dvb_si/descriptors/
smoothing_buffer.rs

1//! Smoothing Buffer Descriptor — ISO/IEC 13818-1 §2.6.30 (tag 0x10).
2//!
3//! Describes the leak rate and size of a smoothing buffer.
4//! `sb_leak_rate` is in units of 400 bits/s; `sb_size` in units of
5//! 1 byte (§2.6.31).
6
7use super::descriptor_body;
8use crate::error::{Error, Result};
9use dvb_common::{Parse, Serialize};
10
11/// Descriptor tag for smoothing_buffer_descriptor.
12pub const TAG: u8 = 0x10;
13const HEADER_LEN: usize = 2;
14const BODY_LEN: u8 = 6;
15
16/// Smoothing Buffer Descriptor.
17#[derive(Debug, Clone, PartialEq, Eq)]
18#[cfg_attr(feature = "serde", derive(serde::Serialize))]
19#[cfg_attr(feature = "yoke", derive(yoke::Yokeable))]
20pub struct SmoothingBufferDescriptor {
21    /// SB leak rate in units of 400 bits/s (22 bits).
22    pub sb_leak_rate: u32,
23    /// SB size in bytes (22 bits).
24    pub sb_size: u32,
25}
26
27impl<'a> Parse<'a> for SmoothingBufferDescriptor {
28    type Error = crate::error::Error;
29
30    fn parse(bytes: &'a [u8]) -> Result<Self> {
31        let body = descriptor_body(
32            bytes,
33            TAG,
34            "SmoothingBufferDescriptor",
35            "unexpected tag for smoothing_buffer_descriptor",
36        )?;
37        if body.len() != BODY_LEN as usize {
38            return Err(Error::InvalidDescriptor {
39                tag: TAG,
40                reason: "smoothing_buffer_descriptor length must equal 6",
41            });
42        }
43        let sb_leak_rate =
44            ((u32::from(body[0]) & 0x3F) << 16) | (u32::from(body[1]) << 8) | u32::from(body[2]);
45        let sb_size =
46            ((u32::from(body[3]) & 0x3F) << 16) | (u32::from(body[4]) << 8) | u32::from(body[5]);
47        Ok(Self {
48            sb_leak_rate,
49            sb_size,
50        })
51    }
52}
53
54impl Serialize for SmoothingBufferDescriptor {
55    type Error = crate::error::Error;
56
57    fn serialized_len(&self) -> usize {
58        HEADER_LEN + (BODY_LEN as usize)
59    }
60
61    fn serialize_into(&self, buf: &mut [u8]) -> Result<usize> {
62        let len = self.serialized_len();
63        if buf.len() < len {
64            return Err(Error::OutputBufferTooSmall {
65                need: len,
66                have: buf.len(),
67            });
68        }
69        buf[0] = TAG;
70        buf[1] = BODY_LEN;
71        let slr = self.sb_leak_rate;
72        buf[HEADER_LEN] = ((slr >> 16) & 0x3F) as u8;
73        buf[HEADER_LEN + 1] = ((slr >> 8) & 0xFF) as u8;
74        buf[HEADER_LEN + 2] = (slr & 0xFF) as u8;
75        let ss = self.sb_size;
76        buf[HEADER_LEN + 3] = ((ss >> 16) & 0x3F) as u8;
77        buf[HEADER_LEN + 4] = ((ss >> 8) & 0xFF) as u8;
78        buf[HEADER_LEN + 5] = (ss & 0xFF) as u8;
79        Ok(len)
80    }
81}
82impl<'a> crate::traits::DescriptorDef<'a> for SmoothingBufferDescriptor {
83    const TAG: u8 = TAG;
84    const NAME: &'static str = "SMOOTHING_BUFFER";
85}
86
87#[cfg(test)]
88mod tests {
89    use super::*;
90
91    #[test]
92    fn parse() {
93        let bytes = [
94            TAG,
95            6,
96            0b00_111111,
97            0xAB,
98            0xCD, // sb_leak_rate=0x3FABCD
99            0b00_000010,
100            0x34,
101            0x56, // sb_size=0x023456
102        ];
103        let d = SmoothingBufferDescriptor::parse(&bytes).unwrap();
104        assert_eq!(d.sb_leak_rate, 0x3FABCD);
105        assert_eq!(d.sb_size, 0x023456);
106    }
107
108    #[test]
109    fn serialize_round_trip() {
110        let d = SmoothingBufferDescriptor {
111            sb_leak_rate: 0x1A2B3C,
112            sb_size: 0x2D4E5F,
113        };
114        let mut buf = vec![0u8; d.serialized_len()];
115        d.serialize_into(&mut buf).unwrap();
116        let reparsed = SmoothingBufferDescriptor::parse(&buf).unwrap();
117        assert_eq!(d, reparsed);
118    }
119
120    #[test]
121    fn parse_rejects_wrong_tag() {
122        let err = SmoothingBufferDescriptor::parse(&[0x11, 6, 0, 0, 0, 0, 0, 0]).unwrap_err();
123        assert!(matches!(err, Error::InvalidDescriptor { tag: 0x11, .. }));
124    }
125
126    #[test]
127    fn parse_rejects_wrong_length() {
128        let err = SmoothingBufferDescriptor::parse(&[TAG, 5, 0, 0, 0, 0, 0]).unwrap_err();
129        assert!(matches!(err, Error::InvalidDescriptor { tag: TAG, .. }));
130    }
131
132    #[test]
133    fn serialize_rejects_small_buffer() {
134        let d = SmoothingBufferDescriptor {
135            sb_leak_rate: 0,
136            sb_size: 0,
137        };
138        let mut tiny = vec![0u8; 4];
139        let err = d.serialize_into(&mut tiny).unwrap_err();
140        assert!(matches!(err, Error::OutputBufferTooSmall { .. }));
141    }
142}
dvb_si/descriptors/smoothing_buffer.rs

dvb_si/descriptors/
smoothing_buffer.rs
