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• Official Website
• Installation
• Documentation

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Cometa.cpp is a C++17 library for Cardano, built on cardano-c. It provides transaction building, signing, staking, governance, and native Plutus evaluation with automatic memory management.

Installation

Download a package from GitHub Releases and set CMAKE_PREFIX_PATH to its directory. Packages include static and shared libraries for Linux and macOS (x64/ARM64), and Windows (x64).

FIND_PACKAGE (Cometa CONFIG REQUIRED)
TARGET_LINK_LIBRARIES (my_application PRIVATE Cometa::Cometa)

Use Cometa::CometaStatic for static linking. See the installation guide for HTTP transport, platform dependencies, and building from source.

First transaction

Build, sign, and submit a payment:

Cometa::TransactionBuilder builder(parameters, slots);

builder.setUtxos(utxos)
  .setChangeAddress(sender)
  .sendLovelace(recipient, 2'000'000);

Cometa::Transaction transaction = builder.build();
transaction.applyVkeyWitnesses(signer.signTransaction(transaction));

Cometa::Blake2bHash transactionId = provider.submitTransaction(transaction);

The examples use protocol parameters, slot configuration, and UTxOs from the target network. See the complete payment example for wallet and provider setup.

Transaction building

Mint a native asset

Cometa::Value output(2'000'000);
output.addAsset(asset, 1);

Cometa::TransactionBuilder builder(parameters, slots);

builder.setUtxos(utxos)
  .setChangeAddress(sender)
  .mintToken(asset, 1)
  .addScript(policyScript)
  .sendValue(recipient, output);

Cometa::Transaction transaction = builder.build();

Full example

Spend from a Plutus validator

Cometa::TransactionBuilder builder(parameters, slots);

builder.setUtxos(paymentUtxos)
  .setCollateralUtxos(collateralUtxos)
  .setCollateralChangeAddress(sender)
  .setChangeAddress(sender)
  .addScript(validator)
  .addInput(scriptUtxo, redeemer)
  .sendLovelace(sender, 1'000'000);

Cometa::Transaction transaction = builder.build();

Full example

Vote on a governance proposal

Cometa::TransactionBuilder builder(parameters, slots);

builder.setUtxos(utxos)
  .setChangeAddress(sender)
  .vote(voter, actionId, Cometa::VotingProcedure(Cometa::Vote::Yes));

Cometa::Transaction transaction = builder.build();

Key DRep example · Script DRep example

Dijkstra era

Dijkstra adds independently signed subtransactions, direct deposits to reward accounts, account balance constraints, key and script guards, and Plutus V4. These features require a network running Dijkstra.

Batch subtransactions

A party signs a subtransaction. The batcher includes it in a top-level transaction and satisfies its guard:

Cometa::SubTransactionBuilder intent(parameters, slots);

intent.addInput(partyUtxo)
  .sendLovelace(partyAddress, 12'000'000)
  .requireTopLevelGuard(batcherCredential);

Cometa::SubTransaction signedIntent = intent.build();
signedIntent.applyVkeyWitnesses(partySigner.signSubTransaction(signedIntent));

Cometa::TransactionBuilder batch(parameters, slots);

batch.setUtxos(batcherUtxos)
  .setChangeAddress(batcherAddress)
  .addSubTransaction(signedIntent, partyUtxos)
  .addGuard(batcherCredential);

Cometa::Transaction transaction = batch.build();

Two-party batch example · Plutus V4 guard example

Deferred redeemers

When a redeemer depends on input or output order, defer its calculation until the builder has balanced a draft:

builder.addInputWithDeferredRedeemer(
  scriptUtxo,
  [scriptInput](const Cometa::Transaction& draft, const Cometa::UtxoList&)
  {
    const std::optional<std::uint64_t> index = draft.findInputIndex(scriptInput);

    if (!index.has_value())
    {
      throw std::runtime_error("Script input is absent from the draft");
    }

    return Cometa::PlutusData::fromUnsigned(*index);
  });

Callbacks may run more than once and must be deterministic. Full example

Extension points

The builder defaults to random-improve coin selection and local Plutus evaluation. Override either through its C++ interface:

const std::shared_ptr<Cometa::CoinSelector> selector =
  std::make_shared<Cometa::LargeFirstCoinSelector>();
builder.setCoinSelector(selector);

const std::shared_ptr<Cometa::TransactionEvaluator> evaluator =
  std::make_shared<Cometa::ProviderTransactionEvaluator>(networkProvider);
builder.setTransactionEvaluator(evaluator);

Implement CoinSelector for custom UTxO selection or TransactionEvaluator for custom script evaluation. Provider supplies network data and submits transactions; HttpTransport lets providers use another HTTP client. Here, networkProvider is a std::shared_ptr<Cometa::Provider>.

More examples

The examples directory includes complete programs for payments, minting, staking, governance, key derivation, and Dijkstra transactions. Network examples use preprod and read BLOCKFROST_API_KEY from the environment.

License

Apache 2.0. See LICENSE.