Frequently Asked Questions
Set up an Express server, install Axios and dotenv, create a POST route '/send-sms', and use Axios to send data to the Sinch SMS API. This route will handle incoming requests with the recipient's number and message body, then securely pass this information to the Sinch API to trigger the SMS delivery. Refer to the article's step-by-step guide for detailed instructions and code snippets.
The Sinch SMS REST API is a web service that allows you to send and receive SMS messages programmatically. You interact with it by sending HTTP requests (typically POST) to specific endpoints, passing data like the recipient number and message content in JSON format. The API handles delivering the message via Sinch's SMS infrastructure.
Dotenv helps secure sensitive credentials like Sinch API keys and service plan IDs. It loads these values from a '.env' file into process.env, keeping them separate from your codebase. This enhances security and avoids accidentally exposing credentials in version control.
For high-volume SMS sending, a message queue like RabbitMQ or Redis is recommended. It decouples API requests from the actual sending process, allowing the server to quickly accept requests and put them on the queue. Background workers then pull messages from the queue and send them via Sinch, improving performance and reliability under heavy load.
Yes, the Sinch SMS API accepts an array of recipient numbers in the 'to' field of the request payload. This lets you send the same SMS message to multiple recipients with a single API call. However, ensure your Sinch account and number are provisioned to send to all intended destinations.
Use a try-catch block around your Axios calls to the Sinch API. Log detailed error information from the error.response, error.request, and error.message properties of the caught error object. Provide informative error messages to the client without exposing sensitive internal details. See the article for examples of enhanced logging and retry strategies.
Input validation is essential to prevent security vulnerabilities and API misuse. Check for missing or invalid fields, enforce correct number formats (E.164), sanitize input to prevent injection attacks, and validate message length to avoid issues. Use robust validation libraries like 'joi' or 'express-validator'.
Use the 'express-rate-limit' middleware to control how many requests a client can make within a specific timeframe. This prevents abuse, protects your Sinch budget, and ensures fair API access. Configure the windowMs and max properties to define the time window and request limits.
E.164 is an international telephone number format that includes a '+' sign followed by the country code and the phone number. It's crucial for Sinch SMS because the API strictly requires numbers in this format. Always ensure all user-provided phone numbers are properly formatted before sending them to the API.
Use logging libraries like Winston or Pino. These tools provide structured logging, allowing you to record details such as timestamp, message, recipient, error codes, and API responses. Configure the logger to write logs to files or output them to the console, offering comprehensive records for debugging and monitoring.
Store Sinch API credentials (SERVICE_PLAN_ID and API_TOKEN) in a .env file. Use the 'dotenv' package to load these variables into process.env at runtime. Never commit the .env file to version control (add it to .gitignore). For production, consider using more secure environment management solutions provided by your deployment platform.
400 errors indicate an issue with the request sent to Sinch. Common causes include incorrect 'from' or 'to' number formatting, missing required fields in the request payload, or an invalid request structure. Check the detailed error message in the Sinch API response for more specific information.
Use the axios-retry library to automatically retry failed Sinch API calls due to transient network issues or server errors. Configure it to retry only on specific error codes (e.g., 5xx) or network errors, and use exponential backoff to increase wait times between retries, improving reliability.
The 'from' field should contain your registered Sinch virtual number. Ensure this number is associated with your Sinch Service Plan ID and is provisioned for sending SMS. Use the E.164 number format for this field as well.
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:
.env
file intoprocess.env
, keeping sensitive credentials out of the codebase.System Architecture:
Prerequisites:
SERVICE_PLAN_ID
andAPI_TOKEN
from the Sinch Customer Dashboard.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.
2. Initialize Node.js Project:
Initialize the project using npm. The
-y
flag accepts the default settings.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.
express
: The web framework.axios
: HTTP client for API calls.dotenv
: Loads environment variables from.env
.4. Project Structure:
Create the basic file structure.
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
andnode_modules
).5. Configure
.gitignore
:Open
.gitignore
and add the following lines to prevent committing sensitive data and unnecessary files:This is crucial for security and repository cleanliness.
6. Create Basic Express Server:
Open
index.js
and set up a minimal Express server:7. Run the Basic Server:
Test if the basic setup works.
Open your browser or use
curl http://localhost:3000
. You should see ""Sinch SMS API Server is running!"". PressCtrl+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 theapp.listen
call:Explanation:
SERVICE_PLAN_ID
,API_TOKEN
,SINCH_NUMBER
, andSINCH_REGION
from environment variables usingprocess.env
.us
,eu
). We default tous
but allow overriding viaSINCH_REGION
./xms/v1/{servicePlanId}/batches
) is constructed. A note has been added to verify this URL.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.Authorization
: UsesBearer
authentication with yourAPI_TOKEN
.Content-Type
: Must beapplication/json
.axios.post
sends the request.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 thesendSms
function definition and theapp.listen
call:Explanation:
POST
route at/send-sms
.express.json()
middleware (added earlier) automatically parses the incoming JSON request body intoreq.body
.recipient
andmessage
fromreq.body
.string
) ofrecipient
andmessage
.recipient
.message
is not empty.400 Bad Request
if validation fails.sendSms
function within atry...catch
block.try
block): Returns a200 OK
status with a success message and the response data from Sinch (which usually includes abatch_id
).catch
block): Returns a500 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:
+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:YOUR_..._HERE
) with your actual credentials.SINCH_NUMBER
includes the leading+
.SINCH_REGION
according to your Sinch account's region.dotenv
loads these intoprocess.env
whenrequire('dotenv').config();
is called at the start ofindex.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
andconsole.error
provide basic information. For production, structured logging libraries likewinston
orpino
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
):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).
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.axios-retry
can simplify adding retry logic to Axios requests.Example (Conceptual - showing
axios-retry
integration):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:
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).If adding a database (e.g., PostgreSQL, MongoDB):
sms_log
with columnsid
,recipient
,sender
,body
,sinch_batch_id
,status
,created_at
,updated_at
)./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:
joi
orexpress-validator
for more complex rules and clearer error reporting.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.
express-rate-limit
.Add this near the top of
index.js
, afterapp.use(express.json());
:3. Authentication/Authorization (If needed):
If this API is part of a larger system or should only be accessible by authenticated clients:
/send-sms
endpoint. This requires additional middleware to verify credentials before allowing access to the route.8. Handling Special Cases
+
followed by country code and number, no spaces or dashes). Ensure any number input is validated or transformed into this format before sending to thesendSms
function. Our basic regex validation helps here.9. Performance Optimizations (Conceptual)
For this simple endpoint, performance bottlenecks are unlikely unless sending extremely high volumes.
async/await
withaxios
leverages this.maxSockets
).10. Monitoring, Observability, and Analytics (Conceptual)
For production readiness:
GET /health
) that returns200 OK
if the server is running. Monitoring services can ping this endpoint./send-sms
.sendSms
function).prom-client
or APM (Application Performance Monitoring) services (Datadog, New Relic, Dynatrace).11. Troubleshooting and Caveats
401 Unauthorized
/403 Forbidden
from Sinch:SERVICE_PLAN_ID
orAPI_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)..env
.400 Bad Request
from Sinch:from
number (not associated with the Service Plan ID, wrong format).to
number format (not E.164).from
,to
,body
).body
(less common).error.request
in Axios):SINCH_REGION
in.env
leading to the wrong hostname. DNS resolution problems. Firewall blocking outbound connections.SINCH_REGION
matches your Sinch dashboard setting. Ensure firewalls allow outbound HTTPS traffic to*.sms.api.sinch.com
.429 Too Many Requests
error.+15551234567
). Ensure client inputs are validated/normalized.from
number (SINCH_NUMBER
) must be a number associated with yourSERVICE_PLAN_ID
in the Sinch dashboard.12. Deployment and CI/CD
Basic Deployment (e.g., Heroku/Render):
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.Procfile
(no extension) in your project root:node index.js
automatically if specified inpackage.json
'sstart
script.package.json
Start Script: Add a start script to yourpackage.json
:CI/CD (Conceptual):
13. Verification and Testing
1. Manual Verification:
node index.js
curl
or Postman to send a POST request to your endpoint.recipient
ormessage
.recipient
format..env
with incorrect credentials to test401
/403
handling.message
.2. Automated Testing (Conceptual):
For robust applications, add automated tests:
/send-sms
route handler in isolation.sendSms
function by mocking theaxios.post
call. You don't want unit tests actually hitting the Sinch API. Assert thataxios.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./send-sms
endpoint by making actual HTTP requests to your running application (again, likely mocking theaxios.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.