Append metadata to transaction from Plutus code

Question

Is there a way to append metadata to transactions that are send from plutus code?

Right now we send transactions from the contracts like follows (or something alike):

ledgerTx <- submitTxConstraintsWith @Cube constraints tx
void $ awaitTxConfirmed $ txId ledgerTx

I know Alonzo is still in development/testing phase, but I was wondering if there is already something in the API do this or there will be (I cant find anything in the code base as of right now).

Answer 1

I'm not sure in what context you need to append metadata to a transaction, but you may want to check this documentation for any of these helper functions used for creating TxContraints:

• mustIncludeDatum :: forall i o. Datum -> TxConstraints i o
• mustPayToOtherScript :: forall i o. ValidatorHash -> Datum -> Value -> TxConstraints i o
• mustPayToTheScript :: forall i o. IsData o => o -> Value -> TxConstraints i o

The first two require a Datum while the last one could be any arbitrary data type converted to a Data using PlutusTx.unstableMakeIsData or its equivalents.

EDIT:

You might want to look into StateMachines. Especially the transition function (which also requires TxConstraints). You may start with this documentation,

Answer 2

No, it is not possible right now.

To change that, we would need a hard fork introducing this functionality.