Don't Trust the 200 OK: Defensive Integration for Synchronous Validation APIs

When working with synchronous APIs, it is tempting to treat a successful HTTP 200 response as a signal that your business logic has been satisfied. However, in modern API design—specifically with services like the TG Validator—the HTTP transport layer and the application-level response envelope are two distinct concerns.

If you treat every 200 OK as a valid "registered" result, you risk poisoning your local cache or application state with error messages disguised as successful network transactions. Here is how to build a robust integration that respects the API's internal error contract.

1. Understand the Envelope

The TG Validator API returns a consistent code / msg / data envelope. A 200 status code only confirms that the network request reached the server and the server successfully returned a response—it does not mean the validation check itself was successful.

Always parse the code field first. A code of 0 indicates success, but other codes (like 42901 for concurrency limits or 50300 for maintenance) represent operational states that require specific handling.

2. Implement a Response Normalization Layer

Instead of passing raw API responses directly to your business logic, wrap the call in a function that normalizes the result. This ensures your application only acts on verified data.

async function performCheck(phoneNumber) {
 const response = await fetch("https://tgvalidator.com/api/v1/check", {
 method: "POST",
 headers: { "X-API-Key": "your_api_key", "Content-Type": "application/json" },
 body: JSON.stringify({ service_type: "tg", identifier: phoneNumber })
 });

 const payload = await response.json();

 // Check the application-level code, not just the HTTP status
 if (payload.code !== 0) {
 throw new Error(`Validation failed with code ${payload.code}: ${payload.msg}`);
 }

 return payload.data;
}

3. Handle Operational Limits

The API defines specific behaviors for rate and concurrency limits. Because the TG Validator is a synchronous, single-number check service, these limits are critical to your integration's reliability:

• Concurrency Limits (42901): If you hit this, your request was not charged and no result was generated. You should implement a short backoff before retrying.
• Service Maintenance (50300): This is a transient state. Do not treat this as a "not registered" result; treat it as an incomplete operation.
• Billing Safety: Since failed checks are automatically refunded, your primary goal is to ensure your application doesn't misinterpret an error code as a definitive "not registered" status.

4. The Checklist for Safe Integration

• Validate the code: Always check payload.code === 0 before reading data.registered.
• Ignore HTTP 200 for Logic: Treat the HTTP status as a transport success, not a business success.
• Respect Concurrency: If you receive 42901, wait for current in-flight requests to complete before retrying.
• E.164 Formatting: Ensure your input is strictly formatted as an E.164 phone number to avoid 40002 (Invalid phone number) errors.

By decoupling the network transport from your business logic, you ensure that your application remains resilient to temporary service states and maintains data integrity. For more details on the response structure, check the official API documentation.

This article was drafted with AI assistance and reviewed before publishing.