surf_action_t(*read) (void *storage, void* ptr, size_t size, size_t nmemb, surf_file_t stream);
surf_action_t(*write) (void *storage, const void* ptr, size_t size, size_t nmemb, surf_file_t stream);
surf_action_t(*stat) (void *storage, int fd, void* buf);
surf_action_t(*read) (void *storage, void* ptr, size_t size, size_t nmemb, surf_file_t stream);
surf_action_t(*write) (void *storage, const void* ptr, size_t size, size_t nmemb, surf_file_t stream);
surf_action_t(*stat) (void *storage, int fd, void* buf);