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Auto-balance multiasset transactions #4450

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Apr 2, 2023
Merged

Auto-balance multiasset transactions #4450

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2 changes: 2 additions & 0 deletions cardano-api/ChangeLog.md
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Original file line number Diff line number Diff line change
Expand Up @@ -36,6 +36,8 @@
New type `BundledProtocolParameters` and new functions `bundleProtocolParams` and `unbundleProtocolParams`.
([PR4903](https://github.com/input-output-hk/cardano-node/pull/4903))

- Auto-balance multi asset transactions ([PR 4450](https://github.com/input-output-hk/cardano-node/pull/4450))

### Bugs

- Allow reading text envelopes from pipes ([PR 4384](https://github.com/input-output-hk/cardano-node/pull/4384))
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48 changes: 27 additions & 21 deletions cardano-api/src/Cardano/Api/Fees.hs
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Expand Up @@ -799,11 +799,6 @@ data TxBodyErrorAutoBalance =
-- | One or more of the scripts were expected to fail validation, but none did.
| TxBodyScriptBadScriptValidity

-- | The balance of the non-ada assets is not zero. The 'Value' here is
-- that residual non-zero balance. The 'makeTransactionBodyAutoBalance'
-- function only automatically balances ada, not other assets.
| TxBodyErrorAssetBalanceWrong Value

-- | There is not enough ada to cover both the outputs and the fees.
-- The transaction should be changed to provide more input ada, or
-- otherwise adjusted to need less (e.g. outputs, script etc).
Expand Down Expand Up @@ -862,13 +857,6 @@ instance Error TxBodyErrorAutoBalance where
displayError TxBodyScriptBadScriptValidity =
"One or more of the scripts were expected to fail validation, but none did."

displayError (TxBodyErrorAssetBalanceWrong _value) =
"The transaction does not correctly balance in its non-ada assets. "
++ "The balance between inputs and outputs should sum to zero. "
++ "The actual balance is: "
++ "TODO: move the Value renderer and parser from the CLI into the API and use them here"
-- TODO: do this ^^

displayError (TxBodyErrorAdaBalanceNegative lovelace) =
"The transaction does not balance in its use of ada. The net balance "
++ "of the transaction is negative: " ++ show lovelace ++ " lovelace. "
Expand Down Expand Up @@ -1005,13 +993,30 @@ makeTransactionBodyAutoBalance systemstart history pparams
-- output and fee. Yes this means this current code will only work for
-- final fee of less than around 4000 ada (2^32-1 lovelace) and change output
-- of less than around 18 trillion ada (2^64-1 lovelace).
-- However, since at this point we know how much non-Ada change to give
-- we can use the true values for that.

let outgoingNonAda = mconcat [filterValue isNotAda v | (TxOut _ (TxOutValue _ v) _ _) <- txOuts txbodycontent]
let incomingNonAda = mconcat [filterValue isNotAda v | (TxOut _ (TxOutValue _ v) _ _) <- Map.elems $ unUTxO utxo]
let mintedNonAda = case txMintValue txbodycontent1 of
TxMintNone -> mempty
TxMintValue _ v _ -> v
let nonAdaChange = mconcat
[ incomingNonAda
, mintedNonAda
, negateValue outgoingNonAda
]

let changeTxOut = case multiAssetSupportedInEra cardanoEra of
Left _ -> lovelaceToTxOutValue $ Lovelace (2^(64 :: Integer)) - 1
Right multiAsset -> TxOutValue multiAsset (lovelaceToValue (Lovelace (2^(64 :: Integer)) - 1) <> nonAdaChange)
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Hi @LudvikGalois

Just curious: do you have any expectations about how the makeTransactionBodyAutoBalance function should behave if the changeTxOut value is larger that the maximum value size? (As defined by the maxValueSize protocol parameter.)

In cardano-wallet, if we detect that a generated (change) output is larger than the maximum size, we partition it into a number of smaller outputs.

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It's not currently handled here, although it'll be caught when trying to submit. My preference for now is to "give up" and require the user to explicitly make change themselves when building the transaction (my understanding is that this is an edge case in most cases). Manually balancing multiassets is much easier for a human (or script) to do than balancing Ada, because it doesn't need to account for some of what its balancing disappearing as transaction fees.
Multiple change UTxOs is straightforward, but given that we don't know how the user plans to spend it, we might sub-optimally divide it, which could end up costing the user more in fees.


let (dummyCollRet, dummyTotColl) = maybeDummyTotalCollAndCollReturnOutput txbodycontent changeaddr
txbody1 <- first TxBodyError $ -- TODO: impossible to fail now
createAndValidateTransactionBody txbodycontent1 {
txFee = TxFeeExplicit explicitTxFees $ Lovelace (2^(32 :: Integer) - 1),
txOuts = TxOut changeaddr
(lovelaceToTxOutValue $ Lovelace (2^(64 :: Integer)) - 1)
changeTxOut
TxOutDatumNone ReferenceScriptNone
: txOuts txbodycontent,
txReturnCollateral = dummyCollRet,
Expand Down Expand Up @@ -1043,13 +1048,7 @@ makeTransactionBodyAutoBalance systemstart history pparams

-- check if the balance is positive or negative
-- in one case we can produce change, in the other the inputs are insufficient
case balance of
TxOutAdaOnly _ _ -> balanceCheck balance
TxOutValue _ v ->
case valueToLovelace v of
Nothing -> Left $ TxBodyErrorNonAdaAssetsUnbalanced v
Just _ -> balanceCheck balance

balanceCheck balance

--TODO: we could add the extra fee for the CBOR encoding of the change,
-- now that we know the magnitude of the change: i.e. 1-8 bytes extra.
Expand Down Expand Up @@ -1177,7 +1176,7 @@ makeTransactionBodyAutoBalance systemstart history pparams

balanceCheck :: TxOutValue era -> Either TxBodyErrorAutoBalance ()
balanceCheck balance
| txOutValueToLovelace balance == 0 = return ()
| txOutValueToLovelace balance == 0 && onlyAda (txOutValueToValue balance) = return ()
| txOutValueToLovelace balance < 0 =
Left . TxBodyErrorAdaBalanceNegative $ txOutValueToLovelace balance
| otherwise =
Expand All @@ -1187,6 +1186,13 @@ makeTransactionBodyAutoBalance systemstart history pparams
Left err -> Left err
Right _ -> Right ()

isNotAda :: AssetId -> Bool
isNotAda AdaAssetId = False
isNotAda _ = True

onlyAda :: Value -> Bool
onlyAda = null . valueToList . filterValue isNotAda

checkMinUTxOValue
:: TxOut CtxTx era
-> BundledProtocolParameters era
Expand Down