Long Polling vs WebSocket in Rust: The Battle for Real-Time

Introduction: Why Rust is the Ideal Candidate for Real-Time?

Imagine this scenario: you are writing a chat server, a trading terminal, or a monitoring system in Rust. Users want to receive updates instantly. Nobody likes clicking the "Refresh" button manually — that's so last century. But how do you organize data delivery from the server to the client?

For a long time, the only method was long polling — an elegant but slightly "hacky" trick. Then came WebSocket and turned the world of web development upside down. And now we have Rust — a language that allows you to get the most out of both approaches without sacrificing memory safety.

In this article, we won't just compare long polling and WebSocket in Rust — we'll write working examples, run them, and see what's happening under the hood. If you are writing a real-time application in Rust and are unsure about which technology to choose — you've come to the right place.

What is Long Polling in Simple Terms

Long polling is a technique where a client opens an HTTP request to the server and... waits. The server doesn't respond immediately but keeps the connection open until a new event occurs or a timeout expires.

Imagine you call a friend and say: "Call me when the package arrives" — and you stay on the line for an hour. That's long polling. Regular polling is when you call back every 5 minutes: "So, has it arrived yet?"

Implementing Long Polling in Rust with Actix-web

Let's write a simple server using actix-web that uses long polling. We'll have a message queue — when a new message appears, all the "waiters" receive it.

use actix_web::{web, App, HttpServer, HttpRequest, HttpResponse};\nuse std::sync::Mutex;\nuse tokio::sync::broadcast;\n\nstruct AppState {\n    tx: broadcast::Sender<String>,\n}\n\nasync fn long_poll_handler(data: web::Data<Mutex<AppState>>) -> HttpResponse {\n    let mut rx = {\n        let state = data.lock().unwrap();\n        state.tx.subscribe()\n    };\n\n    // Wait for a new message for 30 seconds\n    match tokio::time::timeout(\n        std::time::Duration::from_secs(30),\n        rx.recv()\n    ).await {\n        Ok(Ok(msg)) => HttpResponse::Ok().body(msg),\n        Ok(Err(_)) => HttpResponse::InternalServerError().finish(),\n        Err(_) => HttpResponse::NoContent().finish(), // timeout\n    }\n}\n\n#[actix_web::main]\nasync fn main() -> std::io::Result<()> {\n    let (tx, _) = broadcast::channel::<String>(100);\n\n    HttpServer::new(move || {\n        App::new()\n            .app_data(web::Data::new(Mutex::new(AppState { tx: tx.clone() })))\n            .route("/poll", web::get().to(long_poll_handler))\n    })\n    .bind("127.0.0.1:8080")?\n    .run()\n    .await\n}

The client will simply hang on GET /poll. When a message arrives — the server will respond. If there is nothing for 30 seconds — it returns 204 No Content, and the client will re-request.

Pros:

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• Works over regular HTTP — no proxy servers with WebSocket support needed
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• Easy integration with existing REST APIs
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• Great for corporate networks where proxies block WebSocket
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Cons:

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• Each "poll" holds a connection — with 10,000 clients, that's 10,000 open TCP connections
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• Latency: the client still reconnects after a timeout
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• The server spends resources maintaining "hanging" requests
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WebSocket in Rust: When You Want Speed

WebSocket is no longer a "call and wait" — it's a full-fledged two-way channel. The server and client can exchange messages at any time, without the overhead of HTTP headers.

In Rust, the WebSocket ecosystem is rich: tokio-tungstenite for low-level work, actix-web with built-in