HarmonyOS fs模块读取文件的问题

import { BusinessError } from '@ohos.base'; 
import buffer from '@ohos.buffer'; 
let filePath = pathDir + "/test.txt"; 
let file = fs.openSync(filePath, fs.OpenMode.READ_WRITE); 
let arrayBuffer = new ArrayBuffer(4096); 
fs.read(file.fd, arrayBuffer, (err: BusinessError, readLen: number) => { 
  if (err) { 
    console.error("read failed with error message: " + err.message + ", error code: " + err.code); 
  } else { 
    console.info("read file data succeed"); 
    let buf = buffer.from(arrayBuffer, 0, readLen); 
    console.info(`The content of file: ${buf.toString()}`); 
  } 
  fs.closeSync(file); 
});
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