@nexflow-smf/smf

Zero-dependency SDK for NexFlow Smart Meta-Facilitator (SMF).

Route x402 payments to the best facilitator, verify payment intents, and settle batches—all with a single line of code.

Features

• ✅ Zero runtime dependencies — uses native fetch
• ✅ Full TypeScript support — complete type definitions
• ✅ Idempotency built-in — safe retries on network failures
• ✅ Rate limit awareness — exposes remaining quota after each request
• ✅ Error handling — structured errors with status codes and retry hints
• ✅ Tree-shakeable — ESM and CJS builds

Installation

npm install @nexflow-smf/smf
# or
yarn add @nexflow-smf/smf
# or
pnpm add @nexflow-smf/smf

Quick Start

import { NexFlowSMFClient } from '@nexflow-smf/smf';

const smf = new NexFlowSMFClient({
  baseUrl: 'https://api.nexflowapp.app',
  apiKey: process.env.NEXFLOW_API_KEY!,
});

// Route a payment to the best facilitator
const route = await smf.route({
  amount_wei: '1000000',
  token_address: '0xA0b86991c6218b36c1d19D4a2e9Eb0cE3606eB48',  // USDC
  chain_id: 'eip155:8453',  // Base
  payment_id: 'order-12345',  // Idempotency key
});

console.log(`Facilitator: ${route.facilitator_id}`);
console.log(`Platform fee: ${route.expected_fee_wei} wei`);
console.log(`Confidence: ${route.confidence}`);
console.log(`Quote expires: ${route.quote_expires_at}`);

API Reference

new NexFlowSMFClient(options)

Create a new client instance.

const smf = new NexFlowSMFClient({
  baseUrl: 'https://api.nexflowapp.app',  // Required
  apiKey: 'nf_live_xxx',                   // Required
  timeoutMs: 30000,                        // Optional (default: 30s)
  rateLimitThreshold: 0.8,                 // Optional (default: 0.8)
});

smf.route(request, options?)

Route a payment to the best available facilitator.

const route = await smf.route({
  amount_wei: '1000000',
  token_address: '0xA0b86991c6218b36c1d19D4a2e9Eb0cE3606eB48',
  chain_id: 'eip155:8453',
  recipient: '0xabcd...',       // Optional
  payment_id: 'order-123',      // Optional (also used as idempotency key)
  metadata: { orderId: 123 },   // Optional
});

// Response
{
  facilitator_id: 'cdp',
  path: 'scored',
  expected_fee_wei: '2500',        // 0.25% platform fee
  estimated_latency_ms: 150,
  confidence: 0.95,
  quote_expires_at: '2026-01-03T...',
  quote_id: 'order-123',
}

smf.verify(request, options?)

Verify an x402 payment intent.

const verification = await smf.verify({
  payment_intent: 'x402:1:base:0xabc...:1000000:USDC:sig',
  recipient_address: '0xabcd...',
  amount_wei: '1000000',           // Optional
  facilitator_id: 'cdp',           // Optional hint
});

// Response
{
  valid: true,
  facilitator: 'cdp',
  estimated_settlement_ms: 500,
}

// Or if invalid
{
  valid: false,
  reason: 'Recipient mismatch: expected 0x..., got 0x...',
  facilitator: 'none',
  estimated_settlement_ms: 0,
}

smf.settle(request, options?)

Settle a batch of payments.

// Queue for next batch window
const settlement = await smf.settle({
  batch_id: 'batch-xyz',
  facilitator_id: 'cdp',
});

// Force immediate settlement
const immediate = await smf.settle({
  batch_id: 'batch-xyz',
  facilitator_id: 'cdp',
  force: true,
});

// Response
{
  status: 'submitted',            // 'pending' | 'submitted' | 'confirmed' | 'failed'
  transaction_hash: '0xabc...',   // When submitted/confirmed
  settled_at: '2026-01-03T...',   // When confirmed
  error: 'Insufficient funds',    // When failed
}

smf.health()

Get system health status.

const health = await smf.health();

// Response
{
  status: 'healthy',  // 'healthy' | 'degraded' | 'down'
  summary: { total: 5, healthy: 4, degraded: 1, down: 0 },
  facilitators: [
    {
      facilitatorId: 'cdp',
      name: 'Coinbase Developer Platform',
      status: 'healthy',
      metrics: { successRate: 0.99, p95LatencyMs: 150, ... },
    },
    // ...
  ],
  timestamp: '2026-01-03T...',
}

smf.facilitators()

Get list of available facilitators.

const facilitators = await smf.facilitators();

// Response
[
  {
    id: 'cdp',
    label: 'Coinbase Developer Platform',
    url: 'https://cdp.coinbase.com',
    supportedNetworks: ['base', 'ethereum'],
    tokens: ['USDC', 'ETH'],
    priority: 1,
    feeBps: 25,
    enabled: true,
    status: 'healthy',
  },
  // ...
]

smf.getRateLimit()

Get rate limit information from the last request.

await smf.route({ ... });
const rateLimit = smf.getRateLimit();

if (rateLimit) {
  console.log(`${rateLimit.remaining}/${rateLimit.limit} requests remaining`);
  console.log(`Resets at: ${rateLimit.resetAt}`);
}

Error Handling

All errors are wrapped in NexFlowSMFError with structured information.

import { NexFlowSMFClient, NexFlowSMFError } from '@nexflow-smf/smf';

try {
  await smf.route({ ... });
} catch (error) {
  if (error instanceof NexFlowSMFError) {
    console.log(error.statusCode);  // 400, 401, 429, 500, etc.
    console.log(error.code);        // 'INVALID_REQUEST', 'RATE_LIMITED', etc.
    console.log(error.message);     // Human-readable message
    console.log(error.details);     // Additional context from API
    console.log(error.retryable);   // true for 429, 5xx, timeout, network errors

    if (error.retryable) {
      // Implement retry logic
    }
  }
}

Error Codes

| Code | Description | |------|-------------| | MISSING_API_KEY | Authorization header not provided | | INVALID_API_KEY | API key is invalid or expired | | INVALID_REQUEST | Request body validation failed | | INVALID_AMOUNT | Amount must be a positive integer string | | INVALID_CHAIN_ID | Chain ID format is invalid | | MALFORMED_PAYMENT | Payment intent cannot be parsed | | RECIPIENT_MISMATCH | Recipient doesn't match payment intent | | BATCH_NOT_FOUND | Batch ID doesn't exist | | RATE_LIMITED | Rate limit exceeded (retryable) | | TIMEOUT | Request timed out (retryable) | | NETWORK_ERROR | Network request failed (retryable) | | INTERNAL_ERROR | Server error (retryable) |

Idempotency

All POST requests use idempotency keys to prevent accidental duplicate operations.

// Auto-generated idempotency key
const route1 = await smf.route({
  amount_wei: '1000000',
  token_address: '0xabc...',
  chain_id: 'eip155:8453',
});

// Use payment_id as idempotency key
const route2 = await smf.route({
  amount_wei: '1000000',
  token_address: '0xabc...',
  chain_id: 'eip155:8453',
  payment_id: 'order-123',  // Will be used as idempotency key
});

// Explicit idempotency key
const route3 = await smf.route(
  { amount_wei: '1000000', token_address: '0xabc...', chain_id: 'eip155:8453' },
  { idempotencyKey: 'my-custom-key' }
);

Idempotency keys are cached server-side for 5 minutes. Retrying with the same key within that window returns the cached response.

Rate Limiting

The SDK exposes rate limit information after each request.

// Check rate limit after request
const route = await smf.route({ ... });
const rateLimit = smf.getRateLimit();

// Check if approaching limit
if (smf.isApproachingRateLimit()) {
  console.warn('Consider slowing down requests');
}

The SDK automatically logs a warning when utilization exceeds 80% (configurable via rateLimitThreshold).

Validation Utilities

The SDK exports validation helpers for input validation.

import {
  isValidChainId,
  isValidAddress,
  isValidWei,
  isValidPaymentIntent,
  generateIdempotencyKey,
} from '@nexflow-smf/smf';

isValidChainId('eip155:8453');     // true
isValidAddress('0xabc...');        // true
isValidWei('1000000');             // true
isValidPaymentIntent('x402:...');  // true

const key = generateIdempotencyKey();  // '1735939200000-abc123xyz'

TypeScript

Full type definitions are included. Import types as needed:

import type {
  SMFRouteRequest,
  SMFRouteResponse,
  SMFVerifyRequest,
  SMFVerifyResponse,
  SMFSettleRequest,
  SMFSettleResponse,
  SMFHealthResponse,
  SMFFacilitatorInfo,
  RateLimitInfo,
  SMFErrorCode,
} from '@nexflow-smf/smf';

Requirements

• Node.js 18+ (uses native fetch)
• Or any environment with fetch support (browsers, Deno, Bun, etc.)

License

MIT © NexFlow