move config check into config load function

src/config.rs

@@ -438,10 +438,16 @@ where
 
     let path = path.as_ref();
 
-    toml::from_str(
+    let config: Config = toml::from_str(
         &tokio::fs::read_to_string(path)
             .await
             .map_err(|e| Error::Read(e, path.to_owned()))?,
     )
-    .map_err(|e| Error::Parse(e, path.to_owned()))
+    .map_err(|e| Error::Parse(e, path.to_owned()))?;
+
+    if config.registration_token.as_deref() == Some("") {
+        return Err(Error::RegistrationTokenEmpty);
+    }
+
+    Ok(config)
 }

src/database.rs

@@ -353,10 +353,6 @@ impl KeyValueDatabase {
             }
         };
 
-        if config.registration_token == Some(String::new()) {
-            return Err(Error::bad_config("Registration token is empty"));
-        }
-
         let db_raw = Box::new(Self {
             db: builder.clone(),
             userid_password: builder.open_tree("userid_password")?,

src/error.rs

@@ -95,6 +95,9 @@ pub(crate) enum Config {
 
     #[error("failed to parse configuration file {1:?}")]
     Parse(#[source] toml::de::Error, PathBuf),
+
+    #[error("registration token must not be empty")]
+    RegistrationTokenEmpty,
 }
 
 /// Errors that can occur while searching for a config file