docs: def chunkVerified(self, who, chunkNumber, chunkData):
          """A chunk (#chunkNumber) containing the data C{chunkData} was verified, sent
          to us by the Q2QAddress C{who}.
          """
          if self.mask[chunkNumber]:
              # already received that chunk.
              return
          self.file.seek(chunkNumber * CHUNK_SIZE)
          self.file.write(chunkData)
          self.file.flush()
          self.sha1sums[chunkNumber] = sha.new(chunkData).digest()
  
          if not self.mask[chunkNumber]:
              self.nexus.increaseScore(who)
              self.mask[chunkNumber] = 1
              self.writeMaskFile()
              self.changes += 1
  
              if self.changes > self.maximumChangeCountBeforeMaskUpdate:
                  self.call.cancel()
                  self.sendMaskUpdate()
                  self.call = self.nexus.callLater(
                      self.maximumChangeCountBeforeMaskUpdate,
                      self.maybeUpdateMask)
  
              if not self.seed and not self.mask.countbits(0):
                  # we're done, let's let other people get at that file.
                  self.file.close()
                  os.rename(self.incompletePath.path,
                            self.fullPath.path)
                  self.file = self.fullPath.open()
                  self.maskfile.close()
                  os.unlink(self.maskfile.name)
  
              self.ui.updateHostMask(self.mask)