# File lib/net/ssh/authentication/agent/socket.rb, line 74
    def negotiate!
      # determine what type of agent we're communicating with
      type, body = send_and_wait(SSH2_AGENT_REQUEST_VERSION, :string, Transport::ServerVersion::PROTO_VERSION)

      if type == SSH2_AGENT_VERSION_RESPONSE
        raise AgentNotAvailable, "SSH2 agents are not yet supported"
      elsif type == SSH2_AGENT_FAILURE
        debug { "Unexpected response type==#{type}, this will be ignored" }
      elsif type != SSH_AGENT_RSA_IDENTITIES_ANSWER1 && type != SSH_AGENT_RSA_IDENTITIES_ANSWER2
        raise AgentNotAvailable, "unknown response from agent: #{type}, #{body.to_s.inspect}"
      end
    end