dvb_si/descriptors/
metadata_std.rs

1//! Metadata STD Descriptor — ISO/IEC 13818-1 §2.6.62, Table 2-91 (tag 0x27).
2//!
3//! Three 22-bit uimsbf values (stored as u32 with top 10 bits zero),
4//! each preceded by 2 reserved bits. Total body: 9 bytes.
5
6use super::descriptor_body;
7use crate::error::{Error, Result};
8use dvb_common::{Parse, Serialize};
9
10/// Descriptor tag for Metadata_STD_descriptor.
11pub const TAG: u8 = 0x27;
12const HEADER_LEN: usize = 2;
13const BODY_LEN: u8 = 9;
14
15/// Metadata STD Descriptor.
16#[derive(Debug, Clone, Copy, PartialEq, Eq)]
17#[cfg_attr(feature = "serde", derive(serde::Serialize))]
18pub struct MetadataStdDescriptor {
19    /// metadata_input_leak_rate, 22-bit uimsbf, in units of 400 bits/s.
20    pub metadata_input_leak_rate: u32,
21    /// metadata_buffer_size, 22-bit uimsbf, in units of 1024 bytes.
22    pub metadata_buffer_size: u32,
23    /// metadata_output_leak_rate, 22-bit uimsbf, in units of 400 bits/s.
24    pub metadata_output_leak_rate: u32,
25}
26
27/// Extract a 22-bit uimsbf from a 3-byte slice (top 2 bits reserved/zero).
28fn read_u22(bytes: &[u8]) -> u32 {
29    ((bytes[0] as u32) << 16) | ((bytes[1] as u32) << 8) | (bytes[2] as u32)
30}
31
32/// Write a 22-bit value into a 3-byte slice (top 2 bits zero).
33fn write_u22(val: u32, buf: &mut [u8]) {
34    let masked = val & 0x003F_FFFF;
35    buf[0] = ((masked >> 16) & 0x3F) as u8;
36    buf[1] = ((masked >> 8) & 0xFF) as u8;
37    buf[2] = (masked & 0xFF) as u8;
38}
39
40impl<'a> Parse<'a> for MetadataStdDescriptor {
41    type Error = crate::error::Error;
42
43    fn parse(bytes: &'a [u8]) -> Result<Self> {
44        let body = descriptor_body(
45            bytes,
46            TAG,
47            "MetadataStdDescriptor",
48            "unexpected tag for Metadata_STD_descriptor",
49        )?;
50        if body.len() != BODY_LEN as usize {
51            return Err(Error::InvalidDescriptor {
52                tag: TAG,
53                reason: "Metadata_STD_descriptor length must equal 9",
54            });
55        }
56        Ok(Self {
57            metadata_input_leak_rate: read_u22(&body[0..3]),
58            metadata_buffer_size: read_u22(&body[3..6]),
59            metadata_output_leak_rate: read_u22(&body[6..9]),
60        })
61    }
62}
63
64impl Serialize for MetadataStdDescriptor {
65    type Error = crate::error::Error;
66
67    fn serialized_len(&self) -> usize {
68        HEADER_LEN + BODY_LEN as usize
69    }
70
71    fn serialize_into(&self, buf: &mut [u8]) -> Result<usize> {
72        let len = self.serialized_len();
73        if buf.len() < len {
74            return Err(Error::OutputBufferTooSmall {
75                need: len,
76                have: buf.len(),
77            });
78        }
79        buf[0] = TAG;
80        buf[1] = BODY_LEN;
81        write_u22(
82            self.metadata_input_leak_rate,
83            &mut buf[HEADER_LEN..HEADER_LEN + 3],
84        );
85        write_u22(
86            self.metadata_buffer_size,
87            &mut buf[HEADER_LEN + 3..HEADER_LEN + 6],
88        );
89        write_u22(
90            self.metadata_output_leak_rate,
91            &mut buf[HEADER_LEN + 6..HEADER_LEN + 9],
92        );
93        Ok(len)
94    }
95}
96impl<'a> crate::traits::DescriptorDef<'a> for MetadataStdDescriptor {
97    const TAG: u8 = TAG;
98    const NAME: &'static str = "METADATA_STD";
99}
100
101#[cfg(test)]
102mod tests {
103    use super::*;
104
105    #[test]
106    fn parse_extracts_fields() {
107        let bytes = [TAG, 9, 0x10, 0x20, 0x30, 0x01, 0x02, 0x03, 0x3F, 0xFF, 0xFF];
108        let d = MetadataStdDescriptor::parse(&bytes).unwrap();
109        assert_eq!(d.metadata_input_leak_rate, read_u22(&[0x10, 0x20, 0x30]));
110        assert_eq!(d.metadata_buffer_size, read_u22(&[0x01, 0x02, 0x03]));
111        assert_eq!(d.metadata_output_leak_rate, read_u22(&[0x3F, 0xFF, 0xFF]));
112    }
113
114    #[test]
115    fn parse_max_values() {
116        let bytes = [TAG, 9, 0x3F, 0xFF, 0xFF, 0x3F, 0xFF, 0xFF, 0x3F, 0xFF, 0xFF];
117        let d = MetadataStdDescriptor::parse(&bytes).unwrap();
118        assert_eq!(d.metadata_input_leak_rate, 0x003F_FFFF);
119        assert_eq!(d.metadata_buffer_size, 0x003F_FFFF);
120        assert_eq!(d.metadata_output_leak_rate, 0x003F_FFFF);
121    }
122
123    #[test]
124    fn parse_rejects_wrong_tag() {
125        let err = MetadataStdDescriptor::parse(&[0x02, 9, 0, 0, 0, 0, 0, 0, 0, 0, 0]).unwrap_err();
126        assert!(matches!(err, Error::InvalidDescriptor { tag: 0x02, .. }));
127    }
128
129    #[test]
130    fn parse_rejects_wrong_length() {
131        let err = MetadataStdDescriptor::parse(&[TAG, 8, 0, 0, 0, 0, 0, 0, 0, 0]).unwrap_err();
132        assert!(matches!(err, Error::InvalidDescriptor { .. }));
133    }
134
135    #[test]
136    fn serialize_round_trip() {
137        let d = MetadataStdDescriptor {
138            metadata_input_leak_rate: 0x000A_BCDE,
139            metadata_buffer_size: 0x003F_0000,
140            metadata_output_leak_rate: 0x0000_1234,
141        };
142        let mut buf = vec![0u8; d.serialized_len()];
143        d.serialize_into(&mut buf).unwrap();
144        let reparsed = MetadataStdDescriptor::parse(&buf).unwrap();
145        assert_eq!(d, reparsed);
146    }
147
148    #[test]
149    fn serialize_round_trip_zero_upper_bits() {
150        // Ensure top 2 bits of each 3-byte group are zero on serialization
151        let d = MetadataStdDescriptor {
152            metadata_input_leak_rate: 0xFFFF_FFFF, // test mask
153            metadata_buffer_size: 0xFFFF_FFFF,
154            metadata_output_leak_rate: 0xFFFF_FFFF,
155        };
156        let mut buf = vec![0u8; d.serialized_len()];
157        d.serialize_into(&mut buf).unwrap();
158        let reparsed = MetadataStdDescriptor::parse(&buf).unwrap();
159        assert_eq!(reparsed.metadata_input_leak_rate, 0x003F_FFFF);
160        assert_eq!(reparsed.metadata_buffer_size, 0x003F_FFFF);
161        assert_eq!(reparsed.metadata_output_leak_rate, 0x003F_FFFF);
162    }
163
164    #[test]
165    fn serialize_rejects_small_buffer() {
166        let d = MetadataStdDescriptor {
167            metadata_input_leak_rate: 0,
168            metadata_buffer_size: 0,
169            metadata_output_leak_rate: 0,
170        };
171        let mut tiny = vec![0u8; 8];
172        let err = d.serialize_into(&mut tiny).unwrap_err();
173        assert!(matches!(err, Error::OutputBufferTooSmall { .. }));
174    }
175}
dvb_si/descriptors/metadata_std.rs

dvb_si/descriptors/
metadata_std.rs
