Request Validation and Error Handling

Proper request validation ensures data integrity and provides meaningful error messages to clients. The following patterns demonstrate comprehensive validation techniques for different types of request data.

@Route("/api/users", "api.user.create", methods=["POST"])
async def create_user(self, request: Request):
    # Validate content type
    content_type = request.headers.get("content-type", "")
    if not content_type.startswith("application/json"):
        return self.json({
            "error": "Content-Type must be application/json"
        }, status=415)

    # Parse and validate JSON
    try:
        user_data = await request.json()
    except Exception:
        return self.json({
            "error": "Invalid JSON payload"
        }, status=400)

    # Validate required fields
    required_fields = ["name", "email", "password"]
    missing_fields = [field for field in required_fields if not user_data.get(field)]

    if missing_fields:
        return self.json({
            "error": "Missing required fields",
            "missing_fields": missing_fields
        }, status=422)

    # Process validated data
    try:
        user = await self.user_service.create(user_data)
        return self.json({
            "user": user.to_dict(),
            "message": "User created successfully"
        }, status=201)
    except Exception as e:
        return self.json({
            "error": "Failed to create user",
            "details": str(e)
        }, status=500)

Validation Best Practices

Content Type Validation

Always validate the Content-Type header to ensure the request format matches your expectations. This prevents parsing errors and provides clear feedback to clients.

JSON Parsing

Wrap JSON parsing in try-catch blocks to handle malformed data gracefully and return appropriate error responses.

Field Validation

Implement comprehensive field validation that checks for:

• Required fields presence
• Data type validation
• Value range validation
• Format validation (email, phone, etc.)

Error Response Structure

Maintain consistent error response structures with:

• Clear error messages
• Specific error details
• Appropriate HTTP status codes
• Additional context when helpful

HTTP Status Codes

Use appropriate HTTP status codes:

• 400 - Bad Request (malformed data)
• 415 - Unsupported Media Type (wrong content type)
• 422 - Unprocessable Entity (validation errors)
• 500 - Internal Server Error (server-side issues)