Initial Version

Create a module

Run the go mod init command, giving it the path of the module your code will be in.

go mod init literank.com/webchat

Its result:

go: creating new go.mod: module literank.com/webchat

This command creates a go.mod file in which dependencies you add will be listed for tracking.

Installation

Download and install socket.io library:

go get -u github.com/zishang520/socket.io/v2

We don't use github.com/googollee/go-socket.io here because it currently only supports 1.4 version of the Socket.IO client.
The latest version of Socket.IO is 4.x.

This command updates the go.mod file and creates a go.sum file in your project.

Create main.go:

package main

import (
	"fmt"
	"net/http"

	"github.com/zishang520/engine.io/v2/types"
	"github.com/zishang520/socket.io/v2/socket"
)

const port = 4000

func main() {
	// CORS
	opts := &socket.ServerOptions{}
	opts.SetCors(&types.Cors{Origin: "*"})

	io := socket.NewServer(nil, opts)
	io.On("connection", func(clients ...any) {
		client := clients[0].(*socket.Socket)
		fmt.Println("A user connected:", client.Id())
	})

	http.Handle("/socket.io/", io.ServeHandler(nil))
	fmt.Printf("Chat server serving at localhost:%d...\n", port)
	http.ListenAndServe(fmt.Sprintf(":%d", port), nil)
}

Run the program like this:

go run main.go

You will get a result line like this:

Chat server serving at localhost:4000...

Your chat server is running on port 4000 now.