dvb_si/descriptors/
xait_location.rs

1//! XAIT Location Descriptor — ETSI TS 102 727 §10.17.6, Table 96 (tag 0x7D).
2//!
3//! Points at the service carrying the XAIT (deprecated MHP discovery
4//! mechanism). Per the MHP PDF (etsi_ts_102_727_v01.01.01, p. 185, Table 96)
5//! the body is a fixed 5 bytes:
6//!
7//! ```text
8//! xait_original_network_id(16) + xait_service_id(16)
9//!   + xait_version_number(5) + xait_update_policy(3)
10//! ```
11//!
12//! xait_update_policy values (Table 97, p. 185): 0 = reload immediately on
13//! version change, 1 = ignore version changes until reset, 2..=7 reserved.
14
15use crate::error::{Error, Result};
16use crate::traits::Descriptor;
17use dvb_common::{Parse, Serialize};
18
19/// Descriptor tag for xait_location_descriptor.
20pub const TAG: u8 = 0x7D;
21const HEADER_LEN: usize = 2;
22const BODY_LEN: usize = 5;
23
24/// Largest representable 5-bit xait_version_number.
25const VERSION_MAX: u8 = 0x1F;
26/// Largest representable 3-bit xait_update_policy.
27const UPDATE_POLICY_MAX: u8 = 0x07;
28
29/// XAIT Location Descriptor.
30#[derive(Debug, Clone, PartialEq, Eq)]
31#[cfg_attr(feature = "serde", derive(serde::Serialize))]
32pub struct XaitLocationDescriptor {
33    /// 16-bit original_network_id of the service carrying the XAIT.
34    pub xait_original_network_id: u16,
35    /// 16-bit service_id of the service carrying the XAIT.
36    pub xait_service_id: u16,
37    /// 5-bit version number of the referenced XAIT.
38    pub xait_version_number: u8,
39    /// 3-bit update policy (Table 97).
40    pub xait_update_policy: u8,
41}
42
43impl<'a> Parse<'a> for XaitLocationDescriptor {
44    type Error = crate::error::Error;
45    fn parse(bytes: &'a [u8]) -> Result<Self> {
46        if bytes.len() < HEADER_LEN {
47            return Err(Error::BufferTooShort {
48                need: HEADER_LEN,
49                have: bytes.len(),
50                what: "XaitLocationDescriptor header",
51            });
52        }
53        if bytes[0] != TAG {
54            return Err(Error::InvalidDescriptor {
55                tag: bytes[0],
56                reason: "unexpected tag for xait_location_descriptor",
57            });
58        }
59        let length = bytes[1] as usize;
60        let end = HEADER_LEN + length;
61        if bytes.len() < end {
62            return Err(Error::BufferTooShort {
63                need: end,
64                have: bytes.len(),
65                what: "XaitLocationDescriptor body",
66            });
67        }
68        if length < BODY_LEN {
69            return Err(Error::InvalidDescriptor {
70                tag: TAG,
71                reason: "xait_location_descriptor body shorter than 5 bytes",
72            });
73        }
74        let body = &bytes[HEADER_LEN..end];
75        let xait_original_network_id = u16::from_be_bytes([body[0], body[1]]);
76        let xait_service_id = u16::from_be_bytes([body[2], body[3]]);
77        let xait_version_number = (body[4] >> 3) & VERSION_MAX;
78        let xait_update_policy = body[4] & UPDATE_POLICY_MAX;
79        Ok(Self {
80            xait_original_network_id,
81            xait_service_id,
82            xait_version_number,
83            xait_update_policy,
84        })
85    }
86}
87
88impl Serialize for XaitLocationDescriptor {
89    type Error = crate::error::Error;
90    fn serialized_len(&self) -> usize {
91        HEADER_LEN + BODY_LEN
92    }
93
94    fn serialize_into(&self, buf: &mut [u8]) -> Result<usize> {
95        if self.xait_version_number > VERSION_MAX {
96            return Err(Error::InvalidDescriptor {
97                tag: TAG,
98                reason: "xait_version_number exceeds 5 bits",
99            });
100        }
101        if self.xait_update_policy > UPDATE_POLICY_MAX {
102            return Err(Error::InvalidDescriptor {
103                tag: TAG,
104                reason: "xait_update_policy exceeds 3 bits",
105            });
106        }
107        let len = self.serialized_len();
108        if buf.len() < len {
109            return Err(Error::OutputBufferTooSmall {
110                need: len,
111                have: buf.len(),
112            });
113        }
114        buf[0] = TAG;
115        buf[1] = BODY_LEN as u8;
116        buf[2..4].copy_from_slice(&self.xait_original_network_id.to_be_bytes());
117        buf[4..6].copy_from_slice(&self.xait_service_id.to_be_bytes());
118        buf[6] = ((self.xait_version_number & VERSION_MAX) << 3)
119            | (self.xait_update_policy & UPDATE_POLICY_MAX);
120        Ok(len)
121    }
122}
123
124impl<'a> Descriptor<'a> for XaitLocationDescriptor {
125    const TAG: u8 = TAG;
126    fn descriptor_length(&self) -> u8 {
127        BODY_LEN as u8
128    }
129}
130
131impl<'a> crate::traits::DescriptorDef<'a> for XaitLocationDescriptor {
132    const TAG: u8 = TAG;
133    const NAME: &'static str = "XAIT_LOCATION";
134}
135
136#[cfg(test)]
137mod tests {
138    use super::*;
139
140    #[test]
141    fn parse_extracts_fields() {
142        // onid=0x2024, sid=0x1234, version=5, policy=1.
143        let bytes = [TAG, 5, 0x20, 0x24, 0x12, 0x34, (5 << 3) | 1];
144        let d = XaitLocationDescriptor::parse(&bytes).unwrap();
145        assert_eq!(d.xait_original_network_id, 0x2024);
146        assert_eq!(d.xait_service_id, 0x1234);
147        assert_eq!(d.xait_version_number, 5);
148        assert_eq!(d.xait_update_policy, 1);
149    }
150
151    #[test]
152    fn parse_ignores_trailing_bytes() {
153        let bytes = [TAG, 6, 0x00, 0x01, 0x00, 0x02, 0x00, 0xFF];
154        let d = XaitLocationDescriptor::parse(&bytes).unwrap();
155        assert_eq!(d.xait_original_network_id, 0x0001);
156        assert_eq!(d.xait_service_id, 0x0002);
157        assert_eq!(d.xait_version_number, 0);
158        assert_eq!(d.xait_update_policy, 0);
159    }
160
161    #[test]
162    fn parse_rejects_wrong_tag() {
163        let bytes = [0x7C, 5, 0, 0, 0, 0, 0];
164        assert!(matches!(
165            XaitLocationDescriptor::parse(&bytes).unwrap_err(),
166            Error::InvalidDescriptor { tag: 0x7C, .. }
167        ));
168    }
169
170    #[test]
171    fn parse_rejects_body_too_short() {
172        let bytes = [TAG, 4, 0, 0, 0, 0];
173        assert!(matches!(
174            XaitLocationDescriptor::parse(&bytes).unwrap_err(),
175            Error::InvalidDescriptor { .. }
176        ));
177    }
178
179    #[test]
180    fn parse_rejects_length_overrunning_buffer() {
181        let bytes = [TAG, 5, 0, 0, 0];
182        assert!(matches!(
183            XaitLocationDescriptor::parse(&bytes).unwrap_err(),
184            Error::BufferTooShort { .. }
185        ));
186    }
187
188    #[test]
189    fn serialize_round_trip() {
190        let d = XaitLocationDescriptor {
191            xait_original_network_id: 0x233A,
192            xait_service_id: 0x4470,
193            xait_version_number: 0x1F,
194            xait_update_policy: 0,
195        };
196        let mut buf = vec![0u8; d.serialized_len()];
197        d.serialize_into(&mut buf).unwrap();
198        assert_eq!(XaitLocationDescriptor::parse(&buf).unwrap(), d);
199    }
200
201    #[test]
202    fn serialize_rejects_version_over_range() {
203        let d = XaitLocationDescriptor {
204            xait_original_network_id: 0,
205            xait_service_id: 0,
206            xait_version_number: 0x20,
207            xait_update_policy: 0,
208        };
209        let mut buf = vec![0u8; d.serialized_len()];
210        assert!(matches!(
211            d.serialize_into(&mut buf).unwrap_err(),
212            Error::InvalidDescriptor { .. }
213        ));
214    }
215
216    #[test]
217    fn serialize_rejects_update_policy_over_range() {
218        let d = XaitLocationDescriptor {
219            xait_original_network_id: 0,
220            xait_service_id: 0,
221            xait_version_number: 0,
222            xait_update_policy: 0x08,
223        };
224        let mut buf = vec![0u8; d.serialized_len()];
225        assert!(matches!(
226            d.serialize_into(&mut buf).unwrap_err(),
227            Error::InvalidDescriptor { .. }
228        ));
229    }
230
231    #[cfg(feature = "serde")]
232    #[test]
233    fn serde_round_trip() {
234        let d = XaitLocationDescriptor {
235            xait_original_network_id: 0x0001,
236            xait_service_id: 0x0539,
237            xait_version_number: 3,
238            xait_update_policy: 1,
239        };
240        let j = serde_json::to_string(&d).unwrap();
241        // Serialize-only: assert the emitted JSON re-parses (serialize-stable).
242        let _v: serde_json::Value = serde_json::from_str(&j).unwrap();
243    }
244}
dvb_si/descriptors/xait_location.rs

dvb_si/descriptors/
xait_location.rs
