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 crate::error::{Error, Result};
10use crate::traits::Descriptor;
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, serde::Deserialize))]
21pub struct TransportStreamDescriptor<'a> {
22    /// Raw `byte` loop — DVB-compliance marker (conventionally `b"DVB"`).
23    #[cfg_attr(feature = "serde", serde(borrow))]
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        if bytes.len() < HEADER_LEN {
31            return Err(Error::BufferTooShort {
32                need: HEADER_LEN,
33                have: bytes.len(),
34                what: "TransportStreamDescriptor header",
35            });
36        }
37        if bytes[0] != TAG {
38            return Err(Error::InvalidDescriptor {
39                tag: bytes[0],
40                reason: "unexpected tag for transport_stream_descriptor",
41            });
42        }
43        let length = bytes[1] as usize;
44        let end = HEADER_LEN + length;
45        if bytes.len() < end {
46            return Err(Error::BufferTooShort {
47                need: end,
48                have: bytes.len(),
49                what: "TransportStreamDescriptor body",
50            });
51        }
52        Ok(Self {
53            bytes: &bytes[HEADER_LEN..end],
54        })
55    }
56}
57
58impl Serialize for TransportStreamDescriptor<'_> {
59    type Error = crate::error::Error;
60    fn serialized_len(&self) -> usize {
61        HEADER_LEN + self.bytes.len()
62    }
63
64    fn serialize_into(&self, buf: &mut [u8]) -> Result<usize> {
65        if self.bytes.len() > u8::MAX as usize {
66            return Err(Error::InvalidDescriptor {
67                tag: TAG,
68                reason: "transport_stream_descriptor body exceeds 255 bytes",
69            });
70        }
71        let len = self.serialized_len();
72        if buf.len() < len {
73            return Err(Error::OutputBufferTooSmall {
74                need: len,
75                have: buf.len(),
76            });
77        }
78        buf[0] = TAG;
79        buf[1] = self.bytes.len() as u8;
80        buf[HEADER_LEN..len].copy_from_slice(self.bytes);
81        Ok(len)
82    }
83}
84
85impl<'a> Descriptor<'a> for TransportStreamDescriptor<'a> {
86    const TAG: u8 = TAG;
87    fn descriptor_length(&self) -> u8 {
88        self.bytes.len() as u8
89    }
90}
91
92impl<'a> crate::traits::DescriptorDef<'a> for TransportStreamDescriptor<'a> {
93    const TAG: u8 = TAG;
94    const NAME: &'static str = "TRANSPORT_STREAM";
95}
96
97#[cfg(test)]
98mod tests {
99    use super::*;
100
101    #[test]
102    fn parse_extracts_dvb_marker() {
103        let bytes = [TAG, 3, b'D', b'V', b'B'];
104        let d = TransportStreamDescriptor::parse(&bytes).unwrap();
105        assert_eq!(d.bytes, b"DVB");
106    }
107
108    #[test]
109    fn empty_body_is_valid() {
110        let bytes = [TAG, 0];
111        let d = TransportStreamDescriptor::parse(&bytes).unwrap();
112        assert!(d.bytes.is_empty());
113    }
114
115    #[test]
116    fn parse_rejects_wrong_tag() {
117        assert!(matches!(
118            TransportStreamDescriptor::parse(&[0x68, 0]).unwrap_err(),
119            Error::InvalidDescriptor { tag: 0x68, .. }
120        ));
121    }
122
123    #[test]
124    fn parse_rejects_short_header() {
125        assert!(matches!(
126            TransportStreamDescriptor::parse(&[TAG]).unwrap_err(),
127            Error::BufferTooShort { .. }
128        ));
129    }
130
131    #[test]
132    fn parse_rejects_length_overrunning_buffer() {
133        let bytes = [TAG, 5, 1, 2, 3];
134        assert!(matches!(
135            TransportStreamDescriptor::parse(&bytes).unwrap_err(),
136            Error::BufferTooShort { .. }
137        ));
138    }
139
140    #[test]
141    fn serialize_round_trip() {
142        let d = TransportStreamDescriptor { bytes: b"DVB" };
143        let mut buf = vec![0u8; d.serialized_len()];
144        d.serialize_into(&mut buf).unwrap();
145        assert_eq!(TransportStreamDescriptor::parse(&buf).unwrap(), d);
146    }
147
148    #[test]
149    fn serialize_rejects_too_small_buffer() {
150        let d = TransportStreamDescriptor { bytes: b"DVB" };
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 = TransportStreamDescriptor { 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/transport_stream.rs

dvb_si/descriptors/
transport_stream.rs
