watch-party/frontend/lib/reconnecting-web-socket.mjs

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export default class ReconnectingWebSocket {
constructor(url) {
if (url instanceof URL) {
this.url = url;
} else {
this.url = new URL(url);
}
this.connected = false;
this._eventTarget = new EventTarget();
this._backoff = 250; // milliseconds, doubled before use
this._lastConnect = 0;
this._socket = null;
this._unsent = [];
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this._connect(true);
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}
_connect(first) {
if (this._socket)
try {
this._socket.close();
} catch (e) {}
try {
this._socket = new WebSocket(this.url.href);
} catch (e) {
this._reconnecting = false;
return this._reconnect();
}
this._socket.addEventListener("close", () => this._reconnect());
this._socket.addEventListener("error", () => this._reconnect());
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this._socket.addEventListener("message", ({ data }) => {
this._eventTarget.dispatchEvent(new MessageEvent("message", { data }));
});
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this._socket.addEventListener("open", (e) => {
if (first) this._eventTarget.dispatchEvent(new Event("open"));
if (this._reconnecting)
this._eventTarget.dispatchEvent(new Event("reconnected"));
this._reconnecting = false;
this._backoff = 250;
this.connected = true;
while (this._unsent.length > 0) this._socket.send(this._unsent.shift());
});
}
_reconnect() {
if (this._reconnecting) return;
this._eventTarget.dispatchEvent(new Event("reconnecting"));
this._reconnecting = true;
this.connected = false;
this._backoff *= 2; // exponential backoff
setTimeout(() => {
this._connect();
}, Math.floor(this._backoff + Math.random() * this._backoff * 0.25 - this._backoff * 0.125));
}
send(message) {
if (this.connected) {
this._socket.send(message);
} else {
this._unsent.push(message);
}
}
addEventListener(...a) {
return this._eventTarget.addEventListener(...a);
}
removeEventListener(...a) {
return this._eventTarget.removeEventListener(...a);
}
}