Go simple middleware chain, inspired by https://github.com/justinas/alice

httprouter_middleware_chain.go

// Middleware is a type alias for a function that
// accepts an http.Handler as the "next" handler in a chain
// and returns an http.Handler that will be executed before that handler.
type Middleware func(httprouter.Handle) httprouter.Handle

// MiddlewareChain represents a chain of middleware functions that can be
// assigned to wrap a handler function.
type MiddlewareChain []Middleware

// NewMiddlewareChain is a constructor for a chain of middlewares.
func NewMiddlewareChain(middlewares ...Middleware) MiddlewareChain {
	return MiddlewareChain(append([]Middleware{}, middlewares...))
}

// Wrap the final http.Handler with a closure which invokes all
// chained middlewares in the order they were constructed.
// E.g. for New(m1, m2, m3) we get m1(m2(m3(h))) which produces
// an execution chain of m1 -> m2 -> m3 -> h for each request.
func (mw MiddlewareChain) Wrap(h httprouter.Handle) httprouter.Handle {
	if len(mw) == 0 {
		return h
	}

	if h == nil {
		// no-op handler
		h = func(w http.ResponseWriter, r *http.Request, ps httprouter.Params) {
			http.DefaultServeMux.ServeHTTP(w, r)
		}
	}

	// chain all the handlers together in the order they were called
	// i.e. for NewMiddlewareChain(mw1, mw2, mw3) we get h = mw1 -> mw2 -> mw3 -> h
	for i := range mw {
		h = mw[len(mw)-1-i](h) // set h to "next" backwards through the chain
	}

	return h
}

middleware_chain.go

// Middleware is a type alias for a function that
// accepts an http.Handler as the "next" handler in a chain
// and returns an http.Handler that will be executed before that handler.
type Middleware func(http.Handler) http.Handler

// MiddlewareChain represents a chain of middleware functions that can be
// assigned to wrap a handler function.
type MiddlewareChain []Middleware

// NewMiddlewareChain is a constructor for a chain of middlewares.
func NewMiddlewareChain(middlewares ...Middleware) MiddlewareChain {
	return MiddlewareChain(append([]Middleware{}, middlewares...))
}

// Wrap the final http.Handler with a closure which invokes all
// chained middlewares in the order they were constructed.
// E.g. for New(m1, m2, m3) we get m1(m2(m3(h))) which produces
// an execution chain of m1 -> m2 -> m3 -> h for each request.
func (mw MiddlewareChain) Wrap(h http.Handler) http.Handler {
	if len(mw) == 0 {
		return h
	}

	if h == nil {
		h = http.DefaultServeMux
	}

	// chain all the handlers together in the order they were called
	// i.e. for NewMiddlewareChain(mw1, mw2, mw3) we get h = mw1 -> mw2 -> mw3 -> h
	for i := range mw {
		h = mw[len(mw)-1-i](h) // set h to "next" backwards through the chain
	}

	return h
}