Add DTLS support to MQTT-SN client #348

embhorn · 2023-08-25T21:38:15Z

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

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=/<path_to_repo>/wolfssl/certs/server-cert.pem
+#DtlsPrivKey=/etc/ssl/private/privkey.pem
+DtlsPrivKey=/<path_to_repo>/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

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

embhorn · 2023-08-28T14:05:55Z

examples/mqttnet.c

+    #if defined(WOLFMQTT_SN) && defined(WOLFSSL_DTLS)
+                if (wolfSSL_dtls(mqttCtx->client.tls.ssl)) {
+                    break;
+                }
+    #endif


I do not like this, but during the handshake, wolfSSL calls read with a max size of 1900b, never intending to fully fill the buffer. So I needed a way to break out of the loop. I am very open to suggestions here.

This just means you got some data and instead of waiting for "all" data you just break out for DTLS. Seems fine to me. However you can likely do this for the TLS case too...

lealem47

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

embhorn · 2023-08-30T13:34:00Z

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.

examples/mqttexample.c

dgarske · 2023-08-31T20:43:27Z

examples/mqttnet.c

+    #if defined(WOLFMQTT_SN) && defined(WOLFSSL_DTLS)
+                if (wolfSSL_dtls(mqttCtx->client.tls.ssl)) {
+                    break;
+                }
+    #endif


This just means you got some data and instead of waiting for "all" data you just break out for DTLS. Seems fine to me. However you can likely do this for the TLS case too...

dgarske · 2023-08-31T20:44:12Z

src/mqtt_packet.c

-            /* Read first 2 bytes using MSG_PEEK */
-            rc = MqttSocket_Peek(client, rx_buf, 2, timeout_ms);
+            /* Read first 2 bytes */
+            if (client->flags & MQTT_CLIENT_FLAG_IS_TLS) {


Should we have a flag for DTLS? Seems like you could use this flag for the mqtt_socket.c TLS method?

dgarske · 2023-09-01T16:59:17Z

src/mqtt_socket.c

@@ -359,7 +359,21 @@ int MqttSocket_Peek(MqttClient *client, byte* buf, int buf_len, int timeout_ms)

    return rc;
 }
+
+#if defined(ENABLE_MQTT_TLS) && defined(WOLFSSL_DTLS)
+void MqttSocket_SetDTLS(MqttClient *client, int value)


I would prefer the API to be in mqtt_client.c and named MqttClient_SetFlags API that takes in uint32_t of enum MqttClientFlags values as an argument.

Something like:

word32 MqttClient_SetFlags(MqttClient *client, word32 mask, word32 flags) { if (client != NULL) { client->flags &= ~mask; client->flags |= flags; return client->flags; } return 0; }

This is multi-purpose because you can set or clear any flags and return the final state.

dgarske · 2023-09-01T17:58:03Z

src/mqtt_client.c

+#ifdef WOLFMQTT_MULTITHREAD
+        wm_SemUnlock(&client->lockClient);
+#endif
+        return client->flags;


Please get the final flags before unlock.

embhorn · 2023-09-01T19:23:18Z

Ready for merge!

embhorn self-assigned this Aug 25, 2023

embhorn force-pushed the sn-dtls branch 2 times, most recently from 5ff973a to f262a6b Compare August 28, 2023 13:43

embhorn commented Aug 28, 2023

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embhorn requested a review from lealem47 August 28, 2023 15:50

embhorn assigned lealem47 Aug 29, 2023

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embhorn dismissed lealem47’s stale review via 365747a August 30, 2023 13:32

embhorn force-pushed the sn-dtls branch from f262a6b to 365747a Compare August 30, 2023 13:32

embhorn requested a review from dgarske August 30, 2023 13:34

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embhorn force-pushed the sn-dtls branch from 365747a to 4a5a446 Compare September 1, 2023 14:19

embhorn requested a review from dgarske September 1, 2023 14:20

embhorn force-pushed the sn-dtls branch from 28577ae to e5d209c Compare September 1, 2023 14:29

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embhorn force-pushed the sn-dtls branch from e5d209c to 5e0b638 Compare September 1, 2023 17:23

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embhorn dismissed dgarske’s stale review via 0be1608 September 1, 2023 17:54

embhorn force-pushed the sn-dtls branch from 5e0b638 to 0be1608 Compare September 1, 2023 17:54

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embhorn force-pushed the sn-dtls branch from 0be1608 to d5ec692 Compare September 1, 2023 18:01

Add DTLS support to MQTT-SN client

922b072

embhorn force-pushed the sn-dtls branch from d5ec692 to 922b072 Compare September 1, 2023 18:14

dgarske approved these changes Sep 1, 2023

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embhorn assigned dgarske Sep 1, 2023

embhorn assigned lealem47 and unassigned embhorn and dgarske Sep 1, 2023

lealem47 merged commit d5eca1b into wolfSSL:master Sep 1, 2023
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embhorn mentioned this pull request Oct 3, 2023

Support for DTLS? #275

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Add DTLS support to MQTT-SN client #348

Add DTLS support to MQTT-SN client #348

embhorn commented Aug 25, 2023 •

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embhorn commented Sep 1, 2023

Add DTLS support to MQTT-SN client #348

Add DTLS support to MQTT-SN client #348

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