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feat: Add multisig taproot example
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‎examples/src/main/kotlin/MultisigTaprootTransaction.kt‎

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package org.bitcoindevkit
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fun main() {
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// Add your regtest URL here. Regtest environment must have esplora to run this.
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// See here for regtest podman setup https://github.com/thunderbiscuit/podman-regtest-infinity-pro
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val REGTEST_URL = "http://127.0.0.1:3002"
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// An unspendable compressed public key to use as internal key for Taproot multisig
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// This could be any valid compressed public key that no one has the private key for or
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// full descriptor path including derivation.
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val UNSPENDABLE_KEY = "0250929b74c1a04954b78b4b6035e97a5e078a5a0f28ec96d547bfee9ace803ac0"
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// Create 3 wallets using existing helper (P2TR = Taproot)
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val aliceWallet = getNewWallet(ActiveWalletScriptType.P2TR, Network.REGTEST)
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val bobWallet = getNewWallet(ActiveWalletScriptType.P2TR, Network.REGTEST)
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val mattWallet = getNewWallet(ActiveWalletScriptType.P2TR, Network.REGTEST)
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// Get the public descriptors of each wallet. Extract inner key expressions
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var alicePublicDescriptor = aliceWallet.publicDescriptor(KeychainKind.EXTERNAL)
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alicePublicDescriptor = alicePublicDescriptor.substring(alicePublicDescriptor.indexOf("(") + 1, alicePublicDescriptor.indexOf(")"))
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var bobPublicDescriptor = bobWallet.publicDescriptor(KeychainKind.EXTERNAL)
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bobPublicDescriptor = bobPublicDescriptor.substring(bobPublicDescriptor.indexOf("(") + 1, bobPublicDescriptor.indexOf(")"))
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var mattPublicDescriptor = mattWallet.publicDescriptor(KeychainKind.EXTERNAL)
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mattPublicDescriptor = mattPublicDescriptor.substring(mattPublicDescriptor.indexOf("(") + 1, mattPublicDescriptor.indexOf(")"))
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// Get the change descriptors of each wallet (for change path)
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var aliceChangeDescriptor = aliceWallet.publicDescriptor(KeychainKind.INTERNAL)
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aliceChangeDescriptor = aliceChangeDescriptor.substring(aliceChangeDescriptor.indexOf("(") + 1, aliceChangeDescriptor.indexOf(")"))
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var bobChangeDescriptor = bobWallet.publicDescriptor(KeychainKind.INTERNAL)
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bobChangeDescriptor = bobChangeDescriptor.substring(bobChangeDescriptor.indexOf("(") + 1, bobChangeDescriptor.indexOf(")"))
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var mattChangeDescriptor = mattWallet.publicDescriptor(KeychainKind.INTERNAL)
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mattChangeDescriptor = mattChangeDescriptor.substring(mattChangeDescriptor.indexOf("(") + 1, mattChangeDescriptor.indexOf(")"))
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// Define Taproot multisig descriptors. For Taproot, an internal key is required.
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// We use a random unspendable compressed public key as the internal key. This means
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// that the wallet can only be spent via the script path (no key-path spending).
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val externalDescriptor = Descriptor(
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descriptor = "tr($UNSPENDABLE_KEY,multi_a(2,$alicePublicDescriptor,$bobPublicDescriptor,$mattPublicDescriptor))",
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network = Network.REGTEST
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)
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val changeDescriptor = Descriptor(
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descriptor = "tr($UNSPENDABLE_KEY,multi_a(2,$aliceChangeDescriptor,$bobChangeDescriptor,$mattChangeDescriptor))",
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network = Network.REGTEST
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)
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// Create multisig wallet (reuse shared persistence helper)
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val connection: Persister = Persister.newSqlite(generateUniquePersistenceFilePath())
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val multisigWallet = Wallet(externalDescriptor, changeDescriptor, Network.REGTEST, connection)
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val changeAddress = multisigWallet.revealNextAddress(KeychainKind.INTERNAL)
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val address = multisigWallet.revealNextAddress(KeychainKind.EXTERNAL)
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println("Change address: ${changeAddress.address}")
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// Fund this address. Alice, Bob and Matt own funds sent here
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println("receiving address: ${address.address}")
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// Client: wait for funding then scan
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println("Waiting 40 seconds for funds to arrive here before scanning ${address.address} ...")
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Thread.sleep(40000)
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val esploraClient = EsploraClient(REGTEST_URL)
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val fullScanRequest: FullScanRequest = multisigWallet.startFullScan().build()
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val update = esploraClient.fullScan(fullScanRequest, 10uL, 1uL)
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multisigWallet.applyUpdate(update)
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multisigWallet.persist(connection)
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println("Balance: ${multisigWallet.balance().total.toSat()}")
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Thread.sleep(40000)
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// Create PSBT
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val recipient = Address("bcrt1q645m0j78v9pajdfp0g0w6wacl4v8s7mvrwsjx5", Network.REGTEST)
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println("Balance: ${multisigWallet.balance().total.toSat()}")
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val psbt: Psbt = TxBuilder()
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.addRecipient(recipient.scriptPubkey(), Amount.fromSat(4420uL))
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.feeRate(FeeRate.fromSatPerVb(22uL))
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.finish(multisigWallet)
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val psbtTransaction = psbt.extractTx()
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println(psbtTransaction.toString())
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println("Before any signature ${psbt.serialize()}")
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println("Before any signature. Json: ${psbt.jsonSerialize()}")
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// Sign Psbt via script path; do not allow key-path signing so taptree fields are populated
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aliceWallet.sign(psbt, SignOptions(
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trustWitnessUtxo = false,
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assumeHeight = null,
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allowAllSighashes = false,
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tryFinalize = false,
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signWithTapInternalKey = false,
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allowGrinding = false
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))
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println("After signing with aliceWallet ${psbt.serialize()}")
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println("After signing with aliceWallet Json ${psbt.jsonSerialize()}")
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println("Transaction after signing with wallet1: ${psbt.extractTx().toString()}")
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bobWallet.sign(psbt, SignOptions(
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trustWitnessUtxo = false,
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assumeHeight = null,
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allowAllSighashes = false,
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tryFinalize = false,
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signWithTapInternalKey = false,
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allowGrinding = false
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))
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println("After signing with bobWallet ${psbt.serialize()}")
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println("After signing with bobWallet Json ${psbt.jsonSerialize()}")
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println("Transaction after signing with bobWallet: ${psbt.extractTx().toString()}")
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// Matt does not need to sign since it is a 2 of 3 multisig. Alice and Bob have already signed.
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mattWallet.sign(psbt, SignOptions(
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trustWitnessUtxo = false,
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assumeHeight = null,
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allowAllSighashes = false,
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tryFinalize = false,
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signWithTapInternalKey = false,
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allowGrinding = false
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))
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println("After signing with mattWallet ${psbt.serialize()}")
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println("After signing with mattWallet Json ${psbt.jsonSerialize()}")
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println("Transaction after signing with mattWallet: ${psbt.extractTx().toString()}")
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multisigWallet.finalizePsbt(psbt)
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println("After finalize: ${psbt.serialize()}")
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println("After finalize Json: ${psbt.jsonSerialize()}")
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println("Transaction after finalize: ${psbt.extractTx().toString()}")
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val tx: Transaction = psbt.extractTx()
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println("Txid is: ${tx.computeTxid()}")
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// Now you can broadcast the transaction
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esploraClient.broadcast(tx)
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println("Tx was broadcasted")
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}

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