Problem with connection to AWS IoT Broker with TLS with ALPN

[rkalicinski]

I tried to connect to AWS IoT Broker using mqtt_cpp. AWS requires ALPN to be configured on TLS but mqtt_cpp does not support it directly so I needed to use native OpenSSL function to set it up:

    auto c = MQTT_NS::make_tls_sync_client(ioc, "{AWS host}", 443); 
    static const unsigned char protos[5] = {4, 'm','q','t','t'};
    auto res = SSL_CTX_set_alpn_protos(c->get_ssl_context().native_handle(), protos, 5);
    c->connect();

Unfortunately connection does not succeed and end up with "End of file".
What could be missing here?
Additionally, I'm limited to C++14 so cannot use asyc_mqtt instead.

[redboltz]

I don't know much about AWS IoT Broker, but https://github.com/redboltz/mqtt_cpp/blob/master/example/tls_client_with_sni.cpp could help you.

    auto connect =
        [&] {
            // create custom socket
            auto stream =
                std::make_shared<
                    MQTT_NS::tcp_endpoint<
                        MQTT_NS::tls::stream<boost::asio::ip::tcp::socket>,
                        MQTT_NS::strand
                    >
            >(ioc, c->get_ssl_context());

            if (!SSL_set_tlsext_host_name(MQTT_NS::any_cast<SSL*>(stream->native_handle()), host.c_str())) {
                std::cout << "SSL_set_tlsext_host_name return false" << std::endl;
                return false;
            }
            c->connect(MQTT_NS::force_move(stream));
            return true;
        };

FYI: (I understand that you are limitted to C++14)

Doing custom setting for TLS layer is one of complecated part of mqtt_cpp. There is no way to improve it because mqtt_cpp too much holds underlying layters. This is one reason of I started develop async_mqtt.
Here is async_mqtt layer model https://github.com/redboltz/async_mqtt/blob/doc/tutorial/create_endpoint.adoc

[rkalicinski]

@redboltz Thank you for Your kind asist. I confirm that Your hint helped and now connection works like a charm :)

[redboltz]

@rkalicinski you are welcome :)