Add 'describeCardanoTx' for debugging

  Printing a whole 30KB+ transaction via 'Show' on a property failure is unreadable. Most of the time, we are interested in synthetic informations about generated values, especially transactions or UTXO maps (e.g. number of inputs, number of assets, max value, min value, etc..). This function does just that.

hydra-node/src/Hydra/Ledger/Cardano.hs

@@ -20,7 +20,7 @@ import Cardano.Api hiding (UTxO)
 import qualified Cardano.Api
 import Cardano.Api.Byron
 import Cardano.Api.Shelley
-import Cardano.Binary (decodeAnnotator, serialize')
+import Cardano.Binary (decodeAnnotator, serialize, serialize')
 import qualified Cardano.Crypto.DSIGN as CC
 import qualified Cardano.Crypto.Hash.Class as CC
 import qualified Cardano.Ledger.Address as Ledger
@@ -36,6 +36,7 @@ import qualified Cardano.Ledger.Crypto as Ledger (StandardCrypto)
 import qualified Cardano.Ledger.Era as Ledger
 import qualified Cardano.Ledger.Keys as Ledger
 import qualified Cardano.Ledger.Mary as Ledger.Mary
+import qualified Cardano.Ledger.Mary.Value as Ledger.Mary
 import qualified Cardano.Ledger.SafeHash as Ledger
 import qualified Cardano.Ledger.Shelley.API.Mempool as Ledger
 import qualified Cardano.Ledger.Shelley.Address.Bootstrap as Ledger
@@ -53,6 +54,7 @@ import qualified Codec.CBOR.Encoding as CBOR
 import Control.Arrow (left)
 import Control.Monad (foldM)
 import qualified Control.State.Transition as Ledger
+import qualified Data.ByteString.Lazy as BL
 import Data.Default (Default, def)
 import qualified Data.Map.Strict as Map
 import Data.Maybe (fromJust)
@@ -243,6 +245,31 @@ instance Arbitrary CardanoTx where
   -- TODO: shrinker!
   arbitrary = genUtxo >>= genTx
 
+-- | Show (compact) information about a Cardano transaction for debugging purpose.
+--
+-- NOTE: The function is 'incomplete' but can easily be extended to cover new
+-- needs.
+describeCardanoTx :: CardanoTx -> Text
+describeCardanoTx (Tx body _wits) =
+  unlines
+    [ show (getTxId body)
+    , "  Inputs (" <> show (length inputs) <> ")"
+    , "  Outputs (" <> show (length outputs) <> ")"
+    , "    total number of assets: " <> show totalNumberOfAssets
+    , "  Scripts (" <> show (length scripts) <> ")"
+    , "    total size (bytes):  " <> show totalScriptSize
+    ]
+ where
+  ShelleyTxBody _era lbody scripts _scriptsData _auxData _validity = body
+  outputs = Ledger.Alonzo.outputs' lbody
+  inputs = Ledger.Alonzo.inputs' lbody
+  totalScriptSize = sum $ BL.length . serialize <$> scripts
+  totalNumberOfAssets =
+    sum $
+      [ foldl' (\n inner -> n + Map.size inner) 0 outer
+      | Ledger.Alonzo.TxOut _ (Ledger.Mary.Value _ outer) _ <- toList outputs
+      ]
+
 -- | Create a zero-fee, payment cardano transaction.
 mkSimpleCardanoTx ::
   (TxIn, TxOut CtxUTxO Era) ->