Arifa

Arifa is a lightweight, Redis-based realtime pub/sub engine for Rust applications.

It provides a simple abstraction over Redis Pub/Sub and WebSocket sessions, making it easy to build scalable realtime systems that work across multiple application nodes.

Features

• Redis Pub/Sub
• Shared Redis Pub/Sub connection per node
• Automatic reconnect with exponential backoff
• Automatic channel resubscription
• Tokio async runtime
• WebSocket session abstraction
• Channel-based subscriptions
• Multi-node message routing
• Online user tracking
• Lock-free metrics
• Framework agnostic (WsSession trait)

Installation

cargo add arifa

Creating an Arifa Instance

use arifa::prelude::*;

#[tokio::main]
async fn main() {
    let arifa = Arifa::new(
        "redis://127.0.0.1/",
        "node-1",
    )
    .await
    .unwrap();
}

Defining a WebSocket Session

Arifa is transport agnostic. Implement the WsSession trait for your WebSocket framework.

use arifa::prelude::*;
use async_trait::async_trait;

struct MySession;

#[async_trait]
impl WsSession for MySession {
    type Error = anyhow::Error;

    async fn send(&self, event: WsMessage) -> Result<(), Self::Error> {
        println!("{:?}", event);
        Ok(())
    }
}

Subscribing

subscribe() registers the session, marks it online, and returns a generated session id.

let session = MySession;

let channels = vec![
    "Location::891e2040897ffff".to_string(),
    "User::42".to_string(),
];

let session_id = arifa.subscribe(
    channels.clone(),
    session,
    "42",
).await?;

The returned session id is used when removing the connection from the online users set and unsubscribing.

Publishing Messages

use arifa::prelude::*;
use serde_json::json;

let message = WsMessage {
    scope: MessageScope::Broadcast,
    kind: MessageKind::Feeds,
    node_id: None,
    payload: json!({
        "message": "Hello world"
    }),
};

arifa
    .publish("Location::891e2040897ffff", &message)
    .await?;

Unsubscribing

When a WebSocket disconnects, remove the session from the online users set before unsubscribing.

let _ = arifa.remove_online_user(&session_id).await;
arifa.unsubscribe(&session_id, &channels);

Message Model

pub struct WsMessage {
    pub scope: MessageScope,
    pub kind: MessageKind,
    pub node_id: Option<String>,
    pub payload: serde_json::Value,
}

MessageScope

pub enum MessageScope {
    Broadcast,
    Private,
}

MessageKind

pub enum MessageKind {
    Feeds,
    DirectMessage,
    Event,
}

Online Users

A connection is automatically marked online inside subscribe().

Query the current number of active sessions:

let users = arifa.online_users().await?;
println!("{users}");

Remove a session when its WebSocket closes:

let _ = arifa.remove_online_user(&session_id).await;

Check whether a user currently has any active sessions:

let online = arifa.is_user_online("42").await?;

Note: The online count reflects active sessions, not unique users. Multiple browser tabs or devices for the same user count as multiple sessions.

Multi-node Routing

To target only a specific application node, set the node_id field.

let message = WsMessage {
    scope: MessageScope::Private,
    kind: MessageKind::Event,
    node_id: Some("node-2".into()),
    payload: serde_json::json!({
        "status": "updated"
    }),
};

arifa.publish("User::42", &message).await?;

If node_id is None, every subscribed node receives the message.

Metrics

Arifa exposes lightweight runtime metrics.

let metrics = arifa.metrics.snapshot();

println!("Active sessions: {}", metrics.sessions_active);
println!("Messages routed: {}", metrics.messages_routed);
println!("Messages dropped: {}", metrics.messages_dropped);
println!("Redis reconnects: {}", metrics.redis_reconnects);

Graceful Shutdown

Before shutting down your application, stop Arifa's background router and forwarding tasks.

arifa.shutdown();

Example: Actix Web

#[get("/ws/connect")]
pub async fn notification_channel(
    req: HttpRequest,
    body: web::Payload,
    state: web::Data<AppState>,
    query: web::Query<ConnectRequestQuery>,
) -> Result<HttpResponse, Error> {
    let (resp, session, mut stream) = actix_ws::handle(&req, body)?;

    let location = format!("Location::{}", query.get_cell()?);
    let user = format!("User::{}", query.user_id);

    let channels = vec![location.clone(), user.clone()];

    let ws = ActixWsSession::new(session);

    let session_id = state.arifa.subscribe(
        channels.clone(),
        ws,
        query.user_id.to_string(),
    );

    let arifa = state.arifa.clone();

    actix_web::rt::spawn(async move {
        while let Some(message) = stream.next().await {
            match message {
                Ok(actix_ws::Message::Close(_)) => break,
                Err(_) => break,
                _ => {}
            }
        }

        let _ = arifa.remove_online_user(&session_id).await;
        arifa.unsubscribe(&session_id, &channels);
    });

    Ok(resp)
}

Architecture

                   WebSocket Client
                           │
                           ▼
                      WsSession
                           │
                           ▼
                 Per-session forwarder
                           ▲
                           │
                    Routing Table
                           │
                           ▼
          Shared Redis Pub/Sub Router
                (one per application node)
                           │
                           ▼
                     Redis Pub/Sub
                           │
                           ▼
                      Other Nodes

Each Arifa instance maintains a single Redis Pub/Sub connection that is shared by all subscriptions on that node. Incoming messages are routed to subscribed sessions through an in-memory routing table. If the Redis connection drops, Arifa automatically reconnects and resubscribes to all active channels.

Use Cases

• Chat applications
• Notifications
• Live location updates
• Multiplayer games
• Live dashboards
• Social feeds
• Collaborative applications

Notes

• One shared Redis Pub/Sub connection is used per application node.
• Each subscribed session runs in its own forwarding task.
• Session message queues are bounded to prevent slow clients from consuming unbounded memory.
• Redis reconnects and channel resubscriptions happen automatically.
• Call remove_online_user() before unsubscribe() when a client disconnects.

License

Apache-2.0