code: func (file *GridFile) SetUploadDate(t time.Time) {
  	file.assertMode(gfsWriting)
  	file.m.Lock()
  	file.doc.UploadDate = t
  	file.m.Unlock()
  }
docs: // SetUploadDate changes the file upload time.
  //
  // It is a runtime error to call this function when the file is not open
  // for writing.