add filesystem backend

CMakeLists.txt

@@ -12,6 +12,7 @@ message("II SOLANACEAE_OBJECT_STORE_STANDALONE " ${SOLANACEAE_OBJECT_STORE_STAND
 
 #option(SOLANACEAE_OBJECT_STORE_BUILD_PLUGINS "Build the solanaceae_object_store plugins" ${SOLANACEAE_OBJECT_STORE_STANDALONE})
 option(SOLANACEAE_OBJECT_STORE_BUILD_TESTING "Build the solanaceae_object_store tests" ${SOLANACEAE_OBJECT_STORE_STANDALONE})
+message("II SOLANACEAE_OBJECT_BUILD_TESTING " ${SOLANACEAE_OBJECT_STORE_BUILD_TESTING})
 
 if (SOLANACEAE_OBJECT_STORE_STANDALONE)
 	set(CMAKE_POSITION_INDEPENDENT_CODE ON)

src/CMakeLists.txt

@@ -33,3 +33,19 @@ target_link_libraries(solanaceae_file2_zstd PUBLIC
 	zstd::zstd
 )
 
+########################################
+
+add_library(solanaceae_object_store_backend_filesystem
+	./solanaceae/object_store/backends/file2_stack.hpp
+	./solanaceae/object_store/backends/file2_stack.cpp
+	./solanaceae/object_store/backends/filesystem_storage.hpp
+	./solanaceae/object_store/backends/filesystem_storage.cpp
+)
+
+target_include_directories(solanaceae_object_store_backend_filesystem PUBLIC .)
+target_compile_features(solanaceae_object_store_backend_filesystem PUBLIC cxx_std_17)
+target_link_libraries(solanaceae_object_store_backend_filesystem PUBLIC
+	solanaceae_object_store
+	solanaceae_file2_zstd
+)
+

src/solanaceae/object_store/backends/file2_stack.cpp

@@ -0,0 +1,93 @@
+#include "./file2_stack.hpp"
+
+#include <solanaceae/file/file2_std.hpp>
+#include <solanaceae/file/file2_zstd.hpp>
+
+#include <cassert>
+
+#include <iostream>
+
+// add enc and comp file layers
+// assumes a file is already in the stack
+bool buildStackRead(std::stack<std::unique_ptr<File2I>>& file_stack, Encryption encryption, Compression compression) {
+	assert(!file_stack.empty());
+
+	// TODO: decrypt here
+	assert(encryption == Encryption::NONE);
+
+	// add layer based on enum
+	if (compression == Compression::ZSTD) {
+		file_stack.push(std::make_unique<File2ZSTDR>(*file_stack.top().get()));
+	} else {
+		// TODO: make error instead
+		assert(compression == Compression::NONE);
+	}
+
+	if (!file_stack.top()->isGood()) {
+		std::cerr << "FS error: file failed to add " << (int)compression << " decompression layer\n";
+		return false;
+	}
+
+	return true;
+}
+
+// do i need this?
+std::stack<std::unique_ptr<File2I>> buildFileStackRead(std::string_view file_path, Encryption encryption, Compression compression) {
+	std::stack<std::unique_ptr<File2I>> file_stack;
+	file_stack.push(std::make_unique<File2RFile>(file_path));
+
+	if (!file_stack.top()->isGood()) {
+		std::cerr << "FS error: opening file for reading '" << file_path << "'\n";
+		return {};
+	}
+
+	if (!buildStackRead(file_stack, encryption, compression)) {
+		std::cerr << "FS error: file failed to add layers for '" << file_path << "'\n";
+		return {};
+	}
+
+	return file_stack;
+}
+
+// add enc and comp file layers
+// assumes a file is already in the stack
+bool buildStackWrite(std::stack<std::unique_ptr<File2I>>& file_stack, Encryption encryption, Compression compression) {
+	assert(!file_stack.empty());
+
+	// TODO: encrypt here
+	assert(encryption == Encryption::NONE);
+
+	// add layer based on enum
+	if (compression == Compression::ZSTD) {
+		file_stack.push(std::make_unique<File2ZSTDW>(*file_stack.top().get()));
+	} else {
+		// TODO: make error instead
+		assert(compression == Compression::NONE);
+	}
+
+	if (!file_stack.top()->isGood()) {
+		std::cerr << "FS error: file failed to add " << (int)compression << " compression layer\n";
+		return false;
+	}
+
+	return true;
+}
+
+// do i need this?
+std::stack<std::unique_ptr<File2I>> buildFileStackWrite(std::string_view file_path, Encryption encryption, Compression compression) {
+	std::stack<std::unique_ptr<File2I>> file_stack;
+	file_stack.push(std::make_unique<File2WFile>(file_path));
+
+	if (!file_stack.top()->isGood()) {
+		std::cerr << "FS error: opening file for writing '" << file_path << "'\n";
+		return {};
+	}
+
+	if (!buildStackWrite(file_stack, encryption, compression)) {
+		std::cerr << "FS error: file failed to add layers for '" << file_path << "'\n";
+		return {};
+	}
+
+	return file_stack;
+}
+

src/solanaceae/object_store/backends/file2_stack.hpp

@@ -0,0 +1,23 @@
+#pragma once
+
+#include "../types.hpp"
+
+#include <solanaceae/file/file2.hpp>
+
+#include <stack>
+#include <memory>
+#include <string_view>
+
+// add enc and comp file layers
+// assumes a file is already in the stack
+[[nodiscard]] bool buildStackRead(std::stack<std::unique_ptr<File2I>>& file_stack, Encryption encryption, Compression compression);
+
+// do i need this?
+[[nodiscard]] std::stack<std::unique_ptr<File2I>> buildFileStackRead(std::string_view file_path, Encryption encryption, Compression compression);
+
+// add enc and comp file layers
+// assumes a file is already in the stack
+[[nodiscard]] bool buildStackWrite(std::stack<std::unique_ptr<File2I>>& file_stack, Encryption encryption, Compression compression);
+
+// do i need this?
+[[nodiscard]] std::stack<std::unique_ptr<File2I>> buildFileStackWrite(std::string_view file_path, Encryption encryption, Compression compression);

src/solanaceae/object_store/backends/filesystem_storage.cpp

@@ -0,0 +1,627 @@
+#include "./filesystem_storage.hpp"
+
+#include <solanaceae/object_store/meta_components.hpp>
+#include <solanaceae/object_store/serializer_json.hpp>
+
+#include <solanaceae/util/utils.hpp>
+
+#include <entt/container/dense_set.hpp>
+#include <nlohmann/json.hpp>
+
+#include <solanaceae/file/file2_std.hpp>
+#include <solanaceae/file/file2_mem.hpp>
+
+#include "./file2_stack.hpp"
+
+#include <filesystem>
+
+#include <iostream>
+
+static const char* metaFileTypeSuffix(MetaFileType mft) {
+	switch (mft) {
+		case MetaFileType::TEXT_JSON: return ".json";
+		//case MetaFileType::BINARY_ARB: return ".bin";
+		case MetaFileType::BINARY_MSGPACK: return ".msgpack";
+	}
+	return ""; // .unk?
+}
+
+// TODO: move to ... somewhere. (span? file2i?)
+static ByteSpan spanFromRead(const std::variant<ByteSpan, std::vector<uint8_t>>& data_var) {
+	if (std::holds_alternative<std::vector<uint8_t>>(data_var)) {
+		auto& vec = std::get<std::vector<uint8_t>>(data_var);
+		return {vec.data(), vec.size()};
+	} else if (std::holds_alternative<ByteSpan>(data_var)) {
+		return std::get<ByteSpan>(data_var);
+	} else {
+		assert(false);
+		return {};
+	}
+}
+
+
+namespace backend {
+
+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(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)) {
+			return {};
+		}
+	}
+
+	std::filesystem::create_directories(_storage_path);
+
+	if (!std::filesystem::is_directory(_storage_path)) {
+		std::cerr << "FS error: failed to create storage path dir '" << _storage_path << "'\n";
+		return {};
+	}
+
+	const auto id_hex = bin2hex(id);
+	std::filesystem::path object_file_path;
+
+	// TODO: refactor this magic somehow
+	if (id_hex.size() < 6) {
+		object_file_path = std::filesystem::path{_storage_path}/id_hex;
+	} else {
+		// use the first 2hex (1byte) as a subfolder
+		std::filesystem::create_directories(std::string{_storage_path} + id_hex.substr(0, 2));
+		object_file_path = std::filesystem::path{std::string{_storage_path} + id_hex.substr(0, 2)} / id_hex.substr(2);
+	}
+
+	if (std::filesystem::exists(object_file_path)) {
+		std::cerr << "FS error: object already exists in path '" << id_hex << "'\n";
+		return {};
+	}
+
+	ObjectHandle oh{_os.registry(), _os.registry().create()};
+
+	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_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; };
+	if (!write(oh, empty_data_cb)) {
+		std::cerr << "FS error: write failed while creating new object file\n";
+		oh.destroy();
+		return {};
+	}
+
+	// while new metadata might be created here, making sure the file could be created is more important
+	_os.throwEventConstruct(oh);
+
+	return oh;
+}
+
+bool FilesystemStorage::write(Object o, std::function<write_to_storage_fetch_data_cb>& data_cb) {
+	auto& reg = _os.registry();
+
+	if (!reg.valid(o)) {
+		return false;
+	}
+
+	ObjectHandle oh {reg, o};
+
+	if (!oh.all_of<ObjComp::Ephemeral::FilePath>()) {
+		// not a file fragment?
+		return false;
+	}
+
+	// split object storage (meta and data are 2 files)
+
+	MetaFileType meta_type = MetaFileType::TEXT_JSON; // TODO: better defaults?
+	if (reg.all_of<ObjComp::Ephemeral::MetaFileType>(o)) {
+		meta_type = oh.get<ObjComp::Ephemeral::MetaFileType>().type;
+	}
+
+	Encryption meta_enc = Encryption::NONE; // TODO: better defaults?
+	Compression meta_comp = Compression::NONE; // TODO: better defaults?
+
+	if (meta_type != MetaFileType::TEXT_JSON) {
+		if (oh.all_of<ObjComp::Ephemeral::MetaEncryptionType>()) {
+			meta_enc = oh.get<ObjComp::Ephemeral::MetaEncryptionType>().enc;
+		}
+
+		if (oh.all_of<ObjComp::Ephemeral::MetaCompressionType>()) {
+			meta_comp = oh.get<ObjComp::Ephemeral::MetaCompressionType>().comp;
+		}
+	} else {
+		// we cant have encryption or compression
+		// so we force NONE for TEXT JSON
+
+		oh.emplace_or_replace<ObjComp::Ephemeral::MetaEncryptionType>(Encryption::NONE);
+		oh.emplace_or_replace<ObjComp::Ephemeral::MetaCompressionType>(Compression::NONE);
+	}
+
+	std::filesystem::path meta_tmp_path = oh.get<ObjComp::Ephemeral::FilePath>().path + ".meta" + metaFileTypeSuffix(meta_type) + ".tmp";
+	meta_tmp_path.replace_filename("." + meta_tmp_path.filename().generic_u8string());
+	// TODO: make meta comp work with mem compressor
+	//auto meta_file_stack = buildFileStackWrite(std::string_view{meta_tmp_path.generic_u8string()}, meta_enc, meta_comp);
+	std::stack<std::unique_ptr<File2I>> meta_file_stack;
+	meta_file_stack.push(std::make_unique<File2WFile>(std::string_view{meta_tmp_path.generic_u8string()}));
+
+	if (meta_file_stack.empty()) {
+		std::cerr << "FS error: failed to create temporary meta file stack\n";
+		std::filesystem::remove(meta_tmp_path); // might have created an empty file
+		return false;
+	}
+
+	Encryption data_enc = Encryption::NONE; // TODO: better defaults
+	Compression data_comp = Compression::NONE; // TODO: better defaults
+	if (oh.all_of<ObjComp::DataEncryptionType>()) {
+		data_enc = oh.get<ObjComp::DataEncryptionType>().enc;
+	}
+	if (oh.all_of<ObjComp::DataCompressionType>()) {
+		data_comp = oh.get<ObjComp::DataCompressionType>().comp;
+	}
+
+	std::filesystem::path data_tmp_path = oh.get<ObjComp::Ephemeral::FilePath>().path + ".tmp";
+	data_tmp_path.replace_filename("." + data_tmp_path.filename().generic_u8string());
+	auto data_file_stack = buildFileStackWrite(std::string_view{data_tmp_path.generic_u8string()}, data_enc, data_comp);
+	if (data_file_stack.empty()) {
+		while (!meta_file_stack.empty()) { meta_file_stack.pop(); }
+		std::filesystem::remove(meta_tmp_path);
+		std::cerr << "FS error: failed to create temporary data file stack\n";
+		return false;
+	}
+
+	try { // TODO: properly sanitize strings, so this cant throw
+		// sharing code between binary msgpack and text json for now
+		nlohmann::json meta_data_j = nlohmann::json::object(); // metadata needs to be an object, null not allowed
+		// metadata file
+
+		auto& sjc = _os.registry().ctx().get<SerializerJsonCallbacks<Object>>();
+
+		// TODO: refactor extract to OS
+		for (const auto& [type_id, storage] : reg.storage()) {
+			if (!storage.contains(o)) {
+				continue;
+			}
+
+			//std::cout << "storage type: type_id:" << type_id << " name:" << storage.type().name() << "\n";
+
+			// use type_id to find serializer
+			auto s_cb_it = sjc._serl.find(type_id);
+			if (s_cb_it == sjc._serl.end()) {
+				// could not find serializer, not saving
+				continue;
+			}
+
+			// noooo, why cant numbers be keys
+			//if (meta_type == MetaFileType::BINARY_MSGPACK) { // msgpack uses the hash id instead
+				//s_cb_it->second(storage.value(fid), meta_data[storage.type().hash()]);
+			//} else if (meta_type == MetaFileType::TEXT_JSON) {
+			s_cb_it->second(oh, meta_data_j[storage.type().name()]);
+			//}
+		}
+
+		if (meta_type == MetaFileType::BINARY_MSGPACK) { // binary metadata file
+			std::vector<uint8_t> binary_meta_data;
+			{
+				std::stack<std::unique_ptr<File2I>> binary_writer_stack;
+				binary_writer_stack.push(std::make_unique<File2MemW>(binary_meta_data));
+
+				if (!buildStackWrite(binary_writer_stack, meta_enc, meta_comp)) {
+					while (!meta_file_stack.empty()) { meta_file_stack.pop(); }
+					std::filesystem::remove(meta_tmp_path);
+					while (!data_file_stack.empty()) { data_file_stack.pop(); }
+					std::filesystem::remove(data_tmp_path);
+					std::cerr << "FS error: binary writer creation failed '" << oh.get<ObjComp::Ephemeral::FilePath>().path << "'\n";
+					return false;
+				}
+
+				{
+					const std::vector<uint8_t> meta_data = nlohmann::json::to_msgpack(meta_data_j);
+					if (!binary_writer_stack.top()->write(ByteSpan{meta_data})) {
+						// i feel like exceptions or refactoring would be nice here
+						while (!meta_file_stack.empty()) { meta_file_stack.pop(); }
+						std::filesystem::remove(meta_tmp_path);
+						while (!data_file_stack.empty()) { data_file_stack.pop(); }
+						std::filesystem::remove(data_tmp_path);
+						std::cerr << "FS error: binary writer failed '" << oh.get<ObjComp::Ephemeral::FilePath>().path << "'\n";
+						return false;
+					}
+				}
+			}
+
+			//// the meta file is itself msgpack data
+			nlohmann::json meta_header_j = nlohmann::json::array();
+			meta_header_j.emplace_back() = "SOLMET";
+			meta_header_j.push_back(meta_enc);
+			meta_header_j.push_back(meta_comp);
+
+			// with a custom msgpack impl like cmp, we can be smarter here and dont need an extra buffer
+			meta_header_j.push_back(nlohmann::json::binary(binary_meta_data));
+
+			const auto meta_header_data = nlohmann::json::to_msgpack(meta_header_j);
+			meta_file_stack.top()->write({meta_header_data.data(), meta_header_data.size()});
+		} else if (meta_type == MetaFileType::TEXT_JSON) {
+			// cant be compressed or encrypted
+			const auto meta_file_json_str = meta_data_j.dump(2, ' ', true);
+			meta_file_stack.top()->write({reinterpret_cast<const uint8_t*>(meta_file_json_str.data()), meta_file_json_str.size()});
+		}
+
+	} catch (...) {
+		while (!meta_file_stack.empty()) { meta_file_stack.pop(); } // destroy stack // TODO: maybe work with scope?
+		std::filesystem::remove(meta_tmp_path);
+		while (!data_file_stack.empty()) { data_file_stack.pop(); } // destroy stack // TODO: maybe work with scope?
+		std::filesystem::remove(data_tmp_path);
+		std::cerr << "FS error: failed to serialize json data\n";
+		return false;
+	}
+
+	// now data
+	// for zstd compression, chunk size is frame size. (no cross frame referencing)
+	// TODO: add buffering steam layer
+	static constexpr int64_t chunk_size{1024*1024}; // 1MiB should be enough
+	std::vector<uint8_t> buffer(chunk_size);
+	uint64_t buffer_actual_size {0};
+	do {
+		buffer_actual_size = data_cb(buffer.data(), buffer.size());
+		if (buffer_actual_size == 0) {
+			break;
+		}
+		if (buffer_actual_size > buffer.size()) {
+			// wtf
+			break;
+		}
+
+		data_file_stack.top()->write({buffer.data(), buffer_actual_size});
+	} while (buffer_actual_size == buffer.size());
+
+	// flush // TODO: use scope
+	while (!meta_file_stack.empty()) { meta_file_stack.pop(); } // destroy stack // TODO: maybe work with scope?
+	while (!data_file_stack.empty()) { data_file_stack.pop(); } // destroy stack // TODO: maybe work with scope?
+
+	std::filesystem::rename(
+		meta_tmp_path,
+		oh.get<ObjComp::Ephemeral::FilePath>().path + ".meta" + metaFileTypeSuffix(meta_type)
+	);
+
+	std::filesystem::rename(
+		data_tmp_path,
+		oh.get<ObjComp::Ephemeral::FilePath>().path
+	);
+
+	// TODO: check return value of renames
+
+	if (oh.all_of<ObjComp::Ephemeral::DirtyTag>()) {
+		oh.remove<ObjComp::Ephemeral::DirtyTag>();
+	}
+
+	return true;
+}
+
+bool FilesystemStorage::read(Object o, std::function<read_from_storage_put_data_cb>& data_cb) {
+	auto& reg = _os.registry();
+
+	if (!reg.valid(o)) {
+		return false;
+	}
+
+	ObjectHandle oh {reg, o};
+
+	if (!oh.all_of<ObjComp::Ephemeral::FilePath>()) {
+		// not a file
+		return false;
+	}
+
+	const auto& obj_path = oh.get<ObjComp::Ephemeral::FilePath>().path;
+
+	// TODO: check if metadata dirty?
+	// TODO: what if file changed on disk?
+
+	std::cout << "FS: loading fragment '" << obj_path << "'\n";
+
+	Compression data_comp = Compression::NONE;
+	if (oh.all_of<ObjComp::DataCompressionType>()) {
+		data_comp = oh.get<ObjComp::DataCompressionType>().comp;
+	}
+
+	auto data_file_stack = buildFileStackRead(std::string_view{obj_path}, Encryption::NONE, data_comp);
+	if (data_file_stack.empty()) {
+		return false;
+	}
+
+	// TODO: make it read in a single chunk instead?
+	static constexpr int64_t chunk_size {1024 * 1024}; // 1MiB should be good for read
+	do {
+		auto data_var = data_file_stack.top()->read(chunk_size);
+		ByteSpan data = spanFromRead(data_var);
+
+		if (data.empty()) {
+			// error or probably eof
+			break;
+		}
+
+		data_cb(data);
+
+		if (data.size < chunk_size) {
+			// eof
+			break;
+		}
+	} while (data_file_stack.top()->isGood());
+
+	return true;
+}
+
+void FilesystemStorage::scanAsync(void) {
+	scanPathAsync(_storage_path);
+}
+
+size_t FilesystemStorage::scanPath(std::string_view path) {
+	// TODO: extract so async can work (or/and make iteratable generator)
+
+	if (path.empty() || !std::filesystem::is_directory(path)) {
+		std::cerr << "FS error: scan path not a directory '" << path << "'\n";
+		return 0;
+	}
+
+	// step 1: make snapshot of files, validate metafiles and save id/path+meta.ext
+	// can be extra thread (if non vfs)
+	struct ObjFileEntry {
+		std::string id_str;
+		std::filesystem::path obj_path;
+		std::string meta_ext;
+
+		bool operator==(const ObjFileEntry& other) const {
+			// only compare by id
+			return id_str == other.id_str;
+		}
+	};
+	struct ObjFileEntryHash {
+		size_t operator()(const ObjFileEntry& it) const {
+			return entt::hashed_string(it.id_str.data(), it.id_str.size());
+		}
+	};
+	entt::dense_set<ObjFileEntry, ObjFileEntryHash> file_obj_list;
+
+	std::filesystem::path storage_path{path};
+
+	auto handle_file = [&](const std::filesystem::path& file_path) {
+		if (!std::filesystem::is_regular_file(file_path)) {
+			return;
+		}
+		// handle file
+
+		if (file_path.has_extension()) {
+			// skip over metadata, assuming only metafiles have extentions (might be wrong?)
+			// also skips temps
+			return;
+		}
+
+		auto relative_path = std::filesystem::proximate(file_path, storage_path);
+		std::string id_str = relative_path.generic_u8string();
+		// delete all '/'
+		id_str.erase(std::remove(id_str.begin(), id_str.end(), '/'), id_str.end());
+		if (id_str.size() % 2 != 0) {
+			std::cerr << "FS error: non hex object uid detected: '" << id_str << "'\n";
+		}
+
+		if (file_obj_list.contains(ObjFileEntry{id_str, {}, ""})) {
+			std::cerr << "FS error: object duplicate detected: '" << id_str << "'\n";
+			return; // skip
+		}
+
+		const char* meta_ext = ".meta.msgpack";
+		{ // find meta
+			// TODO: this as to know all possible extentions
+			bool has_meta_msgpack = std::filesystem::is_regular_file(file_path.generic_u8string() + ".meta.msgpack");
+			bool has_meta_json = std::filesystem::is_regular_file(file_path.generic_u8string() + ".meta.json");
+			const size_t meta_sum =
+				(has_meta_msgpack?1:0) +
+				(has_meta_json?1:0)
+			;
+
+			if (meta_sum > 1) { // has multiple
+				std::cerr << "FS error: object with multiple meta files detected: " << id_str << "\n";
+				return; // skip
+			}
+
+			if (meta_sum == 0) {
+				std::cerr << "FS error: object missing meta file detected: " << id_str << "\n";
+				return; // skip
+			}
+
+			if (has_meta_json) {
+				meta_ext = ".meta.json";
+			}
+		}
+
+		file_obj_list.emplace(ObjFileEntry{
+			std::move(id_str),
+			file_path,
+			meta_ext
+		});
+	};
+
+	for (const auto& outer_path : std::filesystem::directory_iterator(storage_path)) {
+		if (std::filesystem::is_regular_file(outer_path)) {
+			handle_file(outer_path);
+		} else if (std::filesystem::is_directory(outer_path)) {
+			// subdir, part of id
+			for (const auto& inner_path : std::filesystem::directory_iterator(outer_path)) {
+				//if (std::filesystem::is_regular_file(inner_path)) {
+
+					//// handle file
+				//} // TODO: support deeper recursion?
+				handle_file(inner_path);
+			}
+		}
+	}
+
+	std::cout << "FS: scan found:\n";
+	for (const auto& it : file_obj_list) {
+		std::cout << "  " << it.id_str << "\n";
+	}
+
+	// step 2: check if files preexist in reg
+	// main thread
+	// (merge into step 3 and do more error checking?)
+	// TODO: properly handle duplicates, dups form different backends might be legit
+	// important
+	for (auto it = file_obj_list.begin(); it != file_obj_list.end();) {
+		auto id = hex2bin(it->id_str);
+		auto oh = _os.getOneObjectByID(ByteSpan{id});
+		if (static_cast<bool>(oh)) {
+			// pre exising (handle differently??)
+			// check if store differs?
+			it = file_obj_list.erase(it);
+		} else {
+			it++;
+		}
+	}
+
+	auto& sjc = _os.registry().ctx().get<SerializerJsonCallbacks<Object>>();
+
+	std::vector<Object> scanned_objs;
+	// step 3: parse meta and insert into reg of non preexising
+	// main thread
+	// TODO: check timestamps of preexisting and reload? mark external/remote dirty?
+	for (const auto& it : file_obj_list) {
+		MetaFileType mft {MetaFileType::TEXT_JSON};
+		Encryption meta_enc {Encryption::NONE};
+		Compression meta_comp {Compression::NONE};
+		nlohmann::json j;
+		if (it.meta_ext == ".meta.msgpack") {
+			std::ifstream file(it.obj_path.generic_u8string() + it.meta_ext, std::ios::in | std::ios::binary);
+			if (!file.is_open()) {
+				std::cout << "FS error: failed opening meta " << it.obj_path << "\n";
+				continue;
+			}
+
+			mft = MetaFileType::BINARY_MSGPACK;
+
+			// file is a msgpack within a msgpack
+
+			std::vector<uint8_t> full_meta_data;
+			{ // read meta file
+				// figure out size
+				file.seekg(0, file.end);
+				uint64_t file_size = file.tellg();
+				file.seekg(0, file.beg);
+
+				full_meta_data.resize(file_size);
+
+				file.read(reinterpret_cast<char*>(full_meta_data.data()), full_meta_data.size());
+			}
+
+			const auto meta_header_j = nlohmann::json::from_msgpack(full_meta_data, true, false);
+
+			if (!meta_header_j.is_array() || meta_header_j.size() < 4) {
+				std::cerr << "FS error: broken binary meta " << it.obj_path << "\n";
+				continue;
+			}
+
+			if (meta_header_j.at(0) != "SOLMET") {
+				std::cerr << "FS error: wrong magic '" << meta_header_j.at(0) << "' in meta " << it.obj_path << "\n";
+				continue;
+			}
+
+			meta_enc = meta_header_j.at(1);
+			if (meta_enc != Encryption::NONE) {
+				std::cerr << "FS error: unknown encryption " << it.obj_path << "\n";
+				continue;
+			}
+
+			meta_comp = meta_header_j.at(2);
+			if (meta_comp != Compression::NONE && meta_comp != Compression::ZSTD) {
+				std::cerr << "FS error: unknown compression " << it.obj_path << "\n";
+				continue;
+			}
+
+			//const auto& meta_data_ref = meta_header_j.at(3).is_binary()?meta_header_j.at(3):meta_header_j.at(3).at("data");
+			if (!meta_header_j.at(3).is_binary()) {
+				std::cerr << "FS error: meta data not binary " << it.obj_path << "\n";
+				continue;
+			}
+			const nlohmann::json::binary_t& meta_data_ref = meta_header_j.at(3);
+
+			std::stack<std::unique_ptr<File2I>> binary_reader_stack;
+			binary_reader_stack.push(std::make_unique<File2MemR>(ByteSpan{meta_data_ref.data(), meta_data_ref.size()}));
+
+			if (!buildStackRead(binary_reader_stack, meta_enc, meta_comp)) {
+				std::cerr << "FS error: binary reader creation failed " << it.obj_path << "\n";
+				continue;
+			}
+
+			// HACK: read fixed amout of data, but this way if we have neither enc nor comp we pass the span through
+			auto binary_read_value = binary_reader_stack.top()->read(10*1024*1024); // is 10MiB large enough for meta?
+			const auto binary_read_span = spanFromRead(binary_read_value);
+			assert(binary_read_span.size < 10*1024*1024);
+
+			j = nlohmann::json::from_msgpack(binary_read_span, true, false);
+		} else if (it.meta_ext == ".meta.json") {
+			std::ifstream file(it.obj_path.generic_u8string() + it.meta_ext, std::ios::in | std::ios::binary);
+			if (!file.is_open()) {
+				std::cerr << "FS error: failed opening meta " << it.obj_path << "\n";
+				continue;
+			}
+
+			mft = MetaFileType::TEXT_JSON;
+
+			file >> j;
+		} else {
+			assert(false);
+		}
+
+		if (!j.is_object()) {
+			std::cerr << "FS error: json in meta is broken " << it.id_str << "\n";
+			continue;
+		}
+
+		// TODO: existing fragment file
+		//newFragmentFile();
+		ObjectHandle oh{_os.registry(), _os.registry().create()};
+		oh.emplace<ObjComp::Ephemeral::Backend>(this);
+		oh.emplace<ObjComp::ID>(hex2bin(it.id_str));
+		oh.emplace<ObjComp::Ephemeral::MetaFileType>(mft);
+		oh.emplace<ObjComp::Ephemeral::MetaEncryptionType>(meta_enc);
+		oh.emplace<ObjComp::Ephemeral::MetaCompressionType>(meta_comp);
+
+		oh.emplace<ObjComp::Ephemeral::FilePath>(it.obj_path.generic_u8string());
+
+		for (const auto& [k, v] : j.items()) {
+			// type id from string hash
+			const auto type_id = entt::hashed_string(k.data(), k.size());
+			const auto deserl_fn_it = sjc._deserl.find(type_id);
+			if (deserl_fn_it != sjc._deserl.cend()) {
+				// TODO: check return value
+				deserl_fn_it->second(oh, v);
+			} else {
+				std::cerr << "FS warning: missing deserializer for meta key '" << k << "'\n";
+			}
+		}
+		scanned_objs.push_back(oh);
+	}
+
+	// TODO: mutex and move code to async and return this list ?
+
+	// throw new frag event here, after loading them all
+	for (const Object o : scanned_objs) {
+		_os.throwEventConstruct(o);
+	}
+
+	return scanned_objs.size();
+}
+
+void FilesystemStorage::scanPathAsync(std::string path) {
+	// add path to queue
+	// HACK: if path is known/any fragment is in the path, this operation blocks (non async)
+	scanPath(path); // TODO: make async and post result
+}
+
+} // backend
+

src/solanaceae/object_store/backends/filesystem_storage.hpp

@@ -0,0 +1,41 @@
+#pragma once
+
+#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",
+		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;
+
+	// 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;
+
+	//// convenience function
+	//nlohmann::json loadFromStorageNJ(FragmentID fid);
+
+	void scanAsync(void);
+
+	private:
+		size_t scanPath(std::string_view path);
+		void scanPathAsync(std::string path);
+};
+
+} // backend
+