Ensure Transactional Safety with Idempotent API Requests (Node.js)

const axios = require('axios');
const { v4: uuidv4 } = require('uuid'); // npm install uuid

/**
 * Makes an API request with an idempotency key.
 * Ensures that if the same request is sent multiple times due to network issues,
 * it will only be processed once by the server.
 *
 * @param {string} url The API endpoint URL.
 * @param {string} method The HTTP method (e.g., 'POST', 'PUT').
 * @param {object} data The request payload.
 * @param {string} idempotencyKey Optional. A unique key for this request. If not provided, one will be generated.
 * @returns {Promise<object>} The API response data.
 */
async function makeIdempotentRequest(url, method, data, idempotencyKey = uuidv4()) {
  try {
    const headers = {
      'Content-Type': 'application/json',
      'Idempotency-Key': idempotencyKey, // Crucial header for idempotency
      // Add other headers like Authorization if needed
      // 'Authorization': 'Bearer YOUR_ACCESS_TOKEN'
    };

    const response = await axios({
      method: method,
      url: url,
      data: data,
      headers: headers
    });

    console.log(`Idempotent request successful to ${url}. Status: ${response.status}`);
    return response.data;
  } catch (error) {
    console.error(`Idempotent request failed to ${url}: ${error.message}`);
    // Handle specific error codes related to idempotency (e.g., 409 Conflict if server explicitly indicates a duplicate)
    if (error.response && error.response.status === 409) {
      console.warn('Request was potentially a duplicate and already processed.');
    }
    throw error; // Re-throw the error for upstream handling
  }
}

// Example Usage:
async function processOrder(orderData) {
  const orderId = orderData.id || uuidv4(); // Use an existing order ID or generate a new one
  const uniqueActionKey = `create-order-${orderId}`; // Specific key for this action
  try {
    console.log(`Attempting to process order with idempotency key: ${uniqueActionKey}`);
    const result = await makeIdempotentRequest(
      'https://api.example.com/orders', // Replace with your actual API endpoint
      'POST',
      orderData,
      uniqueActionKey
    );
    console.log('Order processing result:', result);
    return result;
  } catch (e) {
    console.error('Failed to process order:', e.message);
    throw e;
  }
}

// Simulate calling the function
// const myOrder = { id: 'order-123', item: 'Widget A', quantity: 2, amount: 29.99 };
// processOrder(myOrder);
// // If network error, you could retry with the same orderId and uniqueActionKey
// setTimeout(() => processOrder(myOrder), 5000); // Simulate a retry after 5 seconds