some more backend interface changes i realized i had to do

src/fragment_store/backends/filesystem_storage.cpp

@@ -42,13 +42,17 @@ static ByteSpan spanFromRead(const std::variant<ByteSpan, std::vector<uint8_t>>&
 
 namespace backend {
 
-FilesystemStorage::FilesystemStorage(ObjectStore2& os, std::string_view storage_path) : StorageBackendI::StorageBackendI(os), _storage_path(storage_path) {
+FilesystemStorage::FilesystemStorage(
+	ObjectStore2& os,
+	std::string_view storage_path,
+	MetaFileType mft_new
+) : StorageBackendI::StorageBackendI(os), _storage_path(storage_path), _mft_new(mft_new) {
 }
 
 FilesystemStorage::~FilesystemStorage(void) {
 }
 
-ObjectHandle FilesystemStorage::newObject(MetaFileType mft, ByteSpan id) {
+ObjectHandle FilesystemStorage::newObject(ByteSpan id) {
 	{ // first check if id is already used (TODO: solve the multi obj/backend problem)
 		auto exising_oh = _os.getOneObjectByID(id);
 		if (static_cast<bool>(exising_oh)) {
@@ -85,7 +89,7 @@ ObjectHandle FilesystemStorage::newObject(MetaFileType mft, ByteSpan id) {
 	oh.emplace<ObjComp::Ephemeral::Backend>(this);
 	oh.emplace<ObjComp::ID>(std::vector<uint8_t>{id});
 	oh.emplace<ObjComp::Ephemeral::FilePath>(object_file_path.generic_u8string());
-	oh.emplace<ObjComp::Ephemeral::MetaFileType>(mft);
+	oh.emplace<ObjComp::Ephemeral::MetaFileType>(_mft_new);
 
 	// meta needs to be synced to file
 	std::function<write_to_storage_fetch_data_cb> empty_data_cb = [](auto*, auto) -> uint64_t { return 0; };

src/fragment_store/backends/filesystem_storage.hpp

@@ -3,17 +3,26 @@
 #include "../types.hpp"
 #include "../object_store.hpp"
 
+#include <string>
+
 namespace backend {
 
 struct FilesystemStorage : public StorageBackendI {
-	FilesystemStorage(ObjectStore2& os, std::string_view storage_path = "test_obj_store");
+	FilesystemStorage(
+		ObjectStore2& os,
+		std::string_view storage_path = "test_obj_store",
+		MetaFileType mft_new = MetaFileType::BINARY_MSGPACK
+	);
 	~FilesystemStorage(void);
 
 	// TODO: fix the path for this specific fs?
 	// for now we assume a single storage path per backend (there can be multiple per type)
 	std::string _storage_path;
 
-	ObjectHandle newObject(MetaFileType mft, ByteSpan id);
+	// meta file type for new objects
+	MetaFileType _mft_new {MetaFileType::BINARY_MSGPACK};
+
+	ObjectHandle newObject(ByteSpan id) override;
 
 	bool write(Object o, std::function<write_to_storage_fetch_data_cb>& data_cb) override;
 	bool read(Object o, std::function<read_from_storage_put_data_cb>& data_cb) override;

src/fragment_store/convert_frag_to_obj.cpp

@@ -85,7 +85,8 @@ int main(int argc, const char** argv) {
 					}
 				}
 
-				auto oh = _fsb_dst.newObject(e.e.get<ObjComp::Ephemeral::MetaFileType>().type, ByteSpan{e.e.get<ObjComp::ID>().v});
+				// we dont copy meta file type, it will be the same for all "new" objects
+				auto oh = _fsb_dst.newObject(ByteSpan{e.e.get<ObjComp::ID>().v});
 
 				if (!static_cast<bool>(oh)) {
 					// already exists

src/fragment_store/object_store.cpp

@@ -52,6 +52,11 @@ static bool deserl_json_data_comp_type(ObjectHandle oh, const nlohmann::json& in
 StorageBackendI::StorageBackendI(ObjectStore2& os) : _os(os) {
 }
 
+ObjectHandle StorageBackendI::newObject(ByteSpan) {
+	//return {_os.registry(), entt::null};
+	return {};
+}
+
 bool StorageBackendI::write(Object o, const ByteSpan data) {
 	std::function<write_to_storage_fetch_data_cb> fn_cb = [read = 0ull, data](uint8_t* request_buffer, uint64_t buffer_size) mutable -> uint64_t {
 		uint64_t i = 0;

src/fragment_store/object_store.hpp

@@ -22,11 +22,13 @@ struct StorageBackendI {
 
 	StorageBackendI(ObjectStore2& os);
 
+	// default impl fails, acting like a read only store
+	virtual ObjectHandle newObject(ByteSpan id);
+
 	// ========== write object to storage ==========
 	using write_to_storage_fetch_data_cb = uint64_t(uint8_t* request_buffer, uint64_t buffer_size);
 	// calls data_cb with a buffer to be filled in, cb returns actual count of data. if returned < max, its the last buffer.
 	virtual bool write(Object o, std::function<write_to_storage_fetch_data_cb>& data_cb) = 0;
-	//virtual bool write(Object o, const uint8_t* data, const uint64_t data_size); // default impl
 	bool write(Object o, const ByteSpan data);
 
 	// ========== read object from storage ==========