HTTP OPTIONS Method

The HTTP OPTIONS method is used to describe the communication options for a target resource. It’s often used in the context of Cross-Origin Resource Sharing (CORS) to determine what HTTP methods are allowed for a specific URL on a server, which is important for browsers when they interact with servers on different origins.

Here are some key aspects of the OPTIONS method:

1. Purpose: The OPTIONS method asks the server which HTTP methods and other options (like headers) are supported for a specific resource. It doesn’t fetch the actual data but instead serves as a way to check how to interact with the server.

2. Preflight Request in CORS: When a web application makes a cross-origin request using methods other than GET or POST (e.g., PUT, DELETE) or includes custom headers, the browser sends an OPTIONS request first. This is called a preflight request, and it checks if the actual request is safe to send.

3. Response: In response to an OPTIONS request, the server typically includes headers like:
   • Allow: Lists the HTTP methods that the server supports for the resource.
   • Access-Control-Allow-Methods: Specifies which methods are allowed for cross-origin requests.
   • Access-Control-Allow-Headers: Lists headers that can be included in requests.
4. Safe and Idempotent: OPTIONS is a safe method (doesn’t change any server state) and idempotent (repeated requests will have the same effect).

Here’s an example of an OPTIONS request and response:

Request:

OPTIONS /api/data HTTP/1.1
Host: example.com
Origin: http://mywebsite.com
Access-Control-Request-Method: PUT
Access-Control-Request-Headers: Content-Type

Response:

HTTP/1.1 204 No Content
Access-Control-Allow-Origin: http://mywebsite.com
Access-Control-Allow-Methods: GET, POST, PUT, DELETE
Access-Control-Allow-Headers: Content-Type

In this way, OPTIONS helps ensure secure and controlled communication between web clients and servers, especially in cross-origin scenarios.