Refactor handlers package

Fixes #19.

handlers/cors.go

@@ -0,0 +1,27 @@
+package handlers
+
+import (
+	"net/http"
+	"os"
+	"strings"
+)
+
+func corsHandler(h http.Handler) http.Handler {
+	cors := func(w http.ResponseWriter, r *http.Request) {
+		domains := os.Getenv("DOMAINS")
+		allowedDomains := strings.Split(domains, ",")
+		if origin := r.Header.Get("Origin"); origin != "" {
+			for _, s := range allowedDomains {
+				if s == origin {
+					w.Header().Set("Access-Control-Allow-Origin", origin)
+					w.Header().Set("Access-Control-Allow-Headers", r.Header.Get("Access-Control-Request-Headers"))
+					w.Header().Set("Access-Control-Allow-Methods", r.Header.Get("Access-Control-Request-Method"))
+				}
+			}
+		}
+		if r.Method != "OPTIONS" {
+			h.ServeHTTP(w, r)
+		}
+	}
+	return http.HandlerFunc(cors)
+}