rust/pv_core: Fix the argument order in 'LengthMismatch'

Fix the ordering of the parameters in 'TryFrom<Confidential<Vec<u8> for
Confidential<[u8; N>'. While at it, convert 'LengthMismatch' error to a
named struct.

Fixes: 7608cf2de4 ("rust/confidential: Add `From` and `Into` for confidential byes arrays/vectors")
Signed-off-by: Marc Hartmayer <mhartmay@linux.ibm.com>
Reviewed-by: Jan Höppner <hoeppner@linux.ibm.com>
Signed-off-by: Jan Höppner <hoeppner@linux.ibm.com>

rust/pv/src/crypto.rs

@@ -760,7 +760,10 @@ mod tests {
 
         assert!(matches!(
             SymKey::try_from_data(SymKeyType::Aes256Gcm, Confidential::new([0x4u8; 33].into())),
-            Err(Error::PvCore(PvCoreError::LengthMismatch(33, 32)))
+            Err(Error::PvCore(PvCoreError::LengthMismatch {
+                expected: 32,
+                actual: 33
+            }))
         ));
     }
 }

rust/pv_core/src/confidential.rs

@@ -182,7 +182,10 @@ impl<const N: usize> TryFrom<Confidential<Vec<u8>>> for Confidential<[u8; N]> {
                 TryInto::<[u8; N]>::try_into(value.0.clone()).unwrap(),
             ))
         } else {
-            Err(Error::LengthMismatch(len, N))
+            Err(Error::LengthMismatch {
+                expected: N,
+                actual: len,
+            })
         }
     }
 }
@@ -258,7 +261,13 @@ mod test {
 
         let result: Result<Confidential<[u8; 101]>, Error> =
             Confidential::new(data.clone()).try_into();
-        assert!(matches!(result, Err(Error::LengthMismatch(100, 101))));
+        assert!(matches!(
+            result,
+            Err(Error::LengthMismatch {
+                expected: 101,
+                actual: 100
+            })
+        ));
     }
 
     #[test]

rust/pv_core/src/error.rs

@@ -82,8 +82,8 @@ pub enum Error {
     #[error("Cannot decode hex string")]
     InvHexStringChar { source: std::num::ParseIntError },
 
-    #[error("Expected size {0}, found {1}")]
-    LengthMismatch(usize, usize),
+    #[error("Expected size {expected}, actual {actual}")]
+    LengthMismatch { expected: usize, actual: usize },
 }
 
 /// Error cases for I/O operations