WebSockets Example

View full source code or view the compiled example online

This example connects to an echo server on wss://echo.websocket.org, sends a ping message, and receives the response.

Cargo.toml

The Cargo.toml enables features necessary to create a WebSocket object and to access events such as MessageEvent or ErrorEvent.

[package]
authors = ["The wasm-bindgen Developers"]
edition = "2021"
name = "websockets"
publish = false
version = "0.0.0"

[lib]
crate-type = ["cdylib"]

[dependencies]
js-sys = { path = "../../crates/js-sys" }
wasm-bindgen = { path = "../../" }

[dependencies.web-sys]
features = [
  "BinaryType",
  "Blob",
  "ErrorEvent",
  "FileReader",
  "MessageEvent",
  "ProgressEvent",
  "WebSocket",
]
path = "../../crates/web-sys"

[lints]
workspace = true

src/lib.rs

This code shows the basic steps required to work with a WebSocket. At first it opens the connection, then subscribes to events onmessage, onerror, onopen. After the socket is opened it sends a ping message, receives an echoed response and prints it to the browser console.

#![allow(unused)]
fn main() {
use wasm_bindgen::prelude::*;
use web_sys::{ErrorEvent, MessageEvent, WebSocket};

macro_rules! console_log {
    ($($t:tt)*) => (log(&format_args!($($t)*).to_string()))
}

#[wasm_bindgen]
extern "C" {
    #[wasm_bindgen(js_namespace = console)]
    fn log(s: &str);
}

#[wasm_bindgen(start)]
fn start_websocket() -> Result<(), JsValue> {
    // Connect to an echo server
    let ws = WebSocket::new("wss://echo.websocket.events")?;
    // For small binary messages, like CBOR, Arraybuffer is more efficient than Blob handling
    ws.set_binary_type(web_sys::BinaryType::Arraybuffer);
    // create callback
    let cloned_ws = ws.clone();
    let onmessage_callback = Closure::<dyn FnMut(_)>::new(move |e: MessageEvent| {
        // Handle difference Text/Binary,...
        if let Ok(abuf) = e.data().dyn_into::<js_sys::ArrayBuffer>() {
            console_log!("message event, received arraybuffer: {:?}", abuf);
            let array = js_sys::Uint8Array::new(&abuf);
            let len = array.byte_length() as usize;
            console_log!("Arraybuffer received {}bytes: {:?}", len, array.to_vec());
            // here you can for example use Serde Deserialize decode the message
            // for demo purposes we switch back to Blob-type and send off another binary message
            cloned_ws.set_binary_type(web_sys::BinaryType::Blob);
            match cloned_ws.send_with_u8_array(&[5, 6, 7, 8]) {
                Ok(_) => console_log!("binary message successfully sent"),
                Err(err) => console_log!("error sending message: {:?}", err),
            }
        } else if let Ok(blob) = e.data().dyn_into::<web_sys::Blob>() {
            console_log!("message event, received blob: {:?}", blob);
            // better alternative to juggling with FileReader is to use https://crates.io/crates/gloo-file
            let fr = web_sys::FileReader::new().unwrap();
            let fr_c = fr.clone();
            // create onLoadEnd callback
            let onloadend_cb = Closure::<dyn FnMut(_)>::new(move |_e: web_sys::ProgressEvent| {
                let array = js_sys::Uint8Array::new(&fr_c.result().unwrap());
                let len = array.byte_length() as usize;
                console_log!("Blob received {}bytes: {:?}", len, array.to_vec());
                // here you can for example use the received image/png data
            });
            fr.set_onloadend(Some(onloadend_cb.as_ref().unchecked_ref()));
            fr.read_as_array_buffer(&blob).expect("blob not readable");
            onloadend_cb.forget();
        } else if let Ok(txt) = e.data().dyn_into::<js_sys::JsString>() {
            console_log!("message event, received Text: {:?}", txt);
        } else {
            console_log!("message event, received Unknown: {:?}", e.data());
        }
    });
    // set message event handler on WebSocket
    ws.set_onmessage(Some(onmessage_callback.as_ref().unchecked_ref()));
    // forget the callback to keep it alive
    onmessage_callback.forget();

    let onerror_callback = Closure::<dyn FnMut(_)>::new(move |e: ErrorEvent| {
        console_log!("error event: {:?}", e);
    });
    ws.set_onerror(Some(onerror_callback.as_ref().unchecked_ref()));
    onerror_callback.forget();

    let cloned_ws = ws.clone();
    let onopen_callback = Closure::<dyn FnMut()>::new(move || {
        console_log!("socket opened");
        match cloned_ws.send_with_str("ping") {
            Ok(_) => console_log!("message successfully sent"),
            Err(err) => console_log!("error sending message: {:?}", err),
        }
        // send off binary message
        match cloned_ws.send_with_u8_array(&[0, 1, 2, 3]) {
            Ok(_) => console_log!("binary message successfully sent"),
            Err(err) => console_log!("error sending message: {:?}", err),
        }
    });
    ws.set_onopen(Some(onopen_callback.as_ref().unchecked_ref()));
    onopen_callback.forget();

    Ok(())
}
}