chat.go

package main

import (
	"bufio"
	"fmt"
	"log"
	"net/url"
	"os"
	"strings"
	"time"

	"github.com/akamensky/argparse"
	mqtt "github.com/eclipse/paho.mqtt.golang"
)

var QOS_AT_MOST_ONCE = byte(0)

func failOnError(err error, msg string) {
	if err != nil {
		log.Fatalf("%s: %s", msg, err)
	}
}

func parseUserArgs() (string, string) {
	parser := argparse.NewParser("Chat", "Chat using AMQP and Go")

	// Create flags for username and password
	nameOptions := argparse.Options{Required: true, Help: "User name"}
	name := parser.String("u", "user", &nameOptions)
	passwordOptions := argparse.Options{Required: true, Help: "Password"}
	password := parser.String("p", "password", &passwordOptions)

	// Parse input
	err := parser.Parse(os.Args)
	failOnError(err, "Error while parsing arguments")
	return *name, *password
}

func connect(uri *url.URL) mqtt.Client {
	opts := createClientOptions(uri)
	client := mqtt.NewClient(opts)
	token := client.Connect()
	for !token.WaitTimeout(time.Microsecond) {
	}
	failOnError(token.Error(), "Failed while connecting")
	return client
}

func createClientOptions(uri *url.URL) *mqtt.ClientOptions {
	password, _ := uri.User.Password()
	name := uri.User.Username()
	opts := mqtt.NewClientOptions()
	opts.AddBroker(fmt.Sprintf("tcp://%s", uri.Host))
	opts.SetUsername(name)
	opts.SetPassword(password)
	return opts
}

func showMessage(client mqtt.Client, msg mqtt.Message) {
	fmt.Printf("* %s\n", string(msg.Payload()))
}

func listen(uri *url.URL) {
	client := connect(uri)
	client.Subscribe(parseTopic(uri), QOS_AT_MOST_ONCE, showMessage)
}

func sendMessage(msg string, uri *url.URL) {
	client := connect(uri)
	RETAIN_MESSAGE := false
	client.Publish(parseTopic(uri), QOS_AT_MOST_ONCE, RETAIN_MESSAGE, msg)
}

func poolMessage(uri *url.URL, user string) {
	for {
		r := bufio.NewReader(os.Stdin)
		msg, _ := r.ReadString('\n')
		msg = fmt.Sprintf("%s: %s", user, strings.TrimSpace(msg))
		sendMessage(msg, uri)
	}
}

func parseTopic(uri *url.URL) string {
	topic := uri.Path[1:]
	if topic == "" {
		topic = "default"
	}
	return topic
}

func main() {
	user, passwd := parseUserArgs()
	fullUrl := fmt.Sprintf("mqtt://%s:%s@localhost:1883/test", user, passwd)
	uri, err := url.Parse(fullUrl)
	failOnError(err, "Failed to parse given URL")

	forever := make(chan bool)
	go listen(uri)
	go poolMessage(uri, user)
	<-forever
}

Very nice piece of work. The cloud mqtt stuff is indeed a great example. They make it so easy to get started with MQTT. They have the right idea. I learned something from them.

And yet the obvious application is to do chat. One goroutine waits for input, the other prints messages that get received. And your code is so nicely presented. I kind of had something like this in the back of my mind, but the idea was not well formed. It is interesting how seeing a concrete example crystalizes the idea. It focuses the mind. What a great starting point!

I am giving a talk on MQTT at GoDays Berlin on Thursday. The talk is ready, but I thought of doing a bit more. I could use the Cloud MQTT demo, but I think that your demo is more interesting. It is the way a GoLang MQTT demo/tutorial should be.

Can I use this software? What license is it under?

Thank you for all of the hard work.

You can use it as you want (if you still want). I am really sorry for not responding to you in time, I hope everything went fine with your talk 😄