Plutus: Pioneers Program 4th cohort kick start

5th Mar 2023
5 min read
Tags:
haskell,
cardano,
smart contracts

For a long time I have been interested in blockchain ecosystem for multiple reasons:

A wide range of applications
A very innovative field
Lots of advanced technical topics (which are considered "exotic" in day-to-day production code)
An open ecosystem (aligned with my FOSS contributions)

Which leds me to take Plutus Pioneers Program: 1st Cohort two years ago.

My experience with the course was deceiving because:

it was mostly focused on overcoming Haskell mindset specificities (making the homeworks too simple for me)
no action from me (I was just watching the lectures, solving homeworks in few minutes, checking them in the playground)

Since I plan to be involved in blockchains in a near future, it was a good opportunity to register for the 4th Cohort just starting.

Note that it will be a new logs series in which I'll try to document the evolutions of my understanding, I don't intend to provide an uptodate reference of Cardano or Plutus.

Addionally to my regular look for contributions, I'm willing to accept Plutus smart contracts suggestions.

Importants links:

Github: https://github.com/input-output-hk/plutus-pioneer-program/tree/fourth-iteration
Gitbook: https://iog-academy.gitbook.io/plutus-pioneers-program-fourth-cohort/ (currently outdated)
Cardano 101: https://www.essentialcardano.io/article/what-is-cardano-cardano-101

Main differences compare to the 1st cohort:

Homeworks are coming with tests: a great point as I was lacking of feedbacks previously, being unsure I was doing the right thing
Lectures are shorter and more focused
Nix support dropped in favor in devcontainers: which is understandable but which is too bad since my switch to NixOS

Let's start with some definitions:

Era: hard fork changing non-backward-compatible blocks production behavior
Phase: big focus of the Cardano Foundation (with multiple Eras), Voltaire focuses on Governance meaning, making Cardano self-sustainable, independant from IOHK
Stake pool: Stable node responsible of processing transactions going to the ledger
Ourobos: Consensus protocol (from the greek, snake eating its own tail)
Block: Cryptographically verified set of transactions and previous-block reference
Slot: 1 second time-slice, for each slot, elected leaders propose blocks, only one of them are selected, others are discarded
Epoch: 432.000 slots (5 days)
Elected leaders: elected for 20 slots, due to the proof of stake base of Ourobos, the more stake a stake pool manage, the higher share a stake pool manage, the higher chance it has to be elected, they are expected to validate transactions
Smart-contract: Immutable piece of code which defines the conditions triggering the transaction
Transaction: changes on the blockchain's stakes
Plutus core: Native on-chain script language used by Cardano for smart-contracts (it is compiled from the Plutus Application by the Plutus Tx Compiler, Plutus Tx, a GHC plug-in)
Plutus Application Framework: basis used for Plutus Applications, providing a HTTP and Websocket interface
Plutus Application Backend: executes off-chain part of an application, provides an HTTP API, manages requests to the node and the wallet while maintaining the application state
Collateral: monetary deposit used only if the smart contract fails on-chain (supposed to avoid malicious actors)

A transaction is composed of:

inputs: which are spent by redeemers (which are Datum values)
outputs: which are scripts validating spending associated currencies, and can come with Datum

A Datum looks like aeson's Value:

data Data
  = Constr Integer [Data]
  | Map [(Data, Data)]
  | List [Data]
  | I Integer
  | B ByteString

But, if we have a look at a simple validator script:

-- This validator succeeds only if the redeemer is 42
--                  Datum         Redeemer     ScriptContext
mk42Validator :: BuiltinData -> BuiltinData -> BuiltinData -> ()
mk42Validator _ r _
    | r == Builtins.mkI 42 = ()
    | otherwise            = traceError "expected 42"
{-# INLINABLE mk42Validator #-}

validator :: PlutusV2.Validator
validator = PlutusV2.mkValidatorScript $$(PlutusTx.compile [|| mk42Validator ||])

We can notice that:

The validator function uses BuiltinData (and not Data)
The validator function is INLINABLE, to be compiled and inlined in Validator
The validator function is a (), not a Bool or any Monad

Actually BuiltinData is the Plutus Core equivalent of Data, going back and forth via:

class ToData (a :: Type) where
    toBuiltinData :: a -> BuiltinData

class FromData (a :: Type) where
    fromBuiltinData :: BuiltinData -> Maybe a

class UnsafeFromData (a :: Type) where
    unsafeFromBuiltinData :: BuiltinData -> a

We can strengthen the types using wrap (which relies on UnsafeFromData):

mk42Validator :: () -> Integer -> PlutusV2.ScriptContext -> Bool
mk42Validator _ r _ = traceIfFalse "expected 42" $ r == 42
{-# INLINABLE mk42Validator #-}

validator :: PlutusV2.Validator
validator = PlutusV2.mkValidatorScript $$(PlutusTx.compile [|| wrap mk42Validator ||])

You can also create specific types thanks to unstableMakeIsData:

data MyRedeemer = MyRedeemer
    { flag1 :: Bool
    , flag2 :: Bool
    }

PlutusTx.unstableMakeIsData ''MyRedeemer

Let's try a simple validator checking the factorization of a number:

--              Datum  Redeemer        ScriptContext
mkValidator :: Integer -> (Integer, Integer) -> PlutusV2.ScriptContext -> Bool
mkValidator t (x, y) _ = shouldNotBeOne x && shouldNotBeOne y && shouldBeFactors
  where shouldNotBeOne :: Integer -> Bool
        shouldNotBeOne n = traceIfFalse "No factor should be 1" $ n /= 1
        shouldBeFactors  = traceIfFalse "Not factors" $ x * y == t
{-# INLINABLE mkValidator #-}

validator :: PlutusV2.Validator
validator = PlutusV2.mkValidatorScript $$(PlutusTx.compile [|| wrap mkValidator ||])

Compiling it to Plutus Core gives something like:

{
  "type": "PlutusScriptV2",
  "description": "",
  "cborHex": "5908..."
}

CBOR standing for Concise Binary Object Representation and is specified by RFC 7049.

Let's submit our contract with a random Datum:

{"int":42}

We can check it works via:

$ scripts/query-address.sh $(cat code/Week02/experiments/factoring.addr)
                           TxHash                                 TxIx        Amount
--------------------------------------------------------------------------------------
2d1604d8ba3128cd1526b6c68f94f8eddcd83b530dda4560dd327f25ad39164d     0        3000000 lovelace + TxOutDatumInline ReferenceTxInsScriptsInlineDatumsInBabbageEra (ScriptDataNumber 42)

If we then try to collect (using bob's key address first transaction as collateral and above TxHash as txin) with an incorrect Datum:

$ code/Week02/experiments/collect.sh wrong
# Query the protocol parameters
# Build the transaction
Command failed: transaction build  Error: The following scripts have execution failures:
the script for transaction input 0 (in the order of the TxIds) failed with:
transaction input 0 (in the order of the TxIds) points to a script hash that is not known.

# Sign the transaction
# Submit the transaction
Command failed: transaction submit  Error: Error while submitting tx: ShelleyTxValidationError ShelleyBasedEraBabbage (ApplyTxError [UtxowFailure (FromAlonzoUtxowFail (WrappedShelleyEraFailure (ExtraneousScriptWitnessesUTXOW (fromList [ScriptHash "c06d15e27842d0ccd6c825a13b84830a14215e01c98a93567f8cdbf8"])))),UtxowFailure (FromAlonzoUtxowFail (ExtraRedeemers [RdmrPtr Spend 0])),UtxowFailure (FromAlonzoUtxowFail (PPViewHashesDontMatch (SJust (SafeHash "abb568f2abaa14e3f59d0feaceb981033fdb16850af8339863a05343d8ac19f6")) (SJust (SafeHash "29f1fbb67e8a3f06db19ae5a5f8c6f51968e16920f3b486925beafd1c3e27391")))),UtxowFailure (UtxoFailure (FromAlonzoUtxoFail (ValueNotConservedUTxO (Value 0 (fromList [])) (Value 3000000 (fromList []))))),UtxowFailure (UtxoFailure (FromAlonzoUtxoFail (BadInputsUTxO (fromList [TxIn (TxId {_unTxId = SafeHash "2d1604d8ba3128cd1526b6c68f94f8eddcd83b530dda4560dd327f25ad39164d"}) (TxIx 0)]))))])
transaction id: ee269f32f5eb8abaf580f3684221c8c82066136e6e9ea7b8455fba61ee53f590
Cardanoscan: https://preview.cardanoscan.io/transaction/ee269f32f5eb8abaf580f3684221c8c82066136e6e9ea7b8455fba61ee53f590

if fails right away, without going to the blockchain, while a good Datum works:

$ code/Week02/experiments/collect.sh good
Transaction successfully submitted.
transaction id: ee269f32f5eb8abaf580f3684221c8c82066136e6e9ea7b8455fba61ee53f590
Cardanoscan: https://preview.cardanoscan.io/transaction/ee269f32f5eb8abaf580f3684221c8c82066136e6e9ea7b8455fba61ee53f590

Updating transactions:

$ scripts/query-address.sh $(cat keys/bob.addr)
TxHash                                 TxIx        Amount
--------------------------------------------------------------------------------------
2e1fe0fe79677804a70bff96b249d9912143a3464f4788d7a42b1f772bfb2050     0        10000000000 lovelace + TxOutDatumNone
ee269f32f5eb8abaf580f3684221c8c82066136e6e9ea7b8455fba61ee53f590     0        2701365 lovelace + TxOutDatumNone
$ scripts/query-address.sh $(cat keys/alice.addr)
TxHash                                 TxIx        Amount
--------------------------------------------------------------------------------------
2d1604d8ba3128cd1526b6c68f94f8eddcd83b530dda4560dd327f25ad39164d     1        9996833927 lovelace + TxOutDatumNone
$ scripts/query-address.sh $(cat code/Week02/experiments/factoring.addr)
TxHash                                 TxIx        Amount
--------------------------------------------------------------------------------------

Bonus: At some point I did, mistakenly change the validator, which triggered this error:

Command failed: transaction build  Error: The following scripts have execution failures:
the script for transaction input 0 (in the order of the TxIds) failed with: 
The redeemer pointer: RdmrPtr Spend 0 points to a Plutus script that does not exist.
The pointers that can be resolved are: fromList [(RdmrPtr Spend 0,(Spending (TxIn (TxId {_unTxId = SafeHash "2d1604d8ba3128cd1526b6c68f94f8eddcd83b530dda4560dd327f25ad39164d"}) (TxIx 0)),Nothing,ScriptHash "c06d15e27842d0ccd6c825a13b84830a14215e01c98a93567f8cdbf8"))]

In order to detect it, you can recompute it with:

$ cardano-cli address build-script --testnet-magic 2 --script-file code/Week02/experiments/factoring.plutus
addr_test1wr5wslr3utlm0vccvveg2z4p0p0jp02fcrwmyeaqqwmglsc6urkf0
$ cat code/Week02/experiments/factoring.addr
addr_test1wrqx690z0ppdpnxkeqj6zwuysv9pgg27q8yc4y6k07xdh7qyreaje