Implement LNURL-fastWithdrawal

[jackeveritt]

https://github.com/btcontract/lnurl-rfc/blob/master/spec.md#3-lnurl-withdraw

See the new bit about fastWithdrawal. It is an optional optimisation. You can avoid the first GET request if the decoded LNURL already has the payload included.

I tested once with this new style of LNURL in breez and withdrawal didn't work. But please confirm this yourselves as I was in a rush when trying it out.

1. Make sure the new format doesn't break the original flow of the protocol.
2. Implement the optimisation if you want to support fast withdrawals from apps using 'lightning:'

If you have an alpha feel free to add me to the testing as I regularly test the beta on testflight

[kingonly]

When Jack says "it didn't work", he means Breez complained about an invalid lnurl string. The new protocol should be backward compatible. P1: Resolve the backward compatibility issue P2: Implement fast withdraw

[roeierez]

@jackeveritt I have tested the sample url you provided and it seems to work as I got the url expired error. I tested from both a QR generated by the sample string and from a url click (added lightning: scheme as a prefix).

[jackeveritt]

That’s good. It works then.

I think the problem must have been in the way I tested the LNURL. I pasted lightning://lnurl in safari on mobile and it prompted me to open with breez. That’s the path I took.

[jackeveritt]

Don’t wanna keep this open for implementing the optimisation? Or is it done already 😀

[kingonly]

Sorry, my bad. Let's keep it open for the optimization.

[jackeveritt]

I now get an error ""Failed to process link: unknown response tag" when using this type on LNURL. I have sent Roy and example LNURL that I generate. If you need more let me know