Function applySession

src/sessions.ts:1172–1251

(
  session: ClientSession,
  command: Document,
  options: CommandOptions
)

 * @internal
 */
export function applySession(
  session: ClientSession,
  command: Document,
  options: CommandOptions
): MongoDriverError | undefined {
  if (session.hasEnded) {
    return new MongoExpiredSessionError();
  }

  // May acquire serverSession here
  const serverSession = session.serverSession;
  if (serverSession == null) {
    return new MongoRuntimeError('Unable to acquire server session');
  }

  if (options.writeConcern?.w === 0) {
    if (session && session.explicit) {
      // Error if user provided an explicit session to an unacknowledged write (SPEC-1019)
      return new MongoAPIError('Cannot have explicit session with unacknowledged writes');
    }
    return;
  }

  // mark the last use of this session, and apply the `lsid`
  serverSession.lastUse = processTimeMS();
  command.lsid = serverSession.id;

  const inTxnOrTxnCommand = session.inTransaction() || isTransactionCommand(command);
  const isRetryableWrite = !!options.willRetryWrite;

  if (isRetryableWrite || inTxnOrTxnCommand) {
    serverSession.txnNumber += session.txnNumberIncrement;
    session.txnNumberIncrement = 0;
    // TODO(NODE-2674): Preserve int64 sent from MongoDB
    command.txnNumber = Long.fromNumber(serverSession.txnNumber);
  }

  if (!inTxnOrTxnCommand) {
    if (session.transaction.state !== TxnState.NO_TRANSACTION) {
      session.transaction.transition(TxnState.NO_TRANSACTION);
    }

    if (
      session.supports.causalConsistency &&
      session.operationTime &&
      commandSupportsAfterClusterTime(command)
    ) {
      command.readConcern = command.readConcern || {};
      Object.assign(command.readConcern, { afterClusterTime: session.operationTime });
    } else if (session.snapshotEnabled) {
      command.readConcern = command.readConcern || { level: ReadConcernLevel.snapshot };
      if (session.snapshotTime != null) {
        Object.assign(command.readConcern, { atClusterTime: session.snapshotTime });
      }
    }

    return;
  }