Feature request: allow onchain fees to be known before committing to paying them

[danielgranhao]

When either using any of the following methods:

• send_onchain()
• sweep()
• refund()

it would improve UX if we could know the fees that will be paid.

This could be done by splitting the methods into preparation and execution steps, such that after preparing, one can decide whether to execute or not based on the fees.

[roeierez]

That's right @danielgranhao
for sweep we are going to introduce prepareSweep: #294
For send_onchain we have https://github.com/breez/breez-sdk/blob/main/libs/sdk-core/src/breez_services.rs#L630C18-L630C41
for refund perhaps we can add the refund tx weight to the list_refundables ?

[danielgranhao]

That's right @danielgranhao
for sweep we are going to introduce prepareSweep: #294
For send_onchain we have https://github.com/breez/breez-sdk/blob/main/libs/sdk-core/src/breez_services.rs#L630C18-L630C41

Oh, sorry, completely missed that PR and the fetch_reverse_swap_fees() method.

for refund perhaps we can add the refund tx weight to the list_refundables ?

That would be nice!

[danielgranhao]

@roeierez I was working on a PR for adding the refund tx weight to list_refundables and realized that this won't lead to an exact prediction of the fees. Without knowing the address the user chooses, the tx weight will just be a guess (of course, very close to the real one, and one could opt for the worst-case scenario).

Wouldn't it be better to go with a "prepare" approach (similar to #294) that would provide the exact fee that will be used?

[roeierez]

Yes makes sense.

[JssDWt]

For send_onchain we have https://github.com/breez/breez-sdk/blob/main/libs/sdk-core/src/breez_services.rs#L630C18-L630C41

Link currently points to a different line of code.

[roeierez]

Right @JssDWt I meant this one: https://github.com/breez/breez-sdk/blob/main/libs/sdk-core/src/breez_services.rs#L647

[JssDWt]

Permalinking that https://github.com/breez/breez-sdk/blob/3c602db1fb0799ad96922a618c6dbe180a722c5a/libs/sdk-core/src/breez_services.rs#L647

[danielgranhao]

Closed by #294 and #548