Callback URLs

Callback URLs are a core mechanism for implementing asynchronous integration patterns. They enable seamless communication between services without requiring the caller to wait, functioning like a lightweight publish-subscribe (pub-sub) model. The caller specifies a URL where it should be notified once the process completes. This approach aligns perfectly with real-time, asynchronous processing and event-driven architectures, making it good choice in software design and integrations.

However, working with callback URLs often comes with its own set of challenges, especially during development and testing. This is where Beeceptor steps in to make life easier for developers.

What Are Callback URLs?

Callback URLs are endpoints specified by a client when making a request to a service. The service, after completing the requested process, sends a notification or data to the provided URL.

For instance:

• Payment Gateways: Notify the originating system (that initiated the payment request) once the transaction is successfully completed.
• Bulk SMS Sending: Inform the client about the status of sending SMS messages to a list of recipients. These callbacks or notifications can include details such as delivery statistics and completion reports.

Why Use Callback URLs?

When Callback URLs are picked as integration pattern, they allow:

• Real-time Updates: Immediate notification when tasks are completed. No need of continuos polling the server.
• Scalability: Enables decoupling between services, improving system performance. No systems waits.

Development Challenges in Callback URL Testing

Testing callback URLs during development can present significant obstacles:

Testing on Developer Machines

Callbacks require a publicly accessible endpoint, but developer machines typically run on local servers inaccessible to external services. This necessitates either:

• Frequent deployments to a remote server
• Using tunneling tools from Beeceptor can help save time while integration testing.

DevOps/IT Overheads

Setting up a public endpoint for testing often involves coordination with IT or DevOps teams. Challenges include:

• Configuring infrastructure for public-facing endpoints.
• Balancing security with accessibility.
• Managing configurations for different environments (staging, production, etc.).

Slow Integration Testing

Callback workflows often require frequent commits and deployments to test changes, slowing the feedback loop. Developers must:

• Deploy their code to test the changes.
• Reproduce scenarios repeatedly for debugging.

Callback URL With Beeceptor

Testing callback URLs can be challenging. Beeceptor simplifies this process by enabling you to mock services and callbacks, saving time and cost during development and performance testing. With its Proxy Rule feature, you can mock an incoming requests, and later trigger a callback. This proxy rule lets you define an HTTP Callouts to trigger by forwarding or simulating real callback requests. This is an invaluable feature during development.

Let’s walk through setting up an example scenario where you mock an SMS sending API and test its callback behavior.

Mocking an SMS Sending API

Imagine you're developing an application that sends bulk SMS messages via an external SMS API. For cost efficiency, you’ve mocked the API. In a real-world scenario, the SMS API triggers a webhook to notify your system of successful delivery — a typical asynchronous event. With Beeceptor, you can test this callback behavior effortlessly.

Refer to this step-by-step guide.

1. Create an Endpoint: In Beeceptor, an endpoint acts as the mock version of your SMS API domain. For example you may end up with a mock API server as https://my-sms-api.proxy.beeceptor.com. This endpoint will serve as the mock service to mimic the SMS API.
2. Set Up a Proxy Callout Rule: A Proxy Callout Rule defines how Beeceptor handles incoming requests and triggers the callback.
3. Match Requests to the SMS API Path: Here you specify when the proxy rule should activate, matching the SMS API path For example, match the method as POST and path as /api/sms where your application sends SMS requests.
4. Configure the Callback Section: In the callback section of the rule, set it to return an instant response to the incoming SMS request. This simulates the SMS API acknowledging the receipt of your request.
5. Define the Callback URL: In the callout section, configure the URL where delivery notifications will be sent. For example, if your application listens for SMS delivery updates at https://yourapp.com/webhooks/sms/callback, use this URL.
6. Click Save to apply the rule configuration.
7. Now, send a request to this mock SMS API using your application (or an API client curl or Bruno).

   POST https://my-sms-api.beeceptor.com/api/sms

   Content-Type: application/json

   {
       "to": "+1(456)6446503",
       "message": "Hello, this is a test SMS!"
   }
   Observe Beeceptor processing the request. It returns an instant response and trigger a callback to the specified URL.
8. Verify the Callback: Check your callback URL logs or application to confirm that the mock service triggered the callback successfully. Here is an example callback payload:

   {
       "messageId": "234234234232398789238474737173",
       "status": "Delivered",
       "recipient": "+1(456)6446503",
       "timestamp": "2025-01-01T12:00:00Z"
   }

Best Practices for Callback URL Testing

To maximize the reliability of callback URLs, follow these best practices:

• Secure Your Callback URLs: Use authentication mechanisms like API keys or OAuth tokens to validate requests. Ensure HTTPS is enforced to encrypt data transmission.
• Log Callback Requests: Always log the external requests. You can inspect these callbacks live in Beeceptor for better debugging and traceability.
• Manage Multiple Callback Scenarios: With Beeceptor, you can simulate various conditions and payloads to test different use cases efficiently.