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#[derive(Debug, Copy, Clone, Default, PartialEq)]
/// [Meta] data that describes the core structure of each message.
pub struct Meta {
/// Whether this message is reversed or not
pub reversed: bool,
/// Whether this message uses enhanced CRC or not.
/// Enhanced CRC robusties the transmissions a lot.
pub enhanced_crc: bool,
/// Endianess used during encoding process.
pub big_endian: bool,
}
impl Meta {
// Forward stream +LE +standard
const FWD_SYNC_LE_STANDARD_CRC: u8 = 0xc2;
// Forward stream +BE +standard
const FWD_SYNC_BE_STANDARD_CRC: u8 = 0xe2;
// Forward stream +LE +enhanced
const FWD_SYNC_LE_ENHANCED_CRC: u8 = 0xc8;
// Forward stream +BE +enhanced
const FWD_SYNC_BE_ENHANCED_CRC: u8 = 0xe8;
// Reversed stream +LE +standard
const REV_SYNC_LE_STANDARD_CRC: u8 = 0xd2;
// Reversed stream +BE +standard
const REV_SYNC_BE_STANDARD_CRC: u8 = 0xf2;
// Reversed stream +LE +enhanced
const REV_SYNC_LE_ENHANCED_CRC: u8 = 0xd8;
// Reversed stream +BE +enhanced
const REV_SYNC_BE_ENHANCED_CRC: u8 = 0xf8;
}
impl Meta {
/// Generates correct Sync byte to initiate this [Meta] stream
pub(crate) fn sync_byte(&self) -> u8 {
if self.reversed {
if self.big_endian {
if self.enhanced_crc {
Self::REV_SYNC_BE_ENHANCED_CRC
} else {
Self::REV_SYNC_BE_STANDARD_CRC
}
} else if self.enhanced_crc {
Self::REV_SYNC_LE_ENHANCED_CRC
} else {
Self::REV_SYNC_LE_STANDARD_CRC
}
} else if self.big_endian {
if self.enhanced_crc {
Self::FWD_SYNC_BE_ENHANCED_CRC
} else {
Self::FWD_SYNC_BE_STANDARD_CRC
}
} else if self.enhanced_crc {
Self::FWD_SYNC_LE_ENHANCED_CRC
} else {
Self::FWD_SYNC_LE_STANDARD_CRC
}
}
/// Locate SYNC byte in provided buffer
/// ## Returns
/// - [Meta]
/// - sync byte offset
pub(crate) fn find_and_parse(buf: &[u8], size: usize) -> Option<(Self, usize)> {
let mut meta = Meta::default();
for i in 0..size {
if buf[i] == Self::FWD_SYNC_BE_ENHANCED_CRC {
meta.enhanced_crc = true;
meta.big_endian = true;
return Some((meta, i));
} else if buf[i] == Self::FWD_SYNC_LE_ENHANCED_CRC {
meta.enhanced_crc = true;
return Some((meta, i));
} else if buf[i] == Self::FWD_SYNC_BE_STANDARD_CRC {
meta.big_endian = true;
return Some((meta, i));
} else if buf[i] == Self::FWD_SYNC_LE_STANDARD_CRC {
return Some((meta, i));
} else if buf[i] == Self::REV_SYNC_BE_ENHANCED_CRC {
meta.reversed = true;
meta.big_endian = true;
meta.enhanced_crc = true;
return Some((meta, i));
} else if buf[i] == Self::REV_SYNC_LE_ENHANCED_CRC {
meta.reversed = true;
meta.enhanced_crc = true;
return Some((meta, i));
} else if buf[i] == Self::REV_SYNC_BE_STANDARD_CRC {
meta.reversed = true;
meta.big_endian = true;
return Some((meta, i));
} else if buf[i] == Self::REV_SYNC_LE_STANDARD_CRC {
meta.reversed = true;
return Some((meta, i));
}
}
None
}
}
#[cfg(test)]
mod test {
use super::Meta;
#[test]
fn forge_sync_byte() {
for (meta, expected) in [
(
Meta {
reversed: false,
big_endian: true,
enhanced_crc: true,
},
Meta::FWD_SYNC_BE_ENHANCED_CRC,
),
(
Meta {
reversed: false,
big_endian: false,
enhanced_crc: true,
},
Meta::FWD_SYNC_LE_ENHANCED_CRC,
),
(
Meta {
reversed: false,
big_endian: true,
enhanced_crc: false,
},
Meta::FWD_SYNC_BE_STANDARD_CRC,
),
(
Meta {
reversed: false,
big_endian: false,
enhanced_crc: false,
},
Meta::FWD_SYNC_LE_STANDARD_CRC,
),
(
Meta {
reversed: true,
big_endian: false,
enhanced_crc: true,
},
Meta::REV_SYNC_LE_ENHANCED_CRC,
),
(
Meta {
reversed: true,
big_endian: false,
enhanced_crc: false,
},
Meta::REV_SYNC_LE_STANDARD_CRC,
),
(
Meta {
reversed: true,
big_endian: true,
enhanced_crc: true,
},
Meta::REV_SYNC_BE_ENHANCED_CRC,
),
(
Meta {
reversed: true,
big_endian: true,
enhanced_crc: false,
},
Meta::REV_SYNC_BE_STANDARD_CRC,
),
] {
assert_eq!(meta.sync_byte(), expected);
}
}
#[test]
fn test_sync_byte_matcher() {
for i in 0..256 {
let val8 = i as u8;
let buf = [0, val8];
let meta = Meta::find_and_parse(&buf, 2);
match val8 {
0xc2 => {
// FWD +LE +STANDARD
let (meta, size) = meta.expect("did not detect sync byte");
assert_eq!(size, 1);
assert!(!meta.reversed);
assert!(!meta.big_endian);
assert!(!meta.enhanced_crc);
},
0xe2 => {
// FWD +BE +STANDARD
let (meta, size) = meta.expect("did not detect sync byte");
assert_eq!(size, 1);
assert!(!meta.reversed);
assert!(meta.big_endian);
assert!(!meta.enhanced_crc);
},
0xc8 => {
// FWD +LE +ENHANCED
let (meta, size) = meta.expect("did not detect sync byte");
assert_eq!(size, 1);
assert!(!meta.reversed);
assert!(!meta.big_endian);
assert!(meta.enhanced_crc);
},
0xe8 => {
// FWD +BE +ENHANCED
let (meta, size) = meta.expect("did not detect sync byte");
assert_eq!(size, 1);
assert!(!meta.reversed);
assert!(meta.big_endian);
assert!(meta.enhanced_crc);
},
0xd2 => {
// REV +LE +STANDARD
let (meta, size) = meta.expect("did not detect sync byte");
assert_eq!(size, 1);
assert!(meta.reversed);
assert!(!meta.big_endian);
assert!(!meta.enhanced_crc);
},
0xf2 => {
// REV +BE + STANDARD
let (meta, size) = meta.expect("did not detect sync byte");
assert_eq!(size, 1);
assert!(meta.reversed);
assert!(meta.big_endian);
assert!(!meta.enhanced_crc);
},
0xd8 => {
// REV +LE +ENHANCED
let (meta, size) = meta.expect("did not detect sync byte");
assert_eq!(size, 1);
assert!(meta.reversed);
assert!(!meta.big_endian);
assert!(meta.enhanced_crc);
},
0xf8 => {
// REV +BE +ENHANCED
let (meta, size) = meta.expect("did not detect sync byte");
assert_eq!(size, 1);
assert!(meta.reversed);
assert!(meta.big_endian);
assert!(meta.enhanced_crc);
},
_ => {
assert!(meta.is_none(), "found invalid sync byte for 0x{:01x}", val8);
},
}
}
}
}