OliveTin/pkg/cors/cors.go

package cors

import (
	"net/http"
	"strings"
	log "github.com/sirupsen/logrus"
)

func AllowCors(h http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		if origin := r.Header.Get("Origin"); origin != "" {
			log.Infof("Setting CORS header: %v", origin)

			w.Header().Set("Access-Control-Allow-Origin", origin)

			if r.Method == "OPTIONS" && r.Header.Get("Access-Control-Request-Method") != "" {
				preflightHandler(w, r)
				return
			}
		}

		h.ServeHTTP(w, r)
	})
}

func preflightHandler(w http.ResponseWriter, r *http.Request) {
	log.Infof("preflight request for %s", r.URL.Path)

	headers := []string{"Content-Type", "Accept"}
	w.Header().Set("Access-Control-Allow-Headers", strings.Join(headers, ","))
	methods := []string{"GET", "HEAD", "POST", "PUT", "DELETE"}
	w.Header().Set("Access-Control-Allow-Methods", strings.Join(methods, ","))
}