Example of concurrency in Go with web requests to Express

a-main.go

package main

import (
	"demo/lib"
	"sync"
)

func main() {
	connections := lib.GetAllConnections()
	var wg sync.WaitGroup
	wg.Add(len(connections))

	for _, c := range connections {
		go c.Notify(&wg)
	}

	wg.Wait()
}

b-demo-lib.go

package lib

import (
	"demo/httpService"
	"sync"
	"time"
)

type guestConnection struct {
	ip       string
	userName string
	isAdmin  bool
}

type visitorConnection struct {
	ip       string
	connHour int
}

type notifier interface {
	Notify(*sync.WaitGroup)
}

func (g guestConnection) Notify(wg *sync.WaitGroup) {
	httpService.SendNotification()
	wg.Done()
}

func (v visitorConnection) Notify(wg *sync.WaitGroup) {
	httpService.SendNotification()
	wg.Done()
}

func GetAllConnections() []notifier {
	gConn := &guestConnection{ip: "192.168.0.10", userName: "Darth Vader"}
	vConn := &visitorConnection{ip: "192.168.0.11", connHour: time.Now().Hour()}

	return []notifier{gConn, vConn}
}

c-demo-httpService.go

package httpService

import (
	"fmt"
	"log"
	"net/http"
)

func SendNotification() {
	// doing GET cause it's simpler but this should be POST
	resp, err := http.Get("http://localhost:8080/notifications")
	if err != nil {
		log.Fatal("Error sending notification to remote server", err)
	}
	defer resp.Body.Close()
	fmt.Println("Notification Body: ", resp.Body)
}

d-app.js

"use strict";

const app = require("express")();

app.get("/notifications", (req, res) => {
  setTimeout(() => {
    res.json("Response from ExpressJS");
  }, 5000);
});

app.listen(8080, () => console.log("Listening..."));