MQTT TLS session resumption in C

Question

I'm using the Eclipse Paho MQTT C client to connect to a mosquitto broker with TLS using openssl. This is part of my code:

MQTTClient client;
MQTTClient_connectOptions conn_opts = MQTTClient_connectOptions_initializer;
MQTTClient_message pubmsg = MQTTClient_message_initializer;
MQTTClient_SSLOptions sslOptions = MQTTClient_SSLOptions_initializer;
MQTTClient_deliveryToken token;

int rc;

MQTTClient_create(&client, ADDRESS, CLIENTID,
    MQTTCLIENT_PERSISTENCE_NONE, NULL);

conn_opts.keepAliveInterval = 20;
conn_opts.cleansession = 1;

/* TLS */
sslOptions.enableServerCertAuth = 0;
sslOptions.trustStore = "ca_rsp.crt";
conn_opts.ssl = &sslOptions;


if ((rc = MQTTClient_connect(client, &conn_opts)) != MQTTCLIENT_SUCCESS)
{
    printf("Failed to connect, return code %d\n", rc);
    exit(EXIT_FAILURE);
}

Actually every time I reconnect to the broker, the client make a full handshake. I would like to use the TLS session resumption to reduce the overhead. I've search around the web but I haven't found any example of how o implement that in a simple way.

Any suggestion?

Thanks

hardillb hardillb · Accepted Answer · 2017-10-11T18:22:49

This came up recently on the mosquitto dev mailing list here https://dev.eclipse.org/mhonarc/lists/mosquitto-dev/msg01606.html

The following excerpt seams to imply it may not be possible just yet with the code as it is.

How can I use Mosquitto / OpenSSL C API to leverage session tickets in an MQTT C client ?

Not at the moment, this needs code changes that are a bit more involved - it looks like we need to use SSL_set_session() to apply a saved session to your client and SSL_CTX_sess_set_new_cb() to save the session out.

Is there any way I could persist session tickets on the clients, so they would remain valid across reboot ?

With the above changes, yes.

MQTT TLS session resumption in C

3 Answers