Build a Chat Application in Go with Vultr Managed Databases for Redis

Introduction

Redis is an open-source, in-memory data store that supports many data structures like String, Hash, List, Set, and Sorted Set, along with other capabilities such as Pub/Sub messaging and stream processing. It also supports high availability, scalability, and reliability through a combination of asynchronous replication and Redis Cluster. Redis has client libraries for many programming languages. This includes Go, Java, Python, and many others.

This article will walk you through the process of building a chat application with Go client for Redis, and in the process, you will learn:

• How to create and delete a Vultr Redis Managed Database

• How to securely connect to a Vultr Managed Redis Database using TLS and use Redis Pub/Sub feature.

• How to use WebSocket in Go with gorilla library

Prerequisites

To follow the instructions in this article:

1. Install a recent version of the Go programming language (version 1.18 or higher)

2. Install wscat, a command-line WebSocket client.

Application Overview

The application is a simplified version of a chat service built using Redis Pub/Sub and WebSocket. It allows users to join the chat service, send and receive messages, and exit it.

WebSocket and Redis Pub/Sub

WebSocket is a protocol defined by RFC 6455 which allows full-duplex communication between a client and server over a single TCP connection. Either the client or server can send messages. These can be exchanged simultaneously. This is an improvement over communication patterns such as long polling that is used by HTTP based solutions and heavily used in building real-time applications.

Here is how Redis Pub/Sub works with the Go client:

1. Producers send data to a Redis channel using Publish method.

2. Consumers subscribe to the channel to receive messages using Subscribe method and receive messages via a Go channel (with Channel).

3. And finally, unsubscribe and close the connection.

Redis Pub/Sub helps this service work in a scaled-out architecture, where the users connected to the chat service might be associated with any application instance via the WebSocket connection. Without Redis Pub/Sub, only users connected to a specific instance can exchange chat messages. Redis Pub/Sub solves this problem by providing a way to broadcast the messages to all the connected users irrespective of which application instance they are connected to.

Application flow

1. A user connects to an endpoint provided by the application. If successful, this creates a WebSocket connection between the client and application (server).

2. When the user sends a chat message, it's relayed over the WebSocket connection to the application.

3. The application publishes this message to the Redis channel.

4. Because the application is also subscribed to this channel, it receives this message and sends it to all connected users via the WebSocket connection established initially.

Create Vultr Redis Managed Database

Log into your Vultr account, navigate to Add Managed Database and follow the steps below.

1. Choose the Redis database engine.

2. You can choose from several options in the Server Type. This includes Cloud Compute, Cloud Compute High Performance - AMD or Intel, Optimized Cloud Compute - General Purpose, and Storage or Memory Optimized. You can select zero or more replica nodes as well as the cluster location. A replica node is the same server type and plan as the primary node.

3. After you add a label for the database cluster, click Deploy Now to create the cluster. The cluster will take a few minutes to be available, and the Status should change to Running.

The Vultr Redis Managed Database is ready.

Initialize the project

Create a directory and switch to it:

mkdir go-redis-chat

cd go-redis-chat

Create a new Go module:

go mod init go-redis-chat

This will create a new go.mod file

Create a new file, main.go:

touch main.go

Import libraries

To import required Go modules, add the following to main.go file:

package main



import (

    "context"

    "fmt"

    "log"

    "net/http"

    "os"

    "os/signal"

    "strings"

    "syscall"

    "time"



    "github.com/go-redis/redis/v8"

    "github.com/gorilla/websocket"

)

Add the init function and global variables

Add the code below to main.go file:

var client *redis.Client

var Users map[string]*websocket.Conn

var sub *redis.PubSub

var upgrader = websocket.Upgrader{}

var redisURL string



const chatChannel = "chats"



func init() {

    redisURL = os.Getenv("REDIS_URL")

    if redisURL == "" {

        log.Fatal("missing environment variable REDIS_URL")

    }

    Users = map[string]*websocket.Conn{}

}

• The init function reads the Redis URL from the REDIS_URL environment variable and fails if it's missing.

• It also instantiates a map that stores a mapping of the username to the actual websocket.Conn object.

Add the main function

Add the main function to the main.go file:

func main() {

    opt, err := redis.ParseURL(redisURL)

    if err != nil {

        log.Fatal("invalid redis url", err)

    }



    opt.TLSConfig = &tls.Config{}



    client = redis.NewClient(opt)

    startChatBroadcaster()



    http.HandleFunc("/chat/", chat)

    server := http.Server{Addr: ":8080", Handler: nil}



    go func() {

        fmt.Println("started server")

        err := server.ListenAndServe()

        if err != nil && err != http.ErrServerClosed {

            log.Fatal("failed to start server", err)

        }

    }()



    exit := make(chan os.Signal, 1)

    signal.Notify(exit, syscall.SIGTERM, syscall.SIGINT)

    <-exit



    fmt.Println("exit signalled")



    ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)

    defer cancel()



    for _, conn := range Users {

        conn.Close()

    }



    sub.Unsubscribe(context.Background(), chatChannel)

    sub.Close()



    server.Shutdown(ctx)



    fmt.Println("application shut down")

}

The main function is responsible for multiple things:

• It starts by creating a new redis.Client instance and verifies the connectivity to Redis by using the Ping method. If connectivity fails, the program exists with an error message.

• Then, the startChatBroadcaster() function is invoked. Its details will be explained in the subsequent section of this article.`

• Next, http.HandleFunc is used to map the /chat URL to the chat HTTP handler function. The details of this HTTP handler will be explained in the subsequent section of this article.

• The program makes sure it can respond to a termination signal and executes cleanup tasks:

  • Close all the individual websocket.Conn objects for each connected user

  • Unsubscribe from the Redis channel subscription

  • Close the Redis channel subscription

Add the chat HTTP handler function

Add the chat function to main.go file:

func chat(w http.ResponseWriter, r *http.Request) {

    user := strings.TrimPrefix(r.URL.Path, "/chat/")



    upgrader.CheckOrigin = func(r *http.Request) bool {

        return true

    }

    c, err := upgrader.Upgrade(w, r, nil)

    if err != nil {

        log.Print("upgrade:", err)

        return

    }



    Users[user] = c

    fmt.Println(user, "in chat")



    for {

        _, message, err := c.ReadMessage()

        if err != nil {

            _, ok := err.(*websocket.CloseError)

            if ok {

                fmt.Println("connection closed by", user)

                err := c.Close()

                if err != nil {

                    fmt.Println("error closing ws connection", err)

                }

                delete(Users, user)

                fmt.Println("closed websocket connection and removed user session")

            }

            break

        }

        client.Publish(context.Background(), chatChannel, user+":"+string(message)).Err()

        if err != nil {

            fmt.Println("publish failed", err)

        }

    }

}

The chat function is the HTTP handler that provides the core functionality of the service:

• It starts by establishing the WebSocket connection from the HTTP request, using upgrader.Upgrade

• The name of the user that initiated the connection is mapped in this websocket.Conn object, and this mapping is stored as a map.

• It starts a for loop to handle the following:

  • Read each message sent from a user over the WebSocket connection (using ReadMessage)

  • Send this to the Redis channel (using Publish)

  • Respond to error or termination of the WebSocket connection

Add the startChatBroadcaster function

Add the startChatBroadcaster function to the main.go file:

func startChatBroadcaster() {

    go func() {

        fmt.Println("listening to messages")

        sub = client.Subscribe(context.Background(), chatChannel)

        messages := sub.Channel()

        for message := range messages {

            from := strings.Split(message.Payload, ":")[0]

            for user, peer := range Users {

                if from != user {

                    peer.WriteMessage(websocket.TextMessage, []byte(message.Payload))

                }

            }

        }

    }()

}

This function also starts a for loop:

• Acts as a subscriber to the Redis channel

• Receive each message sent to the Redis channel and send it to all the connected users over their respective WebSocket connections. It does so by iterating the map of the user to the websocket.Conn object (as described in previous sections).

Save the main.go file and execute the program to try the chat application.

Run the program

Fetch the Go module dependencies for the program:

go mod download

Get the Redis connection URL of Vultr Redis Managed Database.

1. Click the Manage icon to open the Overview tab.

2. From Connection Details section, choose Copy Redis URL

To run the program, open a terminal and enter the following:

export REDIS_URL=<PASTE THE REDIS URL>

go run main.go

You should see the following output:

listening to messages

started server

Open another terminal, and use wscat to join the chat service as user1:

wscat --connect ws://localhost:8080/chat/user1

You should see output along with the prompt (>)

Connected (press CTRL+C to quit)

>

Open another terminal and use wscat again to join the chat service as user2:

wscat --connect ws://localhost:8080/chat/user2

You should see output along with the prompt (>)

Connected (press CTRL+C to quit)

>

Go back to the terminal where you started the application. You should see the following additional logs:

user1 in chat

user2 in chat

Currently, two users have joined the service. They can exchange messages.

1. To send a message from user1, switch to the terminal where you joined the chat service as user1 and type in a text message such as hello there!.

2. Switch to the terminal where you joined the chat service as user2. You should see the message that user1 sent. From this terminal, send a message as user2 like hi, how are you.

3. Switch to the terminal where you joined the chat service as user1. You should see the message that user2 sent.

You can continue to use the chat application by adding more users and sending messages to one another.

Users can also exit the application. This can be done by pressing CTRL+C in the respective terminal (wscat) from where they joined the service.

Finally, to stop the application, go back to the terminal where the application is running and press CTRL+C. Once the application exits, the WebSocket sessions connected via wscat will terminate, and you should see the following output in the application logs:

exit signalled

application shut down

After completing this article's tutorial, you can delete the database.

Delete Vultr Redis Managed Database

To delete the Vultr Redis Managed Database that you had created, log into your Vultr account and follow the below steps for the database you want to delete:

1. Click the Manage icon to open the Settings tab.

2. Choose Delete Managed Database and click Destroy Database Instance.

3. In the Destroy Managed Database? pop-up window, select the checkbox Yes, destroy this Managed Database. and click Destroy Managed Database.

Conclusion

In this article, you learned how to build a chat application using Go and WebSocket with Vultr Redis Managed Database as the backend data store.

You can also learn more in the following documentation:

• Vultr Managed Databases Quickstart

• Vultr Managed Databases for Redis Reference Guide

• Implement Redis Transactions and Locks with Golang and MySQL on a Linux Server

• Create a Redis Leaderboard with Golang

• Implement Rate-limiting with Redis and Golang on a Linux Server

• How to Securely Connect to Redis with TLS/SSL in Go, NodeJS, PHP, Python, and redis-cli