mosquitto_sub -F "%J" can output invalid JSON

[benbarbour]

If something publishes invalid JSON, like a single "{" or double-quote character, to a given topic and then it's picked up by mosquitto_sub -t <topic> -F "%J" then that will print:

{
  "tst":1554162699,
  "topic":"foo",
  "qos":0,
  "retain":1,
  "payloadlen":2,
  "payload":{
}

which cannot be parsed.

Would it make sense for mosquitto_sub to output something like this if it can't properly format the output? Or maybe print nothing to stdout for that message and instead print to stderr?

{
  "tst":1554162699,
  "topic":"foo",
  "qos":0,
  "retain":1,
  "payloadlen":2,
  "payload": "<INVALID_JSON>"
}

[ralight]

This is a good point. The documentation states the payload must be valid json, but it should definitely handle the case where it isn't.