add: OPTIONS method support

add: relay tag endpoint

endpoints/api_v1_relays_tag_STR.c

@@ -0,0 +1,57 @@
+#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_tag_STR_GET(struct mg_connection *c, endpoint_args_t *args, struct http_message *hm)
+{
+    (void)hm;
+
+    int tag_id = tag_get_id(args[0].value.v_str);
+    int *relays_ids = junction_tag_get_relays_for_tag_id(tag_id);
+    if(relays_ids == 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, "[]");
+        return;
+    }
+
+    cJSON *json = cJSON_CreateArray();
+
+    for(int i = 0; relays_ids[i] != 0; ++i)
+    {
+        relay_t* relay = relay_get_by_id(relays_ids[i]);
+
+        if(!relay)
+        {
+            continue;
+        }
+        cJSON *json_relay = relay_to_json(relay);
+
+        cJSON_AddItemToArray(json, json_relay);
+
+        relay_free(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);
+    free(relays_ids);
+}