# File lib/net/ftp.rb, line 398
    def retrbinary(cmd, blocksize, rest_offset = nil) # :yield: data
      synchronize do
        voidcmd("TYPE I")
        conn = transfercmd(cmd, rest_offset)
        loop do
          data = conn.read(blocksize)
          break if data == nil
          yield(data)
        end
        conn.close
        voidresp
      end
    end