doc: document the plugin interface to gather Bitcoin data

[darosior]

This finally closes #3354 by making the current API final.

There are still things that can get added to the process (namely, notifications for a more optimized polling) but I don't think we'd need to break the interface again (soon).

I have resigned from using WU for transaction sizes as most of the Bitcoin data source seem to actually prefer round ups, and that would have resulted in boutique transformation in plugins to pass from btc/kWU to btc/kVB..

[fiatjaf]

I very much like the estimatefees call. That means I can decide to accept if a peer for any reason wants to pay a very high or low fee by just returning a very large number in max or min?

What happens if I set all fields to null?

[darosior]

That means I can decide to accept if a peer for any reason wants to pay a very high or low fee by just returning a very large number in max or min?

Indirectly, kind of: you can decide of the flexibility you give to your peer regarding transaction fees, but you should prefer using --ignore-fee-limits for this usecase.

What happens if I set all fields to null?

That means your plugin could not estimate the fees.

[fiatjaf]

What happens if I set all fields to null?

That means your plugin could not estimate the fees.

The link doesn't lead anywhere. What happens when the plugin cannot estimate the fees?

[darosior]

The link doesn't lead anywhere. What happens when the plugin cannot estimate the fees?

Yep, because force push. When the plugin cannot estimate fees the feerate is set to:

• Floor (253perkw) if mainnet and not in developer mode
• 0 if testnet and not developer mode
• 0 if developer mode

[rustyrussell]

Ack 8b758de