Add helper for circular rebalancing

[tnull]

We had users interested in circular rebalancing. Of course, selecting two channels (send/receive over) to use, crafting an appropriate path and sending a spontaneous payment should be rather trivial to achieve with LDK's current API, but it would still be nice to have a convenient helper method for it, similar as we do for payment probing.

[valentinewallace]

May be a duplicate of #2462

[tnull]

May be a duplicate of #2462

Yeah, that might be a prereq, but I think this issue is slightly different, as it's about providing convenience helpers to create a circular route mostly.

[Oochenn]

hi can I take this ?

[tnull]

hi can I take this ?

Yes, although we might need #2462 first, as discussed above. Would you also be interested in picking that up?

[Oochenn]

yes sure 🙂

[TheBlueMatt]

I believe #2462 is unrelated. #2462 is about detecting when a payment is to-self and short-circuiting the actual HTLC logic. This is somewhat of the opposite - using the normal HTLC logic for a self-payment anyway.

[tnull]

I believe #2462 is unrelated. #2462 is about detecting when a payment is to-self and short-circuiting the actual HTLC logic. This is somewhat of the opposite - using the normal HTLC logic for a self-payment anyway.

Well, in both cases we'll have to deal with the case where the destination / route's last hop is our own node. The only difference is the length of the circle. I agree it's a bit orthogonal, but at the very least we'll need to make sure that the short-circuiting for the 0-hop case is done in a way that still allows us to send payments across circular paths with >0 length.

[TheBlueMatt]

Sure, indeed, but no reason we can't make progress on this issue while work goes on there.