rg_utils: Added rg_json_fixup to fix json errors

In order to provide a better user experience, rg_json_fixup strips trailing commas. In the future it will also strip comments.

NOTE: The way it finds trailing commas is certainly naive and could break things, so we should always try to parse the raw string before falling back to rg_json_fixup!

components/retro-go/rg_gui.c

@@ -118,11 +118,13 @@ bool rg_gui_set_theme(const char *theme_name)
     if (theme_name && theme_name[0])
     {
         snprintf(pathbuf, RG_PATH_MAX, "%s/%s/theme.json", RG_BASE_PATH_THEMES, theme_name);
-        void *data;
+        char *data;
         size_t data_len;
-        if (rg_storage_read_file(pathbuf, &data, &data_len, 0))
+        if (rg_storage_read_file(pathbuf, (void **)&data, &data_len, 0))
         {
-            new_theme = cJSON_Parse((char *)data);
+            new_theme = cJSON_Parse(data);
+            if (!new_theme) // Parse failure, clean the markup and try again
+                new_theme = cJSON_Parse(rg_json_fixup(data));
             free(data);
         }
         if (!new_theme)

components/retro-go/rg_settings.c

@@ -31,12 +31,14 @@ static cJSON *json_root(const char *name, bool set_dirty)
         cJSON_AddStringToObject(branch, "namespace", name);
         cJSON_AddNumberToObject(branch, "changed", 0);
 
-        void *data; size_t data_len;
+        char *data; size_t data_len;
         char pathbuf[RG_PATH_MAX];
         snprintf(pathbuf, RG_PATH_MAX, "%s/%s.json", RG_BASE_PATH_CONFIG, name);
-        if (rg_storage_read_file(pathbuf, &data, &data_len, 0))
+        if (rg_storage_read_file(pathbuf, (void **)&data, &data_len, 0))
         {
-            cJSON *values = cJSON_Parse((char *)data);
+            cJSON *values = cJSON_Parse(data);
+            if (!values) // Parse failure, clean the markup and try again
+                values = cJSON_Parse(rg_json_fixup(data));
             if (values)
             {
                 RG_LOGI("Config file loaded: '%s'", pathbuf);

components/retro-go/rg_utils.c

@@ -29,6 +29,25 @@ char *rg_strtoupper(char *str)
     return str;
 }
 
+char *rg_json_fixup(char *json)
+{
+    // Strip trailing commas, eg [,1,2,3] {"a":1,}
+    for (char *ptr = json, *prev = ptr; ptr && *ptr; ++ptr)
+    {
+        if ((*ptr == '}' || *ptr == ']' || *ptr == '{' || *ptr == '[' || *ptr == ',') && *prev == ',')
+        {
+            RG_LOGW("Found trailing comma at pos %d", (int)(ptr - json));
+            *prev = ' ';
+        }
+        if (*ptr != '\t' && *ptr != '\n' && *ptr != ' ')
+            prev = ptr;
+    }
+
+    // TODO: We should also strip C-style comments!
+
+    return json;
+}
+
 const char *rg_dirname(const char *path)
 {
     static char buffer[100];

components/retro-go/rg_utils.h

@@ -40,23 +40,31 @@
 #define PRINTF_BINARY_32 PRINTF_BINARY_16 " " PRINTF_BINARY_16
 #define PRINTF_BINVAL_32(i) PRINTF_BINVAL_16((i) >> 16), PRINTF_BINVAL_16(i)
 
+/* String functions */
+
 /**
  * both functions give you an allocation of strlen(str) + 1 valid for the lifetime of the application
  * they cannot be freed. unique avoids keeping multiple copies of an identical string (eg a path)
  * Things like unique_string("abc") == unique_string("abc") are guaranteed to be true
 */
 const char *rg_const_string(const char *str);
 const char *rg_unique_string(const char *str);
-
 char *rg_strtolower(char *str);
 char *rg_strtoupper(char *str);
+char *rg_json_fixup(char *json);
+
+/* Paths functions */
 const char *rg_dirname(const char *path);
 const char *rg_basename(const char *path);
 const char *rg_extension(const char *filename);
 bool rg_extension_match(const char *filename, const char *extensions);
 const char *rg_relpath(const char *path);
+
+/* Hashing */
 uint32_t rg_crc32(uint32_t crc, const uint8_t *buf, size_t len);
 uint32_t rg_hash(const char *buf, size_t len);
+
+/* Misc */
 void *rg_alloc(size_t size, uint32_t caps);
 // rg_usleep behaves like usleep in libc: it will sleep for *at least* `us` microseconds, but possibly more
 // due to scheduling. You should use rg_task_delay() if you don't need more than 10-15ms granularity.