mod_private_sql may crash the login process when using SQL and the DB connection is broken

[marc0s]

As I'm not sure this can be really tagged as a bug, I'll report it here.

Environment

• ejabberd version: main

Configuration (only if needed): grep -Ev '^$|^\s*#' ejabberd.yml

With mod_private enabled and an SQL backend in use.

Errors from error.log/crash.log

17:34:00.671 [error] GenServer #PID<0.1628.0> terminating
** (CaseClauseError) no case clause matching:
{:error, :db_failure}

Bug description

When a deployment using an SQL database and mod_private gets a disconnection from the database, each login attempt will crash because the unmatched clause above. While this is not a real problem feature-wise (if the DB connection is broken, lots of stuff will fail), it may still be a problem of pollution/noise in the logs, IMHO.

By adding a clause to such case (or unwrapping the {error, _} as a plain error in mod_private:get_data/3) the login can be made to fail cleanly instead.