code: function syncToTmp(tmpfd, msgnumber, cb) {
  
          // Pass the last msg
          if (msgnumber > messages.offsets.length) cb();
  
          // Skip deleted messages
          else if (messages.offsets[msgnumber] === undefined) syncToTmp(tmpfd, msgnumber + 1, cb);
          else {
  
              var buffer = new Buffer(omessages.sizes[msgnumber]);
  
              fs.read(fd, buffer, 0, omessages.sizes[msgnumber], messages.offsets[msgnumber], function(err, bytesRead, buffer) {
  
                  fs.write(tmpfd, buffer, 0, bytesRead, null, function(err, written, buffer) {
  
                      syncToTmp(tmpfd, msgnumber + 1, cb);
  
                  });
              });
          }
      }
docs: Private methods follow Write modifications to temp file