Merge pull request #3211 from nymtech/feature/no_creds_err_msg

Better error log for lacking credential in db

common/credential-storage/src/coconut.rs

@@ -48,12 +48,12 @@ impl CoconutCredentialManager {
     /// Tries to retrieve one of the stored, unused credentials.
     pub(crate) async fn get_next_coconut_credential(
         &self,
-    ) -> Result<CoconutCredential, sqlx::Error> {
+    ) -> Result<Option<CoconutCredential>, sqlx::Error> {
         sqlx::query_as!(
             CoconutCredential,
             "SELECT * FROM coconut_credentials WHERE NOT consumed"
         )
-        .fetch_one(&self.connection_pool)
+        .fetch_optional(&self.connection_pool)
         .await
     }
 

common/credential-storage/src/error.rs

@@ -13,4 +13,7 @@ pub enum StorageError {
 
     #[error("Inconsistent data in database")]
     InconsistentData,
+
+    #[error("No unused credential in database. You need to buy at least one")]
+    NoCredential,
 }

common/credential-storage/src/lib.rs

@@ -90,7 +90,8 @@ impl Storage for PersistentStorage {
         let credential = self
             .coconut_credential_manager
             .get_next_coconut_credential()
-            .await?;
+            .await?
+            .ok_or(StorageError::NoCredential)?;
 
         Ok(credential)
     }