How to Efficiently Handle CORS Preflight Requests in Go?

Handling CORS Preflight Requests with Go

In a RESTful backend server written in Go, handling cross-origin HTTP requests requires addressing preflight CORS requests. Here's how to effectively deal with them:

1. Manual Method Check:

In net/http, the request method can be checked in the handler function. For instance:

func AddResourceHandler(rw http.ResponseWriter, r *http.Request) {
  switch r.Method {
  case "OPTIONS":
    // Preflight handling logic
  case "PUT":
    // Actual request response
  }
}

2. Gorilla Mux Package:

Gorilla Mux allows registering a separate preflight handler for each URL path. For example:

r := mux.NewRouter()
r.HandleFunc("/someresource/item", AddResourceHandler).Methods("PUT")
r.HandleFunc("/someresource/item", PreflightAddResourceHandler).Methods("OPTIONS")

3. HTTP Handler Wrapper:

To decouple logic and reuse the CORS handler, consider wrapping the REST handler. For example, in net/http:

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

Usage:

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

These approaches provide elegant solutions for handling CORS preflight requests in Go. Choose the one that aligns best with your application architecture.

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