Can't inferring the conversion type for RabbitListener be a bit smarter?

[hjohn]

See #390.

Signatures like this for RabbitListener do not work when there is no type information (no TypeId):

 void listen(MessageProperties props, SomeJavaClass body);
 void listen(MessageProperties props, @Payload SomeJavaClass body);

What is the real limitation here? If a method is annotated with RabbitListener, I'd expect all messages that match its binding to be delivered to the annotated method, and, if this for whatever reason fails due to a bad method signature, a huge exception if not.

However, if the signature goes "bad", the endpoint silently stops working. For example, if you have this:

 void listen(SomeJavaClass body);

And you at some point need the properties (or a header), and you change the signature to this:

 void listen(MessageProperties props, SomeJavaClass body);

...it stops working completely.

What I don't understand is that there is an exception made for Message, so this does work:

 void listen(Message rawMsg, SomeJavaClass body);

Leaving me to have to add this line:

 MessageProperties props = rawMsg.getMessageProperties();  // this can't be done directly...?

Why not also make exceptions for @Header, MessageProperties, etc?

Looking at the code where this is implemented it seems at a maximum a single inferred type can be handled, either 1 header, 1 unannotated parameter that is not Message or a parameter annotated with @Payload.

[garyrussell]

This is because MessageProperties is not available as a first class argument for argument matching only Message, Message<?> and Channel.

All other types (not annotated as @Headers) become candidates for conversion from the incoming payload.

We can certainly add MessageProperties as an available argument for matching, but the current solution (msg.getMessageProperties()) is correct.

[hjohn]

Okay, thank you for the quick response. I just banged my head on this why it suddenly stopped working, when all that was different in the message was the missing __TypeId__. I'm glad at least I do not need to configure my own converter in order to make it work.