dvb_si/descriptors/
multiplex_buffer.rs

1//! MultiplexBuffer Descriptor — ISO/IEC 13818-1 §2.6.52, Table 2-81 (tag 0x23).
2//!
3//! Two 24-bit uimsbf fields: MB_buffer_size and TB_leak_rate.
4
5use super::descriptor_body;
6use crate::error::{Error, Result};
7use dvb_common::{Parse, Serialize};
8
9/// Descriptor tag for MultiplexBuffer_descriptor.
10pub const TAG: u8 = 0x23;
11const HEADER_LEN: usize = 2;
12const BODY_LEN: u8 = 6;
13
14/// MultiplexBuffer Descriptor.
15#[derive(Debug, Clone, Copy, PartialEq, Eq)]
16#[cfg_attr(feature = "serde", derive(serde::Serialize))]
17pub struct MultiplexBufferDescriptor {
18    /// MB_buffer_size, 24-bit uimsbf, in bytes.
19    pub mb_buffer_size: u32,
20    /// TB_leak_rate, 24-bit uimsbf, in units of 400 bits/s.
21    pub tb_leak_rate: u32,
22}
23
24impl<'a> Parse<'a> for MultiplexBufferDescriptor {
25    type Error = crate::error::Error;
26
27    fn parse(bytes: &'a [u8]) -> Result<Self> {
28        let body = descriptor_body(
29            bytes,
30            TAG,
31            "MultiplexBufferDescriptor",
32            "unexpected tag for MultiplexBuffer_descriptor",
33        )?;
34        if body.len() != BODY_LEN as usize {
35            return Err(Error::InvalidDescriptor {
36                tag: TAG,
37                reason: "MultiplexBuffer_descriptor length must equal 6",
38            });
39        }
40        let mb_buffer_size = u32::from_be_bytes([0, body[0], body[1], body[2]]);
41        let tb_leak_rate = u32::from_be_bytes([0, body[3], body[4], body[5]]);
42        Ok(Self {
43            mb_buffer_size,
44            tb_leak_rate,
45        })
46    }
47}
48
49impl Serialize for MultiplexBufferDescriptor {
50    type Error = crate::error::Error;
51
52    fn serialized_len(&self) -> usize {
53        HEADER_LEN + BODY_LEN as usize
54    }
55
56    fn serialize_into(&self, buf: &mut [u8]) -> Result<usize> {
57        let len = self.serialized_len();
58        if buf.len() < len {
59            return Err(Error::OutputBufferTooSmall {
60                need: len,
61                have: buf.len(),
62            });
63        }
64        buf[0] = TAG;
65        buf[1] = BODY_LEN;
66        buf[HEADER_LEN..HEADER_LEN + 3].copy_from_slice(&self.mb_buffer_size.to_be_bytes()[1..]);
67        buf[HEADER_LEN + 3..HEADER_LEN + 6].copy_from_slice(&self.tb_leak_rate.to_be_bytes()[1..]);
68        Ok(len)
69    }
70}
71impl<'a> crate::traits::DescriptorDef<'a> for MultiplexBufferDescriptor {
72    const TAG: u8 = TAG;
73    const NAME: &'static str = "MULTIPLEX_BUFFER";
74}
75
76#[cfg(test)]
77mod tests {
78    use super::*;
79
80    #[test]
81    fn parse_extracts_fields() {
82        let bytes = [TAG, 6, 0x12, 0x34, 0x56, 0x78, 0x9A, 0xBC];
83        let d = MultiplexBufferDescriptor::parse(&bytes).unwrap();
84        assert_eq!(d.mb_buffer_size, 0x00123456);
85        assert_eq!(d.tb_leak_rate, 0x00789ABC);
86    }
87
88    #[test]
89    fn parse_max_values() {
90        let bytes = [TAG, 6, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF];
91        let d = MultiplexBufferDescriptor::parse(&bytes).unwrap();
92        assert_eq!(d.mb_buffer_size, 0x00FF_FFFF);
93        assert_eq!(d.tb_leak_rate, 0x00FF_FFFF);
94    }
95
96    #[test]
97    fn parse_rejects_wrong_tag() {
98        let err = MultiplexBufferDescriptor::parse(&[0x02, 6, 0, 0, 0, 0, 0, 0]).unwrap_err();
99        assert!(matches!(err, Error::InvalidDescriptor { tag: 0x02, .. }));
100    }
101
102    #[test]
103    fn parse_rejects_wrong_length() {
104        let err = MultiplexBufferDescriptor::parse(&[TAG, 5, 0, 0, 0, 0, 0]).unwrap_err();
105        assert!(matches!(err, Error::InvalidDescriptor { .. }));
106    }
107
108    #[test]
109    fn parse_rejects_short_buffer() {
110        let err = MultiplexBufferDescriptor::parse(&[TAG, 7, 0, 0]).unwrap_err();
111        assert!(matches!(err, Error::BufferTooShort { .. }));
112    }
113
114    #[test]
115    fn serialize_round_trip() {
116        let d = MultiplexBufferDescriptor {
117            mb_buffer_size: 0x00ABCDEF,
118            tb_leak_rate: 0x00123456,
119        };
120        let mut buf = vec![0u8; d.serialized_len()];
121        d.serialize_into(&mut buf).unwrap();
122        let reparsed = MultiplexBufferDescriptor::parse(&buf).unwrap();
123        assert_eq!(d, reparsed);
124    }
125
126    #[test]
127    fn serialize_rejects_small_buffer() {
128        let d = MultiplexBufferDescriptor {
129            mb_buffer_size: 0,
130            tb_leak_rate: 0,
131        };
132        let mut tiny = vec![0u8; 5];
133        let err = d.serialize_into(&mut tiny).unwrap_err();
134        assert!(matches!(err, Error::OutputBufferTooSmall { .. }));
135    }
136}
dvb_si/descriptors/multiplex_buffer.rs

dvb_si/descriptors/
multiplex_buffer.rs
