Add String value to the Error::UnexpectedError variant

To make debugging of unexpected errors easier, this patch adds an
associated String value with a description of the unexpected behavior to
the UnexpectedError variant of the Error enum.

3 files changed, 16 insertions, 11 deletions

diff --git a/src/device/storage.rs b/src/device/storage.rs
index deb2844..1e2c46d 100644
--- a/src/device/storage.rs
+++ b/src/device/storage.rs
@@ -678,7 +678,7 @@ impl<'a> Storage<'a> {
                 if usage_data.write_level_min > usage_data.write_level_max
                     || usage_data.write_level_max > 100
                 {
-                    Err(Error::UnexpectedError)
+                    Err(Error::UnexpectedError("Invalid write levels".to_owned()))
                 } else {
                     Ok(ops::Range {
                         start: usage_data.write_level_min,
@@ -708,10 +708,14 @@ impl<'a> Storage<'a> {
         match status {
             0..=100 => u8::try_from(status)
                 .map(OperationStatus::Ongoing)
-                .map_err(|_| Error::UnexpectedError),
+                .map_err(|_| {
+                    Error::UnexpectedError("Cannot create u8 from operation status".to_owned())
+                }),
             -1 => Ok(OperationStatus::Idle),
             -2 => Err(get_last_error()),
-            _ => Err(Error::UnexpectedError),
+            _ => Err(Error::UnexpectedError(
+                "Invalid operation status".to_owned(),
+            )),
         }
     }
 
diff --git a/src/error.rs b/src/error.rs
index f9af594..7bea3f2 100644
--- a/src/error.rs
+++ b/src/error.rs
@@ -25,7 +25,7 @@ pub enum Error {
     /// An error that occurred during random number generation.
     RandError(Box<dyn error::Error>),
     /// An error that is caused by an unexpected value returned by libnitrokey.
-    UnexpectedError,
+    UnexpectedError(String),
     /// An unknown error returned by libnitrokey.
     UnknownError(i64),
     /// An error caused by a Nitrokey model that is not supported by this crate.
@@ -102,7 +102,7 @@ impl error::Error for Error {
             Error::LibraryError(ref err) => Some(err),
             Error::PoisonError(ref err) => Some(err),
             Error::RandError(ref err) => Some(err.as_ref()),
-            Error::UnexpectedError => None,
+            Error::UnexpectedError(_) => None,
             Error::UnknownError(_) => None,
             Error::UnsupportedModelError => None,
             Error::Utf8Error(ref err) => Some(err),
@@ -119,7 +119,7 @@ impl fmt::Display for Error {
             Error::LibraryError(ref err) => write!(f, "Library error: {}", err),
             Error::PoisonError(_) => write!(f, "Internal error: poisoned lock"),
             Error::RandError(ref err) => write!(f, "RNG error: {}", err),
-            Error::UnexpectedError => write!(f, "An unexpected error occurred"),
+            Error::UnexpectedError(ref s) => write!(f, "An unexpected error occurred: {}", s),
             Error::UnknownError(ref err) => write!(f, "Unknown error: {}", err),
             Error::UnsupportedModelError => write!(f, "Unsupported Nitrokey model"),
             Error::Utf8Error(ref err) => write!(f, "UTF-8 error: {}", err),
diff --git a/src/util.rs b/src/util.rs
index 5a56c55..1b52c3d 100644
--- a/src/util.rs
+++ b/src/util.rs
@@ -39,7 +39,9 @@ pub fn owned_str_from_ptr(ptr: *const c_char) -> Result<String, Error> {
 
 pub fn result_from_string(ptr: *const c_char) -> Result<String, Error> {
     if ptr.is_null() {
-        return Err(Error::UnexpectedError);
+        return Err(Error::UnexpectedError(
+            "libnitrokey returned a null pointer".to_owned(),
+        ));
     }
     let s = owned_str_from_ptr(ptr)?;
     unsafe { free(ptr as *mut c_void) };
@@ -69,10 +71,9 @@ pub fn get_last_result() -> Result<(), Error> {
 }
 
 pub fn get_last_error() -> Error {
-    match get_last_result() {
-        Ok(()) => Error::UnexpectedError,
-        Err(err) => err,
-    }
+    get_last_result().err().unwrap_or_else(|| {
+        Error::UnexpectedError("Expected an error, but command status is zero".to_owned())
+    })
 }
 
 pub fn generate_password(length: usize) -> Result<Vec<u8>, Error> {