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/**
* Copyright (C) 2021-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.
*/
#include "mongo/s/load_balancer_support.h"
#include <memory>
#include "mongo/bson/bsonobjbuilder.h"
#include "mongo/bson/oid.h"
#include "mongo/db/client.h"
#include "mongo/db/operation_context.h"
#include "mongo/db/repl/hello_gen.h"
#include "mongo/db/service_context.h"
#include "mongo/s/load_balancer_feature_flag_gen.h"
#include "mongo/util/assert_util.h"
#include "mongo/util/fail_point.h"
namespace mongo::load_balancer_support {
namespace {
MONGO_FAIL_POINT_DEFINE(clientIsFromLoadBalancer);
bool featureEnabled() {
return feature_flags::gFeatureFlagLoadBalancer.isEnabled(
serverGlobalParams.featureCompatibility);
}
struct PerService {
/**
* When a client reaches a mongos through a load balancer, the `serviceId`
* identifies the mongos to which it is connected. It persists through the
* lifespan of the service context.
*/
OID serviceId = OID::gen();
};
class PerClient {
public:
bool isFromLoadBalancer() const {
if (MONGO_unlikely(clientIsFromLoadBalancer.shouldFail())) {
return true;
}
return _isFromLoadBalancer;
}
void setIsFromLoadBalancer() {
_isFromLoadBalancer = true;
}
bool didHello() const {
return _didHello;
}
void setDidHello() {
_didHello = true;
}
private:
/** True if the connection was established through a load balancer. */
bool _isFromLoadBalancer = false;
/** True after we send this client a hello reply. */
bool _didHello = false;
};
const auto getPerServiceState = ServiceContext::declareDecoration<PerService>();
const auto getPerClientState = Client::declareDecoration<PerClient>();
} // namespace
void setClientIsFromLoadBalancer(Client* client) {
if (!featureEnabled())
return;
auto& perClient = getPerClientState(client);
perClient.setIsFromLoadBalancer();
}
void handleHello(OperationContext* opCtx, BSONObjBuilder* result, bool helloHasLoadBalancedOption) {
if (!featureEnabled())
return;
auto& perClient = getPerClientState(opCtx->getClient());
if (perClient.didHello() || !perClient.isFromLoadBalancer())
return;
uassert(ErrorCodes::LoadBalancerSupportMismatch,
"The server is being accessed through a load balancer, but "
"this driver does not have load balancing enabled",
helloHasLoadBalancedOption);
result->append(HelloCommandReply::kServiceIdFieldName,
getPerServiceState(opCtx->getServiceContext()).serviceId);
perClient.setDidHello();
}
} // namespace mongo::load_balancer_support
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