dvb_si/descriptors/
multiplex_buffer_utilization.rs

1//! Multiplex Buffer Utilization Descriptor — ISO/IEC 13818-1 §2.6.22 (tag 0x0C).
2//!
3//! Bound on the portion of the multiplex buffer occupied without
4//! overflow/underflow of the STD.
5
6use super::descriptor_body;
7use crate::error::{Error, Result};
8use dvb_common::{Parse, Serialize};
9
10/// Descriptor tag for multiplex_buffer_utilization_descriptor.
11pub const TAG: u8 = 0x0C;
12const HEADER_LEN: usize = 2;
13const BODY_LEN: u8 = 4;
14
15/// Multiplex Buffer Utilization Descriptor.
16#[derive(Debug, Clone, PartialEq, Eq)]
17#[cfg_attr(feature = "serde", derive(serde::Serialize))]
18#[cfg_attr(feature = "yoke", derive(yoke::Yokeable))]
19pub struct MultiplexBufferUtilizationDescriptor {
20    /// Bound valid flag.
21    pub bound_valid_flag: bool,
22    /// LTW offset lower bound (15 bits).
23    pub ltw_offset_lower_bound: u16,
24    /// LTW offset upper bound (15 bits).
25    pub ltw_offset_upper_bound: u16,
26}
27
28impl<'a> Parse<'a> for MultiplexBufferUtilizationDescriptor {
29    type Error = crate::error::Error;
30
31    fn parse(bytes: &'a [u8]) -> Result<Self> {
32        let body = descriptor_body(
33            bytes,
34            TAG,
35            "MultiplexBufferUtilizationDescriptor",
36            "unexpected tag for multiplex_buffer_utilization_descriptor",
37        )?;
38        if body.len() != BODY_LEN as usize {
39            return Err(Error::InvalidDescriptor {
40                tag: TAG,
41                reason: "multiplex_buffer_utilization_descriptor length must equal 4",
42            });
43        }
44        let bound_valid_flag = (body[0] & 0x80) != 0;
45        let ltw_offset_lower_bound = ((u16::from(body[0]) & 0x7F) << 8) | u16::from(body[1]);
46        let ltw_offset_upper_bound = ((u16::from(body[2]) & 0x7F) << 8) | u16::from(body[3]);
47        Ok(Self {
48            bound_valid_flag,
49            ltw_offset_lower_bound,
50            ltw_offset_upper_bound,
51        })
52    }
53}
54
55impl Serialize for MultiplexBufferUtilizationDescriptor {
56    type Error = crate::error::Error;
57
58    fn serialized_len(&self) -> usize {
59        HEADER_LEN + (BODY_LEN as usize)
60    }
61
62    fn serialize_into(&self, buf: &mut [u8]) -> Result<usize> {
63        let len = self.serialized_len();
64        if buf.len() < len {
65            return Err(Error::OutputBufferTooSmall {
66                need: len,
67                have: buf.len(),
68            });
69        }
70        buf[0] = TAG;
71        buf[1] = BODY_LEN;
72        buf[HEADER_LEN] = ((self.bound_valid_flag as u8) << 7)
73            | ((self.ltw_offset_lower_bound >> 8) as u8 & 0x7F);
74        buf[HEADER_LEN + 1] = (self.ltw_offset_lower_bound & 0xFF) as u8;
75        buf[HEADER_LEN + 2] = (self.ltw_offset_upper_bound >> 8) as u8 & 0x7F;
76        buf[HEADER_LEN + 3] = (self.ltw_offset_upper_bound & 0xFF) as u8;
77        Ok(len)
78    }
79}
80impl<'a> crate::traits::DescriptorDef<'a> for MultiplexBufferUtilizationDescriptor {
81    const TAG: u8 = TAG;
82    const NAME: &'static str = "MULTIPLEX_BUFFER_UTILIZATION";
83}
84
85#[cfg(test)]
86mod tests {
87    use super::*;
88
89    #[test]
90    fn parse() {
91        let bytes = [
92            TAG,
93            4,
94            0b1_1111111,
95            0xAB, // bound_valid=1, lower_bound=0x7FAB
96            0b1_1111111,
97            0xCD, // reserved(1) in source, upper_bound=0x7FCD
98        ];
99        let d = MultiplexBufferUtilizationDescriptor::parse(&bytes).unwrap();
100        assert!(d.bound_valid_flag);
101        assert_eq!(d.ltw_offset_lower_bound, 0x7FAB);
102        assert_eq!(d.ltw_offset_upper_bound, 0x7FCD);
103    }
104
105    #[test]
106    fn serialize_round_trip() {
107        let d = MultiplexBufferUtilizationDescriptor {
108            bound_valid_flag: false,
109            ltw_offset_lower_bound: 0x1234,
110            ltw_offset_upper_bound: 0x5678,
111        };
112        let mut buf = vec![0u8; d.serialized_len()];
113        d.serialize_into(&mut buf).unwrap();
114        let reparsed = MultiplexBufferUtilizationDescriptor::parse(&buf).unwrap();
115        assert_eq!(d, reparsed);
116    }
117
118    #[test]
119    fn parse_rejects_wrong_tag() {
120        let err = MultiplexBufferUtilizationDescriptor::parse(&[0x0D, 4, 0, 0, 0, 0]).unwrap_err();
121        assert!(matches!(err, Error::InvalidDescriptor { tag: 0x0D, .. }));
122    }
123
124    #[test]
125    fn parse_rejects_wrong_length() {
126        let err = MultiplexBufferUtilizationDescriptor::parse(&[TAG, 3, 0, 0, 0]).unwrap_err();
127        assert!(matches!(err, Error::InvalidDescriptor { tag: TAG, .. }));
128    }
129
130    #[test]
131    fn serialize_rejects_small_buffer() {
132        let d = MultiplexBufferUtilizationDescriptor {
133            bound_valid_flag: false,
134            ltw_offset_lower_bound: 0,
135            ltw_offset_upper_bound: 0,
136        };
137        let mut tiny = vec![0u8; 3];
138        let err = d.serialize_into(&mut tiny).unwrap_err();
139        assert!(matches!(err, Error::OutputBufferTooSmall { .. }));
140    }
141}
dvb_si/descriptors/multiplex_buffer_utilization.rs

dvb_si/descriptors/
multiplex_buffer_utilization.rs
