This guide provides a complete walkthrough for building a Node.js application using the Express framework to send SMS messages via the Sinch SMS REST API. We'll cover everything from project setup to deployment considerations, focusing on creating a robust and functional starting point.

You'll learn how to set up your environment, handle API credentials securely, build an API endpoint to trigger SMS sends, implement basic error handling, and understand common pitfalls.

Project Overview and Goals

What We're Building:

We will create a simple Node.js web server using the Express framework. This server will expose a single API endpoint (POST /send-sms). When this endpoint receives a request containing a recipient phone number and a message body, it will use the Sinch SMS API to send the specified message to the recipient.

Problem Solved:

This application provides a foundational backend service for applications needing to programmatically send SMS messages for notifications, alerts, verification codes, or other communication purposes, leveraging Sinch's infrastructure.

Technologies Used:

• Node.js: A JavaScript runtime environment for building server-side applications.
• Express: A minimal and flexible Node.js web application framework that provides a robust set of features for web and mobile applications.
• Axios: A promise-based HTTP client for making requests from Node.js to the Sinch API.
• dotenv: A module to load environment variables from a .env file into process.env, keeping sensitive credentials out of the codebase.
• Sinch SMS REST API: The API provided by Sinch for sending and receiving SMS messages.

System Architecture:

+-------------+       +-----------------------+       +-----------------+       +-----------------+
| User/Client | ----> | Node.js/Express API   | ----> | Sinch SMS API   | ----> | SMS Recipient   |
| (e.g. curl) |       | (POST /send-sms)      |       | (Region Endpoint) |       | (Mobile Phone)  |
+-------------+       +-----------------------+       +-----------------+       +-----------------+
                      | - Parses Request      |
                      | - Validates Input     |
                      | - Calls Sinch API     |
                      | - Handles Response    |
                      +-----------------------+

Prerequisites:

• Node.js and npm (or yarn): Installed on your system. Download from nodejs.org.
• Sinch Account: A registered account at Sinch.com.
• Sinch API Credentials: You need your SERVICE_PLAN_ID and API_TOKEN from the Sinch Customer Dashboard.
• Sinch Phone Number: A virtual number purchased or assigned within your Sinch account, associated with your Service Plan ID.
• Basic Terminal/Command Line Knowledge: Familiarity with navigating directories and running commands.
• Text Editor or IDE: Such as VS Code, Sublime Text, Atom, etc.

Expected Outcome:

By the end of this guide, you will have a running Node.js Express application capable of accepting POST requests to /send-sms and sending SMS messages via Sinch. You will also understand the core concepts for integrating with the Sinch API securely and effectively.

1. Setting up the Project

Let's initialize our Node.js project and install the necessary dependencies.

1. Create Project Directory:

Open your terminal or command prompt and create a new directory for your project. Navigate into it.

mkdir sinch-sms-express
cd sinch-sms-express

2. Initialize Node.js Project:

Initialize the project using npm. The -y flag accepts the default settings.

npm init -y

This creates a package.json file, which tracks your project's metadata and dependencies.

3. Install Dependencies:

We need Express for the web server, Axios to make HTTP requests to the Sinch API, and dotenv to manage environment variables.

npm install express axios dotenv

• express: The web framework.
• axios: HTTP client for API calls.
• dotenv: Loads environment variables from .env.

4. Project Structure:

Create the basic file structure.

touch index.js .env .gitignore

• index.js: The main entry point for our application logic.
• .env: Stores sensitive configuration like API keys (will not be committed to version control).
• .gitignore: Specifies intentionally untracked files that Git should ignore (like .env and node_modules).

5. Configure .gitignore:

Open .gitignore and add the following lines to prevent committing sensitive data and unnecessary files:

# .env file
.env

# Node modules
node_modules/

# Log files
*.log

# OS generated files
.DS_Store
Thumbs.db

This is crucial for security and repository cleanliness.

6. Create Basic Express Server:

Open index.js and set up a minimal Express server:

// index.js
require('dotenv').config(); // Load environment variables from .env file first

const express = require('express');
const axios = require('axios');

const app = express();
const port = process.env.PORT || 3000; // Use port from env or default to 3000

// Middleware to parse JSON request bodies
app.use(express.json());

// Basic route for testing
app.get('/', (req, res) => {
  res.send('Sinch SMS API Server is running!');
});

// --- SMS Sending Logic will go here ---

// Start the server
app.listen(port, () => {
  console.log(`Server listening at http://localhost:${port}`);
});

7. Run the Basic Server:

Test if the basic setup works.

node index.js

Open your browser or use curl http://localhost:3000. You should see ""Sinch SMS API Server is running!"". Press Ctrl+C in the terminal to stop the server.

2. Implementing Core Functionality: Sending SMS

Now, let's add the logic to interact with the Sinch SMS API.

1. Create the SMS Sending Function:

We'll encapsulate the Sinch API call within a reusable function. Add this function inside index.js, before the app.listen call:

// index.js
// ... (require statements and app setup) ...

/**
 * Sends an SMS message using the Sinch API.
 * @param {string} recipientNumber - The E.164 formatted phone number of the recipient.
 * @param {string} messageBody - The text content of the SMS.
 * @returns {Promise<object&gt;} - A promise that resolves with the Sinch API response data.
 * @throws {Error} - Throws an error if the API call fails.
 */
async function sendSms(recipientNumber, messageBody) {
  const servicePlanId = process.env.SINCH_SERVICE_PLAN_ID;
  const apiToken = process.env.SINCH_API_TOKEN;
  const sinchNumber = process.env.SINCH_NUMBER; // Your Sinch virtual number
  const region = process.env.SINCH_REGION || 'us'; // Default to 'us' if not specified

  // Construct the Sinch API URL based on the region
  // IMPORTANT: Verify this endpoint against the latest official Sinch SMS API documentation
  // as API endpoints can change.
  const sinchApiUrl = `https://${region}.sms.api.sinch.com/xms/v1/${servicePlanId}/batches`;

  if (!servicePlanId || !apiToken || !sinchNumber) {
    console.error(""Error: Sinch API credentials or number missing in .env file."");
    throw new Error(""Sinch configuration is incomplete."");
  }

  const payload = {
    from: sinchNumber,
    to: [recipientNumber], // API expects an array of recipients
    body: messageBody,
  };

  const headers = {
    'Authorization': `Bearer ${apiToken}`,
    'Content-Type': 'application/json',
  };

  console.log(`Attempting to send SMS via Sinch to ${recipientNumber}`);
  console.log(`Using Endpoint: ${sinchApiUrl}`);
  // console.log('Payload:', JSON.stringify(payload, null, 2)); // Uncomment for debugging payload

  try {
    const response = await axios.post(sinchApiUrl, payload, { headers });
    console.log('Sinch API Response Status:', response.status);
    console.log('Sinch API Response Data:', response.data);
    return response.data; // Return the successful response data
  } catch (error) {
    console.error('Error sending SMS via Sinch:');
    if (error.response) {
      // The request was made and the server responded with a status code
      // that falls out of the range of 2xx
      console.error('Status:', error.response.status);
      console.error('Headers:', error.response.headers);
      console.error('Data:', error.response.data);
      // Re-throw a more specific error
      throw new Error(`Sinch API Error: ${error.response.status} - ${JSON.stringify(error.response.data)}`);
    } else if (error.request) {
      // The request was made but no response was received
      console.error('Request Error:', error.request);
      throw new Error('Sinch API Error: No response received from server.');
    } else {
      // Something happened in setting up the request that triggered an Error
      console.error('Axios Setup Error:', error.message);
      throw new Error(`Sinch API Error: ${error.message}`);
    }
  }
}

// ... (app.get('/') route) ...

// --- API Endpoint for sending SMS will go here ---

// ... (app.listen call) ...

Explanation:

• Credentials: We retrieve the SERVICE_PLAN_ID, API_TOKEN, SINCH_NUMBER, and SINCH_REGION from environment variables using process.env.
• Region: The Sinch API endpoint URL depends on the region your account is provisioned in (e.g., us, eu). We default to us but allow overriding via SINCH_REGION.
• URL Construction: The correct endpoint URL for sending batches (/xms/v1/{servicePlanId}/batches) is constructed. A note has been added to verify this URL.
• Payload: The request body is structured according to Sinch API requirements:
  • from: Your registered Sinch virtual number.
  • to: An array containing the recipient's phone number(s) in E.164 format (e.g., +15551234567).
  • body: The message text.
• Headers:
  • Authorization: Uses Bearer authentication with your API_TOKEN.
  • Content-Type: Must be application/json.
• Axios Call: axios.post sends the request.
• Error Handling: The try...catch block handles potential errors during the API call, logging details from the Axios error object (error.response, error.request, error.message) for better debugging.

3. Building the API Layer

Now, let's create the Express endpoint that will use our sendSms function.

1. Create the /send-sms Endpoint:

Add the following route handler in index.js, between the sendSms function definition and the app.listen call:

// index.js
// ... (require statements, app setup, sendSms function) ...

// Basic route for testing
app.get('/', (req, res) => {
  res.send('Sinch SMS API Server is running!');
});

// API Endpoint to send SMS
app.post('/send-sms', async (req, res) => {
  const { recipient, message } = req.body; // Extract recipient and message from request body

  // --- Basic Input Validation ---
  if (!recipient || typeof recipient !== 'string') {
    return res.status(400).json({ error: 'Missing or invalid `recipient` field (must be a string).' });
  }
  if (!message || typeof message !== 'string') {
    return res.status(400).json({ error: 'Missing or invalid `message` field (must be a string).' });
  }
  // Basic E.164 format check (starts with '+', followed by digits)
  if (!/^\+[1-9]\d{1,14}$/.test(recipient)) {
     return res.status(400).json({ error: 'Invalid recipient phone number format. Use E.164 format (e.g., +15551234567).' });
  }
  if (message.trim().length === 0) {
     return res.status(400).json({ error: 'Message body cannot be empty.' });
  }
  // --- End Basic Input Validation ---


  try {
    const sinchResponse = await sendSms(recipient, message);
    console.log(`SMS successfully submitted to Sinch for recipient: ${recipient}`);
    // Respond to the client indicating success
    res.status(200).json({
      message: 'SMS submitted successfully.',
      details: sinchResponse // Include Sinch response details (like batch_id)
    });
  } catch (error) {
    console.error(`Failed to send SMS to ${recipient}:`, error.message);
    // Respond to the client indicating failure
    // Avoid exposing raw internal errors directly in production
    res.status(500).json({
      error: 'Failed to send SMS.',
      // Optionally include a generic error detail or correlation ID in production
      // details: error.message // Be cautious about exposing internal details
    });
  }
});

// ... (app.listen call) ...

Explanation:

• Route: Defines a POST route at /send-sms.
• Body Parsing: express.json() middleware (added earlier) automatically parses the incoming JSON request body into req.body.
• Input Extraction: Destructures recipient and message from req.body.
• Validation: Includes basic checks:
  • Presence and type (string) of recipient and message.
  • A simple regex check for E.164 format for the recipient.
  • Ensures the message is not empty.
  • Returns a 400 Bad Request if validation fails.
• Function Call: Calls the sendSms function within a try...catch block.
• Response:
  • On success (try block): Returns a 200 OK status with a success message and the response data from Sinch (which usually includes a batch_id).
  • On failure (catch block): Returns a 500 Internal Server Error status with an error message. It's good practice not to expose detailed internal error messages to the client in production; log them internally instead.

4. Integrating with Sinch (Credentials)

Securely managing your Sinch API credentials is vital.

1. Obtain Sinch Credentials:

• Log in to your Sinch Customer Dashboard.
• Navigate to SMS -> APIs.
• Under REST API Configuration, you will find:
  • Service plan ID: Copy this value.
  • API Token: Click Show next to the token and copy the value. Treat this like a password (important) – keep it secret!
• Note the Region displayed (e.g., US, EU).
• Navigate to Numbers -> Your Virtual Numbers. Find the number you want to send SMS from and copy its value (in E.164 format, e.g., +12345678900). Make sure this number is associated with the Service Plan ID you are using.

2. Configure .env File:

Open the .env file you created earlier and add your credentials:

# .env - Store sensitive credentials here
# DO NOT COMMIT THIS FILE TO GIT

# Sinch Credentials
SINCH_SERVICE_PLAN_ID=YOUR_SERVICE_PLAN_ID_HERE
SINCH_API_TOKEN=YOUR_API_TOKEN_HERE
SINCH_NUMBER=+YOUR_SINCH_VIRTUAL_NUMBER_HERE # Use E.164 format
SINCH_REGION=us # Or eu, au, br etc. based on your dashboard

# Server Configuration
PORT=3000

• Replace the placeholder values (YOUR_..._HERE) with your actual credentials.
• Ensure SINCH_NUMBER includes the leading +.
• Set SINCH_REGION according to your Sinch account's region.
• Remember that dotenv loads these into process.env when require('dotenv').config(); is called at the start of index.js.

Security Note: The .env file should never be committed to your version control system (Git). Ensure .env is listed in your .gitignore file.

5. Error Handling and Logging

We've added basic error handling, but let's refine logging and consider retries.

1. Enhance Logging:

Our current console.log and console.error provide basic information. For production, structured logging libraries like winston or pino offer better log management, formatting (e.g., JSON), and routing (e.g., sending logs to files or external services).

Example using Winston (Requires npm install winston):

// index.js
// ... other requires
const winston = require('winston');

// Configure a basic Winston logger
const logger = winston.createLogger({
  level: 'info',
  format: winston.format.combine(
    winston.format.timestamp(),
    winston.format.json()
  ),
  transports: [
    // - Write all logs with level `error` and below to `error.log`
    // - Write all logs with level `info` and below to `combined.log`
    // In production, you'd likely use more robust transports (e.g., console, file rotation, external services)
    new winston.transports.Console({ format: winston.format.simple() }), // Simple format for console
    // new winston.transports.File({ filename: 'error.log', level: 'error' }),
    // new winston.transports.File({ filename: 'combined.log' }),
  ],
});


// Inside sendSms function catch block (replace console.error):
// ...
} catch (error) {
    const logData = {
      // timestamp added by winston format
      message: ""Error sending SMS via Sinch"",
      recipient: recipientNumber, // Add context
      errorCode: error.response?.status,
      apiResponse: error.response?.data,
      requestError: error.request ? 'No response received' : undefined,
      setupError: !error.response && !error.request ? error.message : undefined
    };
    logger.error(logData); // Log structured data using Winston
    // Re-throw the error as before
    if (error.response) {
      throw new Error(`Sinch API Error: ${error.response.status} - ${JSON.stringify(error.response.data)}`);
    } else if (error.request) {
      throw new Error('Sinch API Error: No response received from server.');
    } else {
      throw new Error(`Sinch API Error: ${error.message}`);
    }
}

// Inside /send-sms route catch block (replace console.error):
// ...
} catch (error) {
    const logData = {
       // timestamp added by winston format
       message: ""Failed to process /send-sms request"",
       recipient: recipient, // Add context if available
       errorMessage: error.message,
       // Add a correlation ID if implemented
    };
    logger.error(logData); // Log structured data using Winston
    // Respond to client as before
    // ...
}

2. Retry Mechanisms (Conceptual):

Network glitches or temporary Sinch API issues can occur. Implementing a retry strategy with exponential backoff can improve reliability for transient errors (like 5xx errors or network timeouts).

• Identify Retryable Errors: Typically, network errors or server-side errors (like 500, 503) from Sinch are candidates for retries. Client errors (4xx) usually indicate a problem with the request itself and shouldn't be retried without modification.
• Strategy: Wait for a short period (e.g., 1 second), then retry. If it fails again, wait longer (e.g., 2 seconds), then retry, and so on, up to a maximum number of attempts.
• Implementation: Libraries like axios-retry can simplify adding retry logic to Axios requests.

Example (Conceptual - showing axios-retry integration):

// --- Conceptual Example of adding axios-retry ---
// Requires: npm install axios-retry

/*
const axiosRetry = require('axios-retry');

// Apply retry logic to the existing axios instance or a new one
// This should typically be done where you configure axios, potentially
// creating a dedicated instance for Sinch calls.

// Example: Applying to the global axios instance (use with caution)
axiosRetry(axios, {
  retries: 3, // Number of retries
  retryDelay: (retryCount) => {
    console.log(`Retry attempt: ${retryCount}`);
    return retryCount * 1000; // Exponential back-off (1s, 2s, 3s)
  },
  retryCondition: (error) => {
    // Retry on network errors or specific 5xx server errors
    return (
      axiosRetry.isNetworkOrIdempotentRequestError(error) ||
      (error.response && error.response.status >= 500 && error.response.status <= 599)
    );
  },
});

// Now, subsequent calls like axios.post in sendSms will automatically use this retry logic.
// Note: Implementing full retry logic requires careful consideration of which
// errors are safe to retry and is recommended for production systems.
*/
// --- End Conceptual Example ---

6. Database Schema and Data Layer (Optional)

For this simple ""send-only"" example, a database isn't strictly required. However, in a real-world application, you would likely want to:

• Log SMS Status: Store records of sent messages, including recipient, message body, timestamp, the batch_id returned by Sinch, and potentially delivery status updates. Delivery status updates are often received via webhooks. This involves setting up a separate webhook endpoint in your application to receive status updates pushed from Sinch (see Sinch documentation on Delivery Receipts).
• Manage Users/Contacts: Store recipient information if you're sending messages to registered users.
• Queue Messages: For high-volume sending, queue messages in a database or message queue (like RabbitMQ or Redis) and process them asynchronously with background workers.

If adding a database (e.g., PostgreSQL, MongoDB):

• Schema: Define tables/collections for messages (e.g., sms_log with columns id, recipient, sender, body, sinch_batch_id, status, created_at, updated_at).
• Data Access Layer: Use an ORM (like Sequelize, Prisma, Mongoose) or a query builder (like Knex.js) to interact with the database, abstracting the SQL/database queries.
• Integration: Modify the /send-sms endpoint to first save the message record to the database with a ""pending"" status, then attempt to send via Sinch, and update the status upon success or failure.

7. Adding Security Features

Beyond securing API keys, consider these API security measures:

1. Input Validation (Enhanced):

Our basic validation is a start. For production:

• Use robust validation libraries like joi or express-validator for more complex rules and clearer error reporting.
• Sanitize inputs to prevent potential injection attacks (though less common for SMS bodies compared to web forms, it's good practice). Libraries like express-validator often include sanitization features.

2. Rate Limiting:

Protect your API endpoint (and your Sinch budget) from abuse by limiting the number of requests a client can make in a given time window.

• Implementation: Use middleware like express-rate-limit.

npm install express-rate-limit

Add this near the top of index.js, after app.use(express.json());:

// index.js
// ... require statements ...
const rateLimit = require('express-rate-limit');

// ... app = express(); app.use(express.json()); ...

// Apply rate limiting to the SMS endpoint
const smsLimiter = rateLimit({
  windowMs: 15 * 60 * 1000, // 15 minutes
  max: 100, // Limit each IP to 100 requests per windowMs
  message: 'Too many SMS requests created from this IP, please try again after 15 minutes',
  standardHeaders: true, // Return rate limit info in the `RateLimit-*` headers
  legacyHeaders: false, // Disable the `X-RateLimit-*` headers
});

app.use('/send-sms', smsLimiter); // Apply the limiter ONLY to the /send-sms route

// ... routes (app.get, app.post) ...
// ... app.listen ...

3. Authentication/Authorization (If needed):

If this API is part of a larger system or should only be accessible by authenticated clients:

• Implement API key authentication, JWT (JSON Web Tokens), or OAuth tokens for clients calling your /send-sms endpoint. This requires additional middleware to verify credentials before allowing access to the route.

8. Handling Special Cases

• Number Formatting: The Sinch API strictly requires E.164 format (+ followed by country code and number, no spaces or dashes). Ensure any number input is validated or transformed into this format before sending to the sendSms function. Our basic regex validation helps here.
• Character Limits & Encoding: Standard SMS messages have character limits (160 for GSM-7 encoding, 70 for Unicode). Longer messages are split into multiple segments (concatenated SMS). Sinch handles segmentation, but be mindful of potential costs for multi-part messages. Special characters might force Unicode encoding, reducing the per-segment limit. Inform users or truncate messages if necessary.
• Internationalization: Sending SMS internationally involves different costs and potentially different regulations (e.g., sender ID registration requirements). Ensure your Sinch account is enabled for the destination countries.

9. Performance Optimizations (Conceptual)

For this simple endpoint, performance bottlenecks are unlikely unless sending extremely high volumes.

• Asynchronous Operations: Node.js is inherently non-blocking. Our use of async/await with axios leverages this.
• Connection Pooling: Axios manages underlying HTTP connections. For very high throughput, ensure Node's default limits aren't being hit, or consider fine-tuning agent settings (e.g., maxSockets).
• Payload Size: Keep the message body concise where possible.
• Queuing (Mentioned earlier): For high volume, decoupling the API request from the actual Sinch call using a queue is the most significant optimization. The API endpoint simply adds the job to the queue, and a separate worker process handles sending.

10. Monitoring, Observability, and Analytics (Conceptual)

For production readiness:

• Health Checks: Add a simple health check endpoint (e.g., GET /health) that returns 200 OK if the server is running. Monitoring services can ping this endpoint.
• Metrics: Track key metrics:
  • Request rate to /send-sms.
  • Request latency (how long the endpoint takes to respond).
  • Error rate (percentage of 5xx responses).
  • Sinch API call latency and error rate (within the sendSms function).
  • Use tools like Prometheus with prom-client or APM (Application Performance Monitoring) services (Datadog, New Relic, Dynatrace).
• Error Tracking: Integrate services like Sentry or Bugsnag to capture, aggregate, and alert on application errors in real-time.
• Logging (Centralized): Ship logs (using Winston/Pino transports) to a centralized logging platform (Elasticsearch/Logstash/Kibana stack, Datadog Logs, Splunk) for analysis and dashboarding.

11. Troubleshooting and Caveats

• 401 Unauthorized / 403 Forbidden from Sinch:
  • Cause: Incorrect SERVICE_PLAN_ID or API_TOKEN. Double-check values in .env. Ensure the token hasn't expired or been revoked. Ensure you are using the API Token from the REST API section of the Sinch Dashboard, not Key ID/Secret from Access Keys (which might be used by other Sinch products like the Verification API or certain SDKs).
  • Solution: Verify credentials in the Sinch Dashboard and update .env.
• 400 Bad Request from Sinch:
  • Cause: Malformed request body. Common issues:
    • Incorrect from number (not associated with the Service Plan ID, wrong format).
    • Incorrect to number format (not E.164).
    • Missing required fields (from, to, body).
    • Invalid characters in body (less common).
  • Solution: Check the detailed error message in the Sinch response (logged by our error handler). Validate the payload structure and content, especially number formats.
• Connection Errors / Timeouts (error.request in Axios):
  • Cause: Network issue between your server and Sinch. Incorrect SINCH_REGION in .env leading to the wrong hostname. DNS resolution problems. Firewall blocking outbound connections.
  • Solution: Verify network connectivity. Double-check the SINCH_REGION matches your Sinch dashboard setting. Ensure firewalls allow outbound HTTPS traffic to *.sms.api.sinch.com.
• Rate Limiting (by Sinch):
  • Cause: Exceeding Sinch's default or account-specific sending limits (requests per second).
  • Response: Often a 429 Too Many Requests error.
  • Solution: Implement client-side rate limiting (as shown), use queues to smooth out traffic, or contact Sinch support to discuss rate limit increases if necessary.
• Number Formatting: Always use E.164 format (e.g., +15551234567). Ensure client inputs are validated/normalized.
• Sinch Number Provisioning: The from number (SINCH_NUMBER) must be a number associated with your SERVICE_PLAN_ID in the Sinch dashboard.
• Destination Country Restrictions: Some countries have regulations on sender IDs or require pre-registration. Messages might be blocked if these aren't met. Check Sinch documentation or support for country-specific rules.

12. Deployment and CI/CD

Basic Deployment (e.g., Heroku/Render):

1. Ensure Git Repository: Your code should be in a Git repository.
2. Platform Setup: Create an app on your chosen platform (Heroku, Render, Fly.io, etc.).
3. Environment Variables: Configure the production environment variables (SINCH_SERVICE_PLAN_ID, SINCH_API_TOKEN, SINCH_NUMBER, SINCH_REGION, PORT - the platform usually sets PORT) through the platform's dashboard or CLI. Do not commit your .env file.
4. Procfile (for Heroku/some others): Create a file named Procfile (no extension) in your project root:
   procfile

   web: node index.js
   
   This tells the platform how to start your web process. Render often detects node index.js automatically if specified in package.json's start script.
5. package.json Start Script: Add a start script to your package.json:
   json

   // package.json
   {
     // ... other properties
     ""scripts"": {
       ""start"": ""node index.js"",
       ""test"": ""echo \""Error: no test specified\"" && exit 1""
     },
     // ... other properties
   }
   
6. Deployment: Push your code to the platform via Git or use their CLI deployment commands.

CI/CD (Conceptual):

• Set up a pipeline (GitHub Actions, GitLab CI, Jenkins) that automatically:
  • Runs tests on each push/merge.
  • Builds the application (if necessary, though simple Node.js apps often don't need a build step).
  • Deploys to a staging environment.
  • Deploys to production upon approval or automatically from the main branch.
• Manage environment variables securely within the CI/CD platform's secrets management.

13. Verification and Testing

1. Manual Verification:

• Start the server locally: node index.js
• Use a tool like curl or Postman to send a POST request to your endpoint.

# Replace with your recipient number and desired message
# Ensure the number starts with '+' and country code
RECIPIENT_NUMBER=""+15551234567""
MESSAGE_BODY=""Hello from Sinch Express App!""

curl -X POST http://localhost:3000/send-sms \
     -H ""Content-Type: application/json"" \
     -d '{
           ""recipient"": ""'""${RECIPIENT_NUMBER}""'"",
           ""message"": ""'""${MESSAGE_BODY}""'""
         }'

• Check Terminal Logs: Look for logs indicating the request was received, the Sinch API call was attempted, and the success or error response from Sinch. Use your configured logger (e.g., Winston) output.
• Check Phone: Verify that the recipient phone number received the SMS message. (There might be a slight delay).
• Test Error Cases:
  • Send requests with missing recipient or message.
  • Send requests with invalid recipient format.
  • Temporarily modify .env with incorrect credentials to test 401/403 handling.
  • Send an empty message.

2. Automated Testing (Conceptual):

For robust applications, add automated tests:

• Unit Tests (e.g., using Jest, Mocha):
  • Test the validation logic for the /send-sms route handler in isolation.
  • Test the sendSms function by mocking the axios.post call. You don't want unit tests actually hitting the Sinch API. Assert that axios.post was called with the correct URL, payload, and headers based on the function inputs. Test success and error scenarios of the mocked API call.
• Integration Tests (e.g., using Supertest):
  • Test the /send-sms endpoint by making actual HTTP requests to your running application (again, likely mocking the axios.post call to avoid hitting the real Sinch API during tests). Verify that the endpoint returns the correct status codes (200, 400, 500) and response bodies based on different inputs and mocked API outcomes.