fs.read(fd, buffer, offset, length, position, callback)

    fd 指定的文件中读取数据。

    Read data from the file specified by fd.

    The callback is given the three arguments, (err, bytesRead, buffer).

    If the file is not modified concurrently, the end-of-file is reached when the number of bytes read is zero.

    If this method is invoked as its util.promisify()ed version, it returns a promise for an Object with bytesRead and buffer properties.