一次读取文件字节

Question

所以我试图一次读取一个文件字节。基本上我应该读取前50个字节，然后接下来的7个字节应该告诉我长度x。然后我读取x个字节并重复这些步骤直到文件结束。我被卡住了。不知道该怎么办。任何帮助将不胜感激。

app.get('/video', function (req, res) {
    var readStream = fs.createReadStream('video.mjpeg');
    res.writeHead(200, {'Content-Type': 'multipart/x-mixed-      replace;boundary=ThisString'});

    readStream.on("data", (chunk) => {

        console.log(chunk.length); //this always gives me the same number.

        res.write(chunk, 'binary');

        console.log("Writing to client");
    });

    readStream.on("end", () => {
        readStream.destroy();
        res.end();
        console.log("End of data");
    });
});

基本上我想将数据分组到帧中。谢谢。