server/app/ws/StreamTake.js

const stream = require('stream')
const util = require('util')

const Transform = stream.Transform

function Take(options) {
    // allow use without new
    if (!(this instanceof Take)) {
        return new Take(options);
    }

    this._toTake = options.take || undefined

    // init Transform
    Transform.call(this, options);
}

util.inherits(Take, Transform);

Take.prototype._transform = function (chunk, enc, cb) {
    if ( typeof this._toTake == 'undefined' ) {
        this.push(chunk)
    }
    else if (this._toTake > chunk.length) {
        this._toTake -= chunk.length;
        this.push(chunk)
    } else {
        if (this._toTake !== chunk.length) this.push(chunk.slice(0, this._toTake))
        this._toTake = 0;
    }

    cb();
};

module.exports = Take;