Very well written question solbeach. The expression:

$entity = $parser->parse(\*RAW) returns a structure, instead of a True/False, so "or die" gets confused. The parse method will issue a "die" exception if it can't parse the message. So you don't need to do that here. You can check if it returns "undef" though.

You should add checking on the "open" statment as this could fail for any of a number of reasons.