add internal API & ping

ping.go

@@ -0,0 +1,20 @@
+package main
+
+import (
+	"net/http"
+)
+
+func external_ping(w http.ResponseWriter, req *http.Request) {
+	ping(w, "external API")
+}
+
+func internal_ping(w http.ResponseWriter, req *http.Request) {
+	ping(w, "internal API")
+}
+
+func ping(w http.ResponseWriter, message string) {
+	w.Header().Set("Content-Type", "application/json")
+	w.WriteHeader(http.StatusOK)
+	jsonData := []byte(`{"status":"OK","pong":"` + message + `"}`)
+	w.Write(jsonData)
+}