dvb_subtitle/segments/
page_composition.rs

1//! Page Composition Segment — ETSI EN 300 743 §7.2.2, Table 9 (segment_type 0x10).
2
3use crate::error::{Error, Result};
4use broadcast_common::len::{need_in, need_out};
5use broadcast_common::{Parse, Serialize};
6
7/// The page_composition_segment segment_type.
8pub const SEGMENT_TYPE: u8 = 0x10;
9/// Header: sync_byte(1) + segment_type(1) + page_id(2) + segment_length(2) = 6 bytes.
10pub const HEADER_LEN: usize = 6;
11/// Fixed after header: page_time_out(1) + page_version(4b)+page_state(2b)+reserved(2b) = 2 bytes.
12pub const FIXED_LEN: usize = 2;
13/// Each region entry: region_id(1) + reserved(1) + region_horizontal_address(2) + region_vertical_address(2) = 6 bytes.
14pub const REGION_ENTRY_LEN: usize = 6;
15
16/// Page state as defined in Table 10.
17#[derive(Debug, Clone, Copy, PartialEq, Eq)]
18#[cfg_attr(feature = "serde", derive(serde::Serialize))]
19#[repr(u8)]
20#[non_exhaustive]
21pub enum PageState {
22    /// Normal case — page update.
23    Normal = 0x00,
24    /// Acquisition point — page refresh.
25    Acquisition = 0x01,
26    /// Mode change — new page.
27    ModeChange = 0x02,
28    /// Reserved.
29    Reserved(u8),
30}
31
32impl PageState {
33    /// Human-readable name.
34    #[must_use]
35    pub fn name(&self) -> &'static str {
36        match self {
37            Self::Normal => "normal",
38            Self::Acquisition => "acquisition",
39            Self::ModeChange => "mode_change",
40            Self::Reserved(_) => "reserved",
41        }
42    }
43
44    fn to_bits(self) -> u8 {
45        match self {
46            Self::Normal => 0x00,
47            Self::Acquisition => 0x01,
48            Self::ModeChange => 0x02,
49            Self::Reserved(v) => v,
50        }
51    }
52}
53
54broadcast_common::impl_spec_display!(PageState, Reserved);
55
56/// A single region entry within a page composition segment.
57#[derive(Debug, Clone, PartialEq, Eq)]
58#[cfg_attr(feature = "serde", derive(serde::Serialize))]
59pub struct PageRegionEntry {
60    /// Region identifier.
61    pub region_id: u8,
62    /// Reserved byte in the region entry (must be preserved for round-trip).
63    pub reserved: u8,
64    /// Horizontal address of top-left pixel.
65    pub region_horizontal_address: u16,
66    /// Vertical address of top line.
67    pub region_vertical_address: u16,
68}
69
70impl PageRegionEntry {
71    fn serialize_into(&self, buf: &mut [u8]) {
72        buf[0] = self.region_id;
73        buf[1] = self.reserved;
74        buf[2..4].copy_from_slice(&self.region_horizontal_address.to_be_bytes());
75        buf[4..6].copy_from_slice(&self.region_vertical_address.to_be_bytes());
76    }
77
78    fn parse(bytes: &[u8]) -> Result<Self> {
79        need_in(bytes, REGION_ENTRY_LEN, "page_region_entry")?;
80        let reserved = bytes[1];
81        Ok(PageRegionEntry {
82            region_id: bytes[0],
83            reserved,
84            region_horizontal_address: u16::from_be_bytes([bytes[2], bytes[3]]),
85            region_vertical_address: u16::from_be_bytes([bytes[4], bytes[5]]),
86        })
87    }
88}
89
90/// Page Composition Segment.
91#[derive(Debug, Clone, PartialEq, Eq)]
92#[cfg_attr(feature = "serde", derive(serde::Serialize))]
93pub struct PageCompositionSegment {
94    /// The page_id (from generic segment header).
95    pub page_id: u16,
96    /// Time-out period in seconds.
97    pub page_time_out: u8,
98    /// Version number (modulo 16).
99    pub page_version_number: u8,
100    /// Page state.
101    pub page_state: PageState,
102    /// Reserved bits in body byte 1 (bits `[1:0]`).
103    pub reserved: u8,
104    /// Region entries.
105    pub regions: alloc::vec::Vec<PageRegionEntry>,
106}
107
108impl<'a> Parse<'a> for PageCompositionSegment {
109    type Error = Error;
110
111    fn parse(bytes: &'a [u8]) -> Result<Self> {
112        need_in(bytes, HEADER_LEN + FIXED_LEN, "page_composition_segment")?;
113        if bytes[0] != crate::pes_data_field::SYNC_BYTE {
114            return Err(Error::InvalidSync(broadcast_common::error::InvalidSync {
115                what: "sync_byte",
116                expected: u32::from(crate::pes_data_field::SYNC_BYTE),
117                found: u32::from(bytes[0]),
118            }));
119        }
120        if bytes[1] != SEGMENT_TYPE {
121            return Err(Error::UnknownSegmentType(bytes[1]));
122        }
123        let page_id = u16::from_be_bytes([bytes[2], bytes[3]]);
124        let segment_length = u16::from_be_bytes([bytes[4], bytes[5]]) as usize;
125        let total = HEADER_LEN + segment_length;
126        need_in(bytes, total, "page_composition_segment data")?;
127        let body = &bytes[HEADER_LEN..HEADER_LEN + segment_length];
128        need_in(body, FIXED_LEN, "page_composition_segment body")?;
129        let page_time_out = body[0];
130        let page_version_number = body[1] >> 4;
131        let page_state_bits = (body[1] >> 2) & 0x03;
132        let reserved = body[1] & 0x03;
133        let page_state = match page_state_bits {
134            0x00 => PageState::Normal,
135            0x01 => PageState::Acquisition,
136            0x02 => PageState::ModeChange,
137            v => PageState::Reserved(v),
138        };
139
140        let region_data = &body[FIXED_LEN..];
141        let region_count = region_data.len() / REGION_ENTRY_LEN;
142        // Table 9's region loop is `while (processed_length < segment_length)`
143        // over whole 6-byte entries — there is no stuffing/suffix provision,
144        // so a remainder means the segment is malformed, not that trailing
145        // bytes should be captured (#1108/DS-W6: this used to be checked
146        // here and then ALSO stored in a `suffix` field that, because of
147        // this very check, could never end up holding anything).
148        if !region_data.len().is_multiple_of(REGION_ENTRY_LEN) {
149            return Err(Error::BufferTooShort(
150                broadcast_common::error::BufferTooShort {
151                    need: (region_count + 1) * REGION_ENTRY_LEN,
152                    have: region_data.len(),
153                    what: "page_composition_segment regions",
154                },
155            ));
156        }
157        let mut regions = alloc::vec::Vec::with_capacity(region_count);
158        for i in 0..region_count {
159            let entry_bytes = &region_data[i * REGION_ENTRY_LEN..][..REGION_ENTRY_LEN];
160            regions.push(PageRegionEntry::parse(entry_bytes)?);
161        }
162
163        Ok(PageCompositionSegment {
164            page_id,
165            page_time_out,
166            page_version_number,
167            page_state,
168            reserved,
169            regions,
170        })
171    }
172}
173
174impl Serialize for PageCompositionSegment {
175    type Error = Error;
176
177    fn serialized_len(&self) -> usize {
178        HEADER_LEN + FIXED_LEN + self.regions.len() * REGION_ENTRY_LEN
179    }
180
181    fn serialize_into(&self, buf: &mut [u8]) -> core::result::Result<usize, Self::Error> {
182        let len = self.serialized_len();
183        need_out(buf, len)?;
184        buf[0] = 0x0F;
185        buf[1] = SEGMENT_TYPE;
186        buf[2..4].copy_from_slice(&self.page_id.to_be_bytes());
187        let seg_len = crate::segments::check_segment_length(len - HEADER_LEN)?;
188        buf[4..6].copy_from_slice(&seg_len.to_be_bytes());
189
190        buf[6] = self.page_time_out;
191        buf[7] = (broadcast_common::len::fit_mask(
192            self.page_version_number,
193            0x0F,
194            "page_version_number",
195        )? << 4)
196            | (broadcast_common::len::fit_mask(self.page_state.to_bits(), 0x03, "page_state")?
197                << 2)
198            | broadcast_common::len::fit_mask(self.reserved, 0x03, "reserved")?;
199
200        for (i, region) in self.regions.iter().enumerate() {
201            let off = HEADER_LEN + FIXED_LEN + i * REGION_ENTRY_LEN;
202            region.serialize_into(&mut buf[off..off + REGION_ENTRY_LEN]);
203        }
204        Ok(len)
205    }
206}
207
208#[cfg(test)]
209mod tests {
210    use super::*;
211    use broadcast_common::{Parse, Serialize};
212
213    #[test]
214    fn round_trip() {
215        let bytes = [
216            0x0F, 0x10, 0x00, 0x01, 0x00, 0x0E, 0x0A, 0x04, 0x01, 0x00, 0x00, 0x64, 0x00, 0x32,
217            0x02, 0x00, 0x00, 0xC8, 0x00, 0x96,
218        ];
219        let seg = PageCompositionSegment::parse(&bytes).unwrap();
220        assert_eq!(seg.page_time_out, 10);
221        assert_eq!(seg.page_version_number, 0);
222        assert_eq!(seg.page_state, PageState::Acquisition);
223        assert_eq!(seg.regions.len(), 2);
224        assert_eq!(seg.regions[0].region_id, 1);
225        assert_eq!(seg.regions[0].region_horizontal_address, 100);
226        assert_eq!(seg.regions[0].region_vertical_address, 50);
227        let out = seg.try_to_bytes().unwrap();
228        assert_eq!(out, bytes);
229
230        // Biting test: mutate page_time_out changes output
231        let mut seg2 = seg.clone();
232        seg2.page_time_out = 20;
233        let out2 = seg2.try_to_bytes().unwrap();
234        assert_ne!(out2, bytes);
235        let reparse = PageCompositionSegment::parse(&out2).unwrap();
236        assert_eq!(reparse.page_time_out, 20);
237    }
238
239    /// DS-W2 (#1108): sync_byte wasn't checked by any typed segment parser.
240    #[test]
241    fn rejects_bad_sync_byte() {
242        let bytes = [
243            0x00, 0x10, 0x00, 0x01, 0x00, 0x0E, 0x0A, 0x04, 0x01, 0x00, 0x00, 0x64, 0x00, 0x32,
244            0x02, 0x00, 0x00, 0xC8, 0x00, 0x96,
245        ];
246        assert!(matches!(
247            PageCompositionSegment::parse(&bytes),
248            Err(Error::InvalidSync(broadcast_common::error::InvalidSync {
249                found: 0x00,
250                ..
251            }))
252        ));
253    }
254}
dvb_subtitle/segments/page_composition.rs

dvb_subtitle/segments/
page_composition.rs
