code: def set_sync_info(self, filename, mtime, size):
          
          assert self.target.is_local()
          remote_target = self.target.peer
          ps = self.dir["peer_sync"].setdefault(remote_target.get_id(), {})
          ut = time.time()  # UTC time stamp
          ps[":last_sync"] = ut  # this is an invalid file name to avoid conflicts
          pse = ps[filename] = {"m": mtime, "s": size, "u": ut}
          if self.PRETTY:
              ps[":last_sync_str"] = pretty_stamp(
                  ut
              )  # use an invalid file name to avoid conflicts
              pse["mtime_str"] = pretty_stamp(mtime) if mtime else "(directory)"
              pse["uploaded_str"] = pretty_stamp(ut)
          self.modified_sync = True
docs: Store mtime/size when local and remote file was last synchronized.
  
          This is stored in the local file's folder as meta data.
          The information is used to detect conflicts, i.e. if both source and
          remote had been modified by other means since last synchronization.