fetch下载文件读取进度，提示只能读取一次？

Question

 useEffect(() => {
    const videoRef = $('.home_bg_logo_box_video_1')[0] as HTMLVideoElement;
    const videoURL = 'video/0.mp4';
    // 加载视频完成后再播放
    fetch(videoURL).then((response: any) => {
      const contentLength = response.headers.get('Content-Length');
      const fileSizeBytes = parseInt(contentLength, 10);
      let downloadedBytes = 0;
      const reader = response.body.getReader();
      function readChunk() {
        reader.read().then(({ value, done }: any) => {
          if (done) {
            console.log('done', response.body);
            // TODO 读取不到blob
            return;
          }
          downloadedBytes += value.length;
          const progress = (downloadedBytes / fileSizeBytes) * 100;
          setPre(Math.floor(progress));
          readChunk();
        });
      }

      readChunk();
    });
    // .then((blob: Blob) => {
    // init(blob());
    // });

    function init(blob: Blob) {
      videoRef.src = URL.createObjectURL(blob);

      // 当浏览器预计能够在不停下来进行缓冲的情况下持续播放指定的音频/视频时，会发生 canplaythrough 事件。
      videoRef.addEventListener('canplaythrough', () => {
        $('.home_bg_logo_box_loading').css({
          // display: 'none',
        });
        videoRef.play();
      });

      videoRef.addEventListener('ended', function () {
        // 播放结束后的操作 从第N秒开始播放
        videoRef.currentTime = 8;
        videoRef.play();
      });
    }
  }, []);

进度条可以获取到，但是我获取不到blob了。提示错误 TypeError: Failed to execute 'blob' on 'Response': body stream already read。

Answer 1

你这个错误是因为HTTP响应体只能被读一次，用ReadableStream的pipeThrough()方法试试：

fetch(videoURL).then(response => {
  const contentLength = response.headers.get('Content-Length');
  const fileSizeBytes = parseInt(contentLength, 10);
  let downloadedBytes = 0;

  const transformer = new TransformStream({
    transform(chunk, controller) {
      downloadedBytes += chunk.length;
      const progress = (downloadedBytes / fileSizeBytes) * 100;
      setPre(Math.floor(progress));
      controller.enqueue(chunk);
    }
  });

  const blobStream = response.body.pipeThrough(transformer);
  return new Response(blobStream, { headers: response.headers }).blob();
}).then(blob => {
  init(blob);
});

MDN