Golang Middleware example

middleware.go

package main

import (
	"context"
	"fmt"
)

type Middleware = func(ctx context.Context) (bool, error)
type MiddlewareBuilder = func(next Middleware) Middleware

type Manager struct {
	middleware []MiddlewareBuilder
}

func NewManager() *Manager {
	return &Manager{
		middleware: []MiddlewareBuilder{},
	}
}

func (m *Manager) Use(middleware MiddlewareBuilder) {
	m.middleware = append(m.middleware, middleware)
}

func (m *Manager) Execute(ctx context.Context) (bool, error) {
	realTask := func(ctx context.Context) (bool, error) {
		fmt.Printf("execute done\n")
		return true, nil
	}

	next := realTask
	for i := len(m.middleware) - 1; i >= 0; i-- {
		mb := m.middleware[i]
		next = mb(next)
	}

	return next(ctx)
}

func Middleware1(next Middleware) Middleware {
	return func(ctx context.Context) (bool, error) {
		fmt.Printf("middleware 1 in\n")
		ok, err := next(ctx)
		if err != nil {
			return ok, err
		}

		fmt.Printf("middleware 1 out\n")
		return ok, nil
	}
}

func Middleware2(next Middleware) Middleware {
	return func(ctx context.Context) (bool, error) {
		fmt.Printf("middleware 2 in\n")
		ok, err := next(ctx)
		if err != nil {
			return ok, err
		}

		fmt.Printf("middleware 2 out\n")
		return ok, nil
	}
}

func Middleware3(next Middleware) Middleware {
	return func(ctx context.Context) (bool, error) {
		fmt.Printf("middleware 3 in\n")
		ok, err := next(ctx)
		if err != nil {
			return ok, err
		}

		fmt.Printf("middleware 3 out\n")
		return ok, nil
	}
}

func main() {
	ctx := context.Background()

	m := NewManager()
	m.Use(Middleware1)
	m.Use(Middleware2)
	m.Use(Middleware3)

	res, err := m.Execute(ctx)
	fmt.Printf("result=%v, error=%v", res, err)
}