Refactor VFS logic out of ResourceProvider plugin code.

PiperOrigin-RevId: 561302536
Change-Id: I952f9e76e85a7e3a111e0338f307378a6ff58197

src/engine/engine_resource.h

@@ -15,6 +15,8 @@
 #ifndef MUJOCO_SRC_ENGINE_ENGINE_RESOURCE_H_
 #define MUJOCO_SRC_ENGINE_ENGINE_RESOURCE_H_
 
+#include <stddef.h>
+
 #include <mujoco/mjexport.h>
 #include "engine/engine_plugin.h"
 
@@ -23,9 +25,8 @@ extern "C" {
 #endif
 
 // open the given resource; if the name doesn't have a prefix matching with a
-// resource provider, then the default_provider is used
-// if default_provider non-positive, then the OS filesystem is used
-MJAPI mjResource* mju_openResource(const char* name, int default_provider);
+// resource provider, then the OS filesystem is used
+MJAPI mjResource* mju_openResource(const char* name);
 
 // close the given resource; no-op if resource is NULL
 MJAPI void mju_closeResource(mjResource* resource);
@@ -37,11 +38,15 @@ MJAPI int mju_readResource(mjResource* resource, const void** buffer);
 // sets for a resource with a name partitioned as {dir}{filename}, the dir and ndir pointers
 MJAPI void mju_getResourceDir(mjResource* resource, const char** dir, int* ndir);
 
+// Returns > 0 if resource has been modified since last read, 0 if not, and < 0
+// if inconclusive
+MJAPI int mju_isModifiedResource(const mjResource* resource);
+
 // get the length of the dirname portion of a given path
 int mju_dirnamelen(const char* path);
 
 // read file into memory buffer (allocated here with mju_malloc)
-void* mju_fileToMemory(const char* filename, int* filesize);
+void* mju_fileToMemory(const char* filename, size_t* filesize);
 
 #ifdef __cplusplus
 }