ChunkStream.js

const Transform = require('stream').Transform;
const util = require('util');

function ChunkStream(options) {
  if (!(this instanceof ChunkStream))
    return new ChunkStream(options);
  Transform.call(this, options);
  
  this.chunkSize = options.chunkSize || 1500;
  this._chunks = [ ];
  this._size = 0;
}
util.inherits(ChunkStream, Transform);

ChunkStream.prototype._transform = function (_chunk, encoding, callback) {
  let chunk = Buffer.isBuffer(_chunk) ? _chunk : Buffer.from(_chunk, encoding);
  this._chunks.push(chunk);
  this._size += chunk.length;
  if (this._size > this.chunkSize) {
    this._flush(callback);
  } else {
    callback();
  }
};

ChunkStream.prototype._flush = function (callback) {
  this.push(Buffer.concat(this._chunks));
  this._chunks.length = 0;
  this._size = 0;
};

module.exports = ChunkStream;