Implement generating device ID

iot/Makefile

@@ -1,3 +1,3 @@
-all: main.c mqtt.c temperature.c
-	$(CC) -lmosquitto -lpthread -li2c main.c mqtt.c temperature.c
+all: main.c mqtt.c temperature.c device_id.c
+	$(CC) -lmosquitto -lpthread -li2c main.c mqtt.c temperature.c device_id.c
 

iot/device_id.c

@@ -0,0 +1,46 @@
+#include <stdlib.h>
+#include <stdio.h>
+
+#include "device_id.h"
+
+#define DEVICE_ID_SIZE 5
+
+char *get_device_id(void)
+{
+	FILE *file = fopen("device_id.txt", "r");
+
+	if (!file) {
+		char *device_id = generate_device_id();
+
+		file = fopen("device_id.txt", "w");
+		fprintf(file, "%s", device_id);
+		fclose(file);
+
+		return device_id;
+	}
+
+	char *device_id = malloc(DEVICE_ID_SIZE + 1);
+	fgets(device_id, DEVICE_ID_SIZE + 1, file);
+	fclose(file);
+
+	return device_id;
+}
+
+char *generate_device_id(void)
+{
+	char *device_id = malloc(DEVICE_ID_SIZE + 1);
+
+	for (int i = 0; i < DEVICE_ID_SIZE; i++) {
+		device_id[i] = 'A' + (random() % 26);
+	}
+
+	device_id[DEVICE_ID_SIZE] = '\0';
+
+	return device_id;
+}
+
+void destroy_device_id(char *device_id)
+{
+	free(device_id);
+}
+

iot/device_id.h

@@ -0,0 +1,6 @@
+char *get_device_id(void);
+
+char *generate_device_id(void);
+
+void destroy_device_id(char *device_id);
+

iot/main.c

@@ -4,12 +4,18 @@
 #include <stdbool.h>
 #include <string.h>
 #include <stdio.h>
+#include <time.h>
 
 #include "mqtt.h"
 #include "temperature.h"
+#include "device_id.h"
 
 void *watch_temperature(void *arg)
 {
+	char *device_id = get_device_id();
+
+	printf("Device ID: %s\n", device_id);
+
 	temperature_handle_t temp_handle = init_temperature();
 
 	get_temperature(temp_handle);
@@ -20,7 +26,7 @@ void *watch_temperature(void *arg)
 		char *str = malloc(snprintf(NULL, 0, "%lf", temperature) + 1);
 		sprintf(str, "%lf", temperature);
 
-		mqtt_send_message("/temperature", str);
+		mqtt_send_message("temperature", str);
 
 		free(str);
 
@@ -29,6 +35,8 @@ void *watch_temperature(void *arg)
 		sleep(60);
 	}
 
+	destroy_device_id(device_id);
+
 	return NULL;
 }
 
@@ -40,6 +48,8 @@ void mqtt_on_connect(void)
 
 int main(void)
 {
+	srand(time(NULL));
+
 	init_mqtt();
 
 	return EXIT_SUCCESS;