message buffer limit creates invalid JSON

[petere]

While testing pg_logforward with the JSON format against the postgresql regression tests (make installcheck), I noticed that one message (the infinite recursion test) creates a message that exceeds MAX_MESSAGE_SIZE (8192). The message is sent out truncated, and JSON decoding on the receiving side fails.

Some thoughts:

• MAX_MESSAGE_SIZE might as well be closer to the theoretical limit for UDP packet size (somewhere around 65000).
• If message truncation happens, truncated packets should not be sent out, because that can confuse the receiver and falsify data.
• Perhaps a special message (maybe message, detail, hint None) could be sent out of message truncation happened.