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 crate::error::{Error, Result};
8use crate::text::{DvbText, LangCode};
9use crate::traits::Descriptor;
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        if bytes.len() < HEADER_LEN {
43            return Err(Error::BufferTooShort {
44                need: HEADER_LEN,
45                have: bytes.len(),
46                what: "ComponentDescriptor header",
47            });
48        }
49        if bytes[0] != TAG {
50            return Err(Error::InvalidDescriptor {
51                tag: bytes[0],
52                reason: "unexpected tag for component_descriptor",
53            });
54        }
55        let length = bytes[1] as usize;
56        let end = HEADER_LEN + length;
57        if bytes.len() < end {
58            return Err(Error::BufferTooShort {
59                need: end,
60                have: bytes.len(),
61                what: "ComponentDescriptor body",
62            });
63        }
64        if length < PRE_TEXT_LEN {
65            return Err(Error::InvalidDescriptor {
66                tag: TAG,
67                reason: "component_descriptor body shorter than minimum 6 bytes",
68            });
69        }
70        let stream_content_ext = bytes[HEADER_LEN] >> 4;
71        let stream_content = bytes[HEADER_LEN] & STREAM_CONTENT_MASK;
72        let component_type = bytes[HEADER_LEN + 1];
73        let component_tag = bytes[HEADER_LEN + 2];
74        let language_code = LangCode([
75            bytes[HEADER_LEN + 3],
76            bytes[HEADER_LEN + 4],
77            bytes[HEADER_LEN + 5],
78        ]);
79        let text = DvbText::new(&bytes[HEADER_LEN + PRE_TEXT_LEN..end]);
80        Ok(Self {
81            stream_content_ext,
82            stream_content,
83            component_type,
84            component_tag,
85            language_code,
86            text,
87        })
88    }
89}
90
91impl Serialize for ComponentDescriptor<'_> {
92    type Error = crate::error::Error;
93    fn serialized_len(&self) -> usize {
94        HEADER_LEN + PRE_TEXT_LEN + self.text.len()
95    }
96
97    fn serialize_into(&self, buf: &mut [u8]) -> Result<usize> {
98        let len = self.serialized_len();
99        if buf.len() < len {
100            return Err(Error::OutputBufferTooSmall {
101                need: len,
102                have: buf.len(),
103            });
104        }
105        buf[0] = TAG;
106        buf[1] = (len - HEADER_LEN) as u8;
107        // High nibble = stream_content_ext, low nibble = stream_content (§6.2.8).
108        buf[HEADER_LEN] =
109            (self.stream_content_ext << 4) | (self.stream_content & STREAM_CONTENT_MASK);
110        buf[HEADER_LEN + 1] = self.component_type;
111        buf[HEADER_LEN + 2] = self.component_tag;
112        buf[HEADER_LEN + 3..HEADER_LEN + 6].copy_from_slice(&self.language_code.0);
113        buf[HEADER_LEN + PRE_TEXT_LEN..len].copy_from_slice(self.text.raw());
114        Ok(len)
115    }
116}
117
118impl<'a> Descriptor<'a> for ComponentDescriptor<'a> {
119    const TAG: u8 = TAG;
120    fn descriptor_length(&self) -> u8 {
121        (self.serialized_len() - HEADER_LEN) as u8
122    }
123}
124
125impl<'a> crate::traits::DescriptorDef<'a> for ComponentDescriptor<'a> {
126    const TAG: u8 = TAG;
127    const NAME: &'static str = "COMPONENT";
128}
129
130#[cfg(test)]
131mod tests {
132    use super::*;
133
134    #[test]
135    fn parse_extracts_all_fields() {
136        let bytes = [
137            TAG, 12, 0x02, 0x01, 0x42, b'e', b'n', b'g', b'S', b'T', b'E', b'R', b'E', b'O',
138        ];
139        let d = ComponentDescriptor::parse(&bytes).unwrap();
140        assert_eq!(d.stream_content, 2);
141        assert_eq!(d.component_type, 0x01);
142        assert_eq!(d.component_tag, 0x42);
143        assert_eq!(d.language_code, LangCode(*b"eng"));
144        assert_eq!(d.text.raw(), b"STEREO");
145    }
146
147    #[test]
148    fn parse_rejects_wrong_tag() {
149        assert!(matches!(
150            ComponentDescriptor::parse(&[0x51, 6, 0, 0, 0, b'e', b'n', b'g']).unwrap_err(),
151            Error::InvalidDescriptor { tag: 0x51, .. }
152        ));
153    }
154
155    #[test]
156    fn parse_rejects_short_body() {
157        let bytes = [TAG, 5, 0x01, 0x00, 0x00, b'e', b'n'];
158        assert!(matches!(
159            ComponentDescriptor::parse(&bytes).unwrap_err(),
160            Error::InvalidDescriptor { .. }
161        ));
162    }
163
164    #[test]
165    fn parse_rejects_truncated_buffer() {
166        let bytes = [TAG, 6, 0x01];
167        assert!(matches!(
168            ComponentDescriptor::parse(&bytes).unwrap_err(),
169            Error::BufferTooShort { .. }
170        ));
171    }
172
173    #[test]
174    fn parse_with_empty_text_valid() {
175        let bytes = [TAG, 6, 0x01, 0x01, 0x01, b'e', b'n', b'g'];
176        let d = ComponentDescriptor::parse(&bytes).unwrap();
177        assert!(d.text.raw().is_empty());
178    }
179
180    #[test]
181    fn serialize_round_trip() {
182        let d = ComponentDescriptor {
183            stream_content_ext: 0x0F,
184            stream_content: 0x03,
185            component_type: 0x10,
186            component_tag: 0x05,
187            language_code: LangCode(*b"fra"),
188            text: DvbText::new(b"Sous-titres"),
189        };
190        let mut buf = vec![0u8; d.serialized_len()];
191        d.serialize_into(&mut buf).unwrap();
192        assert_eq!(ComponentDescriptor::parse(&buf).unwrap(), d);
193    }
194
195    #[test]
196    fn stream_content_masked_to_low_nibble() {
197        // Byte = 0xF2 → high nibble is stream_content_ext (0xF), low nibble is stream_content=2.
198        let bytes = [TAG, 6, 0xF2, 0x00, 0x00, b'e', b'n', b'g'];
199        let d = ComponentDescriptor::parse(&bytes).unwrap();
200        assert_eq!(d.stream_content, 2);
201    }
202}
dvb_si/descriptors/component.rs

dvb_si/descriptors/
component.rs
