HRN: Emit new event type when Offer has been received and validated

[tnull]

Currently, when using the ChannelManager::pay_for_offer_from_human_readable_name API, the user gets no access to the offer data retrieved. It would be great to add a new event type that is emitted when the offer has been retrieved and validated, e.g. here:

rust-lightning/lightning/src/ln/channelmanager.rs

Line 12790 in b543afe

if let Some((completed_requests, mut offer)) = offer_opt {

[TheBlueMatt]

Hmm, is there a reason you need the Offer directly or can you just access the offer fields via the Bolt12Invoice when the payment ultimately completes (which I believe was added upstream but is not in 0.1)?

[tnull]

Hmm, is there a reason you need the Offer directly or can you just access the offer fields via the Bolt12Invoice when the payment ultimately completes (which I believe was added upstream but is not in 0.1)?

Hmm, IIUC, PaymentSent would only give us the Bolt12Invoice, which doesn't even expose OfferId, for instance. But more generally: the payment might very well fail and we'd still like to be able to fill in some of the metadata fields and maybe even retry using the Offer, which would save us multiple RTTs for resolving/retrieving the offer once more.

[chuksys]

I'd like to pick this up.

[tnull]

I'd like to pick this up.

Sure, go for it!

[TheBlueMatt]

Hmm, IIUC, PaymentSent would only give us the Bolt12Invoice, which doesn't even expose OfferId, for instance.

that's easy to fix, though, and likely it should :).

But more generally: the payment might very well fail and we'd still like to be able to fill in some of the metadata fields

Hmm? Like what? I'm not really sure there's much to fill in from an Offer derived from an HRN - its really just a blinded path to request an Invoice?

maybe even retry using the Offer, which would save us multiple RTTs for resolving/retrieving the offer once more.

That's one RTT, but I guess I'm not clear on the point of that? Like, DNS should move pretty quick, hopefully, and if an Offer request times out its probably already retried a few times and we've waited a while. Adding one RTT on top of the retry seems perfectly fine?

[tnull]

That's one RTT, but I guess I'm not clear on the point of that? Like, DNS should move pretty quick, hopefully, and if an Offer request times out its probably already retried a few times and we've waited a while. Adding one RTT on top of the retry seems perfectly fine?

The point is that we already retrieved the offer and still would have an entirely blank entry in the payment store even though we could provide the user additional metadata.