MqttClientConnectionConfig MqttClientConnectionConfigBuilder::Build()

in source/iot/MqttClient.cpp [300:381]
67 lines of code
14 McCabe index (conditional complexity)

        MqttClientConnectionConfig MqttClientConnectionConfigBuilder::Build() noexcept
        {
            if (m_lastError != 0)
            {
                return MqttClientConnectionConfig::CreateInvalid(m_lastError);
            }

            uint16_t port = m_portOverride;

            if (!m_portOverride)
            {
                if (m_websocketConfig || Crt::Io::TlsContextOptions::IsAlpnSupported())
                {
                    port = 443;
                }
                else
                {
                    port = 8883;
                }
            }

            if (port == 443 && !m_websocketConfig && Crt::Io::TlsContextOptions::IsAlpnSupported())
            {
                if (!m_contextOptions.SetAlpnList("x-amzn-mqtt-ca"))
                {
                    return MqttClientConnectionConfig::CreateInvalid(m_contextOptions.LastError());
                }
            }

            // add metrics string to username (if metrics enabled)
            // note: username isn't currently exposed to users via builder, so it's always empty
            Crt::String username;
            if (m_enableMetricsCollection)
            {
                username += "?SDK=";
                username += m_sdkName;
                username += "&Version=";
                username += m_sdkVersion;
            }

            auto tlsContext = Crt::Io::TlsContext(m_contextOptions, Crt::Io::TlsMode::CLIENT, m_allocator);
            if (!tlsContext)
            {
                return MqttClientConnectionConfig::CreateInvalid(tlsContext.GetInitializationError());
            }

            if (!m_websocketConfig)
            {
                auto config = MqttClientConnectionConfig(
                    m_endpoint, port, m_socketOptions, std::move(tlsContext), m_proxyOptions);
                config.m_username = username;
                return config;
            }

            auto websocketConfig = m_websocketConfig.value();
            auto signerTransform = [websocketConfig](
                                       std::shared_ptr<Crt::Http::HttpRequest> req,
                                       const Crt::Mqtt::OnWebSocketHandshakeInterceptComplete &onComplete) {
                // it is only a very happy coincidence that these function signatures match. This is the callback
                // for signing to be complete. It invokes the callback for websocket handshake to be complete.
                auto signingComplete =
                    [onComplete](const std::shared_ptr<Aws::Crt::Http::HttpRequest> &req1, int errorCode) {
                        onComplete(req1, errorCode);
                    };

                auto signerConfig = websocketConfig.CreateSigningConfigCb();

                websocketConfig.Signer->SignRequest(req, *signerConfig, signingComplete);
            };

            bool useWebsocketProxyOptions = m_websocketConfig->ProxyOptions.has_value() && !m_proxyOptions.has_value();

            auto config = MqttClientConnectionConfig(
                m_endpoint,
                port,
                m_socketOptions,
                std::move(tlsContext),
                signerTransform,
                useWebsocketProxyOptions ? m_websocketConfig->ProxyOptions : m_proxyOptions);
            config.m_username = username;
            return config;
        }