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// SPDX-License-Identifier: Zlib
// SPDX-FileCopyrightText: 2024 CERN (home.cern)
const DELTA = 10;
class StreamClient {
/**
* @param {{ throttle: number|undefined, cb: (arg: Buffer|Error) => void}} arg
*/
constructor({ throttle, cb }) {
/** @type {number|undefined} */
this.throttle = Number(throttle);
/** @type {(Buffer|Error) => void} */
this.cb = cb;
/** @type {number} */
this.next = 0; // last received frame timestamp
}
/** @param {Buffer|Error} data */
throttledCB(data) {
if (!this.throttle) {
this.cb(data);
return;
}
// Otherwise, we check if the required time interval has passed
if (this.next - DELTA < Date.now()) {
/**
* We initialize this.next at 0 to have no throttle before the first frame,
* so on the first receival we will need to initialize it.
*/
const uninitialized = this.next === 0;
/**
* We also absolutely want to avoid the this.next timer to get overdue again
* and again if we have some frames lost because when we will finally receive
* again, all the next frames will be accepted in a row, breaking the framerate.
*
* normal | <----------> (2) <----------> (3) <-------
* [1]____|______|_____[2]_____|_____[3]_____|
* 2nd accepted 3rd accepted
*
* overdue | <----------> (2) <----------> (3) <-------
* [1]____?______?______?______?____[2]____[3]
* missing frames two accepted at once!
*/
const overdue = this.next < Date.now() - this.throttle;
if (overdue) {
console.warn("The client throttling was overdue and was reset");
}
// In both cases, we want to reset the this.next as `now + throttle`
if (uninitialized || overdue) {
this.next = Date.now();
}
this.next += this.throttle;
this.cb(data);
}
}
}
export default StreamClient;
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