TUS FileUpload Class using next generation expo-file-system/next for fast chunked uploads with contant RAM by fair CPU usage

tus-file-reader.tsx

import { File, type FileHandle } from 'expo-file-system/next'

interface FileInput {
  uri: string
}

export default class TusFileReader {
  async openFile({ uri }: FileInput) {
    const handle = new File(uri)
    if (!handle.exists || !handle.size) throw new Error(`File ${uri} not found`)
    return new FileSource(handle.open(), handle.size)
  }
}

class FileSource {
  constructor(
    private h: FileHandle,
    private _size: number
  ) {}
  get size() {
    return this._size
  }

  async slice(start: number, end: number) {
    if (start >= this._size) return { value: new Uint8Array(0), done: true }
    this.h.offset = start
    const chunk = this.h.readBytes(Math.min(end, this._size) - start)
    return { value: chunk, done: false }
  }

  close() {
    this.h.close()
  }
}