code: function validateChecksum(fileName, checksum, cb) {
     if (isUndefined(checksum) || isUndefined(checksum.hashAlgorithm)) {
        cb();
        return;
     }
  
     if (isUndefined(checksum.inline) || isUndefined(checksum.inline.value)) {
        cb(new Error('Installed jobs agent only supports inline checksum value provided in job document'));
        return;
     }
  
     var hash;
     try {
        hash = crypto.createHash(checksum.hashAlgorithm);
     } catch (err) {
        cb(new Error('Unsupported checksum hash algorithm: ' + checksum.hashAlgorithm));
        return;
     }
  
     var stream = fs.createReadStream(fileName);
  
     stream.on('data', function (data) {
        hash.update(data, 'utf8');
     }).on('end', function () {
        if (hash.digest('hex') !== checksum.inline.value) {
           var err = new Error('Checksum mismatch');
           err.fileName = fileName;
           cb(err);
        } else {
           cb();
        }
     }).on('error', function (err) {
        err.fileName = fileName;
        cb(err);
     });
  }
docs: Private function to validate checksum