要实现中间件，您必须创建一个满足http.handler接口的函数。

实现这一点的一种方法是使用decorator函数，它充当中间件:

func middleware(next http.Handler) http.Handler {
  return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
    // middleware code for example logging
    log.Println(r.RemoteAddr)
    next.ServeHTTP(w, r)
  })
}

next参数是实际的http.handler。

下面是一个更完整的示例:

func main() {
    var handler http.HandlerFunc = testHandler

    // Here the handler is wrapped with the middleware
    http.Handle("/test", middleware(handler))
}

func middleware(next http.Handler) http.Handler {
    return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
        // middleware code for example logging
        log.Println(r.RemoteAddr)
        next.ServeHTTP(w, r)
    })
}

func testHandler(w http.ResponseWriter, r *http.Request) {
    // your handler code
}

此模式有时被称为装饰模式，有关更多信息，请参见以下链接:

1. https://www.alexedwards.net/blog/making-and-using-middleware
2. https://en.wikipedia.org/wiki/decorator_pattern