dvb_si/descriptors/
transport_stream.rs

1//! Transport Stream Descriptor — ETSI EN 300 468 §6.2.46 (tag 0x67, Table 105, PDF p. 109).
2//!
3//! Carried inside the NIT transport_stream_loop. The body is a raw byte
4//! sequence "for indication of DVB compliance" — a single
5//! `for (i=0;i<N;i++) { byte }` loop with no internal structure (Table 105).
6//! The de-facto convention is the three ASCII bytes `b"DVB"`, but the spec
7//! defines no semantics so we preserve the raw bytes verbatim.
8
9use super::descriptor_body;
10use crate::error::{Error, Result};
11use dvb_common::{Parse, Serialize};
12
13/// Descriptor tag for transport_stream_descriptor.
14pub const TAG: u8 = 0x67;
15/// Length of the header (tag byte + length byte).
16pub const HEADER_LEN: usize = 2;
17
18/// Transport Stream Descriptor.
19#[derive(Debug, Clone, PartialEq, Eq)]
20#[cfg_attr(feature = "serde", derive(serde::Serialize))]
21#[cfg_attr(feature = "yoke", derive(yoke::Yokeable))]
22pub struct TransportStreamDescriptor<'a> {
23    /// Raw `byte` loop — DVB-compliance marker (conventionally `b"DVB"`).
24    pub bytes: &'a [u8],
25}
26
27impl<'a> Parse<'a> for TransportStreamDescriptor<'a> {
28    type Error = crate::error::Error;
29    fn parse(bytes: &'a [u8]) -> Result<Self> {
30        let body = descriptor_body(
31            bytes,
32            TAG,
33            "TransportStreamDescriptor",
34            "unexpected tag for transport_stream_descriptor",
35        )?;
36        Ok(Self { bytes: body })
37    }
38}
39
40impl Serialize for TransportStreamDescriptor<'_> {
41    type Error = crate::error::Error;
42    fn serialized_len(&self) -> usize {
43        HEADER_LEN + self.bytes.len()
44    }
45
46    fn serialize_into(&self, buf: &mut [u8]) -> Result<usize> {
47        if self.bytes.len() > u8::MAX as usize {
48            return Err(Error::InvalidDescriptor {
49                tag: TAG,
50                reason: "transport_stream_descriptor body exceeds 255 bytes",
51            });
52        }
53        let len = self.serialized_len();
54        if buf.len() < len {
55            return Err(Error::OutputBufferTooSmall {
56                need: len,
57                have: buf.len(),
58            });
59        }
60        buf[0] = TAG;
61        buf[1] = self.bytes.len() as u8;
62        buf[HEADER_LEN..len].copy_from_slice(self.bytes);
63        Ok(len)
64    }
65}
66impl<'a> crate::traits::DescriptorDef<'a> for TransportStreamDescriptor<'a> {
67    const TAG: u8 = TAG;
68    const NAME: &'static str = "TRANSPORT_STREAM";
69}
70
71#[cfg(test)]
72mod tests {
73    use super::*;
74
75    #[test]
76    fn parse_extracts_dvb_marker() {
77        let bytes = [TAG, 3, b'D', b'V', b'B'];
78        let d = TransportStreamDescriptor::parse(&bytes).unwrap();
79        assert_eq!(d.bytes, b"DVB");
80    }
81
82    #[test]
83    fn empty_body_is_valid() {
84        let bytes = [TAG, 0];
85        let d = TransportStreamDescriptor::parse(&bytes).unwrap();
86        assert!(d.bytes.is_empty());
87    }
88
89    #[test]
90    fn parse_rejects_wrong_tag() {
91        assert!(matches!(
92            TransportStreamDescriptor::parse(&[0x68, 0]).unwrap_err(),
93            Error::InvalidDescriptor { tag: 0x68, .. }
94        ));
95    }
96
97    #[test]
98    fn parse_rejects_short_header() {
99        assert!(matches!(
100            TransportStreamDescriptor::parse(&[TAG]).unwrap_err(),
101            Error::BufferTooShort { .. }
102        ));
103    }
104
105    #[test]
106    fn parse_rejects_length_overrunning_buffer() {
107        let bytes = [TAG, 5, 1, 2, 3];
108        assert!(matches!(
109            TransportStreamDescriptor::parse(&bytes).unwrap_err(),
110            Error::BufferTooShort { .. }
111        ));
112    }
113
114    #[test]
115    fn serialize_round_trip() {
116        let d = TransportStreamDescriptor { bytes: b"DVB" };
117        let mut buf = vec![0u8; d.serialized_len()];
118        d.serialize_into(&mut buf).unwrap();
119        assert_eq!(TransportStreamDescriptor::parse(&buf).unwrap(), d);
120    }
121
122    #[test]
123    fn serialize_rejects_too_small_buffer() {
124        let d = TransportStreamDescriptor { bytes: b"DVB" };
125        let mut buf = vec![0u8; 1];
126        assert!(matches!(
127            d.serialize_into(&mut buf).unwrap_err(),
128            Error::OutputBufferTooSmall { .. }
129        ));
130    }
131
132    #[test]
133    fn serialize_rejects_over_range_body() {
134        let big = vec![0u8; 256];
135        let d = TransportStreamDescriptor { bytes: &big };
136        let mut buf = vec![0u8; d.serialized_len()];
137        assert!(matches!(
138            d.serialize_into(&mut buf).unwrap_err(),
139            Error::InvalidDescriptor { tag: TAG, .. }
140        ));
141    }
142
143    // No JSON serde round-trip test: the borrowed `&[u8]` field cannot
144    // round-trip through serde_json (it serializes a slice as a sequence,
145    // not a borrowed byte array). This matches sibling borrowed-bytes
146    // descriptors (linkage.rs, default_authority.rs, content_identifier.rs),
147    // none of which carry a serde_round_trip test. The serde derive itself
148    // is still exercised by compilation under `--all-features`.
149}
dvb_si/descriptors/transport_stream.rs

dvb_si/descriptors/
transport_stream.rs
