dvb_subtitle/segments/
stuffing.rs

1//! Stuffing segment — ETSI EN 300 743 Table 7 (segment_type 0xFF).
2//!
3//! Stuffing bytes have no semantic meaning; their segment_type is 0xFF.
4//! The body is opaque raw bytes.
5
6use crate::error::{Error, Result};
7use broadcast_common::{Parse, Serialize};
8
9/// The stuffing segment_type.
10pub const SEGMENT_TYPE: u8 = 0xFF;
11/// Header: sync_byte(1) + segment_type(1) + page_id(2) + segment_length(2) = 6 bytes.
12pub const HEADER_LEN: usize = 6;
13
14/// A stuffing segment — opaque data bytes following the header.
15#[derive(Debug, Clone, PartialEq, Eq)]
16#[cfg_attr(feature = "serde", derive(serde::Serialize))]
17pub struct StuffingSegment<'a> {
18    /// The page_id from the segment header.
19    pub page_id: u16,
20    /// Opaque stuffing data bytes.
21    #[cfg_attr(feature = "serde", serde(skip))]
22    pub data: &'a [u8],
23}
24
25impl<'a> Parse<'a> for StuffingSegment<'a> {
26    type Error = Error;
27
28    fn parse(bytes: &'a [u8]) -> Result<Self> {
29        if bytes.len() < HEADER_LEN {
30            return Err(Error::BufferTooShort {
31                need: HEADER_LEN,
32                have: bytes.len(),
33                what: "stuffing_segment",
34            });
35        }
36        if bytes[1] != SEGMENT_TYPE {
37            return Err(Error::UnknownSegmentType(bytes[1]));
38        }
39        let page_id = u16::from_be_bytes([bytes[2], bytes[3]]);
40        let segment_length = u16::from_be_bytes([bytes[4], bytes[5]]) as usize;
41        let total = HEADER_LEN + segment_length;
42        if bytes.len() < total {
43            return Err(Error::BufferTooShort {
44                need: total,
45                have: bytes.len(),
46                what: "stuffing_segment data",
47            });
48        }
49        Ok(StuffingSegment {
50            page_id,
51            data: &bytes[HEADER_LEN..total],
52        })
53    }
54}
55
56impl Serialize for StuffingSegment<'_> {
57    type Error = Error;
58
59    fn serialized_len(&self) -> usize {
60        HEADER_LEN + self.data.len()
61    }
62
63    fn serialize_into(&self, buf: &mut [u8]) -> core::result::Result<usize, Self::Error> {
64        let len = self.serialized_len();
65        if buf.len() < len {
66            return Err(Error::BufferTooShort {
67                need: len,
68                have: buf.len(),
69                what: "stuffing_segment serialize",
70            });
71        }
72        buf[0] = 0x0F;
73        buf[1] = SEGMENT_TYPE;
74        buf[2..4].copy_from_slice(&self.page_id.to_be_bytes());
75        let seg_len = self.data.len() as u16;
76        buf[4..6].copy_from_slice(&seg_len.to_be_bytes());
77        buf[6..len].copy_from_slice(self.data);
78        Ok(len)
79    }
80}
81
82#[cfg(test)]
83mod tests {
84    use super::*;
85    use broadcast_common::{Parse, Serialize};
86
87    #[test]
88    fn round_trip() {
89        let bytes = [0x0F, 0xFF, 0x00, 0x00, 0x00, 0x03, 0xAA, 0xBB, 0xCC];
90        let seg = StuffingSegment::parse(&bytes).unwrap();
91        assert_eq!(seg.data, &[0xAA, 0xBB, 0xCC]);
92        let out = seg.to_bytes();
93        assert_eq!(out, bytes);
94
95        // Biting test: page_id changes output
96        let mut seg2 = seg.clone();
97        seg2.page_id = 9;
98        let out2 = seg2.to_bytes();
99        assert_ne!(out2, bytes);
100        let reparse = StuffingSegment::parse(&out2).unwrap();
101        assert_eq!(reparse.page_id, 9);
102    }
103}
dvb_subtitle/segments/stuffing.rs

dvb_subtitle/segments/
stuffing.rs
