Return UTF-8 error if libnitrokey returns an invalid string

Previously, we used lossy UTF-8 conversion.  Yet the user should be
notified if we have a problem instead of silently changing the data.
Therefore, we now return an error if we enocunter an invalid UTF-8
string.  This leads to a change in `get_library_version`’s signature.

1 files changed, 5 insertions, 4 deletions

diff --git a/src/util.rs b/src/util.rs
index f8ad9c9..64dde39 100644
--- a/src/util.rs
+++ b/src/util.rs
@@ -28,17 +28,18 @@ pub enum LogLevel {
     DebugL2,
 }
 
-pub fn owned_str_from_ptr(ptr: *const c_char) -> String {
+pub fn owned_str_from_ptr(ptr: *const c_char) -> Result<String, Error> {
     unsafe { CStr::from_ptr(ptr) }
-        .to_string_lossy()
-        .into_owned()
+        .to_str()
+        .map(String::from)
+        .map_err(Error::from)
 }
 
 pub fn result_from_string(ptr: *const c_char) -> Result<String, Error> {
     if ptr.is_null() {
         return Err(Error::UnexpectedError);
     }
-    let s = owned_str_from_ptr(ptr);
+    let s = owned_str_from_ptr(ptr)?;
     unsafe { free(ptr as *mut c_void) };
     // An empty string can both indicate an error or be a valid return value.  In this case, we
     // have to check the last command status to decide what to return.