HighWaterMarkTransformer.ts

import { Transform } from 'stream'

export class HighWaterMarkTransformer extends Transform {
  highWaterMark: number
  temp = new Uint8Array(0)
  constructor(highWaterMark = 2048) {
    super({ highWaterMark })
    this.highWaterMark = highWaterMark
  }

  _transform(chunk, encoding, callback) {
    this.temp = Uint8Array.from([...this.temp, ...chunk])
    while (this.temp.length > this.highWaterMark) {
      this.push(this.temp.slice(0, this.highWaterMark))
      this.temp = this.temp.slice(this.highWaterMark)
    }
    callback()
  }

  _flush(cb) {
    this.push(this.temp)
    return cb()
  }
}