Build a Chat Room Application with Redpanda and Golang

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 Go 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.

If you’re running Redpanda in a shared development environment, avoid running sudo rpk redpanda tune all or manually configuring Redpanda for production. The optimized production settings might affect your experience with other applications running on your machine.

Set up your environment

Create and set your working directory to the project folder, chat-room:
```
mkdir chat-room
cd chat-room
```
Initialize the project:
```
go mod init com/redpanda/chat-room
```

Install the required dependencies:

go get github.com/twmb/franz-go@v1.15.0
go get github.com/twmb/franz-go/pkg/kadm@v1.10.0
go get github.com/google/uuid@v1.3.0

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.

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

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 the chat-room/ directory, create a source file called admin.go with the following content.

Replace the placeholders with the same values that you used in the Redpanda Quickstart.

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, create a source file called producer.go with the following content.

Replace the placeholders with the same values that you used in the Redpanda Quickstart.

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.

Replace the placeholders with the same values that you used in the Redpanda Quickstart.

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.

Replace the placeholders with the same values that you used in the Redpanda Quickstart.

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.

Open at least two terminals, and for each terminal:
Run the client application:
```
go run .
```
When prompted with Enter user name:, enter a unique name for the chat room.
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.

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Build a Chat Room Application with Redpanda and Golang

Prerequisites

Set up a Redpanda environment

Set up your environment

Create a topic

Confirm that the topic exists on the client side

Create a producer

Create a consumer

Create a client application

Build and run the application

Next steps

Suggested reading

Simple online edits

Contribution guide