UTXO Management

Overview

The UTXO (Unspent Transaction Output) Management component provides essential tools for tracking, selecting, and managing unspent outputs in BSV blockchain applications. While the BSV SDK doesn't include a built-in UTXO manager, it provides all the primitives needed to implement robust UTXO tracking systems.

This documentation demonstrates how to build efficient UTXO management using the SDK's Transaction, UnspentOutput, and wallet interfaces, including coin selection strategies, balance calculation, and UTXO lifecycle management.

Purpose

UTXO Management solves several critical challenges in BSV application development:

• UTXO Tracking: Monitor all unspent outputs across multiple addresses and protocols
• Coin Selection: Choose optimal UTXOs for transaction creation based on various strategies
• Balance Calculation: Calculate spendable balances accurately across different contexts
• UTXO Consolidation: Merge small UTXOs to reduce transaction size and fees
• State Management: Track UTXO states (unspent, pending, spent) throughout lifecycle
• Multi-Protocol Support: Manage UTXOs separately for different application protocols

Proper UTXO management is essential for building efficient, scalable BSV applications that minimize fees and maximize transaction throughput.

Basic Usage

Define UTXO Structure

import { Transaction } from '@bsv/sdk';

// UTXO representation
interface UTXO {
  txid: string;                    // Transaction ID
  outputIndex: number;             // Output index (vout)
  satoshis: number;                // Amount in satoshis
  lockingScript: string;           // Locking script hex
  address?: string;                // Associated address (if P2PKH)
  scriptType?: string;             // Script template type
  sequenceNumber?: number;         // Sequence number for RBF
}

// Example UTXO
const utxo: UTXO = {
  txid: '7f3b4c9a1e2d5f8a6b3c9d2e4f1a8b5c6d7e9f0a1b2c3d4e5f6a7b8c9d0e1f2',
  outputIndex: 0,
  satoshis: 10000,
  lockingScript: '76a914...',
  address: '1A1zP1eP5QGefi2DMPTfTL5SLmv7DivfNa',
  scriptType: 'P2PKH'
};

Basic UTXO Tracker

import { Transaction, P2PKH, PrivateKey } from '@bsv/sdk';

class BasicUTXOTracker {
  private utxos: Map<string, UTXO> = new Map();

  // Add UTXO to tracking
  addUTXO(utxo: UTXO): void {
    const key = `${utxo.txid}:${utxo.outputIndex}`;
    this.utxos.set(key, utxo);
  }

  // Remove spent UTXO
  removeUTXO(txid: string, outputIndex: number): void {
    const key = `${txid}:${outputIndex}`;
    this.utxos.delete(key);
  }

  // Get all UTXOs
  getAllUTXOs(): UTXO[] {
    return Array.from(this.utxos.values());
  }

  // Calculate total balance
  getBalance(): number {
    return this.getAllUTXOs().reduce((sum, utxo) => sum + utxo.satoshis, 0);
  }

  // Get UTXOs by address
  getUTXOsByAddress(address: string): UTXO[] {
    return this.getAllUTXOs().filter(utxo => utxo.address === address);
  }
}

// Usage
const tracker = new BasicUTXOTracker();

// Add UTXOs
tracker.addUTXO({
  txid: 'abc123...',
  outputIndex: 0,
  satoshis: 50000,
  lockingScript: '76a914...',
  address: '1A1zP1eP...'
});

// Get balance
const balance = tracker.getBalance();
console.log(`Total balance: ${balance} satoshis`);

Simple Coin Selection

import { Transaction, P2PKH, PrivateKey } from '@bsv/sdk';

class SimpleCoinSelector {
  private utxos: UTXO[];

  constructor(utxos: UTXO[]) {
    this.utxos = utxos;
  }

  // Select UTXOs for amount (first-fit strategy)
  selectCoins(targetAmount: number): UTXO[] {
    const selected: UTXO[] = [];
    let total = 0;

    // Sort by size descending (use largest first)
    const sorted = [...this.utxos].sort((a, b) => b.satoshis - a.satoshis);

    for (const utxo of sorted) {
      selected.push(utxo);
      total += utxo.satoshis;

      if (total >= targetAmount) {
        break;
      }
    }

    if (total < targetAmount) {
      throw new Error(`Insufficient funds: need ${targetAmount}, have ${total}`);
    }

    return selected;
  }
}

// Usage
const selector = new SimpleCoinSelector([
  { txid: 'tx1', outputIndex: 0, satoshis: 10000, lockingScript: '...' },
  { txid: 'tx2', outputIndex: 0, satoshis: 25000, lockingScript: '...' },
  { txid: 'tx3', outputIndex: 1, satoshis: 5000, lockingScript: '...' }
]);

const selectedUTXOs = selector.selectCoins(30000);
console.log(`Selected ${selectedUTXOs.length} UTXOs`);

Create Transaction from UTXOs

import { Transaction, P2PKH, PrivateKey } from '@bsv/sdk';

async function createTransactionFromUTXOs(
  utxos: UTXO[],
  privateKey: PrivateKey,
  recipientAddress: string,
  amount: number,
  changeAddress: string
): Promise<Transaction> {
  const tx = new Transaction();

  // Add inputs from selected UTXOs
  for (const utxo of utxos) {
    // Create source transaction (simplified - in production, fetch from network)
    const sourceTx = Transaction.fromHex(await fetchTransactionHex(utxo.txid));

    tx.addInput({
      sourceTransaction: sourceTx,
      sourceOutputIndex: utxo.outputIndex,
      unlockingScriptTemplate: new P2PKH().unlock(privateKey)
    });
  }

  // Add payment output
  tx.addOutput({
    lockingScript: new P2PKH().lock(recipientAddress),
    satoshis: amount
  });

  // Add change output
  tx.addOutput({
    lockingScript: new P2PKH().lock(changeAddress),
    change: true
  });

  // Calculate fee and sign
  await tx.fee();
  await tx.sign();

  return tx;
}

async function fetchTransactionHex(txid: string): Promise<string> {
  // Fetch from API (WhatsOnChain, etc.)
  return '...transaction hex...';
}

Key Features

1. UTXO State Management

Track UTXO lifecycle states from creation to spending:

enum UTXOState {
  UNCONFIRMED = 'unconfirmed',  // In mempool
  CONFIRMED = 'confirmed',       // In block
  PENDING = 'pending',           // Being spent (tx in mempool)
  SPENT = 'spent',               // Spent and confirmed
  INVALID = 'invalid'            // Invalid/double-spent
}

interface ManagedUTXO extends UTXO {
  state: UTXOState;
  confirmations: number;
  createdAt: Date;
  spentAt?: Date;
  spentInTx?: string;
}

class UTXOStateManager {
  private utxos: Map<string, ManagedUTXO> = new Map();

  addUTXO(utxo: UTXO, confirmations: number = 0): void {
    const key = `${utxo.txid}:${utxo.outputIndex}`;

    const managed: ManagedUTXO = {
      ...utxo,
      state: confirmations > 0 ? UTXOState.CONFIRMED : UTXOState.UNCONFIRMED,
      confirmations,
      createdAt: new Date()
    };

    this.utxos.set(key, managed);
  }

  markAsPending(txid: string, outputIndex: number): void {
    const key = `${txid}:${outputIndex}`;
    const utxo = this.utxos.get(key);

    if (utxo) {
      utxo.state = UTXOState.PENDING;
    }
  }

  markAsSpent(txid: string, outputIndex: number, spentInTx: string): void {
    const key = `${txid}:${outputIndex}`;
    const utxo = this.utxos.get(key);

    if (utxo) {
      utxo.state = UTXOState.SPENT;
      utxo.spentAt = new Date();
      utxo.spentInTx = spentInTx;
    }
  }

  updateConfirmations(txid: string, outputIndex: number, confirmations: number): void {
    const key = `${txid}:${outputIndex}`;
    const utxo = this.utxos.get(key);

    if (utxo) {
      utxo.confirmations = confirmations;

      if (confirmations > 0 && utxo.state === UTXOState.UNCONFIRMED) {
        utxo.state = UTXOState.CONFIRMED;
      }
    }
  }

  // Get spendable UTXOs (confirmed and not pending/spent)
  getSpendableUTXOs(minConfirmations: number = 1): ManagedUTXO[] {
    return Array.from(this.utxos.values()).filter(utxo =>
      utxo.confirmations >= minConfirmations &&
      (utxo.state === UTXOState.CONFIRMED || utxo.state === UTXOState.UNCONFIRMED)
    );
  }

  // Get pending UTXOs
  getPendingUTXOs(): ManagedUTXO[] {
    return Array.from(this.utxos.values()).filter(
      utxo => utxo.state === UTXOState.PENDING
    );
  }

  // Calculate spendable balance
  getSpendableBalance(minConfirmations: number = 1): number {
    return this.getSpendableUTXOs(minConfirmations).reduce(
      (sum, utxo) => sum + utxo.satoshis,
      0
    );
  }
}

// Usage
const stateManager = new UTXOStateManager();

// Add confirmed UTXO
stateManager.addUTXO({
  txid: 'abc123',
  outputIndex: 0,
  satoshis: 100000,
  lockingScript: '76a914...'
}, 6); // 6 confirmations

// Mark as pending when creating transaction
stateManager.markAsPending('abc123', 0);

// After transaction confirms
stateManager.markAsSpent('abc123', 0, 'def456');

// Get spendable balance
const balance = stateManager.getSpendableBalance(1);
console.log(`Spendable: ${balance} satoshis`);

2. Advanced Coin Selection Strategies

Implement multiple coin selection algorithms:

import { Transaction } from '@bsv/sdk';

interface CoinSelectionStrategy {
  select(utxos: UTXO[], targetAmount: number, feeRate: number): UTXO[];
}

// Strategy 1: Largest First (minimize number of inputs)
class LargestFirstStrategy implements CoinSelectionStrategy {
  select(utxos: UTXO[], targetAmount: number, feeRate: number): UTXO[] {
    const sorted = [...utxos].sort((a, b) => b.satoshis - a.satoshis);
    return this.selectFromSorted(sorted, targetAmount, feeRate);
  }

  private selectFromSorted(sorted: UTXO[], target: number, feeRate: number): UTXO[] {
    const selected: UTXO[] = [];
    let total = 0;

    for (const utxo of sorted) {
      selected.push(utxo);
      total += utxo.satoshis;

      // Estimate fee for current input count
      const estimatedFee = this.estimateFee(selected.length, 2, feeRate);

      if (total >= target + estimatedFee) {
        return selected;
      }
    }

    throw new Error('Insufficient funds');
  }

  private estimateFee(inputs: number, outputs: number, feeRate: number): number {
    // Rough estimate: 148 bytes per input, 34 bytes per output, 10 bytes overhead
    const estimatedSize = (inputs * 148) + (outputs * 34) + 10;
    return Math.ceil(estimatedSize * feeRate);
  }
}

// Strategy 2: Smallest First (maximize UTXO consolidation)
class SmallestFirstStrategy implements CoinSelectionStrategy {
  select(utxos: UTXO[], targetAmount: number, feeRate: number): UTXO[] {
    const sorted = [...utxos].sort((a, b) => a.satoshis - b.satoshis);
    const selected: UTXO[] = [];
    let total = 0;

    for (const utxo of sorted) {
      selected.push(utxo);
      total += utxo.satoshis;

      const estimatedFee = this.estimateFee(selected.length, 2, feeRate);

      if (total >= targetAmount + estimatedFee) {
        return selected;
      }
    }

    throw new Error('Insufficient funds');
  }

  private estimateFee(inputs: number, outputs: number, feeRate: number): number {
    const estimatedSize = (inputs * 148) + (outputs * 34) + 10;
    return Math.ceil(estimatedSize * feeRate);
  }
}

// Strategy 3: Branch and Bound (optimal selection)
class BranchAndBoundStrategy implements CoinSelectionStrategy {
  select(utxos: UTXO[], targetAmount: number, feeRate: number): UTXO[] {
    // Sort descending by value
    const sorted = [...utxos].sort((a, b) => b.satoshis - a.satoshis);

    // Try to find exact match or minimal waste
    const result = this.branchAndBound(sorted, targetAmount, feeRate);

    if (result) {
      return result;
    }

    // Fallback to largest first if no optimal solution
    return new LargestFirstStrategy().select(utxos, targetAmount, feeRate);
  }

  private branchAndBound(
    utxos: UTXO[],
    target: number,
    feeRate: number,
    depth: number = 0,
    selected: UTXO[] = [],
    currentTotal: number = 0
  ): UTXO[] | null {
    // Limit search depth to prevent timeout
    if (depth > 20) return null;

    const estimatedFee = this.estimateFee(selected.length, 2, feeRate);
    const needed = target + estimatedFee;

    // Found solution
    if (currentTotal >= needed && currentTotal - needed < 1000) {
      return selected;
    }

    // Exceeded target too much
    if (currentTotal > needed + 10000) {
      return null;
    }

    // No more UTXOs to try
    if (depth >= utxos.length) {
      return null;
    }

    // Try including current UTXO
    const withCurrent = this.branchAndBound(
      utxos,
      target,
      feeRate,
      depth + 1,
      [...selected, utxos[depth]],
      currentTotal + utxos[depth].satoshis
    );

    if (withCurrent) return withCurrent;

    // Try excluding current UTXO
    return this.branchAndBound(
      utxos,
      target,
      feeRate,
      depth + 1,
      selected,
      currentTotal
    );
  }

  private estimateFee(inputs: number, outputs: number, feeRate: number): number {
    const estimatedSize = (inputs * 148) + (outputs * 34) + 10;
    return Math.ceil(estimatedSize * feeRate);
  }
}

// Strategy selector
class CoinSelector {
  private strategies: Map<string, CoinSelectionStrategy> = new Map();

  constructor() {
    this.strategies.set('largest-first', new LargestFirstStrategy());
    this.strategies.set('smallest-first', new SmallestFirstStrategy());
    this.strategies.set('branch-and-bound', new BranchAndBoundStrategy());
  }

  select(
    strategyName: string,
    utxos: UTXO[],
    targetAmount: number,
    feeRate: number = 0.5
  ): UTXO[] {
    const strategy = this.strategies.get(strategyName);

    if (!strategy) {
      throw new Error(`Unknown strategy: ${strategyName}`);
    }

    return strategy.select(utxos, targetAmount, feeRate);
  }
}

// Usage
const selector = new CoinSelector();

const utxos: UTXO[] = [
  { txid: 'tx1', outputIndex: 0, satoshis: 5000, lockingScript: '...' },
  { txid: 'tx2', outputIndex: 0, satoshis: 10000, lockingScript: '...' },
  { txid: 'tx3', outputIndex: 0, satoshis: 25000, lockingScript: '...' },
  { txid: 'tx4', outputIndex: 0, satoshis: 50000, lockingScript: '...' }
];

// Use largest-first for minimal inputs
const selected1 = selector.select('largest-first', utxos, 30000, 0.5);
console.log(`Largest-first selected ${selected1.length} UTXOs`);

// Use smallest-first for UTXO consolidation
const selected2 = selector.select('smallest-first', utxos, 30000, 0.5);
console.log(`Smallest-first selected ${selected2.length} UTXOs`);

// Use branch-and-bound for optimal selection
const selected3 = selector.select('branch-and-bound', utxos, 30000, 0.5);
console.log(`Branch-and-bound selected ${selected3.length} UTXOs`);

3. UTXO Consolidation

Merge small UTXOs to reduce fragmentation:

import { Transaction, P2PKH, PrivateKey } from '@bsv/sdk';

class UTXOConsolidator {
  private privateKey: PrivateKey;
  private feeRate: number;

  constructor(privateKey: PrivateKey, feeRate: number = 0.5) {
    this.privateKey = privateKey;
    this.feeRate = feeRate;
  }

  // Determine if consolidation is beneficial
  shouldConsolidate(utxos: UTXO[], threshold: number = 10000): boolean {
    const smallUTXOs = utxos.filter(u => u.satoshis < threshold);

    // Consolidate if we have many small UTXOs
    return smallUTXOs.length >= 10;
  }

  // Create consolidation transaction
  async consolidateUTXOs(
    utxos: UTXO[],
    destinationAddress: string,
    maxInputs: number = 100
  ): Promise<Transaction> {
    // Sort by size ascending (consolidate smallest first)
    const sorted = [...utxos].sort((a, b) => a.satoshis - b.satoshis);

    // Take up to maxInputs
    const toConsolidate = sorted.slice(0, maxInputs);

    const tx = new Transaction();

    // Add all inputs
    for (const utxo of toConsolidate) {
      const sourceTx = Transaction.fromHex(await this.fetchTxHex(utxo.txid));

      tx.addInput({
        sourceTransaction: sourceTx,
        sourceOutputIndex: utxo.outputIndex,
        unlockingScriptTemplate: new P2PKH().unlock(this.privateKey)
      });
    }

    // Single output to consolidate into
    const totalInput = toConsolidate.reduce((sum, u) => sum + u.satoshis, 0);
    const estimatedFee = this.estimateConsolidationFee(toConsolidate.length);

    tx.addOutput({
      lockingScript: new P2PKH().lock(destinationAddress),
      satoshis: totalInput - estimatedFee
    });

    await tx.fee();
    await tx.sign();

    return tx;
  }

  // Estimate fee for consolidation
  private estimateConsolidationFee(inputCount: number): number {
    // Size: inputs * 148 bytes + 1 output * 34 bytes + 10 bytes overhead
    const estimatedSize = (inputCount * 148) + 34 + 10;
    return Math.ceil(estimatedSize * this.feeRate);
  }

  // Calculate consolidation savings
  calculateSavings(utxos: UTXO[]): {
    currentCost: number;
    afterConsolidation: number;
    savings: number;
  } {
    // Cost to spend all UTXOs individually in future transactions
    const currentCost = utxos.length * 148 * this.feeRate;

    // Cost to spend 1 UTXO after consolidation
    const afterConsolidation = 148 * this.feeRate;

    // Cost to consolidate now
    const consolidationCost = this.estimateConsolidationFee(utxos.length);

    const savings = currentCost - afterConsolidation - consolidationCost;

    return {
      currentCost: Math.ceil(currentCost),
      afterConsolidation: Math.ceil(afterConsolidation),
      savings: Math.ceil(savings)
    };
  }

  private async fetchTxHex(txid: string): Promise<string> {
    // Fetch from API
    return '...';
  }
}

// Usage
const consolidator = new UTXOConsolidator(PrivateKey.fromWif('...'), 0.5);

const fragmentedUTXOs: UTXO[] = [
  { txid: 'tx1', outputIndex: 0, satoshis: 1000, lockingScript: '...' },
  { txid: 'tx2', outputIndex: 0, satoshis: 1500, lockingScript: '...' },
  { txid: 'tx3', outputIndex: 0, satoshis: 2000, lockingScript: '...' },
  // ... 20 more small UTXOs
];

// Check if consolidation is beneficial
if (consolidator.shouldConsolidate(fragmentedUTXOs, 5000)) {
  const savings = consolidator.calculateSavings(fragmentedUTXOs);
  console.log(`Consolidation savings: ${savings.savings} satoshis`);

  // Perform consolidation
  const consolidationTx = await consolidator.consolidateUTXOs(
    fragmentedUTXOs,
    '1A1zP1eP...',
    50 // Max 50 inputs per transaction
  );

  console.log(`Consolidated ${fragmentedUTXOs.length} UTXOs`);
}

4. Multi-Address UTXO Tracking

Track UTXOs across multiple addresses and key derivation paths:

import { KeyDeriver, PrivateKey, PublicKey } from '@bsv/sdk';

class MultiAddressUTXOTracker {
  private keyDeriver: KeyDeriver;
  private utxosByAddress: Map<string, UTXO[]> = new Map();
  private addressToKeyPath: Map<string, {
    protocolID: [number, string];
    keyID: string;
    counterparty: PublicKey | 'self' | 'anyone';
  }> = new Map();

  constructor(masterKey: PrivateKey) {
    this.keyDeriver = new KeyDeriver(masterKey);
  }

  // Register address with key derivation path
  registerAddress(
    address: string,
    protocolID: [number, string],
    keyID: string,
    counterparty: PublicKey | 'self' | 'anyone' = 'anyone'
  ): void {
    this.addressToKeyPath.set(address, { protocolID, keyID, counterparty });
    this.utxosByAddress.set(address, []);
  }

  // Add UTXO to specific address
  addUTXO(address: string, utxo: UTXO): void {
    const utxos = this.utxosByAddress.get(address) || [];
    utxos.push({ ...utxo, address });
    this.utxosByAddress.set(address, utxos);
  }

  // Get all UTXOs across all addresses
  getAllUTXOs(): UTXO[] {
    const allUTXOs: UTXO[] = [];

    for (const utxos of this.utxosByAddress.values()) {
      allUTXOs.push(...utxos);
    }

    return allUTXOs;
  }

  // Get UTXOs for specific address
  getUTXOsForAddress(address: string): UTXO[] {
    return this.utxosByAddress.get(address) || [];
  }

  // Get private key for address
  getPrivateKeyForAddress(address: string): PrivateKey {
    const keyPath = this.addressToKeyPath.get(address);

    if (!keyPath) {
      throw new Error(`No key path registered for address: ${address}`);
    }

    return this.keyDeriver.derivePrivateKey(
      keyPath.protocolID,
      keyPath.keyID,
      keyPath.counterparty
    );
  }

  // Calculate balance by address
  getBalanceByAddress(): Map<string, number> {
    const balances = new Map<string, number>();

    for (const [address, utxos] of this.utxosByAddress.entries()) {
      const balance = utxos.reduce((sum, utxo) => sum + utxo.satoshis, 0);
      balances.set(address, balance);
    }

    return balances;
  }

  // Get total balance across all addresses
  getTotalBalance(): number {
    let total = 0;

    for (const utxos of this.utxosByAddress.values()) {
      total += utxos.reduce((sum, utxo) => sum + utxo.satoshis, 0);
    }

    return total;
  }

  // Select UTXOs across multiple addresses
  selectUTXOsAcrossAddresses(targetAmount: number): {
    utxos: UTXO[];
    addresses: Set<string>;
  } {
    const allUTXOs = this.getAllUTXOs();
    const sorted = allUTXOs.sort((a, b) => b.satoshis - a.satoshis);

    const selected: UTXO[] = [];
    const addresses = new Set<string>();
    let total = 0;

    for (const utxo of sorted) {
      selected.push(utxo);
      if (utxo.address) addresses.add(utxo.address);
      total += utxo.satoshis;

      if (total >= targetAmount) {
        break;
      }
    }

    if (total < targetAmount) {
      throw new Error('Insufficient funds across all addresses');
    }

    return { utxos: selected, addresses };
  }
}

// Usage
const multiTracker = new MultiAddressUTXOTracker(PrivateKey.fromRandom());

const protocolID: [number, string] = [2, 'payment-v1'];

// Register multiple addresses
multiTracker.registerAddress('1Address1...', protocolID, 'key-0', 'anyone');
multiTracker.registerAddress('1Address2...', protocolID, 'key-1', 'anyone');
multiTracker.registerAddress('1Address3...', protocolID, 'change-0', 'self');

// Add UTXOs to different addresses
multiTracker.addUTXO('1Address1...', {
  txid: 'tx1',
  outputIndex: 0,
  satoshis: 50000,
  lockingScript: '...'
});

multiTracker.addUTXO('1Address2...', {
  txid: 'tx2',
  outputIndex: 0,
  satoshis: 75000,
  lockingScript: '...'
});

// Get balance per address
const balances = multiTracker.getBalanceByAddress();
for (const [address, balance] of balances.entries()) {
  console.log(`${address}: ${balance} satoshis`);
}

// Select UTXOs across addresses
const { utxos, addresses } = multiTracker.selectUTXOsAcrossAddresses(100000);
console.log(`Selected ${utxos.length} UTXOs from ${addresses.size} addresses`);

API Reference

UTXO Interface

interface UTXO {
  txid: string;                    // Transaction ID
  outputIndex: number;             // Output index (vout)
  satoshis: number;                // Amount in satoshis
  lockingScript: string;           // Locking script hex
  address?: string;                // Associated address
  scriptType?: string;             // Script template type
  sequenceNumber?: number;         // Sequence number
}

ManagedUTXO Interface

interface ManagedUTXO extends UTXO {
  state: UTXOState;               // Current state
  confirmations: number;          // Confirmation count
  createdAt: Date;                // Creation timestamp
  spentAt?: Date;                 // Spent timestamp
  spentInTx?: string;             // Spending transaction ID
}

UTXOState Enum

enum UTXOState {
  UNCONFIRMED = 'unconfirmed',   // In mempool
  CONFIRMED = 'confirmed',        // In block
  PENDING = 'pending',            // Being spent
  SPENT = 'spent',                // Spent and confirmed
  INVALID = 'invalid'             // Invalid/double-spent
}

CoinSelectionStrategy Interface

interface CoinSelectionStrategy {
  select(
    utxos: UTXO[],
    targetAmount: number,
    feeRate: number
  ): UTXO[];
}

Common Patterns

Pattern 1: UTXO Discovery and Syncing

Discover and sync UTXOs from blockchain:

import { Transaction, P2PKH } from '@bsv/sdk';

class UTXOSynchronizer {
  private tracker: BasicUTXOTracker;
  private addresses: string[];

  constructor(addresses: string[]) {
    this.tracker = new BasicUTXOTracker();
    this.addresses = addresses;
  }

  // Sync UTXOs from blockchain API
  async syncUTXOs(): Promise<void> {
    for (const address of this.addresses) {
      const utxos = await this.fetchUTXOsFromAPI(address);

      for (const utxo of utxos) {
        this.tracker.addUTXO(utxo);
      }
    }
  }

  // Fetch UTXOs from WhatsOnChain API
  private async fetchUTXOsFromAPI(address: string): Promise<UTXO[]> {
    try {
      const response = await fetch(
        `https://api.whatsonchain.com/v1/bsv/main/address/${address}/unspent`
      );

      const data = await response.json();

      return data.map((item: any) => ({
        txid: item.tx_hash,
        outputIndex: item.tx_pos,
        satoshis: item.value,
        lockingScript: item.script || '',
        address: address
      }));
    } catch (error) {
      console.error(`Error fetching UTXOs for ${address}:`, error);
      return [];
    }
  }

  // Get synced UTXOs
  getUTXOs(): UTXO[] {
    return this.tracker.getAllUTXOs();
  }

  // Get balance
  getBalance(): number {
    return this.tracker.getBalance();
  }
}

// Usage
const synchronizer = new UTXOSynchronizer([
  '1A1zP1eP5QGefi2DMPTfTL5SLmv7DivfNa',
  '1BvBMSEYstWetqTFn5Au4m4GFg7xJaNVN2'
]);

await synchronizer.syncUTXOs();
const balance = synchronizer.getBalance();
console.log(`Synced balance: ${balance} satoshis`);

Pattern 2: Optimistic UTXO Updates

Update UTXO set optimistically before confirmation:

class OptimisticUTXOManager {
  private stateManager: UTXOStateManager;
  private pendingTransactions: Map<string, Transaction> = new Map();

  constructor() {
    this.stateManager = new UTXOStateManager();
  }

  // Create and broadcast transaction with optimistic update
  async createAndBroadcastTransaction(
    utxos: UTXO[],
    outputs: Array<{ address: string; satoshis: number }>,
    changeAddress: string,
    privateKey: PrivateKey
  ): Promise<Transaction> {
    const tx = new Transaction();

    // Add inputs
    for (const utxo of utxos) {
      // Mark as pending immediately
      this.stateManager.markAsPending(utxo.txid, utxo.outputIndex);

      const sourceTx = Transaction.fromHex(await this.fetchTxHex(utxo.txid));

      tx.addInput({
        sourceTransaction: sourceTx,
        sourceOutputIndex: utxo.outputIndex,
        unlockingScriptTemplate: new P2PKH().unlock(privateKey)
      });
    }

    // Add outputs
    for (const output of outputs) {
      tx.addOutput({
        lockingScript: new P2PKH().lock(output.address),
        satoshis: output.satoshis
      });
    }

    // Add change
    tx.addOutput({
      lockingScript: new P2PKH().lock(changeAddress),
      change: true
    });

    await tx.fee();
    await tx.sign();

    // Broadcast
    const txid = await this.broadcastTransaction(tx);

    // Store pending transaction
    this.pendingTransactions.set(txid, tx);

    // Optimistically add change UTXO
    const changeOutput = tx.outputs.find(o => o.change);
    if (changeOutput) {
      this.stateManager.addUTXO({
        txid: txid,
        outputIndex: tx.outputs.indexOf(changeOutput),
        satoshis: changeOutput.satoshis || 0,
        lockingScript: changeOutput.lockingScript.toHex(),
        address: changeAddress
      }, 0); // 0 confirmations
    }

    return tx;
  }

  // Handle transaction confirmation
  async handleConfirmation(txid: string, blockHeight: number): Promise<void> {
    const tx = this.pendingTransactions.get(txid);

    if (!tx) return;

    // Mark spent inputs as spent
    for (const input of tx.inputs) {
      const sourceTxid = input.sourceTransaction?.id('hex');
      const sourceIndex = input.sourceOutputIndex;

      if (sourceTxid !== undefined && sourceIndex !== undefined) {
        this.stateManager.markAsSpent(sourceTxid, sourceIndex, txid);
      }
    }

    // Update change UTXO confirmations
    const changeOutput = tx.outputs.find(o => o.change);
    if (changeOutput) {
      this.stateManager.updateConfirmations(
        txid,
        tx.outputs.indexOf(changeOutput),
        1
      );
    }

    this.pendingTransactions.delete(txid);
  }

  // Rollback on failure
  async handleTransactionFailure(txid: string): Promise<void> {
    const tx = this.pendingTransactions.get(txid);

    if (!tx) return;

    // Restore inputs to spendable state
    for (const input of tx.inputs) {
      const sourceTxid = input.sourceTransaction?.id('hex');
      const sourceIndex = input.sourceOutputIndex;

      if (sourceTxid !== undefined && sourceIndex !== undefined) {
        // Reset to confirmed state
        this.stateManager.updateConfirmations(sourceTxid, sourceIndex, 1);
      }
    }

    this.pendingTransactions.delete(txid);
  }

  private async fetchTxHex(txid: string): Promise<string> {
    return '...';
  }

  private async broadcastTransaction(tx: Transaction): Promise<string> {
    // Broadcast and return txid
    return tx.id('hex');
  }
}

Pattern 3: UTXO-Based Balance Calculation

Calculate balances with different confirmation requirements:

class BalanceCalculator {
  private stateManager: UTXOStateManager;

  constructor(stateManager: UTXOStateManager) {
    this.stateManager = stateManager;
  }

  // Get confirmed balance (6+ confirmations)
  getConfirmedBalance(): number {
    return this.stateManager.getSpendableBalance(6);
  }

  // Get unconfirmed balance (0+ confirmations)
  getUnconfirmedBalance(): number {
    return this.stateManager.getSpendableBalance(0);
  }

  // Get pending balance (being spent)
  getPendingBalance(): number {
    return this.stateManager.getPendingUTXOs().reduce(
      (sum, utxo) => sum + utxo.satoshis,
      0
    );
  }

  // Get total balance (all states)
  getTotalBalance(): number {
    return this.getUnconfirmedBalance() + this.getPendingBalance();
  }

  // Get balance breakdown
  getBalanceBreakdown(): {
    confirmed: number;
    unconfirmed: number;
    pending: number;
    total: number;
  } {
    return {
      confirmed: this.getConfirmedBalance(),
      unconfirmed: this.getUnconfirmedBalance(),
      pending: this.getPendingBalance(),
      total: this.getTotalBalance()
    };
  }

  // Get spendable balance with custom confirmation requirement
  getSpendableBalance(minConfirmations: number = 1): number {
    return this.stateManager.getSpendableBalance(minConfirmations);
  }
}

// Usage
const calculator = new BalanceCalculator(stateManager);

const breakdown = calculator.getBalanceBreakdown();
console.log('Balance breakdown:', {
  confirmed: `${breakdown.confirmed} sats`,
  unconfirmed: `${breakdown.unconfirmed} sats`,
  pending: `${breakdown.pending} sats`,
  total: `${breakdown.total} sats`
});

Security Considerations

Double-Spend Protection

Prevent double-spending by tracking UTXO states:

class DoubleSpendProtection {
  private usedUTXOs: Set<string> = new Set();

  // Check if UTXO is already being used
  isUTXOAvailable(txid: string, outputIndex: number): boolean {
    const key = `${txid}:${outputIndex}`;
    return !this.usedUTXOs.has(key);
  }

  // Mark UTXO as being used
  markUTXOAsUsed(txid: string, outputIndex: number): void {
    const key = `${txid}:${outputIndex}`;

    if (this.usedUTXOs.has(key)) {
      throw new Error(`UTXO ${key} is already being spent`);
    }

    this.usedUTXOs.add(key);
  }

  // Release UTXO if transaction fails
  releaseUTXO(txid: string, outputIndex: number): void {
    const key = `${txid}:${outputIndex}`;
    this.usedUTXOs.delete(key);
  }

  // Select UTXOs safely
  selectSafeUTXOs(utxos: UTXO[], targetAmount: number): UTXO[] {
    const available = utxos.filter(utxo =>
      this.isUTXOAvailable(utxo.txid, utxo.outputIndex)
    );

    const sorted = available.sort((a, b) => b.satoshis - a.satoshis);
    const selected: UTXO[] = [];
    let total = 0;

    for (const utxo of sorted) {
      try {
        this.markUTXOAsUsed(utxo.txid, utxo.outputIndex);
        selected.push(utxo);
        total += utxo.satoshis;

        if (total >= targetAmount) {
          return selected;
        }
      } catch (error) {
        // UTXO already being used, skip
        continue;
      }
    }

    // Rollback if insufficient funds
    for (const utxo of selected) {
      this.releaseUTXO(utxo.txid, utxo.outputIndex);
    }

    throw new Error('Insufficient available funds');
  }
}

Performance Considerations

UTXO Set Pruning

Keep UTXO set size manageable:

class UTXOSetPruner {
  private static readonly MAX_SPENT_AGE_DAYS = 30;
  private static readonly MAX_UTXO_COUNT = 10000;

  // Prune old spent UTXOs
  pruneSpentUTXOs(utxos: Map<string, ManagedUTXO>): void {
    const cutoffDate = new Date();
    cutoffDate.setDate(cutoffDate.getDate() - UTXOSetPruner.MAX_SPENT_AGE_DAYS);

    for (const [key, utxo] of utxos.entries()) {
      if (
        utxo.state === UTXOState.SPENT &&
        utxo.spentAt &&
        utxo.spentAt < cutoffDate
      ) {
        utxos.delete(key);
      }
    }
  }

  // Limit UTXO set size
  limitUTXOSetSize(utxos: Map<string, ManagedUTXO>): void {
    if (utxos.size <= UTXOSetPruner.MAX_UTXO_COUNT) {
      return;
    }

    // Convert to array and sort by creation date
    const sorted = Array.from(utxos.entries()).sort(
      ([, a], [, b]) => a.createdAt.getTime() - b.createdAt.getTime()
    );

    // Remove oldest spent UTXOs first
    const toRemove = sorted
      .filter(([, utxo]) => utxo.state === UTXOState.SPENT)
      .slice(0, utxos.size - UTXOSetPruner.MAX_UTXO_COUNT);

    for (const [key] of toRemove) {
      utxos.delete(key);
    }
  }
}

Related Components

• Transactions: Create transactions from UTXOs
• HD Wallets: Derive addresses for UTXO tracking
• P2PKH: Most common locking script for UTXOs
• SPV: Verify UTXO validity with SPV

Best Practices

1. Always track UTXO states to prevent double-spending
2. Use confirmation thresholds appropriate for transaction value
3. Implement UTXO consolidation when fragmentation increases
4. Choose coin selection strategy based on use case
5. Sync UTXOs regularly from blockchain to stay current
6. Prune old spent UTXOs to keep memory usage reasonable
7. Handle optimistic updates carefully with rollback capability
8. Validate UTXO ownership before spending

Troubleshooting

Issue: Insufficient Funds Despite Balance

Problem: Balance shows funds but coin selection fails.

Solution: Check for pending UTXOs:

const spendable = stateManager.getSpendableUTXOs(1);
const pending = stateManager.getPendingUTXOs();

console.log(`Spendable: ${spendable.length}, Pending: ${pending.length}`);

Issue: UTXO Already Spent Error

Problem: Attempting to spend already-used UTXO.

Solution: Implement double-spend protection and sync UTXOs:

const protection = new DoubleSpendProtection();
const safeUTXOs = protection.selectSafeUTXOs(utxos, targetAmount);

Further Reading

• BRC-8: Transaction Envelopes
• BRC-29: Simple Payment Protocol
• Bitcoin UTXO Model: Understanding UTXO architecture

Status

✅ Complete - Comprehensive UTXO management documentation with tracking, selection strategies, and lifecycle management.