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 crate::error::{Error, Result};
9use crate::traits::Descriptor;
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))]
20pub struct DsngDescriptor<'a> {
21    /// Raw DSNG identifier bytes (ASCII per §6.2.15).
22    pub bytes: &'a [u8],
23}
24
25impl<'a> Parse<'a> for DsngDescriptor<'a> {
26    type Error = crate::error::Error;
27    fn parse(bytes: &'a [u8]) -> Result<Self> {
28        if bytes.len() < HEADER_LEN {
29            return Err(Error::BufferTooShort {
30                need: HEADER_LEN,
31                have: bytes.len(),
32                what: "DsngDescriptor header",
33            });
34        }
35        if bytes[0] != TAG {
36            return Err(Error::InvalidDescriptor {
37                tag: bytes[0],
38                reason: "unexpected tag for DSNG_descriptor",
39            });
40        }
41        let length = bytes[1] as usize;
42        let end = HEADER_LEN + length;
43        if bytes.len() < end {
44            return Err(Error::BufferTooShort {
45                need: end,
46                have: bytes.len(),
47                what: "DsngDescriptor body",
48            });
49        }
50        Ok(Self {
51            bytes: &bytes[HEADER_LEN..end],
52        })
53    }
54}
55
56impl Serialize for DsngDescriptor<'_> {
57    type Error = crate::error::Error;
58    fn serialized_len(&self) -> usize {
59        HEADER_LEN + self.bytes.len()
60    }
61
62    fn serialize_into(&self, buf: &mut [u8]) -> Result<usize> {
63        if self.bytes.len() > u8::MAX as usize {
64            return Err(Error::InvalidDescriptor {
65                tag: TAG,
66                reason: "DSNG_descriptor body exceeds 255 bytes",
67            });
68        }
69        let len = self.serialized_len();
70        if buf.len() < len {
71            return Err(Error::OutputBufferTooSmall {
72                need: len,
73                have: buf.len(),
74            });
75        }
76        buf[0] = TAG;
77        buf[1] = self.bytes.len() as u8;
78        buf[HEADER_LEN..len].copy_from_slice(self.bytes);
79        Ok(len)
80    }
81}
82
83impl<'a> Descriptor<'a> for DsngDescriptor<'a> {
84    const TAG: u8 = TAG;
85    fn descriptor_length(&self) -> u8 {
86        self.bytes.len() as u8
87    }
88}
89
90impl<'a> crate::traits::DescriptorDef<'a> for DsngDescriptor<'a> {
91    const TAG: u8 = TAG;
92    const NAME: &'static str = "DSNG";
93}
94
95#[cfg(test)]
96mod tests {
97    use super::*;
98
99    #[test]
100    fn parse_extracts_ascii() {
101        let bytes = [TAG, 4, b'D', b'S', b'N', b'G'];
102        let d = DsngDescriptor::parse(&bytes).unwrap();
103        assert_eq!(d.bytes, b"DSNG");
104    }
105
106    #[test]
107    fn empty_body_is_valid() {
108        let bytes = [TAG, 0];
109        let d = DsngDescriptor::parse(&bytes).unwrap();
110        assert!(d.bytes.is_empty());
111    }
112
113    #[test]
114    fn parse_rejects_wrong_tag() {
115        assert!(matches!(
116            DsngDescriptor::parse(&[0x69, 0]).unwrap_err(),
117            Error::InvalidDescriptor { tag: 0x69, .. }
118        ));
119    }
120
121    #[test]
122    fn parse_rejects_short_header() {
123        assert!(matches!(
124            DsngDescriptor::parse(&[TAG]).unwrap_err(),
125            Error::BufferTooShort { .. }
126        ));
127    }
128
129    #[test]
130    fn parse_rejects_length_overrunning_buffer() {
131        let bytes = [TAG, 5, 1, 2, 3];
132        assert!(matches!(
133            DsngDescriptor::parse(&bytes).unwrap_err(),
134            Error::BufferTooShort { .. }
135        ));
136    }
137
138    #[test]
139    fn serialize_round_trip() {
140        let d = DsngDescriptor {
141            bytes: b"News Truck 4",
142        };
143        let mut buf = vec![0u8; d.serialized_len()];
144        d.serialize_into(&mut buf).unwrap();
145        assert_eq!(DsngDescriptor::parse(&buf).unwrap(), d);
146    }
147
148    #[test]
149    fn serialize_rejects_too_small_buffer() {
150        let d = DsngDescriptor { bytes: b"DSNG" };
151        let mut buf = vec![0u8; 1];
152        assert!(matches!(
153            d.serialize_into(&mut buf).unwrap_err(),
154            Error::OutputBufferTooSmall { .. }
155        ));
156    }
157
158    #[test]
159    fn serialize_rejects_over_range_body() {
160        let big = vec![0u8; 256];
161        let d = DsngDescriptor { bytes: &big };
162        let mut buf = vec![0u8; d.serialized_len()];
163        assert!(matches!(
164            d.serialize_into(&mut buf).unwrap_err(),
165            Error::InvalidDescriptor { tag: TAG, .. }
166        ));
167    }
168
169    // No JSON serde round-trip test: the borrowed `&[u8]` field cannot
170    // round-trip through serde_json (it serializes a slice as a sequence,
171    // not a borrowed byte array). This matches sibling borrowed-bytes
172    // descriptors (linkage.rs, default_authority.rs, content_identifier.rs),
173    // none of which carry a serde_round_trip test. The serde derive itself
174    // is still exercised by compilation under `--all-features`.
175}
dvb_si/descriptors/dsng.rs

dvb_si/descriptors/
dsng.rs
