１． typeのbuild error

src/main.go:109:25: missing type in composite literal

２．原因:
struct 初期化時にtypeの付け忘れ

３．code
・誤り

rt := M{"err":0,"msg":{"okay":okay,"ng":max-okay}};

・正

rt := M{"err":0,"msg":M{"okay":okay,"ng":max-okay}};

４．type M の定義

type M map[string]interface{};