@solana-payment-channel/client

Drop-in replacement for fetch() with automatic payment channel management

A production-ready client SDK that seamlessly handles payment channels and falls back to x402 protocol. Get started in 5 minutes with zero configuration - the client automatically optimizes between instant, free channel payments and on-chain x402 payments based on usage patterns.

Features

• 🔄 Drop-in Replacement: Works exactly like fetch() but handles payments automatically
• 💳 Overdraft/Credit Limit: Set customizable credit limits (up to any amount) for users
• 🔄 Auto-Settlement: Automatically pays off debt when funds are added
• 🧠 Intelligent Routing: Automatically chooses between channel and x402 based on usage patterns
• ⚡️ Zero Configuration: Works out-of-the-box with sensible defaults
• 🎛️ Full Control: Advanced users can manage channels manually
• 📊 Event System: Monitor payments, channel lifecycle, and errors
• 🔒 Type Safety: Full TypeScript support with comprehensive types
• 🚨 Error Handling: Graceful fallbacks and clear error messages
• ⚡️ High Performance: Request caching, capability caching, efficient payment routing
• 🌐 Universal: Works in Node.js and browsers (with wallet adapter)

Installation

npm install @solana-payment-channel/client @bober3r/solana-payment-channels-core @solana/web3.js
# or
yarn add @solana-payment-channel/client @bober3r/solana-payment-channels-core @solana/web3.js
# or
pnpm add @solana-payment-channel/client @bober3r/solana-payment-channels-core @solana/web3.js

Quick Start (5 Minutes)

1. Initialize the Client

import { createClient } from '@solana-payment-channel/client';
import { Keypair } from '@solana/web3.js';

// Load your wallet (from env, file, or generate)
const wallet = Keypair.fromSecretKey(
  new Uint8Array(JSON.parse(process.env.WALLET_SECRET_KEY))
);

// Create client with minimal configuration
const client = createClient({
  wallet,
  rpcUrl: 'https://api.devnet.solana.com',
  network: 'devnet',
});

2. Use Like Regular fetch()

// That's it! Use client.fetch() instead of fetch()
const response = await client.fetch('https://api.example.com/premium');
const data = await response.json();

// The client automatically:
// 1. Detects 402 response
// 2. Checks if server supports channels
// 3. Opens channel if beneficial (high-frequency use)
// 4. Uses channel payment (instant, free)
// 5. Falls back to x402 for single payments
// 6. Retries request with payment

3. That's It!

Your application now supports automatic payment channels with zero additional code. The client tracks usage patterns and optimizes payment routing for you.

Basic Usage Examples

Simple API Calls

import { createClient } from '@solana-payment-channel/client';

const client = createClient({ wallet, rpcUrl, network: 'devnet' });

// Single request
const data = await client.fetch('https://api.example.com/data').then(r => r.json());

// Multiple requests (client automatically optimizes)
for (let i = 0; i < 100; i++) {
  const result = await client.fetch('https://api.example.com/query');
  console.log(await result.json());
}

POST Requests with Body

const response = await client.fetch('https://api.example.com/search', {
  method: 'POST',
  headers: {
    'Content-Type': 'application/json',
  },
  body: JSON.stringify({ query: 'solana', limit: 10 }),
});

const results = await response.json();

Error Handling

try {
  const response = await client.fetch('https://api.example.com/data');

  if (!response.ok) {
    console.error(`HTTP error: ${response.status}`);
    return;
  }

  const data = await response.json();
  console.log(data);
} catch (error) {
  console.error('Request failed:', error);
}

Configuration Options

Basic Configuration

import { createClient } from '@solana-payment-channel/client';

const client = createClient({
  // Required
  wallet: myKeypair,              // Your Solana keypair
  rpcUrl: 'https://api.devnet.solana.com',
  network: 'devnet',              // 'devnet' | 'mainnet-beta'

  // Optional - Channel Management
  channelThreshold: 10,           // Open channel after N req/hour (default: 10)
  defaultChannelDeposit: BigInt(10_000_000), // 10 USDC (default)
  defaultCreditLimit: BigInt(0),  // Credit limit - 0 = no overdraft (default)
  autoRefillThreshold: BigInt(1_000_000),    // Refill at 1 USDC (default)
  autoRefillAmount: BigInt(10_000_000),      // Refill with 10 USDC (default)
  channelExpiry: 7 * 24 * 60 * 60,          // 7 days (default)

  // Optional - Behavior
  autoManageChannels: true,       // Enable auto-management (default: true)
  trackRequests: true,            // Track for optimization (default: true)
  debug: false,                   // Enable debug logging (default: false)

  // Optional - Performance
  capabilitiesCacheTTL: 300000,   // Cache TTL 5 min (default)
  requestTimeout: 30000,          // Request timeout 30s (default)
});

Advanced Configuration

import { createClient } from '@solana-payment-channel/client';
import { PublicKey } from '@solana/web3.js';

const client = createClient({
  wallet: myKeypair,
  rpcUrl: 'https://api.mainnet-beta.solana.com',
  network: 'mainnet-beta',

  // Custom program ID (if not using default)
  programId: new PublicKey('YourProgramId...'),

  // Custom USDC mint (if needed)
  usdcMint: new PublicKey('CustomUSDCMint...'),

  // Aggressive channel opening (lower threshold)
  channelThreshold: 5,

  // Larger deposits for high-volume usage
  defaultChannelDeposit: BigInt(100_000_000), // 100 USDC

  // More aggressive refilling
  autoRefillThreshold: BigInt(10_000_000),    // 10 USDC
  autoRefillAmount: BigInt(50_000_000),        // 50 USDC

  // Longer channel lifetime
  channelExpiry: 30 * 24 * 60 * 60, // 30 days

  // Enable debug mode
  debug: true,
});

Manual Channel Management

For advanced use cases, you can manage channels manually:

Opening Channels

// Open a channel for a specific server
const channelId = await client.openChannel(
  'https://api.example.com',
  BigInt(10_000_000),  // 10 USDC deposit
  BigInt(5_000_000),   // 5 USDC credit limit (optional)
);

console.log(`Channel opened: ${channelId}`);
console.log('Total spendable: 15 USDC (10 deposit + 5 credit)');

// Now all requests to this server use the channel
const response = await client.fetch('https://api.example.com/data');

Checking Channel Balance

const balance = await client.getChannelBalance(channelId);
console.log(`Remaining balance: ${balance}`);

if (balance < BigInt(1_000_000)) {
  console.log('Balance is low!');
}

Refilling Channels

// Manual refill
await client.autoRefillChannel(channelId);
console.log('Channel refilled');

// Refill with custom amount
await client.autoRefillChannel(channelId, BigInt(20_000_000)); // 20 USDC

Closing Channels

// Close channel and get refund
await client.closeChannel(channelId);
console.log('Channel closed, remaining balance refunded');

Getting Channel Information

const info = client.getChannelInfo(channelId);

console.log(`Server: ${info.serverUrl}`);
console.log(`Balance: ${info.currentBalance}`);
console.log(`Payments made: ${info.paymentCount}`);
console.log(`Expires: ${info.expiry}`);

Listing All Channels

const channels = client.getAllChannels();

console.log(`Active channels: ${channels.length}`);

for (const channel of channels) {
  console.log(`${channel.serverUrl}: ${channel.currentBalance} remaining`);
}

Event Monitoring

Monitor payments, channels, and errors in real-time:

Channel Lifecycle Events

// Channel opened
client.on('channel_opened', ({ channelId, serverUrl, deposit, expiry }) => {
  console.log(`✅ Opened channel ${channelId}`);
  console.log(`   Server: ${serverUrl}`);
  console.log(`   Deposit: ${deposit}`);
  console.log(`   Expires: ${expiry}`);
});

// Channel closed
client.on('channel_closed', ({ channelId, serverUrl, refundedAmount }) => {
  console.log(`🔒 Closed channel ${channelId}`);
  console.log(`   Refunded: ${refundedAmount}`);
});

// Channel refilled
client.on('channel_refilled', ({ channelId, addedAmount, newBalance }) => {
  console.log(`💰 Refilled channel ${channelId}`);
  console.log(`   Added: ${addedAmount}`);
  console.log(`   New balance: ${newBalance}`);
});

// Channel depleted (low balance)
client.on('channel_depleted', ({ channelId, remainingBalance, threshold }) => {
  console.log(`⚠️  Channel ${channelId} low on funds`);
  console.log(`   Remaining: ${remainingBalance}`);
  console.log(`   Threshold: ${threshold}`);
});

Payment Events

// Payment required (402 detected)
client.on('payment_required', ({ serverUrl, amount, requirement }) => {
  console.log(`💳 Payment required for ${serverUrl}`);
  console.log(`   Amount: ${amount} ${requirement.currency}`);
});

// Payment made
client.on('payment_made', ({ method, amount, serverUrl, signature }) => {
  console.log(`✅ Paid ${amount} to ${serverUrl}`);
  console.log(`   Method: ${method}`);
  console.log(`   Signature: ${signature}`);
});

// Payment failed
client.on('payment_failed', ({ method, serverUrl, error, amount }) => {
  console.error(`❌ Payment failed to ${serverUrl}`);
  console.error(`   Method: ${method}`);
  console.error(`   Error: ${error}`);
});

Capability Detection Events

// Server capabilities detected
client.on('capabilities_detected', ({ serverUrl, capabilities }) => {
  console.log(`🔍 Detected capabilities for ${serverUrl}`);
  console.log(`   Supports channels: ${capabilities.supportsChannels}`);
  console.log(`   Supports x402: ${capabilities.supportsX402}`);

  if (capabilities.supportsChannels) {
    console.log(`   Min deposit: ${capabilities.minChannelAmount}`);
  }
});

Complete Event Monitoring Example

import { createClient } from '@solana-payment-channel/client';

const client = createClient({ wallet, rpcUrl, network: 'devnet' });

// Set up all event listeners
client.on('channel_opened', (data) => {
  console.log('Channel opened:', data);
});

client.on('payment_made', (data) => {
  console.log('Payment made:', data);
});

client.on('channel_depleted', async (data) => {
  console.warn('Channel low on funds:', data);
  // Auto-refill
  await client.autoRefillChannel(data.channelId);
});

client.on('payment_failed', (data) => {
  console.error('Payment failed:', data);
  // Handle failure (e.g., retry, notify user)
});

// Now make requests with full observability
await client.fetch('https://api.example.com/data');

Analytics & Monitoring

Track usage patterns and costs:

Basic Analytics

const analytics = client.getAnalytics();

console.log('=== Usage Statistics ===');
console.log(`Total requests: ${analytics.totalRequests}`);
console.log(`Total payments: ${analytics.totalPayments}`);
console.log(`Total spent: ${analytics.totalSpent} lamports`);
console.log(`Active channels: ${analytics.activeChannels}`);
console.log(`Success rate: ${(analytics.successRate * 100).toFixed(2)}%`);

console.log('\n=== Payment Methods ===');
console.log(`Channel payments: ${analytics.channelPayments}`);
console.log(`x402 payments: ${analytics.x402Payments}`);
console.log(`Total savings: ${analytics.totalSavings} lamports`);

Per-Domain Statistics

const analytics = client.getAnalytics();

console.log('\n=== Per-Domain Statistics ===');
for (const [domain, stats] of analytics.domainStats) {
  console.log(`\n${domain}:`);
  console.log(`  Total requests: ${stats.totalRequests}`);
  console.log(`  Paid requests: ${stats.paidRequests}`);
  console.log(`  Total paid: ${stats.totalPaid}`);
  console.log(`  Requests/hour: ${stats.requestsPerHour.toFixed(2)}`);
  console.log(`  Has channel: ${stats.hasActiveChannel}`);

  if (stats.channelId) {
    const channel = client.getChannelInfo(stats.channelId);
    console.log(`  Channel balance: ${channel?.currentBalance}`);
  }
}

Cost Analysis

import { AutoPaymentManager } from '@solana-payment-channel/client';

// Get the auto-payment manager for advanced analytics
const manager = new AutoPaymentManager();

// Track some requests...
manager.trackRequest('https://api.example.com/data', {
  paymentRequired: true,
  amount: BigInt(100_000),
  method: 'x402',
  statusCode: 200,
  responseTime: 150,
});

// Analyze costs
const analysis = manager.analyzeCosts('https://api.example.com');

console.log('=== Cost Analysis ===');
console.log(`Total requests: ${analysis.totalRequests}`);
console.log(`Channel setup cost: ${analysis.channelSetupCost} lamports`);
console.log(`x402 per-payment cost: ${analysis.x402PaymentCost} lamports`);
console.log(`Total x402 cost: ${analysis.totalX402Cost} lamports`);
console.log(`Total channel cost: ${analysis.totalChannelCost} lamports`);
console.log(`Estimated savings: ${analysis.estimatedSavings} lamports`);
console.log(`Break-even at: ${analysis.breakEvenRequests} requests`);
console.log(`Recommendation: ${analysis.recommendation}`);

Payment Flow Diagrams

Automatic Payment Flow

1. Request is made
   ↓
2. Is 402 response?
   ↓ Yes
3. Check server capabilities
   ↓
4. Supports channels?
   ├─ Yes → Check request frequency
   │         ↓
   │         High frequency (>10 req/hr)?
   │         ├─ Yes → Open channel → Use channel payment (free, instant)
   │         └─ No  → Use x402 (on-chain payment)
   │
   └─ No  → Use x402 (on-chain payment)
   ↓
5. Retry request with payment
   ↓
6. Return successful response

Channel Payment Flow

1. Create payment authorization
   ↓
2. Sign with client wallet (off-chain)
   ↓
3. Attach authorization to request headers
   ↓
4. Server verifies signature (instant)
   ↓
5. Server serves request (no blockchain interaction)
   ↓
6. Server claims payment later (batched on-chain)

x402 Payment Flow

1. Parse payment requirement from 402 response
   ↓
2. Create Solana transaction
   ↓
3. Sign and send transaction
   ↓
4. Wait for confirmation
   ↓
5. Attach transaction signature to request
   ↓
6. Server verifies on-chain
   ↓
7. Server serves request

Best Practices

1. Use Auto-Management for Most Cases

// ✅ Good: Let the client manage everything
const client = createClient({
  wallet,
  rpcUrl,
  network: 'devnet',
  autoManageChannels: true, // Default
});

await client.fetch(url); // Automatic optimization

2. Pre-Open Channels for Known High-Frequency APIs

// ✅ Good: Open channel upfront for known usage
const client = createClient({ wallet, rpcUrl, network: 'devnet' });

// If you know you'll make many requests
const channelId = await client.openChannel(
  'https://api.example.com',
  BigInt(50_000_000) // 50 USDC for high volume
);

// Now make requests (all use channel)
for (let i = 0; i < 10000; i++) {
  await client.fetch('https://api.example.com/data');
}

3. Monitor Low Balances

// ✅ Good: Monitor and handle low balances
client.on('channel_depleted', async ({ channelId, remainingBalance }) => {
  console.warn(`Channel ${channelId} low: ${remainingBalance}`);

  // Automatic refill
  await client.autoRefillChannel(channelId);

  // Or close and open new one
  // await client.closeChannel(channelId);
  // await client.openChannel(serverUrl, BigInt(20_000_000));
});

4. Handle Errors Gracefully

// ✅ Good: Comprehensive error handling
try {
  const response = await client.fetch(url);

  if (response.status === 402) {
    // Payment required but failed
    console.error('Payment failed or insufficient funds');
    return;
  }

  if (!response.ok) {
    console.error(`HTTP error: ${response.status}`);
    return;
  }

  const data = await response.json();
  return data;
} catch (error) {
  if (error.name === 'AbortError') {
    console.error('Request timed out');
  } else if (error instanceof TypeError) {
    console.error('Network error');
  } else {
    console.error('Request failed:', error);
  }
}

5. Clean Up Channels When Done

// ✅ Good: Close channels to recover funds
const channels = client.getAllChannels();

for (const channel of channels) {
  // Close expired or unused channels
  if (channel.expiry < new Date() || channel.paymentCount === 0) {
    await client.closeChannel(channel.channelId);
    console.log(`Closed channel ${channel.channelId}, refunded ${channel.currentBalance}`);
  }
}

6. Use Debug Mode During Development

// ✅ Good: Enable debug logging during development
const client = createClient({
  wallet,
  rpcUrl,
  network: 'devnet',
  debug: true, // Shows detailed logs
});

// Debug logs will show:
// - Server capability detection
// - Payment decisions
// - Channel operations
// - Request tracking

7. Configure Based on Usage Patterns

// ✅ Good: Tune configuration to your use case

// High-frequency API calls (>50 req/hr)
const highFrequencyClient = createClient({
  wallet, rpcUrl, network: 'devnet',
  channelThreshold: 5,              // Lower threshold
  defaultChannelDeposit: BigInt(100_000_000), // 100 USDC
  autoRefillThreshold: BigInt(20_000_000),    // 20 USDC
  channelExpiry: 30 * 24 * 60 * 60,           // 30 days
});

// Occasional API calls (<5 req/hr)
const lowFrequencyClient = createClient({
  wallet, rpcUrl, network: 'devnet',
  channelThreshold: 20,             // Higher threshold
  defaultChannelDeposit: BigInt(5_000_000),   // 5 USDC
  autoManageChannels: false,        // Manual management
});

Troubleshooting

Payment Required (402) Not Being Handled

Problem: Requests return 402 but payment isn't automatic.

Solution:

// Check if skipAutoPayment is set
const response = await client.fetch(url, {
  skipAutoPayment: false, // Ensure auto-payment is enabled
});

// Check server capabilities
const capabilities = await fetchServerCapabilities(url);
console.log('Supports channels:', capabilities.supportsChannels);
console.log('Supports x402:', capabilities.supportsX402);

Channel Not Being Opened

Problem: High-frequency requests still using x402.

Solution:

// Check request frequency
const stats = client.getAnalytics();
for (const [domain, domainStats] of stats.domainStats) {
  console.log(`${domain}: ${domainStats.requestsPerHour} req/hr`);
}

// Lower threshold if needed
const client = createClient({
  wallet, rpcUrl, network: 'devnet',
  channelThreshold: 5, // Lower from default 10
});

// Or open manually
await client.openChannel(url, BigInt(10_000_000));

Insufficient Channel Balance

Problem: Channel payments failing due to low balance.

Solution:

// Enable auto-refill
const client = createClient({
  wallet, rpcUrl, network: 'devnet',
  autoManageChannels: true,
  autoRefillThreshold: BigInt(2_000_000),  // Refill at 2 USDC
  autoRefillAmount: BigInt(10_000_000),    // Refill with 10 USDC
});

// Or monitor and refill manually
client.on('channel_depleted', async ({ channelId }) => {
  await client.autoRefillChannel(channelId);
});

Server Doesn't Support Channels

Problem: Server returns 402 but doesn't support channels.

Solution:

// Client will automatically fall back to x402
// Verify by checking capabilities
const capabilities = await fetchServerCapabilities(url);

if (!capabilities.supportsChannels) {
  console.log('Server only supports x402 - will use on-chain payments');
}

// Ensure x402 client is properly configured
// (Integration with @x402-solana/client should be set up)

Request Timeouts

Problem: Requests timing out during payment.

Solution:

// Increase timeout
const client = createClient({
  wallet, rpcUrl, network: 'devnet',
  requestTimeout: 60000, // 60 seconds
});

// Or use custom timeout per request
const response = await client.fetch(url, {
  signal: AbortSignal.timeout(90000), // 90 seconds
});

API Reference

See TypeScript definitions for complete API documentation.

Main Classes

• PaymentChannelClient - Main client for automatic payment handling
• AutoPaymentManager - Intelligent payment routing and cost analysis

Key Methods

• createClient(config) - Create a new client instance
• client.fetch(url, options) - Drop-in fetch replacement
• client.openChannel(serverUrl, deposit) - Open a payment channel
• client.closeChannel(channelId) - Close a channel
• client.getChannelBalance(channelId) - Check channel balance
• client.autoRefillChannel(channelId) - Refill a channel
• client.getAnalytics() - Get usage analytics

Utility Functions

• fetchServerCapabilities(url) - Fetch server capabilities
• parsePaymentRequirements(response) - Parse 402 response
• createChannelPaymentHeaders(...) - Create channel payment headers
• createX402PaymentHeaders(...) - Create x402 payment headers

Contributing

Contributions are welcome! Please see CONTRIBUTING.md for details.

License

MIT License - see LICENSE for details.

Support

• 📚 Documentation: https://docs.x402.dev
• 💬 Discord: https://discord.gg/x402
• 🐛 Issues: GitHub Issues
• 📧 Email: [email protected]

Related Packages

• @bober3r/solana-payment-channels-core - Core payment channel management
• @bober3r/solana-payment-channels-server - Server SDK for accepting payments
• @x402-solana/client - x402 protocol client

Built with ❤️ by the x402 team