diff --git a/cardano-api/internal/Cardano/Api/Experimental/Tx.hs b/cardano-api/internal/Cardano/Api/Experimental/Tx.hs index 2c59b8815..f5c7491a3 100644 --- a/cardano-api/internal/Cardano/Api/Experimental/Tx.hs +++ b/cardano-api/internal/Cardano/Api/Experimental/Tx.hs @@ -42,6 +42,17 @@ module Cardano.Api.Experimental.Tx -- -- You can see how to do this in the documentation of the "Cardano.Api.Tx.Body" module. + -- ** Balancing a transaction + + -- | + -- If we have a UTxO with exactly 12 ADA, and 2 ADA is enough for the fees, we could just construct + -- the transaction like in the previous section directly, and it could be a valid transaction. But still, + -- even if we have exactly 12 ADA, it is unlikely the fees required are exactly 2 ADA, so either we made + -- an invalid transaction, or we are wasting ADA on fees. Also, we may not always want to send all the ADA + -- in the UTxO. So that is were transaction balancing comes in. + -- + -- You can see how to balance a transaction in the documentation of the "Cardano.Api.Fees" module. + -- ** Creating a 'ShelleyWitnessSigningKey' -- | diff --git a/cardano-api/internal/Cardano/Api/Fees.hs b/cardano-api/internal/Cardano/Api/Fees.hs index 61a4daf5b..47651a0fb 100644 --- a/cardano-api/internal/Cardano/Api/Fees.hs +++ b/cardano-api/internal/Cardano/Api/Fees.hs @@ -12,21 +12,306 @@ -- | Fee calculation module Cardano.Api.Fees - ( -- * Transaction fees + ( -- * Introduction + + -- + + -- | + -- The documentation of the "Cardano.Api.Tx.Body" module shows how to create a 'TxBodyContent' for a + -- transaction that takes 12 ADA and sends 10 ADA to an address, and spends 2 ADA on fees. If we have a + -- UTxO with exactly 12 ADA, and 2 ADA is enough for the fees, this could be a valid transaction. But still, + -- even if we have exactly 12 ADA, it is unlikely that the fees required are exactly 2 ADA, so either we + -- made an invalid transaction, or we are wasting ADA on fees. + -- + -- On the other hand, we don't always want to spend all the ADA from a UTxO. Balancing a transaction allows + -- us to send the amount we want to send, pay only the necessary fees (or little more), and it + -- allows us to calculate the amount of extra currency that we can send back to a change address. + -- + -- Because changes to the transaction body will potentially change the amount of fees needed by a transaction, + -- finding this balance can be quite tricky. But fortunately, we have functions that help achieve this. + -- + -- This module provides several different ways of calculating the fees for a transaction or altogether + -- balancing a draft transaciton, which require different amounts of information, and provide different levels + -- of accuracy and automation. + -- + -- Next, we explore three examples of different and representative ways of calculating the fees for a transaction. + -- There are some other ways, but they have similar requirements. + -- + -- In these examples, we are using the following qualified modules: + -- + -- @ + -- import qualified Cardano.Api as Api -- the general `cardano-api` exports + -- @ + + -- ** Example 1: Simple fee calculation and manual balancing + + -- | + -- This method requires very little information, and it requires a little manual + -- work. + -- + -- It simply calculates the fees for a transaction, and then we need to do the + -- balancing ourselves. + -- + -- We just need to know: + -- + -- 1. The shelley based era witness for the current era. We can get it by using 'shelleyBasedEra'. + -- + -- @ + -- let sbe :: Api.ShelleyBasedEra Api.ConwayEra = Api.shelleyBasedEra + -- @ + -- + -- 2. The protocol parameters for the current era. We can get them by using the 'QueryProtocolParameters' + -- query defined in "Cardano.Api.Query". Let's assume we have them in the @exampleProtocolParams@ variable. + -- + -- 3. The draft transaction body. We can get it by using 'createTransactionBody' defined in "Cardano.Api.Tx.Body": + -- + -- @ + -- let (Right txBody) = Api.createTransactionBody sbe txBodyContent + -- @ + -- + -- 4. The number of Byron and Shelley key witnesses. This is just the number of keys that need + -- to sign the transaction. We can get an estimate by using 'estimateTransactionKeyWitnessCount' + -- but for a simple transaction that is using a single UTxO locked by a single modern Shelley key, + -- we would have @0@ Byron witnesses and @1@ Shelley witness. + -- + -- 5. Lastly, the size of the reference scripts in bytes, if any. For simple transactions, + -- this would be @0@. + -- + -- With this in mind we could estimate the fees required by our transaction by calling + -- 'evaluateTransactionFee' as follows: + -- + -- @ + -- let fees = Api.evaluateTransactionFee sbe exampleProtocolParams txBody 0 1 0 + -- @ + -- + -- Once we know the amount of fees required, we could balance the transaction by + -- substracting it from the total value of the UTxO we are spending. + -- + -- For example, if we have a UTxO with 12 ADA, the fees are 0.2 ADA, and we want + -- to send 10 ADA to an address. We could have a transaction with: + -- + -- * 1 input of 12 ADA (from the UTxO) + -- * 1 output of 10 ADA (to the address we want to pay) + -- * 1 output of 1.8 ADA (to the change address) + -- * 0.2 ADA in fees + -- + -- So, we would have to update our 'TxBodyContent' accordingly, and continue with the + -- transaction building as we demonstrate in the 'Cardano.Api.Experimental.Tx' module + + -- ** Example 2: Automated balancing without chain info (no UTxO, no ledger state) + + -- | + -- This method requires a bit more of information, but it does more work for us + -- automatically and we have to guess less. It also works with a 'TxBodyContent', + -- instead of a full 'TxBody'. + -- + -- We need the following info: + -- + -- 1. The MaryEraOnwards witness for the current era. In this case we are using the + -- one for 'Conway' era: + -- + -- @ + -- let meo = Api.MaryEraOnwardsConway + -- @ + -- + -- 2. The draft 'TxBodyContent' for the transaction we want to balance. In "Cardano.Api.Tx.Body" we show + -- how to create one. We assume we have it in the @txBodyContent@ variable. + -- + -- 3. The protocol parameters for the current era. We can get them by using the 'QueryProtocolParameters' + -- query defined in "Cardano.Api.Query". Let's assume we have them in the @exampleProtocolParams@ variable. + -- + -- 4. For stake pool and gov actions, we will also need: + -- + -- * The set of registered stake pools, that are being unregistered in this transaction. + -- * The map of all deposits for stake credentials that are being unregistered in this transaction. + -- * The map of all deposits for drep credentials that are being unregistered in this transaction. + -- * Plutus script execution units for all script witness we are used in the transaction. + -- + -- For this example, we are assuming we are doing nothing like that and using not scripts, + -- so we will use 'mempty' for the four. + -- + -- 5. Counts for: + -- + -- * The collateral amount we are depositing. This is only required for transactions that + -- have scripts in them. So we are assuming this will be @0@. + -- * The number of Shelley key witnesses still to be added to the transaction. We can get an + -- estimate by using 'estimateTransactionKeyWitnessCount' but for a simple transaction that is using + -- a single UTxO locked by a single modern Shelley key, we would have @1@ Shelley witness. + -- * The number of Byron key witnesses still to be added to the transaction. We are assuming + -- this will be @0@ for our transaction. + -- * Size of all reference scripts in bytes. Again, we are not using any reference scripts, so + -- this would be @0@. + -- + -- 6. The address where we want to send the change. We can deserialise it from its bech32 representation + -- by using the 'deserialiseAddress' function defined in "Cardano.Api.Address": + -- + -- @ + -- let Just exampleChangeAddress = + -- Api.deserialiseAddress + -- (Api.AsAddressInEra eraAsType) + -- "addr_test1vzpfxhjyjdlgk5c0xt8xw26avqxs52rtf69993j4tajehpcue4v2v" + -- @ + -- + -- Or we can get it from our signing key + -- + -- @ + -- let exampleChangeAddress = + -- Api.shelleyAddressInEra sbe $ + -- Api.makeShelleyAddress + -- (Api.Testnet $ Api.NetworkMagic 2) -- The magic for the network we are using + -- (Api.PaymentCredentialByKey + -- $ Api.verificationKeyHash + -- $ Api.getVerificationKey + -- signingKey) + -- Api.NoStakeAddress -- Potentially, the stake credential if we want to use one + -- @ + -- + -- 7. Finally, we need to know the total amount in the UTxOs we are spending. In our example, + -- we are spending 12 ADA, so we would have: + -- + -- @ + -- let totalUTxOValue = Api.lovelaceToValue 12_000_000 + -- @ + -- + -- With all this information, we could get a balanced transaction by calling 'estimateBalancedTxBody' + -- as follows: + -- + -- @ + -- let (Right (Api.BalancedTxBody + -- updatedTxBodyContent + -- updatedTxBody + -- changeOutput + -- fees)) = + -- Api.estimateBalancedTxBody + -- meo + -- txBodyContent + -- exampleProtocolParams + -- mempty + -- mempty + -- mempty + -- mempty + -- 0 + -- 1 + -- 0 + -- 0 + -- exampleChangeAddress + -- @ + -- + -- This will give us a balanced transaction, with the fees calculated, and the change output. + -- Now we can just proceed with transaction singing and submission. + + -- ** Example 3: Full automated balancing with chain info (requires UTxO and ledger state info) + + -- | + -- In the previous example, we had to provide a lot of information manually, which was + -- easy because our transaction was simple. But, for more complex transactions, that may have + -- scripts or other advanced functions (like governance actions), there is an approach that + -- will do many of the calculations for us in exchange for some general information about + -- the ledger. + -- + -- We need the following info: + -- + -- 1. The shelley based era witness for the current era. We can get it by using 'shelleyBasedEra'. + -- + -- @ + -- let sbe :: Api.ShelleyBasedEra Api.ConwayEra = Api.shelleyBasedEra + -- @ + -- + -- 2. The time the network started. We can obtain it using the 'QuerySystemStart' query + -- defined in "Cardano.Api.Query". Let's assume we have it in the @exampleSystemStart@ variable. + -- + -- 3. The ledger epoch info. We can obtain it by applying the 'toLedgerEpochInfo' function + -- to the 'EraHistory' that we can obtain using the 'QueryEraHistory' query defined in + -- "Cardano.Api.Query". Let's assume we have it in the @exampleLedgerEpochInfo@ variable. + -- + -- 4. The protocol parameters for the current era. We can get them by using the 'QueryProtocolParameters' + -- query defined in "Cardano.Api.Query". Let's assume we have them in the @exampleProtocolParams@ variable. + -- + -- 5. For stake pool and gov actions, we will also need: + -- + -- * The set of registered stake pools, that are being unregistered in this transaction. + -- * The map of all deposits for stake credentials that are being unregistered in this transaction. + -- * The map of all deposits for drep credentials that are being unregistered in this transaction. + -- + -- For this example, I am assuming we are doing nothing like that, so we will use 'mempty' for the three. + -- + -- 6. The part of the UTxO that we are spending. We can obtain the whole UTxO using the 'QueryUTxO' query + -- defined in "Cardano.Api.Query". Let's assume we have it in the @utxoToUse@ variable. + -- + -- 7. The draft 'TxBodyContent' for the transaction we want to balance. In "Cardano.Api.Tx.Body" we show + -- how to create one. + -- + -- 8. The address where we want to send the change. We can deserialise it from its bech32 representation + -- by using the 'deserialiseAddress' function defined in "Cardano.Api.Address": + -- + -- @ + -- let (Just exampleChangeAddress) = + -- Api.deserialiseAddress + -- (Api.AsAddressInEra eraAsType) + -- "addr_test1vzpfxhjyjdlgk5c0xt8xw26avqxs52rtf69993j4tajehpcue4v2v" + -- @ + -- + -- Or we can get it from our signing key + -- + -- @ + -- let exampleChangeAddress = + -- Api.shelleyAddressInEra sbe $ + -- Api.makeShelleyAddress + -- (Api.Testnet $ Api.NetworkMagic 2) -- The magic for the network we are using + -- (Api.PaymentCredentialByKey + -- $ Api.verificationKeyHash + -- $ Api.getVerificationKey + -- signingKey) + -- Api.NoStakeAddress -- Potentially, the stake credential if we want to use one + -- @ + -- + -- + -- 9. Finally, we have the opportunity to override the number of key witnesses that the transaction + -- will require. But the function will calculate them automatically if we set this to 'Nothing'. + -- + -- With all this information, we could get a balanced transaction by calling 'makeTransactionBodyAutoBalance' + -- as follows: + -- + -- @ + -- let Right (Api.BalancedTxBody + -- updatedTxBodyContent + -- updatedTxBody + -- changeOutput + -- fees) = + -- Api.makeTransactionBodyAutoBalance + -- sbe + -- exampleSystemStart + -- exampleLedgerEpochInfo + -- (Api.LedgerProtocolParameters exampleProtocolParams) + -- mempty + -- mempty + -- mempty + -- utxoToUse + -- txBodyContent + -- exampleChangeAddress + -- Nothing + -- @ + -- + -- This will give us a balanced transaction, with the fees calculated, and the change output. + -- Now we can just proceed with transaction singing and submission. + + -- * Contents + + -- ** Transaction fees evaluateTransactionFee , calculateMinTxFee , estimateTransactionKeyWitnessCount - -- * Script execution units + -- ** Script execution units , evaluateTransactionExecutionUnits , evaluateTransactionExecutionUnitsShelley , ScriptExecutionError (..) , TransactionValidityError (..) - -- * Transaction balance + -- ** Transaction balance , evaluateTransactionBalance - -- * Automated transaction building + -- ** Automated transaction building , estimateBalancedTxBody , estimateOrCalculateBalancedTxBody , makeTransactionBodyAutoBalance @@ -40,10 +325,10 @@ module Cardano.Api.Fees , TxBodyErrorAutoBalance (..) , TxFeeEstimationError (..) - -- * Minimum UTxO calculation + -- ** Minimum UTxO calculation , calculateMinimumUTxO - -- * Internal helpers + -- ** Internal helpers , ResolvablePointers (..) ) where diff --git a/cardano-api/internal/Cardano/Api/Tx/Body.hs b/cardano-api/internal/Cardano/Api/Tx/Body.hs index 3024be140..338088e4a 100644 --- a/cardano-api/internal/Cardano/Api/Tx/Body.hs +++ b/cardano-api/internal/Cardano/Api/Tx/Body.hs @@ -27,7 +27,7 @@ module Cardano.Api.Tx.Body -- In this example, we are using the following qualified modules: -- -- @ - -- import qualified Cardano.Api as Api -- the general `cardano-api` exports (including the old API) + -- import qualified Cardano.Api as Api -- the general `cardano-api` exports -- import qualified Cardano.Api.Script as Script -- types related to scripts (Plutus and native) -- import qualified Cardano.Api.Experimental as Exp -- the experimental API -- @ diff --git a/cardano-api/test/cardano-api-test/Test/Cardano/Api/Experimental.hs b/cardano-api/test/cardano-api-test/Test/Cardano/Api/Experimental.hs index 79766783a..3abadbd85 100644 --- a/cardano-api/test/cardano-api-test/Test/Cardano/Api/Experimental.hs +++ b/cardano-api/test/cardano-api-test/Test/Cardano/Api/Experimental.hs @@ -183,7 +183,7 @@ prop_balance_transaction_two_ways = H.propertyOnce $ do -- H.note_ $ "TxBodyContent 3: " <> show txBodyContent3 -- H.note_ $ "Change output 3: " <> show changeOutput3 - H.failure + H.success exampleProtocolParams :: Ledger.PParams (UnexportedLedger.ConwayEra Ledger.StandardCrypto) exampleProtocolParams =