visgl / loaders.gl / 20352515932

export async function fetchProgress(

  response: Response | Promise<Response>,

  onProgress: any, // TODO better callback types

  onDone = () => {},

  onError = () => {}

) {

  response = await response;

  if (!response.ok) {

    // ERROR checking needs to be done separately

    return response;

  }

  const body = response.body;

  if (!body) {

    // 'ReadableStream not yet supported in this browser.

    return response;

  }

  const contentLength = response.headers.get('content-length') || 0;

  const totalBytes = contentLength ? parseInt(contentLength) : 0;

  if (!(totalBytes > 0)) {

    return response;

  }

  // Currently override only implemented in browser

  if (typeof ReadableStream === 'undefined' || !body.getReader) {

    return response;

  }

  // Create a new stream that invisbly wraps original stream

  const progressStream = new ReadableStream({

    async start(controller) {

      const reader = body.getReader();

      await read(controller, reader, 0, totalBytes, onProgress, onDone, onError);

    }

  });

  return new Response(progressStream);

}

async function read(

  controller: any,

  reader: any,

  loadedBytes: number,

  totalBytes: number,

  onProgress: Function,

  onDone: Function,

  onError: Function

): Promise<void> {

  try {

    const {done, value} = await reader.read();

    if (done) {

      onDone();

      controller.close();

      return;

    }

    loadedBytes += value.byteLength;

    const percent = Math.round((loadedBytes / totalBytes) * 100);

    onProgress(percent, {loadedBytes, totalBytes});

    controller.enqueue(value);

    await read(controller, reader, loadedBytes, totalBytes, onProgress, onDone, onError);

  } catch (error) {

    controller.error(error);

    onError(error);

  }

}