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/**
* Copyright (C) 2020-present MongoDB, Inc.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the Server Side Public License, version 1,
* as published by MongoDB, Inc.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* Server Side Public License for more details.
*
* You should have received a copy of the Server Side Public License
* along with this program. If not, see
* <http://www.mongodb.com/licensing/server-side-public-license>.
*
* As a special exception, the copyright holders give permission to link the
* code of portions of this program with the OpenSSL library under certain
* conditions as described in each individual source file and distribute
* linked combinations including the program with the OpenSSL library. You
* must comply with the Server Side Public License in all respects for
* all of the code used other than as permitted herein. If you modify file(s)
* with this exception, you may extend this exception to your version of the
* file(s), but you are not obligated to do so. If you do not wish to do so,
* delete this exception statement from your version. If you delete this
* exception statement from all source files in the program, then also delete
* it in the license file.
*/
#pragma once
#include <string>
#include "mongo/db/feature_compatibility_version_parser.h"
#include "mongo/db/server_options.h"
#include "mongo/db/server_parameter.h"
#include "mongo/util/version/releases.h"
namespace mongo {
/**
* FeatureFlag contains information about whether a feature flag is enabled and what version it was
* released.
*
* FeatureFlag represents the state of a feature flag and whether it is associated with a particular
* version. It is not implicitly convertible to bool to force all call sites to make a decision
* about what check to use.
*
* It is only set at startup.
*/
class FeatureFlag {
friend class FeatureFlagServerParameter;
public:
FeatureFlag(bool enabled, StringData versionString, bool shouldBeFCVGated);
/**
* Returns true if the flag is set to true and enabled for this FCV version.
*/
bool isEnabled(const ServerGlobalParams::FeatureCompatibility& fcv) const;
/**
* Returns true if the flag is set to true and enabled for this FCV version. If the FCV version
* is unset, instead checks against the default last LTS FCV version.
*/
bool isEnabledUseDefaultFCVWhenUninitialized(
const ServerGlobalParams::FeatureCompatibility& fcv) const;
/**
* Returns true if this flag is enabled regardless of the current FCV version. When using this
* function, you are allowing the feature flag to pass checking during transitional FCV states
* and downgraded FCV, which means the code gated by this feature flag is allowed to run even if
* the FCV requirement of this feature flag is not met.
*
* isEnabled() is prefered over this function since it will prevent upgrade/downgrade issues.
*
* Note: A comment starting with (Ignore FCV check) is required for the use of this function. If
* the feature flag check is before FCV initialization, use isEnabledAndIgnoreFCVUnsafeAtStartup
* instead.
*/
bool isEnabledAndIgnoreFCVUnsafe() const;
/**
* Returns true if this flag is enabled regardless of the current FCV version. When using this
* function, you are allowing the feature flag to pass checking during transitional FCV states
* and downgraded FCV, which means the code gated by this feature flag is allowed to run even if
* the FCV requirement of this feature flag is not met.
*
* This is same as isEnabledAndIgnoreFCVUnsafe() but doesn't require a comment. This should
* only be used before FCV initialization.
*/
bool isEnabledAndIgnoreFCVUnsafeAtStartup() const;
/**
* Returns true if the flag is set to true and enabled on the target FCV version.
*
* This function is used in the 'setFeatureCompatibilityVersion' command where the in-memory FCV
* is in flux.
*/
bool isEnabledOnVersion(multiversion::FeatureCompatibilityVersion targetFCV) const;
/**
* Returns true if the feature flag is disabled on targetFCV but enabled on originalFCV.
*/
bool isDisabledOnTargetFCVButEnabledOnOriginalFCV(
multiversion::FeatureCompatibilityVersion targetFCV,
multiversion::FeatureCompatibilityVersion originalFCV) const;
/**
* Returns true if the feature flag is enabled on targetFCV but disabled on originalFCV.
*/
bool isEnabledOnTargetFCVButDisabledOnOriginalFCV(
multiversion::FeatureCompatibilityVersion targetFCV,
multiversion::FeatureCompatibilityVersion originalFCV) const;
/**
* Return the version associated with this feature flag.
*
* Throws if feature is not enabled.
*/
multiversion::FeatureCompatibilityVersion getVersion() const;
private:
void set(bool enabled);
private:
bool _enabled;
multiversion::FeatureCompatibilityVersion _version;
bool _shouldBeFCVGated;
};
/**
* Specialization of ServerParameter for FeatureFlags used by IDL generator.
*/
class FeatureFlagServerParameter : public ServerParameter {
public:
FeatureFlagServerParameter(StringData name, FeatureFlag& storage);
/**
* Encode the setting into BSON object.
*
* Typically invoked by {getParameter:...} to produce a dictionary
* of ServerParameter settings.
*/
void append(OperationContext* opCtx,
BSONObjBuilder* b,
StringData name,
const boost::optional<TenantId>&) final;
/**
* Encode the feature flag value into a BSON object, discarding the version.
*/
void appendSupportingRoundtrip(OperationContext* opCtx,
BSONObjBuilder* b,
StringData name,
const boost::optional<TenantId>&) override;
/**
* Update the underlying value using a BSONElement
*
* Allows setting non-basic values (e.g. vector<string>)
* via the {setParameter: ...} call.
*/
Status set(const BSONElement& newValueElement, const boost::optional<TenantId>&) final;
/**
* Update the underlying value from a string.
*
* Typically invoked from commandline --setParameter usage.
*/
Status setFromString(StringData str, const boost::optional<TenantId>&) final;
private:
FeatureFlag& _storage;
};
inline FeatureFlagServerParameter* makeFeatureFlagServerParameter(StringData name,
FeatureFlag& storage) {
auto p = std::make_unique<FeatureFlagServerParameter>(name, storage);
registerServerParameter(&*p);
return p.release();
}
} // namespace mongo
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