Codeigniter 7: How to Handle JSON Input and Output in CodeIgniter REST APIs

JSON (JavaScript Object Notation) is a lightweight data-interchange format widely used in REST APIs. In this guide, we’ll demonstrate how to handle JSON input and output in a CodeIgniter REST API.

Why JSON?
 

1. Readability: JSON is human-readable and easy to understand.
2. Lightweight: It minimizes the size of transmitted data.
3. Compatibility: JSON is supported by most programming languages and frameworks.

Step 1: Configuring CodeIgniter for JSON Handling
 

By default, CodeIgniter supports JSON handling. To ensure smooth operations:

1. Set Response Format: Use the ResourceController class, which includes built-in support for JSON responses:

   namespace App\Controllers;
   
   use CodeIgniter\RESTful\ResourceController;
   
   class ExampleController extends ResourceController {
       protected $format = 'json';
   }

2. Enable JSON Requests: Confirm that the Content-Type header in client requests is set to application/json.

Step 2: Handling JSON Input
 

To process JSON input in your API, use CodeIgniter’s getJSON method:

1. Parse Incoming JSON:

   public function create() {
       $json = $this->request->getJSON();
       if (!$json) {
           return $this->fail('Invalid JSON input', 400);
       }
   
       // Access JSON properties
       $name = $json->name;
       $email = $json->email;
   
       return $this->respondCreated([
           'name' => $name,
           'email' => $email,
           'message' => 'Data successfully processed',
       ]);
   }

2. Validate JSON Input: Ensure that the required fields are present and valid:

   if (!isset($json->name) || !isset($json->email)) {
       return $this->fail('Missing required fields', 422);
   }

Step 3: Generating JSON Output
 

CodeIgniter makes it easy to format responses as JSON using the respond and setJSON methods:

1. Return JSON Response:

   public function index() {
       $data = [
           ["id" => 1, "name" => "John Doe", "email" => "john@example.com"],
           ["id" => 2, "name" => "Jane Doe", "email" => "jane@example.com"],
       ];
   
       return $this->respond($data);
   }

2. Customize Response Structure: Add additional metadata or status codes:

   public function show($id = null) {
       $user = ["id" => $id, "name" => "John Doe", "email" => "john@example.com"];
   
       if (!$user) {
           return $this->failNotFound('User not found');
       }
   
       return $this->respond([
           'status' => 'success',
           'data' => $user,
       ]);
   }

3. Set Custom JSON Output: Use the setJSON method for direct JSON output:

   return $this->response->setJSON([
       'message' => 'Custom JSON response',
       'status' => 200
   ]);

Step 4: Testing Your JSON API
 

Use tools like Postman or cURL to test JSON input and output:

1. Send a POST Request:
   
   • URL: http://localhost:8080/api/example
   • Headers: Content-Type: application/json
   • Body:

     {
         "name": "John Doe",
         "email": "john@example.com"
     }

2. Validate Response:
   
   • Ensure the response matches your expected JSON structure.

Common Pitfalls and Debugging Tips
 

1. Invalid JSON Format:
   
   • Always validate JSON input on the client and server sides.
   • Use tools like JSONLint for validation.
2. Content-Type Mismatch:
   
   • Ensure the Content-Type header is set correctly (application/json).
3. Encoding Issues:
   
   • Use json_encode and json_decode functions where needed.
4. Error Messages:
   
   • Provide clear and descriptive error messages for invalid JSON input or processing errors.

Conclusion
 

Handling JSON input and output in CodeIgniter REST APIs is straightforward and efficient. By following these steps, you can ensure that your API is robust, compatible, and easy to integrate with front-end applications. In the next blog, we’ll discuss how to use CodeIgniter models for efficient REST API development.