Debugging Plutus

debugging-plutus.md

Debugging Plutus

This example illustrates manually passing serialized data from a Plutus validator and then deserializing it. It uses Plutus.Debug.

Instrument the validator

Change traceIfFalse to Plutus.Debug.debugIfFalse with added arguments containing the data to be passed out of the script. Here we change

traceIfFalse "R" $ any (checkScriptOutput addr hsh value) allOutputs

to

debugIfFalse "R" (addr, hsh, value, allOutputs) $ any (checkScriptOutput addr hsh value) allOutputs

, which only works if the data being serialized has IsData instances.

Run the script

In this example, we tried to submit a failing script and received the following output:

TxBodyScriptExecutionError [(ScriptWitnessIndexTxIn 2,ScriptErrorEvaluationFailed (CekError An error has occurred:  User error:
The provided Plutus code called 'error'.                                                                                             
Caused by: (unBData #d8799f4152d8799fd8799fd87a9f581c571dc6f3488905883a346746540f94254be3b5151a3845fc83fc1c9effd87a80ffd87a80a140a1401a05f5e1009fd8799fd8799fd8799f581ce1ce601c08286179ae7ae6ef3a38262d4112cab0663a68dfb8e9edc5ffd87a80ffa140a14000d87a80ffd8799fd8799fd87a
9f581cb81ade746787c130f13f0cc28d72d19a755c49684fccc3d5abdd6f62ffd87a80ffa140a1401a002dc6c0d8799f58206d1de149d42e49c15e33104441c1298ce8b11b0eef7d48994bf452c3dea7b427ffffd8799fd8799fd8799f581c90304fe1d67fbcad6ce67e6a32d37f0d75f159701b7328bee5912dc9ffd87a80ffa240a1401a0
5f5e100581c8bb3b343d8e404472337966a722150048c768d0a92a9813596c5338da14f54686f6d61734d6964646c65746f6e01d87a80ffd8799fd8799fd8799f581ce1ce601c08286179ae7ae6ef3a38262d4112cab0663a68dfb8e9edc5ffd87a80ffa240a1401a002dc6c0581c8bb3b343d8e404472337966a722150048c768d0a92a981
3596c5338da14c4a6f686e466c65746368657201d87a80ffffffff)) [])]                                                                        

Deserialize the data

Start a cabal REPL session and import the necessary functions:

import Plutus.Debug
import Plutus.V1.Ledger.Address (Address)
import Plutus.V1.Ledger.Scripts (DatumHash)
import Plutus.V1.Ledger.Value (Value)
import Plutus.V1.Ledger.Api (TxOut)
import PrettyPrinter.Extras (pretty)

Raw Plutus Data

One can see the Plutus Data using the recoverPlutusData function:

message = "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"
pretty $ recoverPlutusData message

(Right <"R",
<<<"W\GS\198\243H\137\ENQ\136:4gFT\SI\148%K\227\181\NAK\SUB8E\252\131\252\FS\158">,
<>>,
<>,
{"": {"": 100000000}},
[<<<"\225\206`\FS\b(ay\174z\230\239:8&-A\DC2\202\176f:h\223\184\233\237\197">,
<>>,
{"": {"": 0}},
<>>,
<<<"\184\SUB\222tg\135\193\&0\241?\f\194\141r\209\154u\\IhO\204\195\213\171\221ob">,
<>>,
{"": {"": 3000000}},
<"m\GS\225I\212.I\193^3\DLEDA\193)\140\232\177\ESC\SO\239}H\153K\244R\195\222\167\180'">>,
<<<"\144\&0O\225\214\DEL\188\173l\230~j2\211\DEL\ru\241Yp\ESCs(\190\229\145-\201">,
<>>,
{"": {"": 100000000},
"\139\179\179C\216\228\EOTG#7\150jr!P\EOT\140v\141\n\146\169\129\&5\150\197\&3\141": {"ThomasMiddleton": 1}},
<>>,
<<<"\225\206`\FS\b(ay\174z\230\239:8&-A\DC2\202\176f:h\223\184\233\237\197">,
<>>,
{"": {"": 3000000},
"\139\179\179C\216\228\EOTG#7\150jr!P\EOT\140v\141\n\146\169\129\&5\150\197\&3\141": {"JohnFletcher": 1}},
<>>]>>)

Deserialization via FromData

The raw plutus data is tedious to read, so we deserialize it with fromData.

recoverFromData message :: Either String (String, (Address, Maybe DatumHash, Value, [TxOut]))

Right (
  "R",
  (
    Address {addressCredential = ScriptCredential 571dc6f3488905883a346746540f94254be3b5151a3845fc83fc1c9e, addressStakingCredential = Nothing},
    Nothing,
    Value (Map [(,Map [("",100000000)])]),
    [
      TxOut {
        txOutAddress = Address {addressCredential = PubKeyCredential e1ce601c08286179ae7ae6ef3a38262d4112cab0663a68dfb8e9edc5, addressStakingCredential = Nothing},
        txOutValue = Value (Map []),
        txOutDatumHash = Nothing
      },
      TxOut {
        txOutAddress = Address {addressCredential = ScriptCredential b81ade746787c130f13f0cc28d72d19a755c49684fccc3d5abdd6f62, addressStakingCredential = Nothing},
        txOutValue = Value (Map [(,Map [("",3000000)])]),
        txOutDatumHash = Just 6d1de149d42e49c15e33104441c1298ce8b11b0eef7d48994bf452c3dea7b427
      },
      TxOut {
        txOutAddress = Address {addressCredential = PubKeyCredential 90304fe1d67fbcad6ce67e6a32d37f0d75f159701b7328bee5912dc9, addressStakingCredential = Nothing},
        txOutValue = Value (Map [(,Map [("",100000000)]),(8bb3b343d8e404472337966a722150048c768d0a92a9813596c5338d,Map [("ThomasMiddleton",1)])]),
        txOutDatumHash = Nothing
      },
      TxOut {
        txOutAddress = Address {addressCredential = PubKeyCredential e1ce601c08286179ae7ae6ef3a38262d4112cab0663a68dfb8e9edc5, addressStakingCredential = Nothing},
        txOutValue = Value (Map [(,Map [("",3000000)]),(8bb3b343d8e404472337966a722150048c768d0a92a9813596c5338d,Map [("JohnFletcher",1)])]),
        txOutDatumHash = Nothing
      }
    ]
  )
)

which gives a clearer view of the on-chain data.

Possible next steps

This manual process could be automated (for Marlowe), by having marlowe-cli interpret the log message when it tried to submit the transaction: it would then appropriately deserialize and pretty-print it.