improvement: scriptRef size double-counted when UTxO appears in both spent and reference inputs

[solidsnakedev]

Summary

calculateReferenceScriptFee receives [...state.selectedUtxos, ...state.referenceInputs]. If the same UTxO appears in both arrays (e.g. spent via collectFrom and also listed via readFrom), its scriptRef size is counted twice.

The Cardano node deduplicates using Set.union before scanning:

-- eras/conway/impl/src/Cardano/Ledger/Conway/UTxO.hs
txNonDistinctRefScriptsSize utxo tx = ...
  where
    inputs = (tx ^. bodyTxL . referenceInputsTxBodyL)
      `Set.union` (tx ^. bodyTxL . inputsTxBodyL)  -- union deduplicates

Impact

Only affects the edge case where the same UTxO is both spent and read. Over-charges the ref script fee for that UTxO. Safe (node accepts fees above minimum) but imprecise.

Fix

Deduplicate by UTxO output reference before scanning:

const seen = new Set<string>()
const deduped = [...state.selectedUtxos, ...state.referenceInputs].filter(utxo => {
  const key = `${utxo.txHash}#${utxo.outputIndex}`
  if (seen.has(key)) return false
  seen.add(key)
  return true
})

Affected File

packages/evolution/src/sdk/builders/phases/FeeCalculation.ts — the call site that builds the utxo array passed to calculateReferenceScriptFee

[danbaruka]

Hi @solidsnakedev,
I can take this issue. Please assign it to me.
Thanks.