dvb_si/descriptors/
frequency_list.rs

1//! Frequency List Descriptor — ETSI EN 300 468 §6.2.17 (tag 0x62).
2//!
3//! Carried inside the NIT's transport_stream_loop second descriptor loop.
4//! Enumerates alternative centre frequencies on which the TS can be found,
5//! for handover when coverage changes.
6
7use super::descriptor_body;
8use crate::error::{Error, Result};
9use alloc::vec::Vec;
10use dvb_common::{Parse, Serialize};
11
12/// Descriptor tag for frequency_list_descriptor.
13pub const TAG: u8 = 0x62;
14/// Length of the header (tag byte + length byte).
15pub const HEADER_LEN: usize = 2;
16/// Length of the coding_type byte inside the descriptor body.
17pub const CODING_BYTE_LEN: usize = 1;
18/// Length of a single frequency entry in bytes.
19pub const ENTRY_LEN: usize = 4;
20/// Mask for the coding_type bits (bottom 2 bits); the top 6 bits are reserved.
21pub const CODING_TYPE_MASK: u8 = 0x03;
22/// Reserved bits (top 6 of the coding byte). Ignored on parse, set to 1 on serialize.
23pub const RESERVED_BITS_MASK: u8 = 0xFC;
24
25/// Coding type selects the interpretation of each 4-byte frequency entry.
26#[derive(Debug, Clone, Copy, PartialEq, Eq)]
27#[cfg_attr(feature = "serde", derive(serde::Serialize))]
28#[non_exhaustive]
29pub enum CodingType {
30    /// Not defined (coding_type = 0b00).
31    Undefined,
32    /// Satellite — 8 BCD digits, 10 kHz resolution (§6.2.13.2).
33    Satellite,
34    /// Cable — 8 BCD digits, 100 Hz resolution (§6.2.13.3).
35    Cable,
36    /// Terrestrial — binary uimsbf 32-bit, 10 Hz resolution (§6.2.13.4).
37    Terrestrial,
38}
39
40impl CodingType {
41    /// Human-readable spec label (ETSI EN 300 468 §6.2.17).
42    #[must_use]
43    pub fn name(self) -> &'static str {
44        match self {
45            Self::Undefined => "not defined",
46            Self::Satellite => "satellite",
47            Self::Cable => "cable",
48            Self::Terrestrial => "terrestrial",
49        }
50    }
51}
52dvb_common::impl_spec_display!(CodingType);
53
54/// Frequency List Descriptor.
55#[derive(Debug, Clone, PartialEq, Eq)]
56#[cfg_attr(feature = "serde", derive(serde::Serialize))]
57pub struct FrequencyListDescriptor {
58    /// Interpretation of every `centre_frequencies_bcd` entry.
59    pub coding_type: CodingType,
60    /// Raw 4-byte centre_frequency entries in wire order. Interpretation
61    /// depends on `coding_type`: BCD for Satellite/Cable, binary for Terrestrial.
62    pub centre_frequencies_bcd: Vec<[u8; 4]>,
63}
64
65impl FrequencyListDescriptor {
66    /// Hz per BCD-decoded unit for Satellite or Cable, or `None` for
67    /// Undefined / Terrestrial (Terrestrial uses binary encoding, not BCD).
68    fn hz_per_unit_bcd(&self) -> Option<u64> {
69        match self.coding_type {
70            CodingType::Satellite => Some(10_000),
71            CodingType::Cable => Some(100),
72            CodingType::Terrestrial | CodingType::Undefined => None,
73        }
74    }
75
76    /// Decode every `centre_frequencies_bcd` entry to Hz, interpreted per
77    /// `coding_type`. Each element is `None` if `coding_type` is `Undefined`
78    /// or a BCD nibble is invalid (Satellite/Cable).
79    #[must_use]
80    pub fn centre_frequencies_hz(&self) -> Vec<Option<u64>> {
81        match self.coding_type {
82            CodingType::Satellite | CodingType::Cable => {
83                let scale = self.hz_per_unit_bcd().unwrap();
84                self.centre_frequencies_bcd
85                    .iter()
86                    .map(|b| {
87                        let value =
88                            dvb_common::bcd::bcd_to_decimal(u64::from(u32::from_be_bytes(*b)), 8)?;
89                        Some(value * scale)
90                    })
91                    .collect()
92            }
93            CodingType::Terrestrial => self
94                .centre_frequencies_bcd
95                .iter()
96                .map(|b| Some(u64::from(u32::from_be_bytes(*b)) * 10))
97                .collect(),
98            CodingType::Undefined => self.centre_frequencies_bcd.iter().map(|_| None).collect(),
99        }
100    }
101
102    /// Replace the entries by encoding each Hz value per `coding_type`
103    /// (values truncate to the field's resolution).
104    ///
105    /// # Errors
106    /// [`ValueOutOfRange`](crate::Error::ValueOutOfRange) if `coding_type`
107    /// is `Undefined`, a BCD value exceeds 8 digits (Satellite/Cable), or
108    /// a binary value exceeds 32 bits (Terrestrial).
109    pub fn set_centre_frequencies_hz(&mut self, frequencies_hz: &[u64]) -> crate::Result<()> {
110        match self.coding_type {
111            CodingType::Satellite | CodingType::Cable => {
112                let scale = self
113                    .hz_per_unit_bcd()
114                    .ok_or(crate::Error::ValueOutOfRange {
115                        field: "FrequencyListDescriptor::centre_frequency",
116                        reason: "coding_type is Undefined; cannot encode frequencies",
117                    })?;
118                let mut out = Vec::with_capacity(frequencies_hz.len());
119                for &hz in frequencies_hz {
120                    let bcd = super::encode_bcd_field(
121                        hz / scale,
122                        8,
123                        "FrequencyListDescriptor::centre_frequency",
124                    )?;
125                    out.push((bcd as u32).to_be_bytes());
126                }
127                self.centre_frequencies_bcd = out;
128                Ok(())
129            }
130            CodingType::Terrestrial => {
131                let mut out = Vec::with_capacity(frequencies_hz.len());
132                for &hz in frequencies_hz {
133                    let units = hz / 10;
134                    if units > u64::from(u32::MAX) {
135                        return Err(Error::ValueOutOfRange {
136                            field: "frequency_list centre_frequency",
137                            reason: "terrestrial frequency exceeds the 32-bit (×10 Hz) wire field",
138                        });
139                    }
140                    out.push((units as u32).to_be_bytes());
141                }
142                self.centre_frequencies_bcd = out;
143                Ok(())
144            }
145            CodingType::Undefined => Err(crate::Error::ValueOutOfRange {
146                field: "FrequencyListDescriptor::centre_frequency",
147                reason: "coding_type is Undefined; cannot encode frequencies",
148            }),
149        }
150    }
151}
152
153impl<'a> Parse<'a> for FrequencyListDescriptor {
154    type Error = crate::error::Error;
155    fn parse(bytes: &'a [u8]) -> Result<Self> {
156        let body = descriptor_body(bytes, TAG, "FrequencyListDescriptor", "expected tag 0x62")?;
157
158        if body.len() < CODING_BYTE_LEN {
159            return Err(Error::InvalidDescriptor {
160                tag: TAG,
161                reason: "body too short (need at least coding_type byte)",
162            });
163        }
164
165        if (body.len() - CODING_BYTE_LEN) % ENTRY_LEN != 0 {
166            return Err(Error::InvalidDescriptor {
167                tag: TAG,
168                reason: "body length minus coding byte must be multiple of 4",
169            });
170        }
171
172        let coding_byte = body[0];
173        // Top 6 bits are reserved_future_use — ignored on parse
174        // (EN 300 468 §5.1: decoders shall ignore reserved bits).
175        let coding_type_value = coding_byte & CODING_TYPE_MASK;
176        let coding_type = match coding_type_value {
177            0b00 => CodingType::Undefined,
178            0b01 => CodingType::Satellite,
179            0b10 => CodingType::Cable,
180            _ => CodingType::Terrestrial,
181        };
182
183        let entry_count = (body.len() - CODING_BYTE_LEN) / ENTRY_LEN;
184        let mut centre_frequencies_bcd = Vec::with_capacity(entry_count);
185
186        let mut offset = CODING_BYTE_LEN;
187        for _ in 0..entry_count {
188            let mut entry = [0u8; ENTRY_LEN];
189            entry.copy_from_slice(&body[offset..offset + ENTRY_LEN]);
190            centre_frequencies_bcd.push(entry);
191            offset += ENTRY_LEN;
192        }
193
194        Ok(FrequencyListDescriptor {
195            coding_type,
196            centre_frequencies_bcd,
197        })
198    }
199}
200
201impl Serialize for FrequencyListDescriptor {
202    type Error = crate::error::Error;
203    fn serialized_len(&self) -> usize {
204        HEADER_LEN + CODING_BYTE_LEN + self.centre_frequencies_bcd.len() * ENTRY_LEN
205    }
206
207    fn serialize_into(&self, buf: &mut [u8]) -> Result<usize> {
208        let need = self.serialized_len();
209        if buf.len() < need {
210            return Err(Error::OutputBufferTooSmall {
211                need,
212                have: buf.len(),
213            });
214        }
215
216        let coding_type_bits = match self.coding_type {
217            CodingType::Undefined => 0b00,
218            CodingType::Satellite => 0b01,
219            CodingType::Cable => 0b10,
220            CodingType::Terrestrial => 0b11,
221        };
222
223        let body_length = CODING_BYTE_LEN + self.centre_frequencies_bcd.len() * ENTRY_LEN;
224
225        buf[0] = TAG;
226        buf[1] = body_length as u8;
227        buf[HEADER_LEN] = RESERVED_BITS_MASK | coding_type_bits;
228
229        let mut offset = HEADER_LEN + CODING_BYTE_LEN;
230        for entry in &self.centre_frequencies_bcd {
231            buf[offset..offset + ENTRY_LEN].copy_from_slice(entry);
232            offset += ENTRY_LEN;
233        }
234
235        Ok(need)
236    }
237}
238impl<'a> crate::traits::DescriptorDef<'a> for FrequencyListDescriptor {
239    const TAG: u8 = TAG;
240    const NAME: &'static str = "FREQUENCY_LIST";
241}
242
243#[cfg(test)]
244mod tests {
245    use super::*;
246
247    /// [TAG, 1, 0xFC] → zero entries, coding=Undefined
248    #[test]
249    fn parse_empty_entries_is_valid() {
250        let raw: Vec<u8> = vec![TAG, 0x01, 0xFC];
251        let desc = FrequencyListDescriptor::parse(&raw).unwrap();
252        assert!(desc.centre_frequencies_bcd.is_empty());
253        assert!(matches!(desc.coding_type, CodingType::Undefined));
254    }
255
256    /// coding_type byte 0xFD → Satellite (0xFC | 0b01)
257    #[test]
258    fn parse_extracts_coding_type_satellite() {
259        let raw: Vec<u8> = vec![TAG, 0x01, 0xFD];
260        let desc = FrequencyListDescriptor::parse(&raw).unwrap();
261        assert!(matches!(desc.coding_type, CodingType::Satellite));
262    }
263
264    /// coding_type byte 0xFE → Cable (0xFC | 0b10)
265    #[test]
266    fn parse_extracts_coding_type_cable() {
267        let raw: Vec<u8> = vec![TAG, 0x01, 0xFE];
268        let desc = FrequencyListDescriptor::parse(&raw).unwrap();
269        assert!(matches!(desc.coding_type, CodingType::Cable));
270    }
271
272    /// coding_type byte 0xFF → Terrestrial (0xFC | 0b11)
273    #[test]
274    fn parse_extracts_coding_type_terrestrial() {
275        let raw: Vec<u8> = vec![TAG, 0x01, 0xFF];
276        let desc = FrequencyListDescriptor::parse(&raw).unwrap();
277        assert!(matches!(desc.coding_type, CodingType::Terrestrial));
278    }
279
280    /// Multiple 4-byte entries parsed correctly.
281    #[test]
282    fn parse_extracts_multiple_frequency_entries() {
283        let raw: Vec<u8> = vec![
284            TAG, 0x09, // body length = 9 (1 coding byte + 2 entries × 4)
285            0xFD, // satellite
286            0x00, 0x30, 0x12, 0x34, // BCD 00301234 → 3_012_340 kHz = 30_123_400_000 Hz
287            0x00, 0x30, 0x00, 0x00, // BCD 00300000 → 3_000_000 kHz = 30_000_000_000 Hz
288        ];
289        let desc = FrequencyListDescriptor::parse(&raw).unwrap();
290        assert_eq!(desc.centre_frequencies_bcd.len(), 2);
291        assert_eq!(desc.centre_frequencies_bcd[0], [0x00, 0x30, 0x12, 0x34]);
292        assert_eq!(desc.centre_frequencies_bcd[1], [0x00, 0x30, 0x00, 0x00]);
293    }
294
295    /// Wrong tag byte should return InvalidDescriptor.
296    #[test]
297    fn parse_rejects_wrong_tag() {
298        let raw: Vec<u8> = vec![0x63, 0x01, 0xFC];
299        let err = FrequencyListDescriptor::parse(&raw).unwrap_err();
300        assert!(
301            matches!(err, Error::InvalidDescriptor { tag: 0x63, .. }),
302            "expected InvalidDescriptor(tag=0x63), got {err:?}"
303        );
304    }
305
306    /// Reserved bits set to zero must be ignored, not rejected (EN 300 468 §5.1).
307    #[test]
308    fn parse_ignores_reserved_bits() {
309        // coding byte 0x03: top 6 reserved bits = 0, coding_type = 0b11 (terrestrial).
310        let raw: Vec<u8> = vec![TAG, 0x01, 0x03];
311        let d = FrequencyListDescriptor::parse(&raw).unwrap();
312        assert_eq!(d.coding_type, CodingType::Terrestrial);
313        assert!(d.centre_frequencies_bcd.is_empty());
314    }
315
316    /// Body length not 1 + multiple of 4 → InvalidDescriptor
317    #[test]
318    fn parse_rejects_length_not_1_plus_multiple_of_4() {
319        let raw: Vec<u8> = vec![TAG, 0x03, 0xFC, 0x01, 0x02]; // body=3, need 1+4K
320        let err = FrequencyListDescriptor::parse(&raw).unwrap_err();
321        assert!(matches!(err, Error::InvalidDescriptor { .. }));
322    }
323
324    /// Buffer shorter than the 2-byte header → BufferTooShort
325    #[test]
326    fn parse_rejects_truncated_buffer() {
327        let raw: &[u8] = &[TAG];
328        let err = FrequencyListDescriptor::parse(raw).unwrap_err();
329        assert!(matches!(err, Error::BufferTooShort { need: 2, .. }));
330    }
331
332    /// Serialize a descriptor with zero entries, re-parse, compare.
333    #[test]
334    fn serialize_round_trip_empty() {
335        let desc = FrequencyListDescriptor {
336            coding_type: CodingType::Satellite,
337            centre_frequencies_bcd: vec![],
338        };
339        let raw: Vec<u8> = vec![TAG, 0x01, 0xFD];
340        let mut buf = vec![0u8; desc.serialized_len()];
341        let written = desc.serialize_into(&mut buf).unwrap();
342        assert_eq!(written, raw.len());
343        assert_eq!(buf, raw);
344
345        let reparsed = FrequencyListDescriptor::parse(&buf).unwrap();
346        assert_eq!(desc.coding_type, reparsed.coding_type);
347        assert_eq!(desc.centre_frequencies_bcd, reparsed.centre_frequencies_bcd);
348    }
349
350    /// Serialize a descriptor with many entries, re-parse, compare.
351    #[test]
352    fn serialize_round_trip_many_entries() {
353        let desc = FrequencyListDescriptor {
354            coding_type: CodingType::Cable,
355            centre_frequencies_bcd: vec![
356                [0x03, 0x46, 0x00, 0x00],
357                [0x04, 0x74, 0x00, 0x10],
358                [0x01, 0x15, 0x50, 0x00],
359                [0x04, 0x90, 0x25, 0x00],
360            ],
361        };
362        let mut buf = vec![0u8; desc.serialized_len()];
363        desc.serialize_into(&mut buf).unwrap();
364        let reparsed = FrequencyListDescriptor::parse(&buf).unwrap();
365        assert_eq!(desc.coding_type, reparsed.coding_type);
366        assert_eq!(desc.centre_frequencies_bcd, reparsed.centre_frequencies_bcd);
367    }
368
369    #[test]
370    fn satellite_frequency_hz_decodes_correctly() {
371        let desc = FrequencyListDescriptor {
372            coding_type: CodingType::Satellite,
373            centre_frequencies_bcd: vec![[0x01, 0x17, 0x25, 0x00]], // 11.72500 GHz
374        };
375        assert_eq!(desc.centre_frequencies_hz(), vec![Some(11_725_000_000)]);
376    }
377
378    #[test]
379    fn cable_frequency_hz_decodes_correctly() {
380        let desc = FrequencyListDescriptor {
381            coding_type: CodingType::Cable,
382            centre_frequencies_bcd: vec![[0x03, 0x46, 0x00, 0x00]], // 346.0000 MHz
383        };
384        assert_eq!(desc.centre_frequencies_hz(), vec![Some(346_000_000)]);
385    }
386
387    #[test]
388    fn terrestrial_frequency_hz_decodes_binary() {
389        let desc = FrequencyListDescriptor {
390            coding_type: CodingType::Terrestrial,
391            // binary 0x04A858F0 = 78_141_680 × 10 Hz = 781_416_800 Hz
392            centre_frequencies_bcd: vec![[0x04, 0xA8, 0x58, 0xF0]],
393        };
394        assert_eq!(desc.centre_frequencies_hz(), vec![Some(781_416_800)]);
395    }
396
397    #[test]
398    fn set_satellite_frequencies_hz_round_trips() {
399        let mut desc = FrequencyListDescriptor {
400            coding_type: CodingType::Satellite,
401            centre_frequencies_bcd: vec![],
402        };
403        desc.set_centre_frequencies_hz(&[11_725_000_000]).unwrap();
404        assert_eq!(desc.centre_frequencies_hz(), vec![Some(11_725_000_000)]);
405        assert_eq!(desc.centre_frequencies_bcd[0], [0x01, 0x17, 0x25, 0x00]);
406    }
407
408    #[test]
409    fn set_terrestrial_frequencies_hz_round_trips() {
410        let mut desc = FrequencyListDescriptor {
411            coding_type: CodingType::Terrestrial,
412            centre_frequencies_bcd: vec![],
413        };
414        desc.set_centre_frequencies_hz(&[781_416_800]).unwrap();
415        assert_eq!(desc.centre_frequencies_hz(), vec![Some(781_416_800)]);
416        assert_eq!(desc.centre_frequencies_bcd[0], [0x04, 0xA8, 0x58, 0xF0]);
417    }
418
419    #[test]
420    fn set_cable_frequencies_hz_round_trips() {
421        let mut desc = FrequencyListDescriptor {
422            coding_type: CodingType::Cable,
423            centre_frequencies_bcd: vec![],
424        };
425        desc.set_centre_frequencies_hz(&[346_000_000]).unwrap();
426        assert_eq!(desc.centre_frequencies_hz(), vec![Some(346_000_000)]);
427    }
428}
dvb_si/descriptors/frequency_list.rs

dvb_si/descriptors/
frequency_list.rs
