/**
 *    Copyright (C) 2017 MongoDB, Inc.
 *
 *    This program is free software: you can redistribute it and/or  modify
 *    it under the terms of the GNU Affero General Public License, version 3,
 *    as published by the Free Software Foundation.
 *
 *    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
 *    GNU Affero General Public License for more details.
 *
 *    You should have received a copy of the GNU Affero General Public License
 *    along with this program.  If not, see <http://www.gnu.org/licenses/>.
 *
 *    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 GNU Affero General 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.
 */

#define MONGO_LOG_DEFAULT_COMPONENT ::mongo::logger::LogComponent::kStorage

#include "mongo/platform/basic.h"

#include "mongo/db/session.h"

#include "mongo/db/catalog/index_catalog.h"
#include "mongo/db/concurrency/lock_state.h"
#include "mongo/db/concurrency/locker.h"
#include "mongo/db/concurrency/write_conflict_exception.h"
#include "mongo/db/db_raii.h"
#include "mongo/db/dbdirectclient.h"
#include "mongo/db/index/index_access_method.h"
#include "mongo/db/namespace_string.h"
#include "mongo/db/operation_context.h"
#include "mongo/db/ops/update.h"
#include "mongo/db/query/get_executor.h"
#include "mongo/db/retryable_writes_stats.h"
#include "mongo/db/transaction_history_iterator.h"
#include "mongo/stdx/memory.h"
#include "mongo/transport/transport_layer.h"
#include "mongo/util/fail_point_service.h"
#include "mongo/util/log.h"
#include "mongo/util/mongoutils/str.h"

namespace mongo {

namespace {

void fassertOnRepeatedExecution(const LogicalSessionId& lsid,
                                TxnNumber txnNumber,
                                StmtId stmtId,
                                const repl::OpTime& firstOpTime,
                                const repl::OpTime& secondOpTime) {
    severe() << "Statement id " << stmtId << " from transaction [ " << lsid.toBSON() << ":"
             << txnNumber << " ] was committed once with opTime " << firstOpTime
             << " and a second time with opTime " << secondOpTime
             << ". This indicates possible data corruption or server bug and the process will be "
                "terminated.";
    fassertFailed(40526);
}

struct ActiveTransactionHistory {
    boost::optional<SessionTxnRecord> lastTxnRecord;
    Session::CommittedStatementTimestampMap committedStatements;
    bool transactionCommitted{false};
    bool hasIncompleteHistory{false};
};

ActiveTransactionHistory fetchActiveTransactionHistory(OperationContext* opCtx,
                                                       const LogicalSessionId& lsid) {
    ActiveTransactionHistory result;

    result.lastTxnRecord = [&]() -> boost::optional<SessionTxnRecord> {
        DBDirectClient client(opCtx);
        auto result =
            client.findOne(NamespaceString::kSessionTransactionsTableNamespace.ns(),
                           {BSON(SessionTxnRecord::kSessionIdFieldName << lsid.toBSON())});
        if (result.isEmpty()) {
            return boost::none;
        }

        return SessionTxnRecord::parse(IDLParserErrorContext("parse latest txn record for session"),
                                       result);
    }();

    if (!result.lastTxnRecord) {
        return result;
    }

    auto it = TransactionHistoryIterator(result.lastTxnRecord->getLastWriteOpTime());
    while (it.hasNext()) {
        try {
            const auto entry = it.next(opCtx);
            invariant(entry.getStatementId());

            if (*entry.getStatementId() == kIncompleteHistoryStmtId) {
                // Only the dead end sentinel can have this id for oplog write history
                invariant(entry.getObject2());
                invariant(entry.getObject2()->woCompare(Session::kDeadEndSentinel) == 0);
                result.hasIncompleteHistory = true;
                continue;
            }

            const auto insertRes =
                result.committedStatements.emplace(*entry.getStatementId(), entry.getOpTime());
            if (!insertRes.second) {
                const auto& existingOpTime = insertRes.first->second;
                fassertOnRepeatedExecution(lsid,
                                           result.lastTxnRecord->getTxnNum(),
                                           *entry.getStatementId(),
                                           existingOpTime,
                                           entry.getOpTime());
            }

            // applyOps oplog entry marks the commit of a transaction.
            if (entry.isCommand() &&
                entry.getCommandType() == repl::OplogEntry::CommandType::kApplyOps) {
                result.transactionCommitted = true;
            }
        } catch (const DBException& ex) {
            if (ex.code() == ErrorCodes::IncompleteTransactionHistory) {
                result.hasIncompleteHistory = true;
                break;
            }

            throw;
        }
    }

    return result;
}

void updateSessionEntry(OperationContext* opCtx, const UpdateRequest& updateRequest) {
    // Current code only supports replacement update.
    dassert(UpdateDriver::isDocReplacement(updateRequest.getUpdates()));

    AutoGetCollection autoColl(opCtx, NamespaceString::kSessionTransactionsTableNamespace, MODE_IX);

    uassert(40527,
            str::stream() << "Unable to persist transaction state because the session transaction "
                             "collection is missing. This indicates that the "
                          << NamespaceString::kSessionTransactionsTableNamespace.ns()
                          << " collection has been manually deleted.",
            autoColl.getCollection());

    WriteUnitOfWork wuow(opCtx);

    auto collection = autoColl.getCollection();
    auto idIndex = collection->getIndexCatalog()->findIdIndex(opCtx);

    uassert(40672,
            str::stream() << "Failed to fetch _id index for "
                          << NamespaceString::kSessionTransactionsTableNamespace.ns(),
            idIndex);

    auto indexAccess = collection->getIndexCatalog()->getIndex(idIndex);
    // Since we are looking up a key inside the _id index, create a key object consisting of only
    // the _id field.
    auto idToFetch = updateRequest.getQuery().firstElement();
    auto toUpdateIdDoc = idToFetch.wrap();
    dassert(idToFetch.fieldNameStringData() == "_id"_sd);
    auto recordId = indexAccess->findSingle(opCtx, toUpdateIdDoc);
    auto startingSnapshotId = opCtx->recoveryUnit()->getSnapshotId();

    if (recordId.isNull()) {
        // Upsert case.
        auto status = collection->insertDocument(
            opCtx, InsertStatement(updateRequest.getUpdates()), nullptr, false);

        if (status == ErrorCodes::DuplicateKey) {
            throw WriteConflictException();
        }

        uassertStatusOK(status);
        wuow.commit();
        return;
    }

    auto originalRecordData = collection->getRecordStore()->dataFor(opCtx, recordId);
    auto originalDoc = originalRecordData.toBson();

    invariant(collection->getDefaultCollator() == nullptr);
    boost::intrusive_ptr<ExpressionContext> expCtx(new ExpressionContext(opCtx, nullptr));

    auto matcher =
        fassert(40673, MatchExpressionParser::parse(updateRequest.getQuery(), std::move(expCtx)));
    if (!matcher->matchesBSON(originalDoc)) {
        // Document no longer match what we expect so throw WCE to make the caller re-examine.
        throw WriteConflictException();
    }

    OplogUpdateEntryArgs args;
    args.nss = NamespaceString::kSessionTransactionsTableNamespace;
    args.uuid = collection->uuid();
    args.update = updateRequest.getUpdates();
    args.criteria = toUpdateIdDoc;
    args.fromMigrate = false;

    collection->updateDocument(opCtx,
                               recordId,
                               Snapshotted<BSONObj>(startingSnapshotId, originalDoc),
                               updateRequest.getUpdates(),
                               false,  // indexesAffected = false because _id is the only index
                               nullptr,
                               &args);

    wuow.commit();
}

// Failpoint which allows different failure actions to happen after each write. Supports the
// parameters below, which can be combined with each other (unless explicitly disallowed):
//
// closeConnection (bool, default = true): Closes the connection on which the write was executed.
// failBeforeCommitExceptionCode (int, default = not specified): If set, the specified exception
//      code will be thrown, which will cause the write to not commit; if not specified, the write
//      will be allowed to commit.
MONGO_FAIL_POINT_DEFINE(onPrimaryTransactionalWrite);

}  // namespace

const BSONObj Session::kDeadEndSentinel(BSON("$incompleteOplogHistory" << 1));

Session::Session(LogicalSessionId sessionId) : _sessionId(std::move(sessionId)) {}

void Session::refreshFromStorageIfNeeded(OperationContext* opCtx) {
    if (opCtx->getClient()->isInDirectClient()) {
        return;
    }

    invariant(!opCtx->lockState()->isLocked());
    invariant(repl::ReadConcernArgs::get(opCtx).getLevel() ==
              repl::ReadConcernLevel::kLocalReadConcern);

    stdx::unique_lock<stdx::mutex> ul(_mutex);

    while (!_isValid) {
        const int numInvalidations = _numInvalidations;

        ul.unlock();

        auto activeTxnHistory = fetchActiveTransactionHistory(opCtx, _sessionId);

        ul.lock();

        // Protect against concurrent refreshes or invalidations
        if (!_isValid && _numInvalidations == numInvalidations) {
            _isValid = true;
            _lastWrittenSessionRecord = std::move(activeTxnHistory.lastTxnRecord);

            if (_lastWrittenSessionRecord) {
                if (!_lastRefreshState) {
                    _lastRefreshState.emplace();
                }

                _lastRefreshState->refreshCount++;

                _activeTxnNumber = _lastWrittenSessionRecord->getTxnNum();
                _lastRefreshState->txnNumber = _activeTxnNumber;

                _activeTxnCommittedStatements = std::move(activeTxnHistory.committedStatements);
                _hasIncompleteHistory = activeTxnHistory.hasIncompleteHistory;
                _lastRefreshState->isCommitted = activeTxnHistory.transactionCommitted;
            }

            break;
        }
    }
}

void Session::beginOrContinueTxn(OperationContext* opCtx, TxnNumber txnNumber) {
    stdx::lock_guard<stdx::mutex> lg(_mutex);
    _beginOrContinueTxn(lg, txnNumber);
}

void Session::onWriteOpCompletedOnPrimary(OperationContext* opCtx,
                                          TxnNumber txnNumber,
                                          std::vector<StmtId> stmtIdsWritten,
                                          const repl::OpTime& lastStmtIdWriteOpTime,
                                          Date_t lastStmtIdWriteDate,
                                          boost::optional<DurableTxnStateEnum> txnState) {
    invariant(opCtx->lockState()->inAWriteUnitOfWork());

    stdx::unique_lock<stdx::mutex> ul(_mutex);

    // Sanity check that we don't double-execute statements
    for (const auto stmtId : stmtIdsWritten) {
        const auto stmtOpTime = _checkStatementExecuted(ul, txnNumber, stmtId);
        if (stmtOpTime) {
            fassertOnRepeatedExecution(
                _sessionId, txnNumber, stmtId, *stmtOpTime, lastStmtIdWriteOpTime);
        }
    }

    const auto updateRequest =
        _makeUpdateRequest(ul, txnNumber, lastStmtIdWriteOpTime, lastStmtIdWriteDate, txnState);

    ul.unlock();

    repl::UnreplicatedWritesBlock doNotReplicateWrites(opCtx);

    updateSessionEntry(opCtx, updateRequest);
    _registerUpdateCacheOnCommit(
        opCtx, txnNumber, std::move(stmtIdsWritten), lastStmtIdWriteOpTime);
}

bool Session::onMigrateBeginOnPrimary(OperationContext* opCtx, TxnNumber txnNumber, StmtId stmtId) {
    beginOrContinueTxn(opCtx, txnNumber);

    try {
        if (checkStatementExecuted(opCtx, txnNumber, stmtId)) {
            return false;
        }
    } catch (const DBException& ex) {
        // If the transaction chain was truncated on the recipient shard, then we
        // are most likely copying from a session that hasn't been touched on the
        // recipient shard for a very long time but could be recent on the donor.
        // We continue copying regardless to get the entire transaction from the donor.
        if (ex.code() != ErrorCodes::IncompleteTransactionHistory) {
            throw;
        }
        if (stmtId == kIncompleteHistoryStmtId) {
            return false;
        }
    }

    return true;
}

void Session::onMigrateCompletedOnPrimary(OperationContext* opCtx,
                                          TxnNumber txnNumber,
                                          std::vector<StmtId> stmtIdsWritten,
                                          const repl::OpTime& lastStmtIdWriteOpTime,
                                          Date_t oplogLastStmtIdWriteDate) {
    invariant(opCtx->lockState()->inAWriteUnitOfWork());

    stdx::unique_lock<stdx::mutex> ul(_mutex);

    _checkValid(ul);
    _checkIsActiveTransaction(ul, txnNumber);

    // If the transaction has a populated lastWriteDate, we will use that as the most up-to-date
    // value. Using the lastWriteDate from the oplog being migrated may move the lastWriteDate
    // back. However, in the case that the transaction doesn't have the lastWriteDate populated,
    // the oplog's value serves as a best-case fallback.
    const auto txnLastStmtIdWriteDate = _getLastWriteDate(ul, txnNumber);
    const auto updatedLastStmtIdWriteDate =
        txnLastStmtIdWriteDate == Date_t::min() ? oplogLastStmtIdWriteDate : txnLastStmtIdWriteDate;

    // We do not migrate transaction oplog entries.
    auto txnState = boost::none;
    const auto updateRequest = _makeUpdateRequest(
        ul, txnNumber, lastStmtIdWriteOpTime, updatedLastStmtIdWriteDate, txnState);

    ul.unlock();

    repl::UnreplicatedWritesBlock doNotReplicateWrites(opCtx);

    updateSessionEntry(opCtx, updateRequest);
    _registerUpdateCacheOnCommit(
        opCtx, txnNumber, std::move(stmtIdsWritten), lastStmtIdWriteOpTime);
}

void Session::invalidate() {
    stdx::lock_guard<stdx::mutex> lg(_mutex);

    if (_isTxnNumberLocked) {
        invariant(_txnNumberLockConflictStatus);
        uasserted(50908,
                  str::stream() << "cannot invalidate session because txnNumber is locked: "
                                << *_txnNumberLockConflictStatus);
    }

    _isValid = false;
    _numInvalidations++;

    _lastWrittenSessionRecord.reset();

    _activeTxnNumber = kUninitializedTxnNumber;
    _activeTxnCommittedStatements.clear();
    _hasIncompleteHistory = false;
}

repl::OpTime Session::getLastWriteOpTime(TxnNumber txnNumber) const {
    stdx::lock_guard<stdx::mutex> lg(_mutex);
    _checkValid(lg);
    _checkIsActiveTransaction(lg, txnNumber);

    if (!_lastWrittenSessionRecord || _lastWrittenSessionRecord->getTxnNum() != txnNumber)
        return {};

    return _lastWrittenSessionRecord->getLastWriteOpTime();
}

boost::optional<repl::OplogEntry> Session::checkStatementExecuted(OperationContext* opCtx,
                                                                  TxnNumber txnNumber,
                                                                  StmtId stmtId) const {
    const auto stmtTimestamp = [&] {
        stdx::lock_guard<stdx::mutex> lg(_mutex);
        return _checkStatementExecuted(lg, txnNumber, stmtId);
    }();

    if (!stmtTimestamp)
        return boost::none;

    TransactionHistoryIterator txnIter(*stmtTimestamp);
    while (txnIter.hasNext()) {
        const auto entry = txnIter.next(opCtx);
        invariant(entry.getStatementId());
        if (*entry.getStatementId() == stmtId)
            return entry;
    }

    MONGO_UNREACHABLE;
}

bool Session::checkStatementExecutedNoOplogEntryFetch(TxnNumber txnNumber, StmtId stmtId) const {
    stdx::lock_guard<stdx::mutex> lg(_mutex);
    return bool(_checkStatementExecuted(lg, txnNumber, stmtId));
}

void Session::_beginOrContinueTxn(WithLock wl, TxnNumber txnNumber) {

    // Check whether the session information needs to be refreshed from disk.
    _checkValid(wl);

    // Check if the given transaction number is valid for this session. The transaction number must
    // be >= the active transaction number.
    _checkTxnValid(wl, txnNumber);

    //
    // Continue an active transaction.
    //
    if (txnNumber == _activeTxnNumber) {
        return;
    }

    invariant(txnNumber > _activeTxnNumber);
    _setActiveTxn(wl, txnNumber);
}

void Session::_checkTxnValid(WithLock, TxnNumber txnNumber) const {
    uassert(ErrorCodes::TransactionTooOld,
            str::stream() << "Cannot start transaction " << txnNumber << " on session "
                          << getSessionId()
                          << " because a newer transaction "
                          << _activeTxnNumber
                          << " has already started.",
            txnNumber >= _activeTxnNumber);
}

void Session::_setActiveTxn(WithLock wl, TxnNumber txnNumber) {
    if (_isTxnNumberLocked) {
        invariant(_txnNumberLockConflictStatus);
        uassertStatusOK(*_txnNumberLockConflictStatus);
    }

    _activeTxnNumber = txnNumber;
    _activeTxnCommittedStatements.clear();
    _hasIncompleteHistory = false;
}

void Session::_checkValid(WithLock) const {
    uassert(ErrorCodes::ConflictingOperationInProgress,
            str::stream() << "Session " << getSessionId()
                          << " was concurrently modified and the operation must be retried.",
            _isValid);
}

void Session::_checkIsActiveTransaction(WithLock, TxnNumber txnNumber) const {
    uassert(ErrorCodes::ConflictingOperationInProgress,
            str::stream() << "Cannot perform operations on transaction " << txnNumber
                          << " on session "
                          << getSessionId()
                          << " because a different transaction "
                          << _activeTxnNumber
                          << " is now active.",
            txnNumber == _activeTxnNumber);
}

boost::optional<repl::OpTime> Session::_checkStatementExecuted(WithLock wl,
                                                               TxnNumber txnNumber,
                                                               StmtId stmtId) const {
    _checkValid(wl);
    _checkIsActiveTransaction(wl, txnNumber);

    const auto it = _activeTxnCommittedStatements.find(stmtId);
    if (it == _activeTxnCommittedStatements.end()) {
        uassert(ErrorCodes::IncompleteTransactionHistory,
                str::stream() << "Incomplete history detected for transaction " << txnNumber
                              << " on session "
                              << _sessionId.toBSON(),
                !_hasIncompleteHistory);

        return boost::none;
    }

    invariant(_lastWrittenSessionRecord);
    invariant(_lastWrittenSessionRecord->getTxnNum() == txnNumber);

    return it->second;
}

Date_t Session::_getLastWriteDate(WithLock wl, TxnNumber txnNumber) const {
    _checkValid(wl);
    _checkIsActiveTransaction(wl, txnNumber);

    if (!_lastWrittenSessionRecord || _lastWrittenSessionRecord->getTxnNum() != txnNumber)
        return {};

    return _lastWrittenSessionRecord->getLastWriteDate();
}

UpdateRequest Session::_makeUpdateRequest(WithLock,
                                          TxnNumber newTxnNumber,
                                          const repl::OpTime& newLastWriteOpTime,
                                          Date_t newLastWriteDate,
                                          boost::optional<DurableTxnStateEnum> newState) const {
    UpdateRequest updateRequest(NamespaceString::kSessionTransactionsTableNamespace);

    const auto updateBSON = [&] {
        SessionTxnRecord newTxnRecord;
        newTxnRecord.setSessionId(_sessionId);
        newTxnRecord.setTxnNum(newTxnNumber);
        newTxnRecord.setLastWriteOpTime(newLastWriteOpTime);
        newTxnRecord.setLastWriteDate(newLastWriteDate);
        newTxnRecord.setState(newState);
        return newTxnRecord.toBSON();
    }();
    updateRequest.setUpdates(updateBSON);
    updateRequest.setQuery(BSON(SessionTxnRecord::kSessionIdFieldName << _sessionId.toBSON()));
    updateRequest.setUpsert(true);

    return updateRequest;
}

void Session::_registerUpdateCacheOnCommit(OperationContext* opCtx,
                                           TxnNumber newTxnNumber,
                                           std::vector<StmtId> stmtIdsWritten,
                                           const repl::OpTime& lastStmtIdWriteOpTime) {
    opCtx->recoveryUnit()->onCommit(
        [ this, newTxnNumber, stmtIdsWritten = std::move(stmtIdsWritten), lastStmtIdWriteOpTime ](
            boost::optional<Timestamp>) {
            RetryableWritesStats::get(getGlobalServiceContext())
                ->incrementTransactionsCollectionWriteCount();

            stdx::lock_guard<stdx::mutex> lg(_mutex);

            if (!_isValid)
                return;

            // The cache of the last written record must always be advanced after a write so that
            // subsequent writes have the correct point to start from.
            if (!_lastWrittenSessionRecord) {
                _lastWrittenSessionRecord.emplace();

                _lastWrittenSessionRecord->setSessionId(_sessionId);
                _lastWrittenSessionRecord->setTxnNum(newTxnNumber);
                _lastWrittenSessionRecord->setLastWriteOpTime(lastStmtIdWriteOpTime);
            } else {
                if (newTxnNumber > _lastWrittenSessionRecord->getTxnNum())
                    _lastWrittenSessionRecord->setTxnNum(newTxnNumber);

                if (lastStmtIdWriteOpTime > _lastWrittenSessionRecord->getLastWriteOpTime())
                    _lastWrittenSessionRecord->setLastWriteOpTime(lastStmtIdWriteOpTime);
            }

            if (newTxnNumber > _activeTxnNumber) {
                // This call is necessary in order to advance the txn number and reset the cached
                // state in the case where just before the storage transaction commits, the cache
                // entry gets invalidated and immediately refreshed while there were no writes for
                // newTxnNumber yet. In this case _activeTxnNumber will be less than newTxnNumber
                // and we will fail to update the cache even though the write was successful.
                _beginOrContinueTxn(lg, newTxnNumber);
            }

            if (newTxnNumber == _activeTxnNumber) {
                for (const auto stmtId : stmtIdsWritten) {
                    if (stmtId == kIncompleteHistoryStmtId) {
                        _hasIncompleteHistory = true;
                        continue;
                    }

                    const auto insertRes =
                        _activeTxnCommittedStatements.emplace(stmtId, lastStmtIdWriteOpTime);
                    if (!insertRes.second) {
                        const auto& existingOpTime = insertRes.first->second;
                        fassertOnRepeatedExecution(_sessionId,
                                                   newTxnNumber,
                                                   stmtId,
                                                   existingOpTime,
                                                   lastStmtIdWriteOpTime);
                    }
                }
            }
        });

    MONGO_FAIL_POINT_BLOCK(onPrimaryTransactionalWrite, customArgs) {
        const auto& data = customArgs.getData();

        const auto closeConnectionElem = data["closeConnection"];
        if (closeConnectionElem.eoo() || closeConnectionElem.Bool()) {
            opCtx->getClient()->session()->end();
        }

        const auto failBeforeCommitExceptionElem = data["failBeforeCommitExceptionCode"];
        if (!failBeforeCommitExceptionElem.eoo()) {
            const auto failureCode = ErrorCodes::Error(int(failBeforeCommitExceptionElem.Number()));
            uasserted(failureCode,
                      str::stream() << "Failing write for " << _sessionId << ":" << newTxnNumber
                                    << " due to failpoint. The write must not be reflected.");
        }
    }
}

boost::optional<repl::OplogEntry> Session::createMatchingTransactionTableUpdate(
    const repl::OplogEntry& entry) {
    auto sessionInfo = entry.getOperationSessionInfo();
    if (!sessionInfo.getTxnNumber()) {
        return boost::none;
    }

    invariant(sessionInfo.getSessionId());
    invariant(entry.getWallClockTime());

    const auto updateBSON = [&] {
        SessionTxnRecord newTxnRecord;
        newTxnRecord.setSessionId(*sessionInfo.getSessionId());
        newTxnRecord.setTxnNum(*sessionInfo.getTxnNumber());
        newTxnRecord.setLastWriteOpTime(entry.getOpTime());
        newTxnRecord.setLastWriteDate(*entry.getWallClockTime());

        if (entry.isCommand() &&
            entry.getCommandType() == repl::OplogEntry::CommandType::kApplyOps) {
            newTxnRecord.setState(entry.shouldPrepare() ? DurableTxnStateEnum::kPrepared
                                                        : DurableTxnStateEnum::kCommitted);
        }
        return newTxnRecord.toBSON();
    }();

    return repl::OplogEntry(
        entry.getOpTime(),
        0,  // hash
        repl::OpTypeEnum::kUpdate,
        NamespaceString::kSessionTransactionsTableNamespace,
        boost::none,  // uuid
        false,        // fromMigrate
        repl::OplogEntry::kOplogVersion,
        updateBSON,
        BSON(SessionTxnRecord::kSessionIdFieldName << sessionInfo.getSessionId()->toBSON()),
        {},    // sessionInfo
        true,  // upsert
        *entry.getWallClockTime(),
        boost::none,  // statementId
        boost::none,  // prevWriteOpTime
        boost::none,  // preImangeOpTime
        boost::none   // postImageOpTime
        );
}

boost::optional<Session::RefreshState> Session::getLastRefreshState() const {
    stdx::lock_guard<stdx::mutex> lg(_mutex);
    return _lastRefreshState;
}

void Session::lockTxnNumber(const TxnNumber lockThisNumber, Status conflictError) {
    stdx::lock_guard<stdx::mutex> lg(_mutex);
    uassert(50907,
            str::stream() << "cannot lock txnNumber to " << lockThisNumber
                          << " because current txnNumber is "
                          << _activeTxnNumber,
            _activeTxnNumber == lockThisNumber);
    // TODO: remove this if we need to support recursive locking.
    invariant(!_isTxnNumberLocked);

    _isTxnNumberLocked = true;
    _txnNumberLockConflictStatus = conflictError;
}

void Session::unlockTxnNumber() {
    stdx::lock_guard<stdx::mutex> lg(_mutex);

    _isTxnNumberLocked = false;
    _txnNumberLockConflictStatus = boost::none;
}

}  // namespace mongo