cors.go

package rest

//
//Copyright 2018 Telenor Digital AS
//
//Licensed under the Apache License, Version 2.0 (the "License");
//you may not use this file except in compliance with the License.
//You may obtain a copy of the License at
//
//http://www.apache.org/licenses/LICENSE-2.0
//
//Unless required by applicable law or agreed to in writing, software
//distributed under the License is distributed on an "AS IS" BASIS,
//WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
//See the License for the specific language governing permissions and
//limitations under the License.
//
import "net/http"

// AddCORSHeaders adds CORS headers to the response.
func AddCORSHeaders(handler http.HandlerFunc) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		origin := r.Header.Get("Origin")
		if origin == "" {
			origin = "*"
		}
		w.Header().Set("Access-Control-Allow-Origin", origin)
		w.Header().Set("Access-Control-Allow-Methods", "POST, GET, DELETE, PATCH, PUT")
		w.Header().Set("Access-Control-Allow-Credentials", "true")

		requestedHeaders := r.Header.Get("Access-Control-Request-Headers")
		if requestedHeaders != "" {
			w.Header().Set("Access-Control-Allow-Headers", requestedHeaders)
		}

		// If this is a preflight request just return 200 OK without any further
		// processing.
		if r.Method == http.MethodOptions {
			w.WriteHeader(http.StatusOK)
			return
		}
		handler(w, r)
	}
}