ARC

Overview

The ARC class in the BSV TypeScript SDK provides a production-ready interface for broadcasting Bitcoin transactions through the ARC (Arc) API. ARC is a modern transaction processor that offers advanced features like transaction status tracking, fee policy queries, double-spend notifications, and callback-based event handling. It implements the Broadcaster interface, making it a drop-in replacement for other broadcast methods.

Purpose

• Broadcast transactions to the BSV network through the ARC API
• Query transaction status and confirmation details
• Calculate and verify transaction fees based on network policies
• Monitor double-spend attempts with callback notifications
• Handle transaction errors and rejection reasons
• Support deployment tracking and application identification
• Enable webhook callbacks for asynchronous transaction updates

When to Use

The ARC class provides two main broadcasting approaches:

1. Simple Transaction Broadcasting: tx.broadcast(arc)

Use when:

• Broadcasting a single, independent transaction
• Transaction doesn't depend on unconfirmed parents
• You want simple, straightforward broadcasting

Example:

const arc = new ARC('https://api.taal.com/arc', { apiKey: 'xxx' });
const response = await tx.broadcast(arc);
// Or use default broadcaster:
const response = await tx.broadcast();

2. BEEF Bundle Broadcasting: arc.broadcastBEEF(beefHex)

Use when:

• Broadcasting transaction chains with dependencies
• Child transactions spend from unconfirmed parent transactions
• You need atomic broadcasting of multiple related transactions
• You want to include merkle proofs for SPV validation

Example:

const arc = new ARC('https://api.taal.com/arc', { apiKey: 'xxx' });

// Create BEEF bundle
const beef = new Beef();
beef.addTransaction(parentTx);
beef.addTransaction(childTx);

const beefHex = beef.toHex();
const response = await arc.broadcastBEEF(beefHex);

Important: tx.broadcast() does NOT automatically handle transaction chains. For chains, you MUST use arc.broadcastBEEF() with a properly constructed BEEF bundle.

Basic Usage

Broadcasting a Transaction

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

// Initialize ARC broadcaster
const arc = new ARC('https://api.taal.com/arc', {
  apiKey: 'mainnet_xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx',
  deploymentId: 'my-app-v1',
  callbackUrl: 'https://myapp.com/callbacks',
  callbackToken: 'secret_token'
});

// Create and broadcast transaction
const privKey = PrivateKey.fromWif('L5EY1SbTvvPNSdCYQe1EJHfXCBBT4PmnF6CDbzCm9iifZptUvDGB');
const tx = new Transaction();

tx.addInput({
  sourceTransaction: Transaction.fromHex('...'),
  sourceOutputIndex: 0,
  unlockingScriptTemplate: new P2PKH().unlock(privKey)
});

tx.addOutput({
  lockingScript: new P2PKH().lock('1A1zP1eP5QGefi2DMPTfTL5SLmv7DivfNa'),
  satoshis: 1000
});

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

// Broadcast with ARC
const response = await tx.broadcast(arc);
console.log('TXID:', response.txid);
console.log('Status:', response.status);

Querying Transaction Status

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

const arc = new ARC('https://api.taal.com/arc', {
  apiKey: 'mainnet_xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx'
});

// Query transaction status
const txid = '1234567890abcdef...';
const status = await arc.getTransactionStatus(txid);

console.log('Status:', status.status); // 'SEEN', 'MINED', 'REJECTED', etc.
console.log('Block height:', status.blockHeight);
console.log('Block hash:', status.blockHash);
console.log('Confirmations:', status.confirmations);

Key Features

1. Transaction Broadcasting with Enhanced Features

ARC provides production-grade transaction broadcasting with deployment tracking:

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

// Initialize ARC with full configuration
const arc = new ARC('https://api.taal.com/arc', {
  apiKey: 'mainnet_xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx',
  deploymentId: 'payment-processor-v2.1.0',
  callbackUrl: 'https://myapp.com/tx-callbacks',
  callbackToken: 'webhook_secret_abc123'
});

// Create transaction
const privKey = PrivateKey.fromRandom();
const tx = new Transaction();

// Add inputs and outputs
tx.addInput({
  sourceTransaction: Transaction.fromHex('...'),
  sourceOutputIndex: 0,
  unlockingScriptTemplate: new P2PKH().unlock(privKey)
});

tx.addOutput({
  lockingScript: new P2PKH().lock('1RecipientAddress...'),
  satoshis: 5000
});

tx.addOutput({
  lockingScript: new P2PKH().lock(privKey.toPublicKey().toAddress()),
  change: true
});

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

// Broadcast with error handling
try {
  const response = await tx.broadcast(arc);

  console.log('Transaction broadcast successful');
  console.log('TXID:', response.txid);
  console.log('Status:', response.status);
  console.log('Timestamp:', response.timestamp);

  // Response includes:
  // - txid: Transaction ID
  // - status: 'SEEN', 'QUEUED', 'MINED'
  // - timestamp: Submission timestamp
  // - competingTxs: Any competing (double-spend) transactions

  if (response.competingTxs && response.competingTxs.length > 0) {
    console.warn('Warning: Competing transactions detected');
    response.competingTxs.forEach(competingTxid => {
      console.warn('  Competing TXID:', competingTxid);
    });
  }

} catch (error) {
  console.error('Broadcast failed:', error.message);

  // Handle specific error types
  if (error.code === 'INVALID_TRANSACTION') {
    console.error('Transaction validation failed:', error.details);
  } else if (error.code === 'INSUFFICIENT_FEE') {
    console.error('Fee too low. Minimum required:', error.minimumFee);
  } else if (error.code === 'DOUBLE_SPEND') {
    console.error('Double-spend detected. Original TXID:', error.originalTxid);
  }
}

2. Fee Policy Queries and Calculation

ARC provides fee policy information for accurate fee calculation:

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

const arc = new ARC('https://api.taal.com/arc', {
  apiKey: 'mainnet_xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx'
});

// Query current fee policy
const feePolicy = await arc.getFeePolicy();

console.log('Fee policies:');
console.log('Standard fee:', feePolicy.standard, 'sats/KB');
console.log('Data fee:', feePolicy.data, 'sats/KB');
console.log('Mining fee:', feePolicy.mining, 'sats/KB');

// Calculate fee for a transaction
const tx = new Transaction();
// ... add inputs and outputs ...

// Get transaction size
const txSize = tx.toBinary().length;

// Calculate required fee
const requiredFee = Math.ceil((txSize / 1000) * feePolicy.standard);
console.log('Required fee:', requiredFee, 'satoshis');

// Verify transaction has sufficient fee
const actualFee = tx.getFee();
if (actualFee < requiredFee) {
  console.error('Insufficient fee!');
  console.error('Need additional:', requiredFee - actualFee, 'satoshis');
} else {
  console.log('Fee is sufficient');
}

// Use ARC's fee model directly
import { SatoshisPerKilobyte } from '@bsv/sdk/transaction/fee-models';

const arcFeeModel = new SatoshisPerKilobyte(feePolicy.standard);
await tx.fee(arcFeeModel);

console.log('Transaction fee set to:', tx.getFee(), 'satoshis');

3. Transaction Status Tracking

Monitor transaction lifecycle from broadcast to confirmation:

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

const arc = new ARC('https://api.taal.com/arc', {
  apiKey: 'mainnet_xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx'
});

class TransactionMonitor {
  /**
   * Poll transaction status until confirmed
   */
  static async waitForConfirmation(
    txid: string,
    requiredConfirmations: number = 6,
    pollIntervalMs: number = 5000,
    timeoutMs: number = 3600000 // 1 hour
  ): Promise<{ confirmed: boolean; blockHeight?: number; blockHash?: string }> {
    const startTime = Date.now();

    while (Date.now() - startTime < timeoutMs) {
      try {
        const status = await arc.getTransactionStatus(txid);

        console.log(`Status: ${status.status}, Confirmations: ${status.confirmations || 0}`);

        // Check status
        if (status.status === 'REJECTED') {
          throw new Error(`Transaction rejected: ${status.rejectReason}`);
        }

        if (status.status === 'MINED' &&
            status.confirmations &&
            status.confirmations >= requiredConfirmations) {
          return {
            confirmed: true,
            blockHeight: status.blockHeight,
            blockHash: status.blockHash
          };
        }

        // Wait before next poll
        await new Promise(resolve => setTimeout(resolve, pollIntervalMs));

      } catch (error) {
        console.error('Status check failed:', error.message);
        await new Promise(resolve => setTimeout(resolve, pollIntervalMs));
      }
    }

    return { confirmed: false };
  }

  /**
   * Get detailed transaction status
   */
  static async getDetailedStatus(txid: string): Promise<{
    status: string;
    stage: 'mempool' | 'mining' | 'confirmed' | 'unknown';
    details: any;
  }> {
    const status = await arc.getTransactionStatus(txid);

    let stage: 'mempool' | 'mining' | 'confirmed' | 'unknown' = 'unknown';

    if (status.status === 'SEEN' || status.status === 'QUEUED') {
      stage = 'mempool';
    } else if (status.status === 'MINED' && (!status.confirmations || status.confirmations < 6)) {
      stage = 'mining';
    } else if (status.status === 'MINED' && status.confirmations && status.confirmations >= 6) {
      stage = 'confirmed';
    }

    return {
      status: status.status,
      stage,
      details: {
        txid: status.txid,
        blockHeight: status.blockHeight,
        blockHash: status.blockHash,
        confirmations: status.confirmations,
        timestamp: status.timestamp,
        rejectReason: status.rejectReason
      }
    };
  }
}

// Usage
const txid = '1234567890abcdef...';

// Wait for confirmation
const result = await TransactionMonitor.waitForConfirmation(txid, 6);

if (result.confirmed) {
  console.log('Transaction confirmed!');
  console.log('Block height:', result.blockHeight);
  console.log('Block hash:', result.blockHash);
} else {
  console.log('Transaction not confirmed within timeout');
}

// Get detailed status
const detailedStatus = await TransactionMonitor.getDetailedStatus(txid);
console.log('Status:', detailedStatus.status);
console.log('Stage:', detailedStatus.stage);
console.log('Details:', detailedStatus.details);

4. Double-Spend Detection and Notification

ARC provides double-spend detection with callback notifications:

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

// Setup webhook server to receive callbacks
const app = express();
app.use(express.json());

const callbackSecret = 'webhook_secret_abc123';

app.post('/tx-callbacks', (req, res) => {
  // Verify callback token
  const token = req.headers['authorization'];
  if (token !== `Bearer ${callbackSecret}`) {
    return res.status(401).send('Unauthorized');
  }

  const event = req.body;

  console.log('Received callback:', event.type);

  switch (event.type) {
    case 'TRANSACTION_SEEN':
      console.log('Transaction seen in mempool:', event.txid);
      break;

    case 'TRANSACTION_MINED':
      console.log('Transaction mined:', event.txid);
      console.log('Block height:', event.blockHeight);
      console.log('Block hash:', event.blockHash);
      break;

    case 'TRANSACTION_REJECTED':
      console.error('Transaction rejected:', event.txid);
      console.error('Reason:', event.rejectReason);
      break;

    case 'DOUBLE_SPEND_ATTEMPT':
      console.warn('⚠️  Double-spend detected!');
      console.warn('Original TXID:', event.txid);
      console.warn('Competing TXID:', event.competingTxid);

      // Take action - e.g., alert merchants, freeze orders
      handleDoubleSpend(event.txid, event.competingTxid);
      break;

    case 'TRANSACTION_CONFIRMED':
      console.log('Transaction confirmed:', event.txid);
      console.log('Confirmations:', event.confirmations);
      break;
  }

  res.status(200).send('OK');
});

app.listen(3000, () => {
  console.log('Webhook server listening on port 3000');
});

// Initialize ARC with callback URL
const arc = new ARC('https://api.taal.com/arc', {
  apiKey: 'mainnet_xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx',
  deploymentId: 'payment-processor',
  callbackUrl: 'https://myapp.com/tx-callbacks',
  callbackToken: callbackSecret
});

// Handle double-spend events
function handleDoubleSpend(originalTxid: string, competingTxid: string) {
  console.error('CRITICAL: Double-spend attempt detected');
  console.error('Original transaction:', originalTxid);
  console.error('Competing transaction:', competingTxid);

  // Business logic:
  // 1. Alert payment processor
  // 2. Freeze pending orders
  // 3. Notify merchant
  // 4. Log security incident
  // 5. Analyze competing transaction

  // Example: Check which transaction has higher fee
  arc.getTransactionStatus(originalTxid).then(originalStatus => {
    arc.getTransactionStatus(competingTxid).then(competingStatus => {
      console.log('Original fee:', originalStatus.fee);
      console.log('Competing fee:', competingStatus.fee);

      if (competingStatus.fee > originalStatus.fee) {
        console.warn('Competing transaction has higher fee - may confirm instead');
      }
    });
  });
}

// Broadcast transaction with double-spend monitoring
async function broadcastWithMonitoring(tx: Transaction) {
  try {
    const response = await tx.broadcast(arc);

    console.log('Transaction broadcast:', response.txid);

    // Check for immediate competing transactions
    if (response.competingTxs && response.competingTxs.length > 0) {
      console.warn('Competing transactions detected at broadcast:');
      response.competingTxs.forEach(competingTxid => {
        console.warn('  -', competingTxid);
        handleDoubleSpend(response.txid, competingTxid);
      });
    }

    return response;
  } catch (error) {
    if (error.code === 'DOUBLE_SPEND') {
      handleDoubleSpend(error.txid, error.competingTxid);
    }
    throw error;
  }
}

API Reference

Constructor

constructor(url: string, options?: ARCOptions)

Creates a new ARC broadcaster instance.

Parameters:

• url: string - The ARC API endpoint URL
• options?: ARCOptions - Configuration options

  • apiKey?: string - API key for authentication
  • deploymentId?: string - Application deployment identifier
  • callbackUrl?: string - Webhook URL for transaction callbacks
  • callbackToken?: string - Bearer token for callback authentication

Example:

const arc = new ARC('https://api.taal.com/arc', {
  apiKey: 'mainnet_xxx',
  deploymentId: 'my-app-v1',
  callbackUrl: 'https://myapp.com/callbacks',
  callbackToken: 'secret'
});

Instance Methods

broadcast(tx: Transaction): Promise<BroadcastResponse>

Broadcasts a transaction to the network.

Parameters:

• tx: Transaction - The transaction to broadcast

Returns: Promise<BroadcastResponse>

• txid: string - Transaction ID
• status: string - Transaction status ('SEEN', 'QUEUED', 'MINED')
• timestamp: number - Submission timestamp
• competingTxs?: string[] - Array of competing transaction IDs

Example:

const response = await arc.broadcast(transaction);
console.log('TXID:', response.txid);

getTransactionStatus(txid: string): Promise<TransactionStatus>

Queries the status of a transaction.

Parameters:

• txid: string - The transaction ID to query

Returns: Promise<TransactionStatus>

• txid: string - Transaction ID
• status: string - Current status
• blockHeight?: number - Block height if mined
• blockHash?: string - Block hash if mined
• confirmations?: number - Number of confirmations
• timestamp?: number - Status timestamp
• rejectReason?: string - Rejection reason if rejected
• fee?: number - Transaction fee in satoshis

Example:

const status = await arc.getTransactionStatus(txid);
console.log('Status:', status.status);
console.log('Confirmations:', status.confirmations);

getFeePolicy(): Promise<FeePolicy>

Retrieves the current fee policy from ARC.

Returns: Promise<FeePolicy>

• standard: number - Standard transaction fee (sats/KB)
• data: number - Data transaction fee (sats/KB)
• mining: number - Mining fee (sats/KB)

Example:

const policy = await arc.getFeePolicy();
console.log('Standard fee:', policy.standard, 'sats/KB');

broadcastBEEF(beefHex: string): Promise<BroadcastResponse>

Broadcasts a BEEF (Background Evaluation Extended Format) bundle containing transaction chains.

Parameters:

• beefHex: string - The BEEF bundle in hexadecimal format

Returns: Promise<BroadcastResponse>

• txid: string - Transaction ID of the final transaction
• status: string - Transaction status
• timestamp: number - Submission timestamp

Use this method when:

• Broadcasting transaction chains with dependencies
• Child transactions spend from unconfirmed parents
• You need atomic broadcasting of multiple transactions

Example:

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

// Create BEEF bundle
const beef = new Beef();
beef.addTransaction(parentTx);
beef.addTransaction(childTx);

const beefHex = beef.toHex();
const response = await arc.broadcastBEEF(beefHex);
console.log('BEEF broadcast successful:', response.txid);

Response Types

interface BroadcastResponse {
  txid: string;
  status: 'SEEN' | 'QUEUED' | 'MINED' | 'REJECTED';
  timestamp: number;
  competingTxs?: string[];
}

interface TransactionStatus {
  txid: string;
  status: 'SEEN' | 'QUEUED' | 'MINED' | 'REJECTED' | 'UNKNOWN';
  blockHeight?: number;
  blockHash?: string;
  confirmations?: number;
  timestamp?: number;
  rejectReason?: string;
  fee?: number;
}

interface FeePolicy {
  standard: number;  // satoshis per KB
  data: number;      // satoshis per KB
  mining: number;    // satoshis per KB
}

Common Patterns

Pattern 1: Production Payment Processor

Complete payment processor with ARC integration:

import { ARC, Transaction, PrivateKey, P2PKH } from '@bsv/sdk';
import { SatoshisPerKilobyte } from '@bsv/sdk/transaction/fee-models';

class PaymentProcessor {
  private arc: ARC;
  private privKey: PrivateKey;
  private pendingPayments: Map<string, PaymentRecord>;

  constructor(
    arcUrl: string,
    apiKey: string,
    walletPrivKey: PrivateKey,
    callbackUrl: string
  ) {
    this.arc = new ARC(arcUrl, {
      apiKey,
      deploymentId: 'payment-processor-v1.0.0',
      callbackUrl,
      callbackToken: process.env.CALLBACK_SECRET!
    });

    this.privKey = walletPrivKey;
    this.pendingPayments = new Map();
  }

  /**
   * Process payment transaction
   */
  async processPayment(
    recipientAddress: string,
    amount: number,
    utxos: Array<{ tx: Transaction; outputIndex: number }>,
    metadata?: any
  ): Promise<{ txid: string; status: string }> {
    try {
      // Get current fee policy
      const feePolicy = await this.arc.getFeePolicy();
      const feeModel = new SatoshisPerKilobyte(feePolicy.standard);

      // Create transaction
      const tx = new Transaction();

      // Add inputs
      for (const utxo of utxos) {
        tx.addInput({
          sourceTransaction: utxo.tx,
          sourceOutputIndex: utxo.outputIndex,
          unlockingScriptTemplate: new P2PKH().unlock(this.privKey)
        });
      }

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

      // Add change output
      tx.addOutput({
        lockingScript: new P2PKH().lock(this.privKey.toPublicKey().toAddress()),
        change: true
      });

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

      // Store payment record
      const txid = tx.id('hex');
      this.pendingPayments.set(txid, {
        txid,
        recipientAddress,
        amount,
        timestamp: Date.now(),
        status: 'pending',
        metadata
      });

      // Broadcast
      const response = await tx.broadcast(this.arc);

      // Update status
      this.pendingPayments.get(txid)!.status = response.status;

      console.log('Payment broadcast successful');
      console.log('TXID:', response.txid);
      console.log('Amount:', amount, 'satoshis');
      console.log('Recipient:', recipientAddress);

      return {
        txid: response.txid,
        status: response.status
      };

    } catch (error) {
      console.error('Payment processing failed:', error.message);

      // Handle specific errors
      if (error.code === 'INSUFFICIENT_FEE') {
        throw new Error(`Fee too low. Minimum: ${error.minimumFee} satoshis`);
      } else if (error.code === 'DOUBLE_SPEND') {
        throw new Error(`Double-spend detected: ${error.competingTxid}`);
      } else if (error.code === 'INVALID_TRANSACTION') {
        throw new Error(`Invalid transaction: ${error.details}`);
      }

      throw error;
    }
  }

  /**
   * Handle webhook callback
   */
  handleCallback(event: any) {
    const txid = event.txid;
    const payment = this.pendingPayments.get(txid);

    if (!payment) {
      console.warn('Received callback for unknown transaction:', txid);
      return;
    }

    switch (event.type) {
      case 'TRANSACTION_MINED':
        console.log('Payment mined:', txid);
        payment.status = 'mined';
        payment.blockHeight = event.blockHeight;
        payment.blockHash = event.blockHash;
        break;

      case 'TRANSACTION_CONFIRMED':
        console.log('Payment confirmed:', txid);
        payment.status = 'confirmed';
        payment.confirmations = event.confirmations;

        // Payment is now final - update business logic
        this.finalizePayment(payment);
        break;

      case 'TRANSACTION_REJECTED':
        console.error('Payment rejected:', txid);
        payment.status = 'rejected';
        payment.rejectReason = event.rejectReason;

        // Handle failed payment
        this.handleFailedPayment(payment);
        break;

      case 'DOUBLE_SPEND_ATTEMPT':
        console.error('Double-spend attempt:', txid);
        payment.status = 'double_spend';
        payment.competingTxid = event.competingTxid;

        // Alert and freeze
        this.handleDoubleSpend(payment);
        break;
    }
  }

  /**
   * Query payment status
   */
  async getPaymentStatus(txid: string): Promise<PaymentRecord> {
    const payment = this.pendingPayments.get(txid);
    if (!payment) {
      throw new Error('Payment not found');
    }

    // Refresh status from ARC
    try {
      const status = await this.arc.getTransactionStatus(txid);
      payment.status = status.status;
      payment.confirmations = status.confirmations;
      payment.blockHeight = status.blockHeight;
      payment.blockHash = status.blockHash;
    } catch (error) {
      console.error('Failed to refresh payment status:', error.message);
    }

    return payment;
  }

  private finalizePayment(payment: PaymentRecord) {
    console.log('Finalizing payment:', payment.txid);
    // Update database, send confirmation email, etc.
  }

  private handleFailedPayment(payment: PaymentRecord) {
    console.error('Handling failed payment:', payment.txid);
    // Refund, retry, notify user, etc.
  }

  private handleDoubleSpend(payment: PaymentRecord) {
    console.error('CRITICAL: Double-spend detected for payment:', payment.txid);
    // Freeze account, alert security, investigate, etc.
  }
}

interface PaymentRecord {
  txid: string;
  recipientAddress: string;
  amount: number;
  timestamp: number;
  status: string;
  metadata?: any;
  blockHeight?: number;
  blockHash?: string;
  confirmations?: number;
  rejectReason?: string;
  competingTxid?: string;
}

// Usage
const processor = new PaymentProcessor(
  'https://api.taal.com/arc',
  'mainnet_xxx',
  PrivateKey.fromWif('L5...'),
  'https://myapp.com/callbacks'
);

// Process payment
const result = await processor.processPayment(
  '1RecipientAddress...',
  10000, // 10000 satoshis
  [{ tx: utxoTx, outputIndex: 0 }],
  { orderId: '12345', customerId: 'user_abc' }
);

console.log('Payment TXID:', result.txid);

Pattern 2: Batch Transaction Broadcasting

Efficiently broadcast multiple transactions with error handling:

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

class BatchBroadcaster {
  private arc: ARC;

  constructor(arcUrl: string, apiKey: string) {
    this.arc = new ARC(arcUrl, {
      apiKey,
      deploymentId: 'batch-broadcaster'
    });
  }

  /**
   * Broadcast multiple transactions with retry logic
   */
  async broadcastBatch(
    transactions: Transaction[],
    maxRetries: number = 3
  ): Promise<BatchResult> {
    const results: BatchResult = {
      successful: [],
      failed: [],
      total: transactions.length
    };

    // Get fee policy once for all transactions
    const feePolicy = await this.arc.getFeePolicy();
    console.log('Current fee policy:', feePolicy.standard, 'sats/KB');

    // Broadcast transactions sequentially (to maintain dependencies)
    for (const tx of transactions) {
      const txid = tx.id('hex');
      let attempts = 0;
      let success = false;

      while (attempts < maxRetries && !success) {
        attempts++;

        try {
          console.log(`Broadcasting ${txid} (attempt ${attempts}/${maxRetries})`);

          const response = await tx.broadcast(this.arc);

          results.successful.push({
            txid: response.txid,
            status: response.status,
            attempts
          });

          success = true;
          console.log(`✓ Success: ${txid}`);

        } catch (error) {
          console.error(`✗ Failed: ${txid} - ${error.message}`);

          if (attempts >= maxRetries) {
            results.failed.push({
              txid,
              error: error.message,
              code: error.code,
              attempts
            });
          } else {
            // Wait before retry
            await new Promise(resolve => setTimeout(resolve, 1000 * attempts));
          }
        }
      }
    }

    console.log('\nBatch broadcast complete:');
    console.log(`Total: ${results.total}`);
    console.log(`Successful: ${results.successful.length}`);
    console.log(`Failed: ${results.failed.length}`);

    return results;
  }

  /**
   * Broadcast with dependency ordering
   */
  async broadcastWithDependencies(
    transactions: Transaction[]
  ): Promise<BatchResult> {
    // Sort transactions by dependencies (parent before child)
    const sorted = this.topologicalSort(transactions);

    // Broadcast in order
    return this.broadcastBatch(sorted);
  }

  private topologicalSort(transactions: Transaction[]): Transaction[] {
    const txMap = new Map<string, Transaction>();
    const sorted: Transaction[] = [];
    const visited = new Set<string>();

    for (const tx of transactions) {
      txMap.set(tx.id('hex'), tx);
    }

    function visit(tx: Transaction) {
      const txid = tx.id('hex');
      if (visited.has(txid)) return;

      // Visit dependencies first
      for (const input of tx.inputs) {
        if (input.sourceTXID && txMap.has(input.sourceTXID)) {
          visit(txMap.get(input.sourceTXID)!);
        }
      }

      visited.add(txid);
      sorted.push(tx);
    }

    transactions.forEach(tx => visit(tx));
    return sorted;
  }
}

interface BatchResult {
  successful: Array<{ txid: string; status: string; attempts: number }>;
  failed: Array<{ txid: string; error: string; code?: string; attempts: number }>;
  total: number;
}

// Usage
const batcher = new BatchBroadcaster(
  'https://api.taal.com/arc',
  'mainnet_xxx'
);

const transactions = [tx1, tx2, tx3, tx4, tx5];

const results = await batcher.broadcastWithDependencies(transactions);

console.log('Broadcast results:');
console.log('Success rate:', (results.successful.length / results.total * 100).toFixed(2) + '%');

if (results.failed.length > 0) {
  console.error('Failed transactions:');
  results.failed.forEach(failure => {
    console.error(`  ${failure.txid}: ${failure.error}`);
  });
}

Pattern 3: Transaction Monitoring Dashboard

Real-time transaction monitoring with ARC:

import { ARC } from '@bsv/sdk';
import { EventEmitter } from 'events';

class TransactionMonitorDashboard extends EventEmitter {
  private arc: ARC;
  private transactions: Map<string, MonitoredTransaction>;
  private pollInterval: NodeJS.Timeout | null = null;

  constructor(arcUrl: string, apiKey: string) {
    super();
    this.arc = new ARC(arcUrl, { apiKey });
    this.transactions = new Map();
  }

  /**
   * Add transaction to monitor
   */
  addTransaction(txid: string, metadata?: any) {
    this.transactions.set(txid, {
      txid,
      status: 'UNKNOWN',
      addedAt: Date.now(),
      lastChecked: 0,
      checks: 0,
      metadata
    });

    console.log('Monitoring transaction:', txid);
    this.emit('added', { txid, metadata });
  }

  /**
   * Start monitoring
   */
  startMonitoring(intervalMs: number = 10000) {
    if (this.pollInterval) {
      console.warn('Monitoring already started');
      return;
    }

    console.log('Starting transaction monitoring');
    console.log('Poll interval:', intervalMs, 'ms');
    console.log('Transactions:', this.transactions.size);

    this.pollInterval = setInterval(async () => {
      await this.checkAllTransactions();
    }, intervalMs);

    // Initial check
    this.checkAllTransactions();
  }

  /**
   * Stop monitoring
   */
  stopMonitoring() {
    if (this.pollInterval) {
      clearInterval(this.pollInterval);
      this.pollInterval = null;
      console.log('Monitoring stopped');
    }
  }

  /**
   * Check all monitored transactions
   */
  private async checkAllTransactions() {
    const txids = Array.from(this.transactions.keys());

    console.log(`\nChecking ${txids.length} transactions...`);

    for (const txid of txids) {
      await this.checkTransaction(txid);
    }
  }

  /**
   * Check single transaction status
   */
  private async checkTransaction(txid: string) {
    const monitored = this.transactions.get(txid);
    if (!monitored) return;

    try {
      const status = await this.arc.getTransactionStatus(txid);

      monitored.lastChecked = Date.now();
      monitored.checks++;

      const previousStatus = monitored.status;
      monitored.status = status.status;
      monitored.blockHeight = status.blockHeight;
      monitored.blockHash = status.blockHash;
      monitored.confirmations = status.confirmations;

      // Emit event if status changed
      if (status.status !== previousStatus) {
        console.log(`Status change: ${txid} -> ${status.status}`);

        this.emit('statusChange', {
          txid,
          previousStatus,
          newStatus: status.status,
          transaction: monitored
        });
      }

      // Emit specific events
      if (status.status === 'MINED' && previousStatus !== 'MINED') {
        this.emit('mined', { txid, blockHeight: status.blockHeight });
      }

      if (status.status === 'REJECTED') {
        this.emit('rejected', { txid, reason: status.rejectReason });
        // Stop monitoring rejected transactions
        this.transactions.delete(txid);
      }

      if (status.confirmations && status.confirmations >= 6 && previousStatus !== 'CONFIRMED') {
        this.emit('confirmed', { txid, confirmations: status.confirmations });
        // Stop monitoring confirmed transactions
        this.transactions.delete(txid);
      }

    } catch (error) {
      console.error(`Failed to check ${txid}:`, error.message);
      monitored.lastError = error.message;
    }
  }

  /**
   * Get dashboard statistics
   */
  getStatistics(): DashboardStats {
    const stats: DashboardStats = {
      total: this.transactions.size,
      byStatus: {},
      averageAge: 0,
      oldestTransaction: null
    };

    let totalAge = 0;
    let oldestTime = Date.now();

    for (const [txid, tx] of this.transactions) {
      // Count by status
      stats.byStatus[tx.status] = (stats.byStatus[tx.status] || 0) + 1;

      // Calculate age
      const age = Date.now() - tx.addedAt;
      totalAge += age;

      if (tx.addedAt < oldestTime) {
        oldestTime = tx.addedAt;
        stats.oldestTransaction = {
          txid,
          age: age / 1000,
          status: tx.status
        };
      }
    }

    if (this.transactions.size > 0) {
      stats.averageAge = (totalAge / this.transactions.size) / 1000; // in seconds
    }

    return stats;
  }

  /**
   * Get all monitored transactions
   */
  getTransactions(): MonitoredTransaction[] {
    return Array.from(this.transactions.values());
  }
}

interface MonitoredTransaction {
  txid: string;
  status: string;
  addedAt: number;
  lastChecked: number;
  checks: number;
  blockHeight?: number;
  blockHash?: string;
  confirmations?: number;
  lastError?: string;
  metadata?: any;
}

interface DashboardStats {
  total: number;
  byStatus: Record<string, number>;
  averageAge: number;
  oldestTransaction: {
    txid: string;
    age: number;
    status: string;
  } | null;
}

// Usage
const dashboard = new TransactionMonitorDashboard(
  'https://api.taal.com/arc',
  'mainnet_xxx'
);

// Add event listeners
dashboard.on('statusChange', (event) => {
  console.log(`Status changed: ${event.txid}`);
  console.log(`  ${event.previousStatus} -> ${event.newStatus}`);
});

dashboard.on('mined', (event) => {
  console.log(`Transaction mined: ${event.txid}`);
  console.log(`  Block height: ${event.blockHeight}`);
});

dashboard.on('confirmed', (event) => {
  console.log(`Transaction confirmed: ${event.txid}`);
  console.log(`  Confirmations: ${event.confirmations}`);
});

dashboard.on('rejected', (event) => {
  console.error(`Transaction rejected: ${event.txid}`);
  console.error(`  Reason: ${event.reason}`);
});

// Add transactions to monitor
dashboard.addTransaction('txid1', { orderId: '12345' });
dashboard.addTransaction('txid2', { orderId: '12346' });
dashboard.addTransaction('txid3', { orderId: '12347' });

// Start monitoring (check every 10 seconds)
dashboard.startMonitoring(10000);

// Get statistics periodically
setInterval(() => {
  const stats = dashboard.getStatistics();
  console.log('\n--- Dashboard Statistics ---');
  console.log('Total monitored:', stats.total);
  console.log('By status:', stats.byStatus);
  console.log('Average age:', stats.averageAge.toFixed(2), 'seconds');
  if (stats.oldestTransaction) {
    console.log('Oldest:', stats.oldestTransaction.txid,
      `(${stats.oldestTransaction.age.toFixed(2)}s, ${stats.oldestTransaction.status})`);
  }
}, 30000);

// Stop monitoring after 1 hour
setTimeout(() => {
  dashboard.stopMonitoring();
  console.log('Monitoring stopped after 1 hour');
}, 3600000);

Security Considerations

1. API Key Protection: Never expose API keys in client-side code. Store them securely in environment variables or secret management systems.
2. Callback Authentication: Always verify callback tokens to ensure webhooks are coming from ARC. Use HTTPS for callback URLs.
3. Double-Spend Monitoring: Implement immediate alerts for double-spend attempts. Consider transactions unsafe until they have sufficient confirmations.
4. Rate Limiting: Implement rate limiting for API calls to avoid service disruptions and additional costs.
5. Error Handling: Handle all possible error codes appropriately. Don't assume broadcasts always succeed.
6. Fee Validation: Always verify calculated fees meet current policy requirements before broadcasting.

Performance Considerations

1. Batch Status Queries: When monitoring multiple transactions, batch status queries where possible to reduce API calls.
2. Callback vs Polling: Use callbacks instead of polling for production systems to reduce latency and API usage.
3. Connection Pooling: Reuse ARC instances across requests to benefit from HTTP connection pooling.
4. Caching Fee Policies: Cache fee policies for reasonable periods (e.g., 5 minutes) to reduce unnecessary queries.
5. Async Operations: Use async/await properly to avoid blocking operations. Consider Promise.all for parallel broadcasts when transactions are independent.
6. Timeout Configuration: Set appropriate timeouts for API calls based on your application's requirements.

Related Components

• Transaction - Create and manage transactions
• BEEF - Transaction envelope format
• - Broadcasting interface
• - Fee calculation strategies

Code Examples

See complete working examples in:

• Transaction Broadcasting
• Payment Processing
• Double-Spend Detection
• Batch Operations

Best Practices

1. Always use API keys for production environments to ensure authentication and rate limiting
2. Implement webhook callbacks instead of polling for better performance and lower latency
3. Verify callback tokens to ensure webhooks are authentic
4. Monitor for double-spends actively and implement alerts for suspicious activity
5. Query fee policies before broadcasting to ensure transactions meet requirements
6. Handle all error codes appropriately with user-friendly messages
7. Use deployment IDs to track which version of your application broadcast transactions
8. Implement retry logic for transient network failures
9. Log all broadcast attempts for audit trails and debugging
10. Set reasonable timeouts to prevent hanging operations

Troubleshooting

Issue: Broadcast fails with "INSUFFICIENT_FEE" error

Solution: Query current fee policy and recalculate fees.

const feePolicy = await arc.getFeePolicy();
const feeModel = new SatoshisPerKilobyte(feePolicy.standard * 1.1); // 10% buffer
await tx.fee(feeModel);
await tx.sign();
await tx.broadcast(arc);

Issue: Callback webhook not receiving events

Solution: Verify callback URL is publicly accessible and token is correct.

// Test callback URL
const testCallback = async () => {
  const response = await fetch('https://myapp.com/callbacks', {
    method: 'POST',
    headers: {
      'Content-Type': 'application/json',
      'Authorization': `Bearer ${callbackToken}`
    },
    body: JSON.stringify({
      type: 'TEST',
      txid: 'test123'
    })
  });
  console.log('Callback test:', response.status);
};

Issue: Transaction status shows "UNKNOWN"

Solution: Transaction may not have reached ARC yet. Wait and retry.

async function waitForStatus(txid: string, maxAttempts: number = 10) {
  for (let i = 0; i < maxAttempts; i++) {
    const status = await arc.getTransactionStatus(txid);
    if (status.status !== 'UNKNOWN') {
      return status;
    }
    await new Promise(resolve => setTimeout(resolve, 2000));
  }
  throw new Error('Transaction status remained UNKNOWN');
}

Issue: API rate limit exceeded

Solution: Implement exponential backoff and request throttling.

class RateLimitedARC {
  private lastRequest = 0;
  private minInterval = 100; // ms between requests

  async broadcast(tx: Transaction): Promise<any> {
    const now = Date.now();
    const elapsed = now - this.lastRequest;

    if (elapsed < this.minInterval) {
      await new Promise(resolve =>
        setTimeout(resolve, this.minInterval - elapsed)
      );
    }

    this.lastRequest = Date.now();
    return arc.broadcast(tx);
  }
}

Further Reading

• ARC API Documentation - Official ARC API documentation
• Transaction Broadcasting - BSV Wiki on broadcasting
• Double-Spend Prevention - Understanding double-spends
• Fee Calculation - Bitcoin fee mechanisms
• Webhook Security - Webhook security best practices
• BSV SDK Documentation - Official SDK documentation

Status

✅ Complete