code: def _writeBlock(self):
          
  
          if self.interrupted or self.fp is None:
              if self.debug:
                  log.msg('WorkerFileUploadCommand._writeBlock(): end')
              return True
  
          length = self.blocksize
          if self.remaining is not None and length > self.remaining:
              length = self.remaining
  
          if length <= 0:
              if self.stderr is None:
                  self.stderr = 'Maximum filesize reached, truncating file \'{0}\''.format(
                      self.path)
                  self.rc = 1
              data = ''
          else:
              data = self.fp.read(length)
  
          if self.debug:
              log.msg('WorkerFileUploadCommand._writeBlock(): ' +
                      'allowed={0} readlen={1}'.format(length, len(data)))
          if not data:
              log.msg("EOF: callRemote(close)")
              return True
  
          if self.remaining is not None:
              self.remaining = self.remaining - len(data)
              assert self.remaining >= 0
          d = self.writer.callRemote('write', data)
          d.addCallback(lambda res: False)
          return d
docs: Write a block of data to the remote writer