resource-pool compatibility

[supki]

While connection pooling is of limited use as LDAP connections are generally pretty stateful, it would be nice to support the use case. This is related to #2, where the problem with the way we manage exceptions currently is described.

[dminuoso]

Here is a working concept:

https://github.com/dminuoso/ldap-client/tree/poolable

withLdap :: MonadUnliftIO m
         => Pool Ldap
         -> (Ldap -> m a)
         -> m a
withLdap pool act = withRunInIO $ \io -> do
  (ldap, local) <- liftIO (takeResource pool)
  res <- liftIO (runsInEither (io . act) ldap) `onException` liftIO (putResource local ldap)
  case res of
    Right a -> liftIO (putResource local ldap) *> pure a
    Left e  -> liftIO (destroyResource pool local ldap) *> throwIO e

and then you can simply do

withLdap pool $ \ldap -> 
  ...