add: relay endpoint

fix: discovery invalid read

endpoints/api_v1_relays.c

@@ -0,0 +1,40 @@
+#include <cJSON.h>
+#include <constants.h>
+#include <endpoints/api_v1_relays.h>
+#include <logger.h>
+#include <models/junction_tag.h>
+#include <models/relay.h>
+#include <models/tag.h>
+
+void
+api_v1_relays_GET(struct mg_connection *c, endpoint_args_t *args, struct http_message *hm)
+{
+    (void)args;
+    (void)hm;
+    relay_t** all_relays = relay_get_all();
+
+    cJSON *json = cJSON_CreateArray();
+
+    for(int i = 0; all_relays[i] != NULL; ++i)
+    {
+        cJSON *json_relay = relay_to_json(all_relays[i]);
+
+        cJSON_AddItemToArray(json, json_relay);
+    }
+
+    char *json_str = cJSON_Print(json);
+    if (json_str == NULL)
+    {
+        LOG_ERROR("failed to print relays json\n");
+        mg_send_head(c, 500, 2, "Content-Type: application/json\r\n" STANDARD_HEADERS);
+        mg_printf(c, "[]");
+    }
+    else
+    {
+        mg_send_head(c, 200, strlen(json_str), "Content-Type: application/json\r\n" STANDARD_HEADERS);
+        mg_printf(c, "%s", json_str);
+        free(json_str);
+    }
+    cJSON_Delete(json);
+    relay_free_list(all_relays);
+}