middleware

package main

import (
	"context"
	"fmt"
)

func main() {
	e := Chain(
		annotate("first"),
		annotate("second"),
		annotate("third"),
	)(myHandler)

	if _, err := e(ctx, req); err != nil {
		panic(err)
	}

}

var (
	ctx = context.Background()
	req = struct{}{}
)

func annotate(s string) Middleware {
	return func(next Handler) Handler {
		return func(ctx context.Context, request interface{}) (interface{}, error) {
			fmt.Println(s, "pre")
			defer fmt.Println(s, "post")
			return next(ctx, request)
		}
	}
}

func myHandler(context.Context, interface{}) (interface{}, error) {
	fmt.Println("my handler!")
	return struct{}{}, nil
}

Output:

first pre
second pre
third pre
my handler!
third post
second post
first post