foundationdb/flow/ObjectSerializer.h

/*
 * serialize.h
 *
 * This source file is part of the FoundationDB open source project
 *
 * Copyright 2013-2022 Apple Inc. and the FoundationDB project authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#pragma once
#include "flow/Error.h"
#include "flow/Arena.h"
#include "flow/flat_buffers.h"
#include "flow/ProtocolVersion.h"

template <class Ar>
struct LoadContext {
	Ar* ar;
	LoadContext(Ar* ar) : ar(ar) {}
	Arena& arena() { return ar->arena(); }

	ProtocolVersion protocolVersion() const { return ar->protocolVersion(); }

	const uint8_t* tryReadZeroCopy(const uint8_t* ptr, unsigned len) {
		if constexpr (Ar::ownsUnderlyingMemory) {
			return ptr;
		} else {
			if (len == 0)
				return nullptr;
			uint8_t* dat = new (arena()) uint8_t[len];
			std::copy(ptr, ptr + len, dat);
			return dat;
		}
	}

	void addArena(Arena& arena) { arena = ar->arena(); }

	LoadContext& context() { return *this; }
};

template <class Ar, class Allocator>
struct SaveContext {
	Ar* ar;
	Allocator allocator;

	SaveContext(Ar* ar, const Allocator& allocator) : ar(ar), allocator(allocator) {}

	ProtocolVersion protocolVersion() const { return ar->protocolVersion(); }

	void addArena(Arena& arena) {}

	uint8_t* allocate(size_t s) { return allocator(s); }

	SaveContext& context() { return *this; }
};

template <class ReaderImpl>
class _ObjectReader {
protected:
	ProtocolVersion mProtocolVersion;

public:
	ProtocolVersion protocolVersion() const { return mProtocolVersion; }
	void setProtocolVersion(ProtocolVersion v) { mProtocolVersion = v; }

	template <class... Items>
	void deserialize(FileIdentifier file_identifier, Items&... items) {
		const uint8_t* data = static_cast<ReaderImpl*>(this)->data();
		LoadContext<ReaderImpl> context(static_cast<ReaderImpl*>(this));
		if (read_file_identifier(data) != file_identifier) {
			// Some file identifiers are changed in 7.0, so file identifier mismatches
			// are expected during a downgrade from 7.0 to 6.3
			bool expectMismatch = mProtocolVersion >= ProtocolVersion(0x0FDB00B070000000LL);
			{
				TraceEvent te(expectMismatch ? SevInfo : SevError, "MismatchedFileIdentifier");
				if (expectMismatch) {
					te.suppressFor(1.0);
				}
				te.detail("Expected", file_identifier).detail("Read", read_file_identifier(data));
			}
			if (!expectMismatch) {
				ASSERT(false);
			}
		}
		load_members(data, context, items...);
	}

	template <class Item>
	void deserialize(Item& item) {
		deserialize(FileIdentifierFor<Item>::value, item);
	}
};

class ObjectReader : public _ObjectReader<ObjectReader> {
	friend struct _IncludeVersion;
	ObjectReader& operator>>(ProtocolVersion& version) {
		uint64_t result;
		memcpy(&result, _data, sizeof(result));
		_data += sizeof(result);
		version = ProtocolVersion(result);
		return *this;
	}

public:
	static constexpr bool ownsUnderlyingMemory = false;

	template <class VersionOptions>
	ObjectReader(const uint8_t* data, VersionOptions vo) : _data(data) {
		vo.read(*this);
	}

	template <class T, class VersionOptions>
	static T fromStringRef(StringRef sr, VersionOptions vo) {
		T t;
		ObjectReader reader(sr.begin(), vo);
		reader.deserialize(t);
		return t;
	}

	const uint8_t* data() { return _data; }

	Arena& arena() { return _arena; }

private:
	const uint8_t* _data;
	Arena _arena;
};

class ArenaObjectReader : public _ObjectReader<ArenaObjectReader> {
	friend struct _IncludeVersion;
	ArenaObjectReader& operator>>(ProtocolVersion& version) {
		uint64_t result;
		memcpy(&result, _data, sizeof(result));
		_data += sizeof(result);
		version = ProtocolVersion(result);
		return *this;
	}

public:
	static constexpr bool ownsUnderlyingMemory = true;

	template <class VersionOptions>
	ArenaObjectReader(Arena const& arena, const StringRef& input, VersionOptions vo)
	  : _data(input.begin()), _arena(arena) {
		vo.read(*this);
	}

	const uint8_t* data() { return _data; }

	Arena& arena() { return _arena; }

private:
	const uint8_t* _data;
	Arena _arena;
};

class ObjectWriter {
	friend struct _IncludeVersion;
	bool writeProtocolVersion = false;
	ObjectWriter& operator<<(const ProtocolVersion& version) {
		writeProtocolVersion = true;
		return *this;
	}
	ProtocolVersion mProtocolVersion;

public:
	template <class VersionOptions>
	ObjectWriter(VersionOptions vo) {
		vo.write(*this);
	}
	template <class VersionOptions>
	explicit ObjectWriter(std::function<uint8_t*(size_t)> customAllocator, VersionOptions vo)
	  : customAllocator(customAllocator) {
		vo.write(*this);
	}
	template <class... Items>
	void serialize(FileIdentifier file_identifier, Items const&... items) {
		int allocations = 0;
		auto allocator = [this, &allocations](size_t size_) {
			++allocations;
			this->size = writeProtocolVersion ? size_ + sizeof(uint64_t) : size_;
			if (customAllocator) {
				data = customAllocator(this->size);
			} else {
				data = new (arena) uint8_t[this->size];
			}
			if (writeProtocolVersion) {
				auto v = protocolVersion().versionWithFlags();
				memcpy(data, &v, sizeof(uint64_t));
				return data + sizeof(uint64_t);
			}
			return data;
		};
		ASSERT(data == nullptr); // object serializer can only serialize one object
		SaveContext<ObjectWriter, decltype(allocator)> context(this, allocator);
		save_members(context, file_identifier, items...);
		ASSERT(allocations == 1);
	}

	template <class Item>
	void serialize(Item const& item) {
		serialize(FileIdentifierFor<Item>::value, item);
	}

	StringRef toStringRef() const { return StringRef(data, size); }

	Standalone<StringRef> toString() const {
		ASSERT(!customAllocator);
		return Standalone<StringRef>(toStringRef(), arena);
	}

	template <class Item, class VersionOptions>
	static Standalone<StringRef> toValue(Item const& item, VersionOptions vo) {
		ObjectWriter writer(vo);
		writer.serialize(item);
		return writer.toString();
	}

	ProtocolVersion protocolVersion() const { return mProtocolVersion; }
	void setProtocolVersion(ProtocolVersion v) {
		mProtocolVersion = v;
		ASSERT(mProtocolVersion.isValid());
	}

private:
	Arena arena;
	std::function<uint8_t*(size_t)> customAllocator;
	uint8_t* data = nullptr;
	int size = 0;
};

// this special case is needed - the code expects
// Standalone<T> and T to be equivalent for serialization
namespace detail {

template <class T, class Context>
struct LoadSaveHelper<Standalone<T>, Context> : Context {
	LoadSaveHelper(const Context& context) : Context(context), helper(context) {}

	void load(Standalone<T>& member, const uint8_t* current) {
		helper.load(member.contents(), current);
		this->addArena(member.arena());
	}

	template <class Writer>
	RelativeOffset save(const Standalone<T>& member, Writer& writer, const VTableSet* vtables) {
		return helper.save(member.contents(), writer, vtables);
	}

private:
	LoadSaveHelper<T, Context> helper;
};

} // namespace detail