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createtx: Add change output to size estimation. #2057

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merged 1 commit into from Sep 13, 2021
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createtx: Add change output to size estimation. #2057

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11 changes: 6 additions & 5 deletions wallet/createtx.go
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Expand Up @@ -629,11 +629,12 @@ func (w *Wallet) txToMultisigInternal(ctx context.Context, op errors.Op, dbtx wa
}
msgtx.AddTxOut(txOut)

// Add change if we need it. The case in which
// totalInput == amount+feeEst is skipped because
// we don't need to add a change output in this
// case.
feeSize := txsizes.EstimateSerializeSize(scriptSizes, msgtx.TxOut, 0)
// Add change if we need it.
changeSize := 0
if totalInput > amount+feeEstForTx {
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@matheusd matheusd Jun 3, 2021 •
edited

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This isn't exactly right, since it could be the case that totalInput is greater than amount+feeEstForTx but lower than the dust limit, which shouldn't create a change amount, but since feeEstForTx is significantly overestimated (0.5 dcr) this shouldn't happen in ordinary usage.

Fixing this edge case (dust limit change) would require tweaking this entire function to do a proper fee estimation, so unless this is really needed, the proposed change fixes the original issue.

changeSize = txsizes.P2PKHPkScriptSize
}
feeSize := txsizes.EstimateSerializeSize(scriptSizes, msgtx.TxOut, changeSize)
feeEst := txrules.FeeForSerializeSize(w.RelayFee(), feeSize)

if totalInput < amount+feeEst {
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