Add DTLS support to MQTT-SN client

[embhorn]

Tested with mosquitto as broker, https://github.com/eclipse/paho.mqtt-sn.embedded-c as gateway.

1. To use with local mosquitto broker, edit MQTTSNGateway/gateway.conf. Also set paths to DTLS cert / key.

   
   -BrokerName=mqtt.eclipseprojects.io
   +BrokerName=localhost

...

-DtlsCertsKey=/etc/ssl/certs/gateway.pem -DtlsPrivKey=/etc/ssl/private/privkey.pem +#DtlsCertsKey=/etc/ssl/certs/gateway.pem +DtlsCertsKey=//wolfssl/certs/server-cert.pem +#DtlsPrivKey=/etc/ssl/private/privkey.pem +DtlsPrivKey=//wolfssl/certs/server-key.pem

* I had to fix a bug in the gateway (could be related to the openssl or compiler version):

diff --git a/MQTTSNGateway/src/linux/dtls/SensorNetwork.cpp b/MQTTSNGateway/src/linux/dtls/SensorNetwork.cpp index 3f2dcf3..363d0ba 100644 --- a/MQTTSNGateway/src/linux/dtls/SensorNetwork.cpp +++ b/MQTTSNGateway/src/linux/dtls/SensorNetwork.cpp @@ -308,7 +308,7 @@ Connections::~Connections() { for (int i = 0; i < _numfds; i++) {

• if (_ssls[i] > 0)

• if (_ssls[i] > (SSL *)0) { SSL_shutdown(_ssls[i]); SSL_free(_ssls[i]); @@ -416,7 +416,7 @@ void Connections::close(int index) } }

• if (ssl > 0)

• if (ssl > (SSL *)0) { _numfds--; SSL_shutdown(ssl);

• Build gateway with DTLS: <gateway-folder>/MQTTSNGateway$ ./build.sh dtls

2. Build wolfSSL with DTLS: ./configure --enable-dtls && make && sudo make install
3. Build wolfMQTT with SN support: ./configure --enable-sn && make
4. Run the broker: mosquitto
5. Run the gateway: <gateway-folder>/MQTTSNGateway$ ./bin/MQTT-SNGateway
6. To run the wolfMQTT sn-client example with DTLS: ./examples/sn-client/sn-client -t

[embhorn]

Tested and working. Perhaps add some of the PR notes into the SN example section of the README

I added a new README for the MQTT-SN examples. It was getting pretty long, so makes sense to move it.

[embhorn]

Ready for merge!