69 lines
2.4 KiB
C
69 lines
2.4 KiB
C
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/*
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* LogProtocolMessage.h
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*
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* This source file is part of the FoundationDB open source project
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*
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* Copyright 2013-2018 Apple Inc. and the FoundationDB project authors
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#ifndef FDBSERVER_LOGPROTOCOLMESSAGE_H
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#define FDBSERVER_LOGPROTOCOLMESSAGE_H
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#pragma once
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#include "fdbclient/FDBTypes.h"
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#include "fdbclient/CommitTransaction.h"
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template <class Ar, class VersionOptions>
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typename Ar::READER& applyVersionStartingHere(Ar& ar, VersionOptions vo) {
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vo.read(ar);
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return ar;
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}
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template <class Ar, class VersionOptions>
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typename Ar::WRITER& applyVersionStartingHere(Ar& ar, VersionOptions vo) {
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vo.write(ar);
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return ar;
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}
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struct LogProtocolMessage {
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// This message is pushed into the log system tag for each storage server to inform it what protocol version
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// should be used to deserialize subsequent MutationRefs.
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// It's legitimate to add extra information here (using the protocol version for backward compatibility) but
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// currently there is none.
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// This mechanism passes various ASSERTs in simulation, but has never been used in anger (because MutationRef's
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// serialization format has never changed) so think about testing when it does change.
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// Storage servers merging these messages with MutationRefs need to distinguish the two, so the first byte of
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// the serialization of this message is a type code which is reserved in the MutationRef::Type enum and will thus
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// never be the first byte of a MutationRef message.
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LogProtocolMessage() {}
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template <class Ar>
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void serialize(Ar& ar) {
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uint8_t poly = MutationRef::Reserved_For_LogProtocolMessage;
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ar & poly;
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applyVersionStartingHere(ar, IncludeVersion());
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}
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static bool startsLogProtocolMessage(uint8_t byte) {
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return byte == MutationRef::Reserved_For_LogProtocolMessage;
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}
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template <class Ar> static bool isNextIn(Ar& ar) { return startsLogProtocolMessage(*(const uint8_t*)ar.peekBytes(1)); }
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};
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#endif
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