Is there a reason why GNUnet forcefully sends a message of type 6?

[Alessio Vanni]

Hello,

I wrote a small service which is meant to be part of a bigger project.
While I was checking stdout to see if everything worked correctly, I was
notified that there was no handle for a message of type 6 and size 4
(and subsequently that the handle in the service didn't call
`GNUNET_SERVICE_client_continue' before the timeout.)

Due to the fact that this specific service is not meant to talk with
other GNUnet services (it simply uses GNUnet's utilites to talk to
services that actually use GNUnet and to operate on the received data),
I enumerated the types of message starting from 0, instead of checking
which numbers were "free" (i.e. not used by GNUnet itself).  I only have
3 message types so far, so receiving a message of type 6 is something
that can't happen.

Looking at the source code, it appears that GNUnet forcefully adds a
handler for this message type upon starting the service in
`GNUNET_SERVICE_start', but for some reason when starting my service
this handle was not added, yet the message was sent to the service.

I can't find where the message is sent in the code, so my research stops
here, but the question remains: why is GNUnet asking to send an AGPL
URL, even though the application has nothing to do with the GNUnet core
itself and might even be licensed differently?

In particular, this behaviour is not documented at all as far as I know,
so if by disgrace I had more than 6 message types I would be here trying
to debug a piece of code that would otherwise have no problems.

Thanks,
A.V.