routerrpc: add log line for probing the invoice request

[ziggie1984]

Was testing some estimateRoute probing and could barely see whats happening in the background, so added those important logs.

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[ziggie1984]

@hieblmi we might think also of defaulting LSP to false if the LSP node is not known to the network.

[kilrau]

@hieblmi we might think also of defaulting LSP to false if the LSP node is not known to the network.

Please!

[kilrau]

@hieblmi we might think also of defaulting LSP to false if the LSP node is not known to the network.

Please!

If you are looking for context why I am in favor of dropping the strict "one routing hint = LSP" assumption, check this dirty workaround we had to do in order to not have all probes to us fail: BoltzExchange/boltz-backend#975

[hieblmi]

@hieblmi we might think also of defaulting LSP to false if the LSP node is not known to the network.

Please!

If you are looking for context why I am in favor of dropping the strict "one routing hint = LSP" assumption, check this dirty workaround we had to do in order to not have all probes to us fail: BoltzExchange/boltz-backend#975

IIUC you have an invoice to be probed that has a single non-existent route hint? If that's the case, why is the route hint in the invoice if you want to probe the public node of the invoice? Route hints in an invoice will be interpreted.

[hieblmi]

The change LGTM pending guggero's comment.

@ziggie1984 would you mind adding another commit that renames idMatchesRefNode in isLsp with matchesDestNode? RefNode was used before but forgotten to change, so just for consistency.

[kilrau]

IIUC you have an invoice to be probed that has a single non-existent route hint?

Correct.

If that's the case, why is the route hint in the invoice if you want to probe the public node of the invoice? Route hints in an invoice will be interpreted.

Because it's a special routing hint, see https://docs.boltz.exchange/api/magic-routing-hints. I think it makes a lot of sense instead of failing probes to non-existent routing hints to drop the assumption that this is an LSP. And instead probe the invoice's node. Just like Ziggie said.

Let me add some background info of how we even got here: It started out with the issue that Binance Lightning withdrawals into Boltz swaps were failing. We then went on a very tedious journey to find out that they do probing, figured out which exact probing method in LND Binance was using (EstimateRouteFee with payment_request + timeout, NOT dest+amt_sat) to then read LND's code to find out that it assumes that our Magic Routing Hints, which are present in a lot of swap invoices by now, is seen as a LSP and thus make the probe and thus the withdrawal fail.

Setting LSP to false if the routing hint is not a known public node solves the issue and hopefully saves this incredible debug timesink to anyone who does similar things in the future.

Hope that helps!