        let d = TeletextDescriptor::parse(&bytes).unwrap();
177        assert_eq!(d.entries.len(), 1);
178        assert_eq!(d.entries[0].language_code, LangCode(*b"eng"));
179        assert_eq!(d.entries[0].teletext_type, TeletextType::InitialPage);
180        assert_eq!(d.entries[0].magazine_number, 2);
181        assert_eq!(d.entries[0].page_number, 0x10);
182    }
183
184    #[test]
185    fn parse_multiple_entries() {
186        let bytes = [
187            TAG,
188            10,
189            b'e',
190            b'n',
191            b'g',
192            (1 << 3) | 1,
193            0x10,
194            b'f',
195            b'r',
196            b'a',
197            (2 << 3) | 1,
198            0x20,
199        ];
200        let d = TeletextDescriptor::parse(&bytes).unwrap();
201        assert_eq!(d.entries.len(), 2);
202        assert_eq!(d.entries[1].teletext_type, TeletextType::SubtitlePage);
203    }
204
205    #[test]
206    fn parse_rejects_wrong_tag() {
207        assert!(matches!(
208            TeletextDescriptor::parse(&[0x57, 0]).unwrap_err(),
209            Error::InvalidDescriptor { tag: 0x57, .. }
210        ));
211    }
212
213    #[test]
214    fn parse_rejects_length_not_multiple_of_5() {
215        let bytes = [TAG, 4, 0, 0, 0, 0];
216        assert!(matches!(
217            TeletextDescriptor::parse(&bytes).unwrap_err(),
218            Error::InvalidDescriptor { .. }
219        ));
220    }
221
222    #[test]
223    fn serialize_round_trip() {
224        let d = TeletextDescriptor {
225            entries: vec![TeletextEntry {
226                language_code: LangCode(*b"fra"),
227                teletext_type: TeletextType::SubtitlePage,
228                magazine_number: 8 & 0x07,
229                page_number: 0x88,
230            }],
231        };
232        let mut buf = vec![0u8; d.serialized_len()];
233        d.serialize_into(&mut buf).unwrap();
234        assert_eq!(TeletextDescriptor::parse(&buf).unwrap(), d);
235    }
236
237    #[test]
238    fn empty_descriptor_valid() {
239        let bytes = [TAG, 0];
240        let d = TeletextDescriptor::parse(&bytes).unwrap();
241        assert_eq!(d.entries.len(), 0);
242    }
243
244    #[test]
245    fn teletext_type_full_range_round_trip() {
246        for b in 0..=0xFF_u8 {
247            let tt = TeletextType::from_u8(b);
248            assert_eq!(tt.to_u8(), b, "round-trip failed for byte 0x{b:02X}");
249        }
250    }
251
252    #[test]
253    fn teletext_type_name_for_known() {
254        assert_eq!(TeletextType::InitialPage.name(), "initial teletext page");
255        assert_eq!(
256            TeletextType::HearingImpairedSubtitlePage.name(),
257            "teletext subtitle page for hearing impaired people"
258        );
259        assert_eq!(TeletextType::Reserved(0x06).name(), "reserved");
260    }
261}
dvb_si/descriptors/teletext.rs

dvb_si/descriptors/
teletext.rs
