added readme and config example

config example might missing config examples... ?! :D

README.md

@@ -0,0 +1,7 @@
+## build
+```bash
+apt install libmosquitto-dev
+cp config.h.example config.h
+# edit config.h
+make
+```

config.h.example

@@ -0,0 +1,2 @@
+#define MQTT_USER1 "<user>"
+#define MQTT_PASS "<pass>"

mqtt.c

@@ -32,6 +32,7 @@ struct mosquitto *connectMqtt(char *user, char *pass, void (*messageCallback)(st
         return NULL;
     }
 
+    // FIXME: I am hard coded :(
     err = mosquitto_connect(mqtt, "openhab.sugarland.lan", 1883, 10);
     if (err)
     {

readref.c

@@ -24,6 +24,15 @@ const int MQTT_RREF_REQUEST_MIN_LENGTH = MQTT_RREF_REQUEST_LENGTH_ID + MQTT_RREF
 int xPlaneSocket;
 struct mosquitto *mqtt;
 
+struct valueCacheElement
+{
+    float value;
+    bool force;
+};
+
+struct valueCacheElement *valueCache = NULL;
+int valueCacheCount = 0;
+
 #define XPLANE_RREF_MAX_LENGTH 400
 struct dref_struct_in
 {
@@ -49,7 +58,8 @@ int *strtoint(char *in, size_t start, size_t n)
         return NULL;
     }
 
-    for (int i = 0; i < n; i++) {
+    for (int i = 0; i < n; i++)
+    {
         int position = offset - i;
         if (in[position] >= '0' && in[position] <= '9')
         {
@@ -64,35 +74,57 @@ int *strtoint(char *in, size_t start, size_t n)
     return ret;
 }
 
-void onMessage(struct mosquitto *mqtt, void *obj, const struct mosquitto_message *message)
+void requestRrefFromXPlane(const struct mosquitto_message *message)
 {
-    int *id, *frequency;
-    char rref[XPLANE_RREF_MAX_LENGTH];
+    int *index, *frequency;
 
-    printf("Received message %.*s on topic %s\n", message->payloadlen, (char *)message->payload, message->topic);
-
-    if (strcmp(message->topic, "/xplane/meta/rref") == 0)
-    {
-        printf("found rref request\n");
     if (message->payloadlen >= MQTT_RREF_REQUEST_MIN_LENGTH)
     {
-            id = strtoint(message->payload, MQTT_RREF_REQUEST_START_ID, MQTT_RREF_REQUEST_LENGTH_ID);
+        index = strtoint(message->payload, MQTT_RREF_REQUEST_START_ID, MQTT_RREF_REQUEST_LENGTH_ID);
         frequency = strtoint(message->payload, MQTT_RREF_REQUEST_START_FREQ, MQTT_RREF_REQUEST_LENGTH_FREQ);
 
-            if (id == NULL || frequency == NULL) {
+        if (index == NULL || frequency == NULL)
+        {
             return;
         }
 
+        if (*index < valueCacheCount)
+        {
+            valueCache[*index].force = true;
+        }
+
         // prepare struct to send, make sure padding is with NULL bytes
         struct dref_struct_in drefToRead = {
             .dref_freq = *frequency,
-                .dref_sender_index = *id
-            };
+            .dref_sender_index = *index};
         memset(drefToRead.dref_string, 0, sizeof(drefToRead.dref_string));
         strncpy(drefToRead.dref_string, &((char *)message->payload)[MQTT_RREF_REQUEST_START_RREF], message->payloadlen - MQTT_RREF_REQUEST_START_RREF);
 
         sendToXPlane(xPlaneSocket, DEST_SERVER, DEST_PORT, "RREF", (char *)&drefToRead, sizeof(drefToRead));
     }
+}
+
+void sendCommandToXPlane(const struct mosquitto_message *message)
+{
+    char *command;
+
+    if (message->payloadlen > 0)
+    {
+        sendToXPlane(xPlaneSocket, DEST_SERVER, DEST_PORT, "CMND", (char *)message->payload, message->payloadlen);
+    }
+}
+
+void onMessage(struct mosquitto *mqtt, void *obj, const struct mosquitto_message *message)
+{
+    printf("Received message %.*s on topic %s\n", message->payloadlen, (char *)message->payload, message->topic);
+
+    if (strcmp(message->topic, "/xplane/meta/rref") == 0)
+    {
+        requestRrefFromXPlane(message);
+    }
+    else if (strcmp(message->topic, "/xplane/meta/cmnd") == 0)
+    {
+        sendCommandToXPlane(message);
     }
     else
     {
@@ -110,7 +142,7 @@ int main()
     }
 
     // mqtt
-    mqtt = connectMqtt(MQTT_USER, MQTT_PASS, onMessage);
+    mqtt = connectMqtt(MQTT_USER1, MQTT_PASS, onMessage);
     if (mqtt == NULL)
     {
         exit(EXIT_FAILURE);
@@ -151,12 +183,37 @@ int main()
                         struct dref_struct_out drefRead;
                         memcpy(&drefRead, &payload[i], sizeof(struct dref_struct_out));
 
+                        // add new element to array
+                        if (valueCache == NULL)
+                        {
+                            valueCacheCount = drefRead.dref_sender_index + 10;
+                            valueCache = calloc(valueCacheCount, sizeof(struct valueCacheElement));
+                        }
+                        else if (drefRead.dref_sender_index >= valueCacheCount)
+                        {
+                            valueCacheCount = drefRead.dref_sender_index + 10;
+                            valueCache = reallocarray(valueCache, valueCacheCount, sizeof(struct valueCacheElement));
+                        }
+                        else
+                        {
+                            // size of array is sufficient
+                        }
+
+                        if (valueCache[drefRead.dref_sender_index].force || valueCache[drefRead.dref_sender_index].value != drefRead.dref_flt_value)
+                        {
+                            valueCache[drefRead.dref_sender_index].value = drefRead.dref_flt_value;
                             printf("%d: %f\n", drefRead.dref_sender_index, drefRead.dref_flt_value);
 
                             sprintf(mqttTopic, "/xplane/rref/%d", drefRead.dref_sender_index);
                             sprintf(mqttPayload, "%f", drefRead.dref_flt_value);
 
                             sendMqtt(mqtt, mqttTopic, mqttPayload, strlen(mqttPayload));
+                            valueCache[drefRead.dref_sender_index].force = false;
+                        }
+                        else
+                        {
+                            // neither changed nor forced
+                        }
                     }
                 }
                 else
@@ -174,7 +231,7 @@ int main()
             exit(EXIT_FAILURE);
         }
 
-        mosquitto_loop(mqtt, 100, 1);
+        mosquitto_loop(mqtt, 0, 1);
     }
 
     // bye bye (and no, I don't care about error anymore; I'll exit anyway?!)