feature_flag.cpp

/**
 *    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
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 *    it in the license file.
 */

#include "mongo/idl/feature_flag.h"
#include "mongo/db/commands/feature_compatibility_version_parser.h"
#include "mongo/util/debug_util.h"
#include "mongo/util/version/releases.h"

namespace mongo {

// (Generic FCV reference): feature flag support
FeatureFlag::FeatureFlag(bool enabled, StringData versionString)
    : _enabled(enabled), _version(multiversion::GenericFCV::kLatest) {

    // Verify the feature flag invariants. IDL binder verifies these hold but we add these checks to
    // prevent incorrect direct instantiation.
    //
    // If default is true, then version should be present.
    // If default is false, then no version is allowed.
    if (kDebugBuild) {
        if (enabled) {
            dassert(!versionString.empty());
        } else {
            dassert(versionString.empty());
        }
    }

    if (!versionString.empty()) {
        _version = FeatureCompatibilityVersionParser::parseVersionForFeatureFlags(versionString);
    }
}

bool FeatureFlag::isEnabled(const ServerGlobalParams::FeatureCompatibility& fcv) const {
    if (!_enabled) {
        return false;
    }

    return fcv.isGreaterThanOrEqualTo(_version);
}

bool FeatureFlag::isEnabledAndIgnoreFCV() const {
    return _enabled;
}

bool FeatureFlag::isEnabledOnVersion(multiversion::FeatureCompatibilityVersion targetFCV) const {
    if (!_enabled) {
        return false;
    }

    return targetFCV >= _version;
}

multiversion::FeatureCompatibilityVersion FeatureFlag::getVersion() const {
    uassert(5111001, "Feature Flag is not enabled, cannot retrieve version", _enabled);

    return _version;
}

void FeatureFlag::set(bool enabled) {
    _enabled = enabled;
}

FeatureFlagServerParameter::FeatureFlagServerParameter(StringData name, FeatureFlag& storage)
    : ServerParameter(name, ServerParameterType::kStartupOnly), _storage(storage) {}

void FeatureFlagServerParameter::append(OperationContext* opCtx,
                                        BSONObjBuilder& b,
                                        const std::string& name) {
    bool enabled = _storage.isEnabledAndIgnoreFCV();

    {
        auto sub = BSONObjBuilder(b.subobjStart(name));
        sub.append("value"_sd, enabled);

        if (enabled) {
            sub.append("version",
                       FeatureCompatibilityVersionParser::serializeVersionForFeatureFlags(
                           _storage.getVersion()));
        }
    }
}

void FeatureFlagServerParameter::appendSupportingRoundtrip(OperationContext* opCtx,
                                                           BSONObjBuilder& b,
                                                           const std::string& name) {
    bool enabled = _storage.isEnabledAndIgnoreFCV();
    b.append(name, enabled);
}

Status FeatureFlagServerParameter::set(const BSONElement& newValueElement) {
    bool newValue;

    if (auto status = newValueElement.tryCoerce(&newValue); !status.isOK()) {
        return {status.code(),
                str::stream() << "Failed setting " << name() << ": " << status.reason()};
    }

    _storage.set(newValue);

    return Status::OK();
}

Status FeatureFlagServerParameter::setFromString(const std::string& str) {
    auto swNewValue = idl_server_parameter_detail::coerceFromString<bool>(str);
    if (!swNewValue.isOK()) {
        return swNewValue.getStatus();
    }

    _storage.set(swNewValue.getValue());

    return Status::OK();
}

}  // namespace mongo