Feature: [Network] Ensure players fill in a name instead of defaulting to "Player"

src/network/network_client.cpp

@@ -1264,6 +1264,42 @@ bool NetworkIsValidClientName(const char *client_name)
 	return true;
 }
 
+/**
+ * Trim the given client name in place, i.e. remove leading and trailing spaces.
+ * After the trim check whether the client name is valid. A client name is valid
+ * whenever the name is not empty and does not start with spaces. This check is
+ * done via \c NetworkIsValidClientName.
+ * When the client name is valid, this function returns true.
+ * When the client name is not valid a GUI error message is shown telling the
+ * user to set the client name and this function returns false.
+ *
+ * This function is not suitable for ensuring a valid client name at the server
+ * as the error message will then be shown to the host instead of the client.
+ * @param client_name The client name to validate. It will be trimmed of leading
+ *                    and trailing spaces.
+ * @return True iff the client name is valid.
+ */
+bool NetworkValidateClientName(char *client_name)
+{
+	StrTrimInPlace(client_name);
+	if (NetworkIsValidClientName(client_name)) return true;
+
+	ShowErrorMessage(STR_NETWORK_ERROR_BAD_PLAYER_NAME, INVALID_STRING_ID, WL_ERROR);
+	return false;
+}
+
+/**
+ * Convenience method for NetworkValidateClientName on _settings_client.network.client_name.
+ * It trims the client name and checks whether it is empty. When it is empty
+ * an error message is shown to the GUI user.
+ * See \c NetworkValidateClientName(char*) for details about the functionality.
+ * @return True iff the client name is valid.
+ */
+bool NetworkValidateClientName()
+{
+	return NetworkValidateClientName(_settings_client.network.client_name);
+}
+
 /**
  * Send the server our name.
  */