themanifold commented on pull request #4552:
URL: https://github.com/apache/nifi/pull/4552#issuecomment-700503064
> @themanifold Could you please clarify your use case and the problem you
would like to solve in more detail?
>
> If I understand correctly, `ConsumeAMQP` can emit the following
`amqp$headers` attribute values (as strings):
>
> * `{a=1}` if there is 1 key=value pair in the message headers
>
> * `{a=1,b=2}` if there are 2 key=value pairs in the headers of the
received message
>
> * `{}` if the headers of the received message is empty
>
>
> And you would like `PublishAMQP` to be able to parse these strings
properly. Eg. in case of `{a=1,b=2}`, remove the curly braces and add 2 headers
(`a=1` and `b=2`), and in case of `{}`, no headers need to be added.
>
> So your flow is `ConsumeAMQP` (from a queue) => process data =>
`PublishAMQP` (to another queue with keeping the same headers). Is my
understanding correct?
Everything here is correct apart from the flow. My initial attempt in NiFi
didn't actually do any data processing. I did: `ConsumeAMQP` (from a queue) =>
`PublishAMQP` (exchange). If you try this in NiFi, you'll find that the
`PublishAMQP` can't cope with `{}` (if your incoming message has no headers).
Additionally, you'll see that `ConsumeAMQP` actually can't cope with curly
braces full stop and will end up making some invalid headers - specifically the
first key and the last key will have `{` and `}` appended and prepended,
respectively. When I say that it can't cope, I mean that throws up a warning
that will obscure any real errors.
My work around right now is to actually delete the empty header using the
`update attribute` processor.
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