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 alloc::vec::Vec;
10use dvb_common::{Parse, Serialize};
11
12/// Descriptor tag for teletext_descriptor.
13pub const TAG: u8 = 0x56;
14const HEADER_LEN: usize = 2;
15const ENTRY_LEN: usize = 5;
16const LANG_LEN: usize = 3;
17
18/// Teletext type — ETSI EN 300 468 Table 102.
19#[derive(Debug, Clone, Copy, PartialEq, Eq)]
20#[cfg_attr(feature = "serde", derive(serde::Serialize))]
21#[non_exhaustive]
22pub enum TeletextType {
23    /// 0x01 — initial teletext page.
24    InitialPage,
25    /// 0x02 — teletext subtitle page.
26    SubtitlePage,
27    /// 0x03 — additional information page.
28    AdditionalInformationPage,
29    /// 0x04 — programme schedule page.
30    ProgrammeSchedulePage,
31    /// 0x05 — teletext subtitle page for hearing impaired people.
32    HearingImpairedSubtitlePage,
33    /// Reserved/unallocated wire value, preserved verbatim for round-trip.
34    Reserved(u8),
35}
36
37impl TeletextType {
38    #[must_use]
39    /// Creates a value from a wire byte, preserving every possible
40    /// byte value for lossless round-trip.
41    pub fn from_u8(v: u8) -> Self {
42        match v {
43            0x01 => Self::InitialPage,
44            0x02 => Self::SubtitlePage,
45            0x03 => Self::AdditionalInformationPage,
46            0x04 => Self::ProgrammeSchedulePage,
47            0x05 => Self::HearingImpairedSubtitlePage,
48            v => Self::Reserved(v),
49        }
50    }
51
52    #[must_use]
53    /// Returns the wire byte for this value.
54    pub fn to_u8(self) -> u8 {
55        match self {
56            Self::InitialPage => 0x01,
57            Self::SubtitlePage => 0x02,
58            Self::AdditionalInformationPage => 0x03,
59            Self::ProgrammeSchedulePage => 0x04,
60            Self::HearingImpairedSubtitlePage => 0x05,
61            Self::Reserved(v) => v,
62        }
63    }
64
65    #[must_use]
66    /// Returns a human-readable spec name for this value.
67    pub fn name(self) -> &'static str {
68        match self {
69            Self::InitialPage => "initial teletext page",
70            Self::SubtitlePage => "teletext subtitle page",
71            Self::AdditionalInformationPage => "additional information page",
72            Self::ProgrammeSchedulePage => "programme schedule page",
73            Self::HearingImpairedSubtitlePage => {
74                "teletext subtitle page for hearing impaired people"
75            }
76            Self::Reserved(_) => "reserved",
77        }
78    }
79}
80dvb_common::impl_spec_display!(TeletextType, Reserved);
81
82/// One teletext component.
83#[derive(Debug, Clone, PartialEq, Eq)]
84#[cfg_attr(feature = "serde", derive(serde::Serialize))]
85pub struct TeletextEntry {
86    /// ISO 639-2 language code of this teletext service.
87    pub language_code: LangCode,
88    /// 5-bit teletext_type (ETSI Table 102).
89    pub teletext_type: TeletextType,
90    /// 3-bit teletext_magazine_number.
91    pub magazine_number: u8,
92    /// 8-bit BCD teletext_page_number.
93    pub page_number: u8,
94}
95
96/// Teletext Descriptor.
97#[derive(Debug, Clone, PartialEq, Eq)]
98#[cfg_attr(feature = "serde", derive(serde::Serialize))]
99pub struct TeletextDescriptor {
100    /// Teletext components listed in wire order.
101    pub entries: Vec<TeletextEntry>,
102}
103
104impl<'a> Parse<'a> for TeletextDescriptor {
105    type Error = crate::error::Error;
106    fn parse(bytes: &'a [u8]) -> Result<Self> {
107        let body = descriptor_body(
108            bytes,
109            TAG,
110            "TeletextDescriptor",
111            "unexpected tag for teletext_descriptor",
112        )?;
113        if body.len() % ENTRY_LEN != 0 {
114            return Err(Error::InvalidDescriptor {
115                tag: TAG,
116                reason: "teletext_descriptor length must be a multiple of 5",
117            });
118        }
119        let mut entries = Vec::with_capacity(body.len() / ENTRY_LEN);
120        for chunk in body.chunks_exact(ENTRY_LEN) {
121            let language_code = LangCode([chunk[0], chunk[1], chunk[2]]);
122            let type_and_mag = chunk[LANG_LEN];
123            let teletext_type = TeletextType::from_u8((type_and_mag >> 3) & 0x1F);
124            let magazine_number = type_and_mag & 0x07;
125            let page_number = chunk[LANG_LEN + 1];
126            entries.push(TeletextEntry {
127                language_code,
128                teletext_type,
129                magazine_number,
130                page_number,
131            });
132        }
133        Ok(Self { entries })
134    }
135}
136
137impl Serialize for TeletextDescriptor {
138    type Error = crate::error::Error;
139    fn serialized_len(&self) -> usize {
140        HEADER_LEN + self.entries.len() * ENTRY_LEN
141    }
142
143    fn serialize_into(&self, buf: &mut [u8]) -> Result<usize> {
144        let len = self.serialized_len();
145        if buf.len() < len {
146            return Err(Error::OutputBufferTooSmall {
147                need: len,
148                have: buf.len(),
149            });
150        }
151        buf[0] = TAG;
152        buf[1] = (self.entries.len() * ENTRY_LEN) as u8;
153        let mut pos = HEADER_LEN;
154        for e in &self.entries {
155            buf[pos..pos + LANG_LEN].copy_from_slice(&e.language_code.0);
156            buf[pos + LANG_LEN] =
157                ((e.teletext_type.to_u8() & 0x1F) << 3) | (e.magazine_number & 0x07);
158            buf[pos + LANG_LEN + 1] = e.page_number;
159            pos += ENTRY_LEN;
160        }
161        Ok(len)
162    }
163}
164impl<'a> crate::traits::DescriptorDef<'a> for TeletextDescriptor {
165    const TAG: u8 = TAG;
166    const NAME: &'static str = "TELETEXT";
167}
168
169#[cfg(test)]
170mod tests {
171    use super::*;
172
173    #[test]
174    fn parse_single_entry() {
175        // lang=eng, type=1, mag=2, page=0x10
176        let bytes = [TAG, 5, b'e', b'n', b'g', (1 << 3) | 2, 0x10];
177        let d = TeletextDescriptor::parse(&bytes).unwrap();
178        assert_eq!(d.entries.len(), 1);
179        assert_eq!(d.entries[0].language_code, LangCode(*b"eng"));
180        assert_eq!(d.entries[0].teletext_type, TeletextType::InitialPage);
181        assert_eq!(d.entries[0].magazine_number, 2);
182        assert_eq!(d.entries[0].page_number, 0x10);
183    }
184
185    #[test]
186    fn parse_multiple_entries() {
187        let bytes = [
188            TAG,
189            10,
190            b'e',
191            b'n',
192            b'g',
193            (1 << 3) | 1,
194            0x10,
195            b'f',
196            b'r',
197            b'a',
198            (2 << 3) | 1,
199            0x20,
200        ];
201        let d = TeletextDescriptor::parse(&bytes).unwrap();
202        assert_eq!(d.entries.len(), 2);
203        assert_eq!(d.entries[1].teletext_type, TeletextType::SubtitlePage);
204    }
205
206    #[test]
207    fn parse_rejects_wrong_tag() {
208        assert!(matches!(
209            TeletextDescriptor::parse(&[0x57, 0]).unwrap_err(),
210            Error::InvalidDescriptor { tag: 0x57, .. }
211        ));
212    }
213
214    #[test]
215    fn parse_rejects_length_not_multiple_of_5() {
216        let bytes = [TAG, 4, 0, 0, 0, 0];
217        assert!(matches!(
218            TeletextDescriptor::parse(&bytes).unwrap_err(),
219            Error::InvalidDescriptor { .. }
220        ));
221    }
222
223    #[test]
224    fn serialize_round_trip() {
225        let d = TeletextDescriptor {
226            entries: vec![TeletextEntry {
227                language_code: LangCode(*b"fra"),
228                teletext_type: TeletextType::SubtitlePage,
229                magazine_number: 8 & 0x07,
230                page_number: 0x88,
231            }],
232        };
233        let mut buf = vec![0u8; d.serialized_len()];
234        d.serialize_into(&mut buf).unwrap();
235        assert_eq!(TeletextDescriptor::parse(&buf).unwrap(), d);
236    }
237
238    #[test]
239    fn empty_descriptor_valid() {
240        let bytes = [TAG, 0];
241        let d = TeletextDescriptor::parse(&bytes).unwrap();
242        assert_eq!(d.entries.len(), 0);
243    }
244
245    #[test]
246    fn teletext_type_full_range_round_trip() {
247        for b in 0..=0xFF_u8 {
248            let tt = TeletextType::from_u8(b);
249            assert_eq!(tt.to_u8(), b, "round-trip failed for byte 0x{b:02X}");
250        }
251    }
252
253    #[test]
254    fn teletext_type_name_for_known() {
255        assert_eq!(TeletextType::InitialPage.name(), "initial teletext page");
256        assert_eq!(
257            TeletextType::HearingImpairedSubtitlePage.name(),
258            "teletext subtitle page for hearing impaired people"
259        );
260        assert_eq!(TeletextType::Reserved(0x06).name(), "reserved");
261    }
262}
dvb_si/descriptors/teletext.rs

dvb_si/descriptors/
teletext.rs
