dvb_si/descriptors/
application_signalling.rs

1//! Application Signalling Descriptor — ETSI TS 102 809 §5.3.5.2.1, Table 17
2//! (tag 0x6F).
3//!
4//! Carried in the PMT to point at the AIT and enumerate the application types
5//! present alongside the AIT version expected. Per ts_102_809_apps.md
6//! "Table 17 — Application signalling descriptor syntax" (PDF p. 37) each loop
7//! entry is 3 bytes: reserved_future_use(1) + application_type(15), then
8//! reserved_future_use(3) + AIT_version_number(5).
9
10use crate::error::{Error, Result};
11use crate::traits::Descriptor;
12use dvb_common::{Parse, Serialize};
13
14/// Descriptor tag for application_signalling_descriptor.
15pub const TAG: u8 = 0x6F;
16const HEADER_LEN: usize = 2;
17const ENTRY_LEN: usize = 3;
18
19/// Largest representable 15-bit application_type.
20const APPLICATION_TYPE_MAX: u16 = 0x7FFF;
21/// Largest representable 5-bit AIT_version_number.
22const AIT_VERSION_MAX: u8 = 0x1F;
23
24/// One application-signalling loop entry.
25#[derive(Debug, Clone, PartialEq, Eq)]
26#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
27pub struct ApplicationSignallingEntry {
28    /// 15-bit application_type (e.g. 0x0001 = DVB-J, 0x0010 = DVB-HTML).
29    pub application_type: u16,
30    /// 5-bit AIT_version_number this entry refers to.
31    pub ait_version_number: u8,
32}
33
34/// Application Signalling Descriptor.
35#[derive(Debug, Clone, PartialEq, Eq)]
36#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
37pub struct ApplicationSignallingDescriptor {
38    /// Entries in wire order.
39    pub entries: Vec<ApplicationSignallingEntry>,
40}
41
42impl<'a> Parse<'a> for ApplicationSignallingDescriptor {
43    type Error = crate::error::Error;
44    fn parse(bytes: &'a [u8]) -> Result<Self> {
45        if bytes.len() < HEADER_LEN {
46            return Err(Error::BufferTooShort {
47                need: HEADER_LEN,
48                have: bytes.len(),
49                what: "ApplicationSignallingDescriptor header",
50            });
51        }
52        if bytes[0] != TAG {
53            return Err(Error::InvalidDescriptor {
54                tag: bytes[0],
55                reason: "unexpected tag for application_signalling_descriptor",
56            });
57        }
58        let length = bytes[1] as usize;
59        let end = HEADER_LEN + length;
60        if bytes.len() < end {
61            return Err(Error::BufferTooShort {
62                need: end,
63                have: bytes.len(),
64                what: "ApplicationSignallingDescriptor body",
65            });
66        }
67        if length % ENTRY_LEN != 0 {
68            return Err(Error::InvalidDescriptor {
69                tag: TAG,
70                reason: "application_signalling_descriptor length must be a multiple of 3",
71            });
72        }
73        let body = &bytes[HEADER_LEN..end];
74        let mut entries = Vec::with_capacity(length / ENTRY_LEN);
75        for chunk in body.chunks_exact(ENTRY_LEN) {
76            // reserved_future_use(1) ignored on parse.
77            let application_type = u16::from_be_bytes([chunk[0], chunk[1]]) & APPLICATION_TYPE_MAX;
78            // reserved_future_use(3) ignored on parse.
79            let ait_version_number = chunk[2] & AIT_VERSION_MAX;
80            entries.push(ApplicationSignallingEntry {
81                application_type,
82                ait_version_number,
83            });
84        }
85        Ok(Self { entries })
86    }
87}
88
89impl Serialize for ApplicationSignallingDescriptor {
90    type Error = crate::error::Error;
91    fn serialized_len(&self) -> usize {
92        HEADER_LEN + self.entries.len() * ENTRY_LEN
93    }
94
95    fn serialize_into(&self, buf: &mut [u8]) -> Result<usize> {
96        for e in &self.entries {
97            if e.application_type > APPLICATION_TYPE_MAX {
98                return Err(Error::InvalidDescriptor {
99                    tag: TAG,
100                    reason: "application_type exceeds 15 bits",
101                });
102            }
103            if e.ait_version_number > AIT_VERSION_MAX {
104                return Err(Error::InvalidDescriptor {
105                    tag: TAG,
106                    reason: "ait_version_number exceeds 5 bits",
107                });
108            }
109        }
110        if self.entries.len() * ENTRY_LEN > u8::MAX as usize {
111            return Err(Error::InvalidDescriptor {
112                tag: TAG,
113                reason: "application_signalling_descriptor body exceeds 255 bytes",
114            });
115        }
116        let len = self.serialized_len();
117        if buf.len() < len {
118            return Err(Error::OutputBufferTooSmall {
119                need: len,
120                have: buf.len(),
121            });
122        }
123        buf[0] = TAG;
124        buf[1] = (self.entries.len() * ENTRY_LEN) as u8;
125        let mut pos = HEADER_LEN;
126        for e in &self.entries {
127            // reserved_future_use(1) emitted as 1.
128            let word = 0x8000 | (e.application_type & APPLICATION_TYPE_MAX);
129            buf[pos..pos + 2].copy_from_slice(&word.to_be_bytes());
130            // reserved_future_use(3) emitted as 1s.
131            buf[pos + 2] = 0xE0 | (e.ait_version_number & AIT_VERSION_MAX);
132            pos += ENTRY_LEN;
133        }
134        Ok(len)
135    }
136}
137
138impl<'a> Descriptor<'a> for ApplicationSignallingDescriptor {
139    const TAG: u8 = TAG;
140    fn descriptor_length(&self) -> u8 {
141        (self.entries.len() * ENTRY_LEN) as u8
142    }
143}
144
145#[cfg(test)]
146mod tests {
147    use super::*;
148
149    #[test]
150    fn parse_single_entry() {
151        // application_type=0x0010 (DVB-HTML), AIT_version=3, reserved bits set.
152        let bytes = [TAG, 3, 0x80, 0x10, 0xE3];
153        let d = ApplicationSignallingDescriptor::parse(&bytes).unwrap();
154        assert_eq!(d.entries.len(), 1);
155        assert_eq!(d.entries[0].application_type, 0x0010);
156        assert_eq!(d.entries[0].ait_version_number, 3);
157    }
158
159    #[test]
160    fn parse_multiple_entries() {
161        let bytes = [TAG, 6, 0x00, 0x01, 0x05, 0x7F, 0xFF, 0x1F];
162        let d = ApplicationSignallingDescriptor::parse(&bytes).unwrap();
163        assert_eq!(d.entries.len(), 2);
164        assert_eq!(d.entries[0].application_type, 0x0001);
165        assert_eq!(d.entries[0].ait_version_number, 5);
166        assert_eq!(d.entries[1].application_type, 0x7FFF);
167        assert_eq!(d.entries[1].ait_version_number, 0x1F);
168    }
169
170    #[test]
171    fn parse_ignores_reserved_bits() {
172        // top bit of word + top 3 bits of version byte are reserved → masked out.
173        let bytes = [TAG, 3, 0xFF, 0xFF, 0xFF];
174        let d = ApplicationSignallingDescriptor::parse(&bytes).unwrap();
175        assert_eq!(d.entries[0].application_type, 0x7FFF);
176        assert_eq!(d.entries[0].ait_version_number, 0x1F);
177    }
178
179    #[test]
180    fn parse_rejects_wrong_tag() {
181        assert!(matches!(
182            ApplicationSignallingDescriptor::parse(&[0x70, 0]).unwrap_err(),
183            Error::InvalidDescriptor { tag: 0x70, .. }
184        ));
185    }
186
187    #[test]
188    fn parse_rejects_length_not_multiple_of_3() {
189        let bytes = [TAG, 4, 0, 0, 0, 0];
190        assert!(matches!(
191            ApplicationSignallingDescriptor::parse(&bytes).unwrap_err(),
192            Error::InvalidDescriptor { .. }
193        ));
194    }
195
196    #[test]
197    fn empty_descriptor_valid() {
198        let bytes = [TAG, 0];
199        let d = ApplicationSignallingDescriptor::parse(&bytes).unwrap();
200        assert!(d.entries.is_empty());
201    }
202
203    #[test]
204    fn serialize_round_trip() {
205        let d = ApplicationSignallingDescriptor {
206            entries: vec![
207                ApplicationSignallingEntry {
208                    application_type: 0x0001,
209                    ait_version_number: 7,
210                },
211                ApplicationSignallingEntry {
212                    application_type: 0x0010,
213                    ait_version_number: 0,
214                },
215            ],
216        };
217        let mut buf = vec![0u8; d.serialized_len()];
218        d.serialize_into(&mut buf).unwrap();
219        assert_eq!(ApplicationSignallingDescriptor::parse(&buf).unwrap(), d);
220    }
221
222    #[test]
223    fn serialize_rejects_application_type_over_range() {
224        let d = ApplicationSignallingDescriptor {
225            entries: vec![ApplicationSignallingEntry {
226                application_type: 0x8000,
227                ait_version_number: 0,
228            }],
229        };
230        let mut buf = vec![0u8; d.serialized_len()];
231        assert!(matches!(
232            d.serialize_into(&mut buf).unwrap_err(),
233            Error::InvalidDescriptor { .. }
234        ));
235    }
236
237    #[test]
238    fn serialize_rejects_ait_version_over_range() {
239        let d = ApplicationSignallingDescriptor {
240            entries: vec![ApplicationSignallingEntry {
241                application_type: 0,
242                ait_version_number: 0x20,
243            }],
244        };
245        let mut buf = vec![0u8; d.serialized_len()];
246        assert!(matches!(
247            d.serialize_into(&mut buf).unwrap_err(),
248            Error::InvalidDescriptor { .. }
249        ));
250    }
251
252    #[cfg(feature = "serde")]
253    #[test]
254    fn serde_round_trip() {
255        let d = ApplicationSignallingDescriptor {
256            entries: vec![ApplicationSignallingEntry {
257                application_type: 0x0010,
258                ait_version_number: 4,
259            }],
260        };
261        let j = serde_json::to_string(&d).unwrap();
262        let back: ApplicationSignallingDescriptor = serde_json::from_str(&j).unwrap();
263        assert_eq!(back, d);
264    }
265}
dvb_si/descriptors/application_signalling.rs

dvb_si/descriptors/
application_signalling.rs
