Slack Realtime Events

Slack Real-time Events

Socket Mode vs Events API

Socket Mode (WebSocket)

Use when:

• App runs behind a firewall
• No public HTTPS endpoint available
• Development and testing
• Running on localhost

import "github.com/slack-go/slack/socketmode"

client := socketmode.New(
    api,
    socketmode.OptionDebug(true),
)

See socket-mode-setup.md for complete Socket Mode implementation.

Events API (HTTP Webhooks)

Use when:

• Public HTTPS endpoint available
• Production cloud deployments
• Webhook-based architecture preferred

See events-api-webhooks.md for HTTP webhook patterns.

Socket Mode Basic Setup

api := slack.New(
    os.Getenv("SLACK_BOT_TOKEN"),
    slack.OptionAppLevelToken(os.Getenv("SLACK_APP_TOKEN")),
)

client := socketmode.New(api)

go func() {
    for envelope := range client.Events {
        switch envelope.Type {
        case socketmode.EventTypeEventsAPI:
            client.Ack(*envelope.Request)
            // Handle event
        }
    }
}()

client.Run()

Event Handling Patterns

Message Events

func handleMessageEvent(event *slackevents.MessageEvent, api *slack.Client) {
    // Ignore bot messages
    if event.BotID != "" {
        return
    }

    fmt.Printf("Message from %s in %s: %s\n", event.User, event.Channel, event.Text)

    // Respond
    api.PostMessage(event.Channel, slack.MsgOptionText("Got your message!", false))
}

App Mention Events

func handleAppMention(event *slackevents.AppMentionEvent, api *slack.Client) {
    text := strings.TrimSpace(strings.Replace(event.Text, fmt.Sprintf("<@%s>", botUserID), "", 1))

    response := processCommand(text)

    api.PostMessage(
        event.Channel,
        slack.MsgOptionText(response, false),
        slack.MsgOptionTS(event.TimeStamp), // Reply in thread
    )
}

Reaction Events

func handleReaction(event *slackevents.ReactionAddedEvent, api *slack.Client) {
    fmt.Printf("User %s added reaction :%s: to message %s\n",
        event.User, event.Reaction, event.Item.Timestamp)

    // React back
    api.AddReaction(event.Reaction, slack.ItemRef{
        Channel:   event.Item.Channel,
        Timestamp: event.Item.Timestamp,
    })
}

Interactive Components

Button Clicks

func handleButtonClick(interaction slack.InteractionCallback, api *slack.Client) {
    action := interaction.ActionCallback.BlockActions[0]

    switch action.ActionID {
    case "approve_deployment":
        // Handle approval
        updateMessage(api, interaction.Channel.ID, interaction.Message.Timestamp, "Approved!")

    case "reject_deployment":
        // Handle rejection
        updateMessage(api, interaction.Channel.ID, interaction.Message.Timestamp, "Rejected!")
    }
}

Modal Submissions

func handleModalSubmission(interaction slack.InteractionCallback, api *slack.Client) {
    values := interaction.View.State.Values

    // Extract form data
    rating := values["rating_block"]["rating_select"].SelectedOption.Value
    comments := values["comments_block"]["comments_input"].Value

    // Process submission
    fmt.Printf("Feedback: %s stars - %s\n", rating, comments)

    // Acknowledge
    api.UpdateView(slack.View{}, interaction.View.ExternalID, "", interaction.View.ID)
}

See interactive-components.md for comprehensive interactive patterns.

Slash Commands

Handle slash command invocations:

func handleSlashCommand(command slack.SlashCommand, api *slack.Client) slack.Message {
    switch command.Command {
    case "/deploy":
        return slack.Message{
            Text: fmt.Sprintf("Deploying %s to %s...", command.Text, "production"),
        }

    case "/status":
        return slack.Message{
            Text: "All systems operational",
        }

    default:
        return slack.Message{
            Text: "Unknown command",
        }
    }
}

See slash-commands.md for command patterns and delayed responses.

Event Types

Common event types to handle:

• message - New messages in channels
• app_mention - Bot mentioned in message
• reaction_added/removed - Message reactions
• channel_created/renamed - Channel lifecycle
• team_join - New workspace members
• user_change - User profile updates

See event-types.md for comprehensive event catalog.

Connection Management

Graceful Shutdown

ctx, cancel := context.WithCancel(context.Background())
defer cancel()

go func() {
    sigChan := make(chan os.Signal, 1)
    signal.Notify(sigChan, os.Interrupt, syscall.SIGTERM)
    <-sigChan
    cancel()
}()

client.RunContext(ctx)

Error Handling

for envelope := range client.Events {
    switch envelope.Type {
    case socketmode.EventTypeErrorBadMessage:
        fmt.Printf("Error: Bad message - %v\n", envelope.Request)

    case socketmode.EventTypeConnectionError:
        fmt.Printf("Connection error: %v\n", envelope.Request)
    }
}

Common Pitfalls

• Not acknowledging events (causes timeouts)
• Blocking in event handlers (use goroutines for long operations)
• Missing bot vs user message filtering
• Not handling reconnections in Socket Mode
• Forgetting to verify request signatures in Events API

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