Receiver create_session should accept an amount param

[benalleng]

In our liana integration in creating our receiver session @arminsabouri realized that it would be nice to allow the amount as a param to be passed to the session for rust-payjoin to handle the bip-21 amount creation instead of leaving that up to the wallet.

The code is minimal but considering it is required it seems like a footgun to require the integration dev to know to do this after starting a receiver session.

rust-payjoin/payjoin-cli/src/app/v2/mod.rs

Lines 112 to 113 in 5ecfed7

	let mut pj_uri = session.pj_uri();
	pj_uri.amount = Some(amount);

[nothingmuch]

note that this is not just a convenience thing but is important for representing payjoin history accurately (because unless it's stored, and the two parties pay at different effective feerates, the actual payment amount is underdetermined and cannot be inferred from the confirmed transaction reliably)

#336

[DanGould]

Yes, I agree the constructor taking Option<Amount> would be convenient.

I'm not sure if saving the amount in the URI necessarily helps recall payjoin history. I think The diff between original PSBT and payjoin PSBT is necessary, because a sender is not compelled to pay the amount posted in the URI.

[nothingmuch]

Yes, I agree the constructor taking Option<Amount> would be convenient.

I'm not sure if saving the amount in the URI necessarily helps recall payjoin history. I think The diff between original PSBT and payjoin PSBT is necessary, because a sender is not compelled to pay the amount posted in the URI.

Yes, I kinda conflated two things, but I think both are important:

1. the amount the receiver requested
2. the amount the sender gave the receiver, not counting the fees both parties paid

there's also the net balance change for the receiver, but this is inferred from just the on chain tx

[spacebear21]

Closed by #920