func()

in ssh/client_auth.go [398:493]
84 lines of code
21 McCabe index (conditional complexity)

func (cb KeyboardInteractiveChallenge) auth(session []byte, user string, c packetConn, rand io.Reader) (authResult, []string, error) {
	type initiateMsg struct {
		User       string `sshtype:"50"`
		Service    string
		Method     string
		Language   string
		Submethods string
	}

	if err := c.writePacket(Marshal(&initiateMsg{
		User:    user,
		Service: serviceSSH,
		Method:  "keyboard-interactive",
	})); err != nil {
		return authFailure, nil, err
	}

	for {
		packet, err := c.readPacket()
		if err != nil {
			return authFailure, nil, err
		}

		// like handleAuthResponse, but with less options.
		switch packet[0] {
		case msgUserAuthBanner:
			if err := handleBannerResponse(c, packet); err != nil {
				return authFailure, nil, err
			}
			continue
		case msgUserAuthInfoRequest:
			// OK
		case msgUserAuthFailure:
			var msg userAuthFailureMsg
			if err := Unmarshal(packet, &msg); err != nil {
				return authFailure, nil, err
			}
			if msg.PartialSuccess {
				return authPartialSuccess, msg.Methods, nil
			}
			return authFailure, msg.Methods, nil
		case msgUserAuthSuccess:
			return authSuccess, nil, nil
		default:
			return authFailure, nil, unexpectedMessageError(msgUserAuthInfoRequest, packet[0])
		}

		var msg userAuthInfoRequestMsg
		if err := Unmarshal(packet, &msg); err != nil {
			return authFailure, nil, err
		}

		// Manually unpack the prompt/echo pairs.
		rest := msg.Prompts
		var prompts []string
		var echos []bool
		for i := 0; i < int(msg.NumPrompts); i++ {
			prompt, r, ok := parseString(rest)
			if !ok || len(r) == 0 {
				return authFailure, nil, errors.New("ssh: prompt format error")
			}
			prompts = append(prompts, string(prompt))
			echos = append(echos, r[0] != 0)
			rest = r[1:]
		}

		if len(rest) != 0 {
			return authFailure, nil, errors.New("ssh: extra data following keyboard-interactive pairs")
		}

		answers, err := cb(msg.User, msg.Instruction, prompts, echos)
		if err != nil {
			return authFailure, nil, err
		}

		if len(answers) != len(prompts) {
			return authFailure, nil, fmt.Errorf("ssh: incorrect number of answers from keyboard-interactive callback %d (expected %d)", len(answers), len(prompts))
		}
		responseLength := 1 + 4
		for _, a := range answers {
			responseLength += stringLength(len(a))
		}
		serialized := make([]byte, responseLength)
		p := serialized
		p[0] = msgUserAuthInfoResponse
		p = p[1:]
		p = marshalUint32(p, uint32(len(answers)))
		for _, a := range answers {
			p = marshalString(p, []byte(a))
		}

		if err := c.writePacket(serialized); err != nil {
			return authFailure, nil, err
		}
	}
}