Bitcoin-Qt: Tx fee weirdness

[Diapolo]

Using current Git master and want to send all coins from a wallet to another one.

• try to send 0.0128772 BTC
• message that a Tx fee of 0.001 BTC is needed, so I can't send
• try to send 0.0113772 BTC (All coins - Tx fee of 0.001 BTC)
• message that Tx is over size and I need a Tx fee of 0.0005

Is there a way to get the final Tx fee sum in one info message?

[gmaxwell]

0.0128772 - 0.001 = 0.0118772 > 0.0113772.

By lowering it more than you needed to you left an input out, making the transaction smaller... thus needing less fee. I don't see any way of solving that directly.

What I think would help would be options to "take any fee out of the amount being sent" which would remove that problem since the coin selection wouldn't change, and would do exactly what you wanted for the 'send all my coins case'. Also, an option to "round sent amount up, up to X btc", useful when sending to another account of yours, would also tend to reduce fees fairly considerably... but I don't know how UI for that stuff could be done in a non-confusing way.

[Diapolo]

At least a "send all and subtract the Tx fee"-option should be not that confusing in terms of UX as it's rather straight forward. I never looked at that part of the code, but perhaps that get's one of my next "targets".

[gmaxwell]

@Diapolo Perhaps just a third option on the fee question? "yes, no, take it out of the amount being sent" ?

[laanwj]

Or add a checkbox/combobox, otherwise you'd end up with a lot of text on a button.

In banking software this is generally posed as "who pays the fee", you or the recipient.

Maybe show a warning when the sender wants to pay the fee but there isn't enough balance to add the fee.

BTW what if the fee counts towards the amount being sent, but it consumes the entire amount so that the recipient doesn't receive anything? Can this happen?

[gmaxwell]

@laanwj It could certainly happen if the implementation was simplistic and if the payment was small (0.05 or less) or the user manually set a high BTC/KB. Good catch. I'm not quite sure how to avoid that without further complexifying the UI.

[laanwj]

Please help testing #4331, it tries to solve this.

[laanwj]

Closing as duplicate of #2724.
Note: that pull (#4331) still desperately needs testing, if no one tests it and verifies the functionality, it cannot be merged.