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//文件转base64 
readFileToBase64(path: string): string { 
  // 打开文件 
  let srcFile = fs.openSync(path, fs.OpenMode.READ_ONLY); 
  console.info(`file.size=${fs.statSync(srcFile.fd).size}`) 
  let bufSize = 4096; 
  let readSize = 0; 
  let arrayBuf = new ArrayBuffer(bufSize); 
  class Option { 
    public offset: number = 0; 
    public length: number = bufSize; 
  } 
  let option = new Option(); 
  option.offset = readSize; 
  let readLen = fs.readSync(srcFile.fd, arrayBuf, option); 
 
  let buffs: buffer.Buffer[] = [] 
  while (readLen > 0) { 
    buffs.push(buffer.from(arrayBuf, 0, readLen)) 
    readSize += readLen; 
    option.offset = readSize; 
    arrayBuf = new ArrayBuffer(bufSize); 
    readLen = fs.readSync(srcFile.fd, arrayBuf, option); 
  } 
  let allBuff = buffer.concat(buffs) 
  console.info(`readSize=${readSize} allbuff=${allBuff.buffer.byteLength}`) 
  // 关闭文件 
  fs.closeSync(srcFile); 
 
  return new util.Base64Helper().encodeToStringSync(new Uint8Array(allBuff.buffer)) 
}