Rust WebSocket

Rust WebSocket

This example shows how to run a WebSocket server in Rust on Vercel using the Axum framework. The Vercel Rust runtime enables HTTP/1.1 upgrades, so axum's WebSocketUpgrade extractor works without any extra configuration.

How it works

api/websocket.rs serves an Axum router behind the VercelLayer:

• GET / — an interactive HTML page to connect and exchange messages.
• GET /ws — the WebSocket endpoint. The handler upgrades the connection and then runs two concurrent tasks over a single writer:
  • a heartbeat that pushes a tick event to the client every second (server-initiated messages), and
  • an echo loop that mirrors any message the client sends back to it (client-initiated messages).

A single writer task owns the WebSocket sink and is fed by an mpsc channel, so both the heartbeat and echo loops can send frames without sharing the non-clonable sink.

All server messages are JSON tagged with a type field (welcome, echo, tick), which the front-end renders in the live log.

Project Structure

• api/websocket.rs — Axum application with the WebSocket handler
• index.html — interactive WebSocket client (embedded via include_str!)
• Cargo.toml — Rust dependencies and binary configuration
• vercel.json — rewrites all routes to the function

Development

Clone the repository:

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git clone https://github.com/vercel/examples.git
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cd examples/rust/websocket

Install Rust if you haven't already:

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curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh

Test locally:

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vc dev

Then open the printed URL, click Connect, and send a message. You'll see the welcome event, periodic tick heartbeats, and your echo replies in the log.