HTTP with Go: Middleware

Implementing HTTP middleware with Golang.

Last updated on: 2024-12-11

In Go, HTTP middleware can be implemented using a closure over a http.Handler. Like so:

type Middleware = func(http.Handler) http.Handler

Go type definition.

For example:

func myMiddleware(h http.Handler) http.Handler {
    return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
        log.Println("before handling")
        h.ServeHTTP(w, r)
        log.Println("after handling")
    })
}

Go code

To use a middleware, simply wrap it around a `http.Handler`.

wrapped := myMiddleware(handler)

Go code

You may want to define a utility function to wrap middleware (ordered from outermost to innermost):

func Wrap(h http.Handler, v ...Middleware) http.Handler {
    for i := len(v) - 1; i >= 0; i-- {
        h = v[i](h)
    }
	return h
}

Go code

h := Wrap(handler,
    trueIPMiddleware,
    loggingMiddleware,
)

Go code