How Can Go Middleware Simplify Preflight Request Handling for CORS?

Preflight Request Handling in Go for CORS

Cross-Origin Resource Sharing (CORS) often requires browsers to send preflight OPTIONS requests to verify whether an actual request is safe to send. Handling these preflight requests efficiently in Go can be a challenge.

One approach is to check the request method within a handler function using the standard net/http package. However, this can be tedious, especially for multiple handlers.

Alternatively, Gorilla's mux package offers a cleaner solution. You can register a separate "OPTIONS" handler for each relevant URL path. While both methods are viable, they may not always be the most elegant.

Improved Solution using Middleware

To simplify further, consider using a middleware approach. By wrapping your REST handlers with a middleware function, you can separate the CORS-handling logic from the actual request handling. For instance, using net/http:

func corsHandler(h http.Handler) http.HandlerFunc {
  return func(w http.ResponseWriter, r *http.Request) {
    if (r.Method == "OPTIONS") {
      // Handle preflight here
    } else {
      h.ServeHTTP(w,r)
    }
  }
}

You can then wrap your REST handler like this:

http.Handle("/endpoint/", corsHandler(restHandler))

This approach provides a clean and reusable way to handle preflight requests, allowing you to focus on your business logic while ensuring seamless cross-origin interactions.

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