Impl to_* and from_be_bytes function for transit type

lib-bms-protocol/src/types.rs

@@ -53,6 +53,7 @@ pub enum U26Error {
     InvalidCodeWord,
     IncorrectibleError,
     Overflow,
+    ChecksumError,
 }
 
 #[derive(Debug, PartialEq)]
@@ -122,7 +123,7 @@ impl TryFrom<u32> for Stored_U26 {
     }
 }
 
-#[derive(Debug)]
+#[derive(Debug, PartialEq)]
 /// this type is used for transmitting data, the concern here is protection against transmission errors which most likely occur
 /// as burst errors effecting multiple bits, hemming codes would be a waist of space here so instead a 6 bit crc code is used
 ///
@@ -136,6 +137,21 @@ impl Transit_U26 {
         let crc6 = calc_crc6(value);
         Self((value << 6) | (crc6 & 0x3F) as u32)
     }
+
+    pub fn from_be_bytes(bytes: [u8; 4]) -> Result<Self, U26Error> {
+        let raw_val = u32::from_be_bytes(bytes);
+        let crc = (raw_val & 0x3F) as u8;
+        let val = raw_val >> 6;
+        if check_crc6(val, crc) {
+            Ok(Self(raw_val))
+        } else {
+            Err(U26Error::ChecksumError)
+        }
+    }
+
+    pub fn to_be_bytes(&self) -> [u8; 4] {
+        self.0.to_be_bytes()
+    }
 }
 
 impl From<Transit_U26> for u32 {
@@ -459,20 +475,21 @@ mod base_type_tests {
 
     #[test]
     fn crc6_consistency() {
-        // Test that same input always produces same output
+        // Test that calc crc6 and check crc6 agree on validity
         let data = 0x123456;
         let crc = calc_crc6(data);
         assert!(check_crc6(data, crc))
     }
 
     #[test]
-    fn crc6_different_inputs_different_outputs() {
-        // Test that different inputs produce different CRCs (with high probability)
-        let data1 = 0x123456;
-        let data2 = 0x123457;
-        let crc1 = calc_crc6(data1);
-        let crc2 = calc_crc6(data2);
-        assert_ne!(crc1, crc2);
+    fn transit_u26_to_from_bytes() {
+        let data1 = Transit_U26::new(0x123456);
+        // check that to from bytes conversion produces the same value
+        let mut bytes = data1.to_be_bytes();
+        assert_eq!(data1, Transit_U26::from_be_bytes(bytes).unwrap());
+        // test that changed data leads to checksum error
+        bytes[1] = 0x00;
+        assert!(Transit_U26::from_be_bytes(bytes).unwrap_err() == U26Error::ChecksumError)
     }
 
     #[test]