fix timeout event lead to OS error

Author: LukasKarel

connectivity/netsocket/include/netsocket/DTLSSocketWrapper.h

@@ -40,6 +40,14 @@ class DTLSSocketWrapper : public TLSSocketWrapper {
      * @param control      Transport control mode. See @ref control_transport.
      */
     DTLSSocketWrapper(Socket *transport, const char *hostname = NULL, control_transport control = TRANSPORT_CONNECT_AND_CLOSE);
+
+    /** Destroy a socket wrapper.
+     *
+     *  Closes socket wrapper if the socket wrapper is still open.
+     */
+    ~DTLSSocketWrapper();
+
+    nsapi_error_t close() override;
 private:
     static void timing_set_delay(void *ctx, uint32_t int_ms, uint32_t fin_ms);
     static int timing_get_delay(void *ctx);

connectivity/netsocket/source/DTLSSocketWrapper.cpp

@@ -36,6 +36,10 @@ DTLSSocketWrapper::DTLSSocketWrapper(Socket *transport, const char *hostname, co
 #endif /* !defined(MBEDTLS_SSL_CONF_SET_TIMER) && !defined(MBEDTLS_SSL_CONF_GET_TIMER) */
 }
 
+DTLSSocketWrapper::~DTLSSocketWrapper() {
+    close();
+}
+
 void DTLSSocketWrapper::timing_set_delay(void *ctx, uint32_t int_ms, uint32_t fin_ms)
 {
     DTLSSocketWrapper *context = static_cast<DTLSSocketWrapper *>(ctx);
@@ -74,6 +78,15 @@ int DTLSSocketWrapper::timing_get_delay(void *ctx)
     }
 }
 
+nsapi_error_t DTLSSocketWrapper::close() {
+    if (_timer_event_id != 0) {
+        mbed::mbed_event_queue()->cancel(_timer_event_id);
+        _timer_event_id = 0;
+    }
+
+    return TLSSocketWrapper::close();
+}
+
 void DTLSSocketWrapper::timer_event(void)
 {
     _timer_expired = true;