Partial roll back VFS refactor due internal breakages

PiperOrigin-RevId: 862210191
Change-Id: Ia15a345a267bcef4b593d507d54f1668da0c0611

src/user/user_vfs.h

@@ -17,115 +17,45 @@
 #ifndef MUJOCO_SRC_USER_USER_VFS_H_
 #define MUJOCO_SRC_USER_USER_VFS_H_
 
-#include <functional>
-#include <memory>
-#include <mutex>
-#include <string>
-#include <string_view>
-#include <unordered_map>
+#include <stddef.h>
 
+#include <mujoco/mjexport.h>
 #include <mujoco/mjmodel.h>
-#include <mujoco/mujoco.h>
-#include "user/user_util.h"
+#include <mujoco/mjplugin.h>
 
-namespace mujoco::user {
+#ifdef __cplusplus
+extern "C" {
+#endif
 
-// Underlying Virtual File System implementation for opaque mjVFS struct.
-//
-// This class owns and manages all the mjResource instances that are created
-// using the mju_openResource. Its main job is to find the correct
-// mjpResourceProvider to handle the mju open/read/close operations. It does
-// this by "mounting" mjpResourceProviders at specific paths such that any
-// operation within that path will be handled by the mjpResourceProvider.
-//
-// Mounting can be done explicitly (using mj_mountVFS) or implicitly (using
-// mjp_registerResourceProvider). If no provider is found for a given path,
-// then a "default" provider is used that uses normal C file operations to
-// open/read/close files.
-//
-// To support legacy use-cases (where the VFS is an optional argument), a
-// "self-destruct" mode can be configured so that a temporary VFS instance can
-// be created with a lifetime tied to the opened mjResource instance.
-//
-// This class itself is thread-safe, but it makes no guarantees about the
-// thread-safety of the underlying mjResourceProviders.
-class VFS {
- public:
-  explicit VFS(mjVFS* vfs);
-  ~VFS();
+// Initialize an empty VFS, mj_deleteVFS must be called to deallocate the VFS
+MJAPI void mj_defaultVFS(mjVFS* vfs);
 
-  VFS(const VFS&) = delete;
-  VFS& operator=(const VFS&) = delete;
+// add file to VFS, return 0: success, 2: repeated name, -1: not found on disk
+MJAPI int mj_addFileVFS(mjVFS* vfs, const char* directory, const char* filename);
 
-  // Status codes for VFS operations. Values are based on the mj_VFS APIs.
-  enum Status {
-    kSuccess = 0,
-    kFailedToLoad = -1,
-    kFailedToRead = -1,
-    kNotFound = -1,
-    kRepeatedName = 2,
-    kInvalidVfs = -1,
-    kInvalidResource = -1,
-    kInvalidResourceProvider = -1,
-  };
+// add file from buffer into VFS, return 0: success, 2: repeated name, -1: failed to load
+MJAPI int mj_addBufferVFS(mjVFS* vfs, const char* filename, const void* buffer, int nbuffer);
 
-  // Opens a mjResource for the given path, or nullptr on error. If successful,
-  // will invoke the 'open' callback for the mjpResourceProvider associated with
-  // the path/dir.
-  mjResource* Open(const char* dir, const char* name);
+// mount a ResourceProvider to handle file operations under the given path; return 0: success,
+// 2: repeated name, -1: invalid resource provider
+MJAPI int mj_mountVFS(mjVFS* vfs, const char* filepath, const mjpResourceProvider* provider);
 
-  // Sets `buffer` to the contents of the resource and returns the number of
-  // bytes of the content. This is done by invoking the 'read' callback for the
-  // mjpResourceProvider associated with the resource. Returns -1 on error.
-  int Read(mjResource* resource, const void** buffer);
+// unmount a previously mounted ResourceProvider; return 0: success, -1: not found in VFS
+MJAPI int mj_unmountVFS(mjVFS* vfs, const char* filename);
 
-  // Closes the resource by invoking the 'close' callback for the
-  // mjpResourceProvider associated with the resource.
-  Status Close(mjResource* resource);
+// return file index in VFS, or -1 if not found in VFS
+MJAPI int mj_findFileVFS(const mjVFS* vfs, const char* filename);
 
-  // Mounts a ResourceProvider at the given path. All subsequent operations
-  // under `path` will be delegated to the `provider` until it is unmounted.
-  Status Mount(const FilePath& path, const mjpResourceProvider* provider);
+// delete file from VFS, return 0: success, -1: not found in VFS
+MJAPI int mj_deleteFileVFS(mjVFS* vfs, const char* filename);
 
-  // Unmounts the ResourceProvider from the given path.
-  Status Unmount(const FilePath& path);
+// delete all files from VFS
+MJAPI void mj_deleteVFS(mjVFS* vfs);
 
-  // Sets a destructor to be called when the VFS has no more open resources.
-  // Assumes that `destructor` will delete `this`.
-  //
-  // This is useful for when you want to create a temporary VFS instance with
-  // a lifetime tied to a single mjResource to be opened. The `destructor`
-  // should be set to `delete this` and any other cleanup that needs to happen.
-  void SetToSelfDestruct(std::function<void(mjVFS*)> destructor);
+#ifdef __cplusplus
+}
+#endif
 
-  // Converts the public C-API pointer to the internal C++ class.
-  static VFS* Upcast(mjVFS* vfs);
-  static const VFS* Upcast(const mjVFS* vfs);
-
- private:
-  using ResourcePtr = std::unique_ptr<mjResource, void (*)(mjResource*)>;
-  ResourcePtr CreateResource(std::string_view name,
-                             const mjpResourceProvider* provider);
-
-  // Returns a mounted mjResource* that matches the given path. If no explicitly
-  // mounted mjResource* is found, returns a "default" mounting that uses the
-  // C file system.
-  mjResource* FindMount(const std::string& fullpath);
-
-  // Invokes the `destructor_, but only if it has been set previously. This
-  // should be only called when resources_ is empty and callers should assume
-  // that `this` will be invalidated after this call.
-  void MaybeSelfDestruct();
-
-  mjVFS* self_;
-  std::mutex mutex_;  // Protects open_resources_ and mounts_.
-  std::unordered_map<mjResource*, ResourcePtr> open_resources_;
-  std::unordered_map<std::string, ResourcePtr> mounts_;
-  mjResource default_mount_;
-  mjpResourceProvider default_provider_;
-  std::function<void(mjVFS*)> destructor_;
-};
-
-}  // namespace mujoco::user
+const mjpResourceProvider* GetVfsResourceProvider();
 
 #endif  // MUJOCO_SRC_USER_USER_VFS_H_