my $result = $client->do_task( ... );
if( not defined $result ) {
  ## Presumably there may be some other information about the failure but I don't
  ## see offhand how to retrieve that; but that's a good thing to include in your
  ## error message here
  die "isok not ok for ip '$ip'!\n";
}

my $json_result = decode_json( ${ $result } );
if( not ref $json_result or not ref $json_result->{ $ip } or ref $json_result->{$ip} ne q{HASH} ) {
  die "Did not get back the hashref expected for '$ip'\n";
}

my @result = keys %{ $json_result->{ $ip } }