dvb_si/descriptors/
component.rs

1//! Component Descriptor — ETSI EN 300 468 §6.2.8 (tag 0x50).
2//!
3//! Describes one elementary component (audio/video/data/teletext/subtitle)
4//! with a language code and free-text label. Carried inside EIT event
5//! descriptor loops.
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 component_descriptor.
13pub const TAG: u8 = 0x50;
14const HEADER_LEN: usize = 2;
15/// stream_content(1) + component_type(1) + component_tag(1) + language_code(3) = 6
16const PRE_TEXT_LEN: usize = 6;
17const STREAM_CONTENT_MASK: u8 = 0x0F;
18
19/// Component Descriptor.
20#[derive(Debug, Clone, PartialEq, Eq)]
21#[cfg_attr(feature = "serde", derive(serde::Serialize))]
22#[cfg_attr(feature = "yoke", derive(yoke::Yokeable))]
23pub struct ComponentDescriptor<'a> {
24    /// 4-bit stream_content_ext (high nibble) — combines with `stream_content`
25    /// to identify the component (EN 300 468 §6.2.8 Table 25).
26    pub stream_content_ext: u8,
27    /// 4-bit stream_content (0x01 video, 0x02 audio, 0x03 teletext, …).
28    pub stream_content: u8,
29    /// component_type byte (sub-classification inside the stream_content).
30    pub component_type: u8,
31    /// component_tag for cross-reference with stream_identifier_descriptor.
32    pub component_tag: u8,
33    /// ISO 639-2 language code.
34    pub language_code: LangCode,
35    /// DVB Annex-A encoded text label for this component.
36    pub text: DvbText<'a>,
37}
38
39impl<'a> Parse<'a> for ComponentDescriptor<'a> {
40    type Error = crate::error::Error;
41    fn parse(bytes: &'a [u8]) -> Result<Self> {
42        let body = descriptor_body(
43            bytes,
44            TAG,
45            "ComponentDescriptor",
46            "unexpected tag for component_descriptor",
47        )?;
48        if body.len() < PRE_TEXT_LEN {
49            return Err(Error::InvalidDescriptor {
50                tag: TAG,
51                reason: "component_descriptor body shorter than minimum 6 bytes",
52            });
53        }
54        let stream_content_ext = body[0] >> 4;
55        let stream_content = body[0] & STREAM_CONTENT_MASK;
56        let component_type = body[1];
57        let component_tag = body[2];
58        let language_code = LangCode([body[3], body[4], body[5]]);
59        let text = DvbText::new(&body[PRE_TEXT_LEN..]);
60        Ok(Self {
61            stream_content_ext,
62            stream_content,
63            component_type,
64            component_tag,
65            language_code,
66            text,
67        })
68    }
69}
70
71impl Serialize for ComponentDescriptor<'_> {
72    type Error = crate::error::Error;
73    fn serialized_len(&self) -> usize {
74        HEADER_LEN + PRE_TEXT_LEN + self.text.len()
75    }
76
77    fn serialize_into(&self, buf: &mut [u8]) -> Result<usize> {
78        let len = self.serialized_len();
79        if buf.len() < len {
80            return Err(Error::OutputBufferTooSmall {
81                need: len,
82                have: buf.len(),
83            });
84        }
85        buf[0] = TAG;
86        buf[1] = (len - HEADER_LEN) as u8;
87        // High nibble = stream_content_ext, low nibble = stream_content (§6.2.8).
88        buf[HEADER_LEN] =
89            (self.stream_content_ext << 4) | (self.stream_content & STREAM_CONTENT_MASK);
90        buf[HEADER_LEN + 1] = self.component_type;
91        buf[HEADER_LEN + 2] = self.component_tag;
92        buf[HEADER_LEN + 3..HEADER_LEN + 6].copy_from_slice(&self.language_code.0);
93        buf[HEADER_LEN + PRE_TEXT_LEN..len].copy_from_slice(self.text.raw());
94        Ok(len)
95    }
96}
97impl<'a> crate::traits::DescriptorDef<'a> for ComponentDescriptor<'a> {
98    const TAG: u8 = TAG;
99    const NAME: &'static str = "COMPONENT";
100}
101
102#[cfg(test)]
103mod tests {
104    use super::*;
105
106    #[test]
107    fn parse_extracts_all_fields() {
108        let bytes = [
109            TAG, 12, 0x02, 0x01, 0x42, b'e', b'n', b'g', b'S', b'T', b'E', b'R', b'E', b'O',
110        ];
111        let d = ComponentDescriptor::parse(&bytes).unwrap();
112        assert_eq!(d.stream_content, 2);
113        assert_eq!(d.component_type, 0x01);
114        assert_eq!(d.component_tag, 0x42);
115        assert_eq!(d.language_code, LangCode(*b"eng"));
116        assert_eq!(d.text.raw(), b"STEREO");
117    }
118
119    #[test]
120    fn parse_rejects_wrong_tag() {
121        assert!(matches!(
122            ComponentDescriptor::parse(&[0x51, 6, 0, 0, 0, b'e', b'n', b'g']).unwrap_err(),
123            Error::InvalidDescriptor { tag: 0x51, .. }
124        ));
125    }
126
127    #[test]
128    fn parse_rejects_short_body() {
129        let bytes = [TAG, 5, 0x01, 0x00, 0x00, b'e', b'n'];
130        assert!(matches!(
131            ComponentDescriptor::parse(&bytes).unwrap_err(),
132            Error::InvalidDescriptor { .. }
133        ));
134    }
135
136    #[test]
137    fn parse_rejects_truncated_buffer() {
138        let bytes = [TAG, 6, 0x01];
139        assert!(matches!(
140            ComponentDescriptor::parse(&bytes).unwrap_err(),
141            Error::BufferTooShort { .. }
142        ));
143    }
144
145    #[test]
146    fn parse_with_empty_text_valid() {
147        let bytes = [TAG, 6, 0x01, 0x01, 0x01, b'e', b'n', b'g'];
148        let d = ComponentDescriptor::parse(&bytes).unwrap();
149        assert!(d.text.raw().is_empty());
150    }
151
152    #[test]
153    fn serialize_round_trip() {
154        let d = ComponentDescriptor {
155            stream_content_ext: 0x0F,
156            stream_content: 0x03,
157            component_type: 0x10,
158            component_tag: 0x05,
159            language_code: LangCode(*b"fra"),
160            text: DvbText::new(b"Sous-titres"),
161        };
162        let mut buf = vec![0u8; d.serialized_len()];
163        d.serialize_into(&mut buf).unwrap();
164        assert_eq!(ComponentDescriptor::parse(&buf).unwrap(), d);
165    }
166
167    #[test]
168    fn stream_content_masked_to_low_nibble() {
169        // Byte = 0xF2 → high nibble is stream_content_ext (0xF), low nibble is stream_content=2.
170        let bytes = [TAG, 6, 0xF2, 0x00, 0x00, b'e', b'n', b'g'];
171        let d = ComponentDescriptor::parse(&bytes).unwrap();
172        assert_eq!(d.stream_content, 2);
173    }
174}
dvb_si/descriptors/component.rs

dvb_si/descriptors/
component.rs
