dvb_si/descriptors/
scrambling.rs

1//! Scrambling Descriptor — ETSI EN 300 468 §6.2.32 (tag 0x65).
2//!
3//! A single byte identifying the scrambling mode in use (Table 86 syntax /
4//! Table 87 coding, PDF pp. 98-99): 0x01 = DVB-CSA1, 0x02 = DVB-CSA2,
5//! 0x03 = DVB-CSA3, 0x10 = DVB-CISSA v1, etc.
6
7use super::descriptor_body;
8use crate::error::{Error, Result};
9use dvb_common::{Parse, Serialize};
10
11/// Descriptor tag for scrambling_descriptor.
12pub const TAG: u8 = 0x65;
13const HEADER_LEN: usize = 2;
14/// Fixed payload length: a single scrambling_mode byte (EN 300 468 Table 86).
15const BODY_LEN: u8 = 1;
16
17/// Scrambling Descriptor (tag 0x65).
18#[derive(Debug, Clone, PartialEq, Eq)]
19#[cfg_attr(feature = "serde", derive(serde::Serialize))]
20pub struct ScramblingDescriptor {
21    /// 8-bit scrambling_mode (ETSI Table 87, PDF p. 99).
22    pub scrambling_mode: u8,
23}
24
25impl<'a> Parse<'a> for ScramblingDescriptor {
26    type Error = crate::error::Error;
27    fn parse(bytes: &'a [u8]) -> Result<Self> {
28        let body = descriptor_body(
29            bytes,
30            TAG,
31            "ScramblingDescriptor",
32            "unexpected tag for scrambling_descriptor",
33        )?;
34        if body.len() != BODY_LEN as usize {
35            return Err(Error::InvalidDescriptor {
36                tag: TAG,
37                reason: "scrambling_descriptor length must equal 1",
38            });
39        }
40        Ok(Self {
41            scrambling_mode: body[0],
42        })
43    }
44}
45
46impl Serialize for ScramblingDescriptor {
47    type Error = crate::error::Error;
48    fn serialized_len(&self) -> usize {
49        HEADER_LEN + BODY_LEN as usize
50    }
51
52    fn serialize_into(&self, buf: &mut [u8]) -> Result<usize> {
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] = BODY_LEN;
62        buf[HEADER_LEN] = self.scrambling_mode;
63        Ok(len)
64    }
65}
66impl<'a> crate::traits::DescriptorDef<'a> for ScramblingDescriptor {
67    const TAG: u8 = TAG;
68    const NAME: &'static str = "SCRAMBLING";
69}
70
71#[cfg(test)]
72mod tests {
73    use super::*;
74
75    #[test]
76    fn parse_extracts_scrambling_mode() {
77        let bytes = [TAG, 1, 0x02];
78        let d = ScramblingDescriptor::parse(&bytes).unwrap();
79        assert_eq!(d.scrambling_mode, 0x02);
80    }
81
82    #[test]
83    fn parse_rejects_wrong_tag() {
84        let err = ScramblingDescriptor::parse(&[0x66, 1, 0x02]).unwrap_err();
85        assert!(matches!(err, Error::InvalidDescriptor { tag: 0x66, .. }));
86    }
87
88    #[test]
89    fn parse_rejects_short_buffer() {
90        let err = ScramblingDescriptor::parse(&[TAG]).unwrap_err();
91        assert!(matches!(err, Error::BufferTooShort { .. }));
92    }
93
94    #[test]
95    fn parse_rejects_truncated_body() {
96        // length=1 but no payload byte present.
97        let err = ScramblingDescriptor::parse(&[TAG, 1]).unwrap_err();
98        assert!(matches!(err, Error::BufferTooShort { .. }));
99    }
100
101    #[test]
102    fn parse_rejects_wrong_length() {
103        let err = ScramblingDescriptor::parse(&[TAG, 2, 0x02, 0x03]).unwrap_err();
104        assert!(matches!(err, Error::InvalidDescriptor { .. }));
105    }
106
107    #[test]
108    fn serialize_round_trip() {
109        let d = ScramblingDescriptor {
110            scrambling_mode: 0x10,
111        };
112        let mut buf = vec![0u8; d.serialized_len()];
113        d.serialize_into(&mut buf).unwrap();
114        let re = ScramblingDescriptor::parse(&buf).unwrap();
115        assert_eq!(d, re);
116    }
117
118    #[test]
119    fn serialize_rejects_too_small_buffer() {
120        let d = ScramblingDescriptor {
121            scrambling_mode: 0x03,
122        };
123        let mut tiny = [0u8; 1];
124        let err = d.serialize_into(&mut tiny).unwrap_err();
125        assert!(matches!(err, Error::OutputBufferTooSmall { .. }));
126    }
127
128    #[test]
129    fn descriptor_length_matches_payload() {
130        let d = ScramblingDescriptor {
131            scrambling_mode: 0x01,
132        };
133        assert_eq!(d.serialized_len() - 2, 1);
134    }
135
136    #[cfg(feature = "serde")]
137    #[test]
138    fn serde_round_trip() {
139        let d = ScramblingDescriptor {
140            scrambling_mode: 0x02,
141        };
142        let json = serde_json::to_string(&d).unwrap();
143        // Serialize-only: assert the emitted JSON re-parses (serialize-stable).
144        let _v: serde_json::Value = serde_json::from_str(&json).unwrap();
145    }
146}
dvb_si/descriptors/scrambling.rs

dvb_si/descriptors/
scrambling.rs
