# File lib/net/ssh/proxy/command.rb, line 36
    def open(host, port)
      command_line = @command_line_template.gsub(/%(.)/) {
        case $1
        when 'h'
          host
        when 'p'
          port.to_s
        when '%'
          '%'
        else
          raise ArgumentError, "unknown key: #{$1}"
        end
      }
      begin
        io = IO.popen(command_line, "r+")
        if result = Net::SSH::Compat.io_select([io], nil, [io], 60)
          if result.last.any?
            raise "command failed"
          end
        else
          raise "command timed out"
        end
      rescue => e
        raise ConnectError, "#{e}: #{command_line}"
      end
      @command_line = command_line
      class << io
        def send(data, flag)
          write_nonblock(data)
        end

        def recv(size)
          read_nonblock(size)
        end
      end
      io
    end