EXCEPTION clause not identified

Hi,
In one of my trigger functions, i'm trying to catch invalid ip address exception

CREATE OR REPLACE FUNCTION func_client_socket()
  RETURNS "trigger" AS
$BODY$
        DECLARE
                      ip_address_present int4;
BEGIN
                      ip_address_present = 1;
SELECT inet(NEW.canonical_name);
            EXCEPTION WHEN invalid_text_representation THEN
                    ip_address=0;
END;
$BODY$
  LANGUAGE 'plpgsql' VOLATILE;

when i run this function, it gives me the followin error

ERROR:  syntax error at or near "EXCEPTION" at character 1343
which is the line where I have the EXCEPTION clause.

Can anyone please tell me whats going wrong here?

Thanks,
~Jas