dvb_si/descriptors/
dsng.rs

1//! DSNG Descriptor — ETSI EN 300 468 §6.2.15 (tag 0x68, Table 52, PDF p. 78).
2//!
3//! Digital Satellite News Gathering. Carried in the NIT. The body is a single
4//! `for (i=0;i<N;i++) { byte }` loop (Table 52); §6.2.15 defines the bytes as
5//! the textual DSNG identifier carried as ASCII characters. We preserve the
6//! raw bytes verbatim.
7
8use super::descriptor_body;
9use crate::error::{Error, Result};
10use dvb_common::{Parse, Serialize};
11
12/// Descriptor tag for DSNG_descriptor.
13pub const TAG: u8 = 0x68;
14/// Length of the header (tag byte + length byte).
15pub const HEADER_LEN: usize = 2;
16
17/// DSNG Descriptor.
18#[derive(Debug, Clone, PartialEq, Eq)]
19#[cfg_attr(feature = "serde", derive(serde::Serialize))]
20#[cfg_attr(feature = "yoke", derive(yoke::Yokeable))]
21pub struct DsngDescriptor<'a> {
22    /// Raw DSNG identifier bytes (ASCII per §6.2.15).
23    pub bytes: &'a [u8],
24}
25
26impl<'a> Parse<'a> for DsngDescriptor<'a> {
27    type Error = crate::error::Error;
28    fn parse(bytes: &'a [u8]) -> Result<Self> {
29        let body = descriptor_body(
30            bytes,
31            TAG,
32            "DsngDescriptor",
33            "unexpected tag for DSNG_descriptor",
34        )?;
35        Ok(Self { bytes: body })
36    }
37}
38
39impl Serialize for DsngDescriptor<'_> {
40    type Error = crate::error::Error;
41    fn serialized_len(&self) -> usize {
42        HEADER_LEN + self.bytes.len()
43    }
44
45    fn serialize_into(&self, buf: &mut [u8]) -> Result<usize> {
46        if self.bytes.len() > u8::MAX as usize {
47            return Err(Error::InvalidDescriptor {
48                tag: TAG,
49                reason: "DSNG_descriptor body exceeds 255 bytes",
50            });
51        }
52        let len = self.serialized_len();
53        if buf.len() < len {
54            return Err(Error::OutputBufferTooSmall {
55                need: len,
56                have: buf.len(),
57            });
58        }
59        buf[0] = TAG;
60        buf[1] = self.bytes.len() as u8;
61        buf[HEADER_LEN..len].copy_from_slice(self.bytes);
62        Ok(len)
63    }
64}
65impl<'a> crate::traits::DescriptorDef<'a> for DsngDescriptor<'a> {
66    const TAG: u8 = TAG;
67    const NAME: &'static str = "DSNG";
68}
69
70#[cfg(test)]
71mod tests {
72    use super::*;
73
74    #[test]
75    fn parse_extracts_ascii() {
76        let bytes = [TAG, 4, b'D', b'S', b'N', b'G'];
77        let d = DsngDescriptor::parse(&bytes).unwrap();
78        assert_eq!(d.bytes, b"DSNG");
79    }
80
81    #[test]
82    fn empty_body_is_valid() {
83        let bytes = [TAG, 0];
84        let d = DsngDescriptor::parse(&bytes).unwrap();
85        assert!(d.bytes.is_empty());
86    }
87
88    #[test]
89    fn parse_rejects_wrong_tag() {
90        assert!(matches!(
91            DsngDescriptor::parse(&[0x69, 0]).unwrap_err(),
92            Error::InvalidDescriptor { tag: 0x69, .. }
93        ));
94    }
95
96    #[test]
97    fn parse_rejects_short_header() {
98        assert!(matches!(
99            DsngDescriptor::parse(&[TAG]).unwrap_err(),
100            Error::BufferTooShort { .. }
101        ));
102    }
103
104    #[test]
105    fn parse_rejects_length_overrunning_buffer() {
106        let bytes = [TAG, 5, 1, 2, 3];
107        assert!(matches!(
108            DsngDescriptor::parse(&bytes).unwrap_err(),
109            Error::BufferTooShort { .. }
110        ));
111    }
112
113    #[test]
114    fn serialize_round_trip() {
115        let d = DsngDescriptor {
116            bytes: b"News Truck 4",
117        };
118        let mut buf = vec![0u8; d.serialized_len()];
119        d.serialize_into(&mut buf).unwrap();
120        assert_eq!(DsngDescriptor::parse(&buf).unwrap(), d);
121    }
122
123    #[test]
124    fn serialize_rejects_too_small_buffer() {
125        let d = DsngDescriptor { bytes: b"DSNG" };
126        let mut buf = vec![0u8; 1];
127        assert!(matches!(
128            d.serialize_into(&mut buf).unwrap_err(),
129            Error::OutputBufferTooSmall { .. }
130        ));
131    }
132
133    #[test]
134    fn serialize_rejects_over_range_body() {
135        let big = vec![0u8; 256];
136        let d = DsngDescriptor { bytes: &big };
137        let mut buf = vec![0u8; d.serialized_len()];
138        assert!(matches!(
139            d.serialize_into(&mut buf).unwrap_err(),
140            Error::InvalidDescriptor { tag: TAG, .. }
141        ));
142    }
143
144    // No JSON serde round-trip test: the borrowed `&[u8]` field cannot
145    // round-trip through serde_json (it serializes a slice as a sequence,
146    // not a borrowed byte array). This matches sibling borrowed-bytes
147    // descriptors (linkage.rs, default_authority.rs, content_identifier.rs),
148    // none of which carry a serde_round_trip test. The serde derive itself
149    // is still exercised by compilation under `--all-features`.
150}
dvb_si/descriptors/dsng.rs

dvb_si/descriptors/
dsng.rs
