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fastwebsockets is a fast WebSocket protocol implementation.

Passes the Autobahn|TestSuite¹ and fuzzed with LLVM's libfuzzer.

You can use it as a raw websocket frame parser and deal with spec compliance yourself, or you can use it as a full-fledged websocket client/server.

use fastwebsockets::{Frame, OpCode, WebSocket};

async fn handle_client(
  mut socket: TcpStream,
) -> Result<(), WebSocketError> {
  handshake(&mut socket).await?;

  let mut ws = WebSocket::after_handshake(socket);
  ws.set_writev(true);
  ws.set_auto_close(true);
  ws.set_auto_pong(true);

  loop {
    let frame = ws.read_frame().await?;

    match frame {
      OpCode::Close => break,
      OpCode::Text | OpCode::Binary => {
        let frame = Frame::new(true, frame.opcode, None, frame.payload);
        ws.write_frame(frame).await?;
      }
    }
  }

  Ok(())
}

Fragmentation

By default, fastwebsockets will give the application raw frames with FIN set. Other crates like tungstenite which will give you a single message with all the frames concatenated.

For concanated frames, use FragmentCollector:

let mut ws = WebSocket::after_handshake(socket);
let mut ws = FragmentCollector::new(ws);

let incoming = ws.read_frame().await?;
// Always returns full messages
assert!(incoming.fin);

permessage-deflate is not supported yet.

HTTP Upgrade

Enable the upgrade feature to do server-side upgrades and client-side handshakes.

This feature is powered by hyper.

use fastwebsockets::upgrade::upgrade;
use hyper::{Request, body::{Incoming, Bytes}, Response};
use http_body_util::Empty;
use anyhow::Result;

async fn server_upgrade(
  mut req: Request<Incoming>,
) -> Result<Response<Empty<Bytes>>> {
  let (response, fut) = upgrade::upgrade(&mut req)?;

  tokio::spawn(async move {
    if let Err(e) = handle_client(fut).await {
      eprintln!("Error in websocket connection: {}", e);
    }
  });

  Ok(response)
}

Use the handshake module for client-side handshakes.

use fastwebsockets::handshake;
use fastwebsockets::WebSocket;
use hyper::{Request, body::Bytes, upgrade::Upgraded, header::{UPGRADE, CONNECTION}};
use http_body_util::Empty;
use tokio::net::TcpStream;
use std::future::Future;
use anyhow::Result;

async fn connect() -> Result<WebSocket<Upgraded>> {
  let stream = TcpStream::connect("localhost:9001").await?;

  let req = Request::builder()
    .method("GET")
    .uri("http://localhost:9001/")
    .header("Host", "localhost:9001")
    .header(UPGRADE, "websocket")
    .header(CONNECTION, "upgrade")
    .header(
      "Sec-WebSocket-Key",
      fastwebsockets::handshake::generate_key(),
    )
    .header("Sec-WebSocket-Version", "13")
    .body(Empty::<Bytes>::new())?;

  let (ws, _) = handshake::client(&SpawnExecutor, req, stream).await?;
  Ok(ws)
}

// Tie hyper's executor to tokio runtime
struct SpawnExecutor;

impl<Fut> hyper::rt::Executor<Fut> for SpawnExecutor
where
  Fut: Future + Send + 'static,
  Fut::Output: Send + 'static,
{
  fn execute(&self, fut: Fut) {
    tokio::task::spawn(fut);
  }
}

Usage with Axum

Enable the Axum integration with features = ["upgrade", "with_axum"] in Cargo.toml.

use axum::{response::IntoResponse, routing::get, Router};
use fastwebsockets::upgrade;
use fastwebsockets::OpCode;
use fastwebsockets::WebSocketError;

#[tokio::main]
async fn main() {
  let app = Router::new().route("/", get(ws_handler));

  let listener = tokio::net::TcpListener::bind("0.0.0.0:3000").await.unwrap();
  axum::serve(listener, app).await.unwrap();
}

async fn handle_client(fut: upgrade::UpgradeFut) -> Result<(), WebSocketError> {
  let mut ws = fastwebsockets::FragmentCollector::new(fut.await?);

  loop {
    let frame = ws.read_frame().await?;
    match frame.opcode {
      OpCode::Close => break,
      OpCode::Text | OpCode::Binary => {
        ws.write_frame(frame).await?;
      }
      _ => {}
    }
  }

  Ok(())
}

async fn ws_handler(ws: upgrade::IncomingUpgrade) -> impl IntoResponse {
  let (response, fut) = ws.upgrade().unwrap();

  tokio::task::spawn(async move {
    if let Err(e) = handle_client(fut).await {
      eprintln!("Error in websocket connection: {}", e);
    }
  });

  response
}