Build a Chat Room Application with Redpanda and Golang

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Create a basic chat room application with Redpanda and Kafka clients developed with franz-go.

This tutorial describes how to:

• Start a Redpanda cluster to store and stream chat room messages.
• Write a client application in Typescript to produce and consume chat room messages.
• Build and run multiple clients to exchange chat messages streamed through Redpanda.

Prerequisites

Download and install Go from go.dev.

Set up a Redpanda environment

Complete the Redpanda Quickstart before continuing. This tutorial expands on the quickstart. You can choose to run either one or three brokers.

caution

If you're running Redpanda on your laptop, or in a shared development environment, then avoid Redpanda's optimized production settings. Avoid running sudo rpk redpanda tune all or manually configuring Redpanda for production, as they might affect your experience with other applications running on your machine.

Set up your environment

1. Create and set your working directory to the project folder, chat-room:

   mkdir chat-room
   cd chat-room

2. Initialize the project:

   go mod init com/redpanda/chat-room

3. Install the required dependencies:

   go get github.com/twmb/franz-go
   go get github.com/twmb/franz-go/pkg/kadm
   go get github.com/google/uuid

Create a topic

You need a topic named chat-room for both Redpanda and the client to use to store chat room messages. If you completed the Redpanda Quickstart, this topic already exists in your cluster.

1. Verify that the chat-room topic exists in your cluster by listing all topics:

   docker exec -it redpanda-0 rpk topic list

   Output:

   NAME       PARTITIONS  REPLICAS
   chat-room  1           1

2. If the topic doesn't exist yet, use rpk to create a chat-room topic:

   docker exec -it redpanda-0 rpk topic create chat-room

   Output:

   TOPIC      STATUS
   chat-room  OK

Confirm that the topic exists on the client side

The client may not always know that the topic exists. You can verify that it exists and create it if not. In chat-room/ create a source file called admin.go with the following content.

admin.go

package main

import (
    "context"
    "fmt"
    "github.com/twmb/franz-go/pkg/kadm"
    "github.com/twmb/franz-go/pkg/kgo"
)

type Admin struct {
    client *kadm.Client
}

func NewAdmin(brokers []string) *Admin {
    client, err := kgo.NewClient(
        kgo.SeedBrokers(brokers...),
    )
    if err != nil {
        panic(err)
    }

    admin := kadm.NewClient(client)
    return &Admin{client: admin}
}

func (a *Admin) TopicExists(topic string) bool {
    ctx := context.Background()
    topicsMetadata, err := a.client.ListTopics(ctx)
    if err != nil {
        panic(err)
    }

    for _, metadata := range topicsMetadata {
        if metadata.Topic == topic {
            return true
        }
    }

    return false
}

func (a *Admin) CreateTopic(topic string) {
    ctx := context.Background()
    resp, err := a.client.CreateTopics(ctx, 1, 1, nil, topic)
    if err != nil {
        panic(err)
    }

    for _, ctr := range resp {
        if ctr.Err != nil {
            fmt.Printf("Unable to create topic '%s': %s", ctr.Topic, ctr.Err)
        } else {
            fmt.Printf("Created topic '%s'\n", ctr.Topic)
        }
    }
}

func (a *Admin) Close() {
    a.client.Close()
}

Create a producer

A client needs a producer to publish chat-room topic messages.

To create a producer for the client, in chat-room/ create a source file producer.go with the following content.

producer.go

package main

import (
    "context"
    "encoding/json"
    "github.com/twmb/franz-go/pkg/kgo"
)

type Producer struct {
    client *kgo.Client
    topic  string
}

func NewProducer(brokers []string, topic string) *Producer {
    client, err := kgo.NewClient(
        kgo.SeedBrokers(brokers...),
    )
    if err != nil {
        panic(err)
    }

    return &Producer{client: client, topic: topic}
}

func (p *Producer) SendMessage(user, message string) {
    ctx := context.Background()

    msg := Message{User: user, Message: message}
    b, _ := json.Marshal(msg)

    p.client.Produce(ctx, &kgo.Record{Topic: p.topic, Value: b}, nil)
}

func (p *Producer) Close() {
    p.client.Close()
}

You now have a working producer that sends strings entered by the user to the chat-room topic. Messages are sent as JSON encoded strings here, but keep in mind that the producer only sends buffers, so you can encode the messages however you like.

Create a consumer

A client needs a consumer to receive chat-room topic messages.

To create a consumer for the client, in chat-room/ create a source file consumer.go with the following content.

consumer.go

package main

import (
    "context"
    "encoding/json"
    "fmt"
    "github.com/twmb/franz-go/pkg/kgo"
    "github.com/google/uuid"
)

type Consumer struct {
    client *kgo.Client
    topic  string
}

func NewConsumer(brokers []string, topic string) *Consumer {
    groupID := uuid.New().String()
    client, err := kgo.NewClient(
        kgo.SeedBrokers(brokers...),
        kgo.ConsumerGroup(groupID),
        kgo.ConsumeTopics(topic),
        kgo.ConsumeResetOffset(kgo.NewOffset().AtStart()),
    )
    if err != nil {
        panic(err)
    }

    return &Consumer{client: client, topic: topic}
}


func (c *Consumer) PrintMessages() {
    ctx := context.Background()

    for {
        fetches := c.client.PollFetches(ctx)
        iter := fetches.RecordIter()
        for !iter.Done() {
            record := iter.Next()

            var msg Message
            if err := json.Unmarshal(record.Value, &msg); err != nil {
                fmt.Printf("Error decoding message: %v\n", err)
                continue
            }
            fmt.Printf("%s: %s\n", msg.User, msg.Message)
        }
    }
}

func (c *Consumer) Close() {
    c.client.Close()
}

You now have a consumer that reads all messages from the chat-room topic and prints them to the console. You can start as many consumer groups as you like, but remember that each group reads a message only once, which is why the example is using a generated UUID for the group ID. This way, each time you run the application, you see all previous messages.

Create a client application

The client needs an application that creates the topic, producer, and consumer and implements the chat logic.

To create a client application, in chat-room/ create a source file main.go with the following content.

note

The broker settings in this code are from the Redpanda Quickstart, where the external port for broker redpanda-0 is set to port 19092. If you're not using the Redpanda Quickstart, make sure that the broker's port is correct for your deployment.

main.go

package main

import (
    "bufio"
    "fmt"
    "os"
    "strings"
)

type Message struct {
    User    string `json:"user"`
    Message string `json:"message"`
}

func main() {
    topic := "chat-room"
    brokers := []string{"localhost:19092"}

    admin := NewAdmin(brokers)
    defer admin.Close()

    if !admin.TopicExists(topic) {
        admin.CreateTopic(topic)
    }

    username := ""
    fmt.Print("Enter your username: ")
    fmt.Scanln(&username)

    producer := NewProducer(brokers, topic)
    defer producer.Close()

    consumer := NewConsumer(brokers, topic)
    defer consumer.Close()

    go consumer.PrintMessages()

    fmt.Println("Connected. Press Ctrl+C to exit")
    reader := bufio.NewReader(os.Stdin)
    for {
        message, _ := reader.ReadString('\n')
        message = strings.TrimSpace(message)
        producer.SendMessage(username, message)
    }
}

Build and run the application

Build the client chat application, run it from multiple client terminals, and chat between the clients.

1. Open at least two terminals, and for each terminal:

2. Run the client application:

   go run .

3. When prompted with Enter user name:, enter a unique name for the chat room.

4. Use the chat application: enter a message in a terminal, and verify that the message is received in the other terminals.

   For example:

   Enter user name:
   Alice
   Connected, press Ctrl+C to exit
   Alice: Hi, I'm Alice
   Bob: Hi Alice, I'm Bob, nice to meet you

Next steps

This is a basic example of a chat room application. You can improve this application by implementing additional features and components, such as:

• A user interface to make it more interactive and user-friendly.
• A user registration and login system to authenticate users before they can access the chat room.
• Rate limiting and other measures to prevent spamming and abuse in the chat room.

For additional resources to help you build stream processing applications that can aggregate, join, and filter your data streams, see:

• Redpanda University
• Redpanda Blog
• Resources