Allow ports to decline a connection

[bergie]

In NoFlo we have situations where a port will not allow a new connection. This means that in Dataflow too we need to be able to decline a connection.

[forresto]

What situation?

[bergie]

@forresto some examples (note that some of this will change with noflo/noflo#90)

• Regular port that already has a connection
• Regular port that already has an IIP
• Particular ArrayPort index that already has a connection (related to noflo/noflo-ui#14)

Of course the other option would be to always destructively remove whatever was there when dragging a new connection in.

[forresto]

Seems better to reject the new.

I see #72 (remove state/iip) is related as well.

[bergie]

Another affected issue is #63

[hacfi]

Should there be some kind of notification system informing the user or do you want to use Dataflow.log(..) for that?

[bergie]

@hacfi I think the ports that decline connections should simply not be connectable, i.e. no highlight (#63, #37), and dropping on top of them shouldn't establish a connection.

However, we do have a notification mechanism already in Dataflow, for example:

[hacfi]

@bergie I checked out the demos and noticed the highlighting..thanks! I was mainly working with the demo of this repo which doesn’t use highlighting (yet!?).