server.ts

import { promisify } from 'util';

import type { Document } from '../bson';
import { type AutoEncrypter } from '../client-side-encryption/auto_encrypter';
import { type CommandOptions, Connection, type DestroyOptions } from '../cmap/connection';
import {
  ConnectionPool,
  type ConnectionPoolEvents,
  type ConnectionPoolOptions
} from '../cmap/connection_pool';
import { PoolClearedError } from '../cmap/errors';
import {
  APM_EVENTS,
  CLOSED,
  CMAP_EVENTS,
  CONNECT,
  DESCRIPTION_RECEIVED,
  ENDED,
  HEARTBEAT_EVENTS,
  SERVER_HEARTBEAT_FAILED,
  SERVER_HEARTBEAT_STARTED,
  SERVER_HEARTBEAT_SUCCEEDED
} from '../constants';
import {
  type AnyError,
  isNetworkErrorBeforeHandshake,
  isNodeShuttingDownError,
  isSDAMUnrecoverableError,
  MongoError,
  MongoErrorLabel,
  MongoInvalidArgumentError,
  MongoNetworkError,
  MongoNetworkTimeoutError,
  MongoRuntimeError,
  MongoServerClosedError,
  type MongoServerError,
  MongoUnexpectedServerResponseError,
  needsRetryableWriteLabel
} from '../error';
import type { ServerApi } from '../mongo_client';
import { TypedEventEmitter } from '../mongo_types';
import type { GetMoreOptions } from '../operations/get_more';
import type { ClientSession } from '../sessions';
import { isTransactionCommand } from '../transactions';
import {
  type Callback,
  type EventEmitterWithState,
  makeStateMachine,
  maxWireVersion,
  type MongoDBNamespace,
  supportsRetryableWrites
} from '../utils';
import {
  type ClusterTime,
  STATE_CLOSED,
  STATE_CLOSING,
  STATE_CONNECTED,
  STATE_CONNECTING,
  TopologyType
} from './common';
import type {
  ServerHeartbeatFailedEvent,
  ServerHeartbeatStartedEvent,
  ServerHeartbeatSucceededEvent
} from './events';
import { Monitor, type MonitorOptions } from './monitor';
import { compareTopologyVersion, ServerDescription } from './server_description';
import type { Topology } from './topology';

const stateTransition = makeStateMachine({
  [STATE_CLOSED]: [STATE_CLOSED, STATE_CONNECTING],
  [STATE_CONNECTING]: [STATE_CONNECTING, STATE_CLOSING, STATE_CONNECTED, STATE_CLOSED],
  [STATE_CONNECTED]: [STATE_CONNECTED, STATE_CLOSING, STATE_CLOSED],
  [STATE_CLOSING]: [STATE_CLOSING, STATE_CLOSED]
});

/** @internal */
export type ServerOptions = Omit<ConnectionPoolOptions, 'id' | 'generation' | 'hostAddress'> &
  MonitorOptions;

/** @internal */
export interface ServerPrivate {
  /** The server description for this server */
  description: ServerDescription;
  /** A copy of the options used to construct this instance */
  options: ServerOptions;
  /** The current state of the Server */
  state: string;
  /** MongoDB server API version */
  serverApi?: ServerApi;
  /** A count of the operations currently running against the server. */
  operationCount: number;
}

/** @public */
export type ServerEvents = {
  serverHeartbeatStarted(event: ServerHeartbeatStartedEvent): void;
  serverHeartbeatSucceeded(event: ServerHeartbeatSucceededEvent): void;
  serverHeartbeatFailed(event: ServerHeartbeatFailedEvent): void;
  /** Top level MongoClient doesn't emit this so it is marked: @internal */
  connect(server: Server): void;
  descriptionReceived(description: ServerDescription): void;
  closed(): void;
  ended(): void;
} & ConnectionPoolEvents &
  EventEmitterWithState;

/** @internal */
export class Server extends TypedEventEmitter<ServerEvents> {
  /** @internal */
  s: ServerPrivate;
  /** @internal */
  topology: Topology;
  /** @internal */
  pool: ConnectionPool;
  serverApi?: ServerApi;
  hello?: Document;
  commandAsync: (ns: MongoDBNamespace, cmd: Document, options: CommandOptions) => Promise<Document>;
  monitor: Monitor | null;

  /** @event */
  static readonly SERVER_HEARTBEAT_STARTED = SERVER_HEARTBEAT_STARTED;
  /** @event */
  static readonly SERVER_HEARTBEAT_SUCCEEDED = SERVER_HEARTBEAT_SUCCEEDED;
  /** @event */
  static readonly SERVER_HEARTBEAT_FAILED = SERVER_HEARTBEAT_FAILED;
  /** @event */
  static readonly CONNECT = CONNECT;
  /** @event */
  static readonly DESCRIPTION_RECEIVED = DESCRIPTION_RECEIVED;
  /** @event */
  static readonly CLOSED = CLOSED;
  /** @event */
  static readonly ENDED = ENDED;

  /**
   * Create a server
   */
  constructor(topology: Topology, description: ServerDescription, options: ServerOptions) {
    super();

    this.commandAsync = promisify(
      (
        ns: MongoDBNamespace,
        cmd: Document,
        options: CommandOptions,
        // callback type defines Document result because result is never nullish when it succeeds, otherwise promise rejects
        callback: (error: Error | undefined, result: Document) => void
      ) => this.command(ns, cmd, options, callback as any)
    );

    this.serverApi = options.serverApi;

    const poolOptions = { hostAddress: description.hostAddress, ...options };

    this.topology = topology;
    this.pool = new ConnectionPool(this, poolOptions);

    this.s = {
      description,
      options,
      state: STATE_CLOSED,
      operationCount: 0
    };

    for (const event of [...CMAP_EVENTS, ...APM_EVENTS]) {
      this.pool.on(event, (e: any) => this.emit(event, e));
    }

    this.pool.on(Connection.CLUSTER_TIME_RECEIVED, (clusterTime: ClusterTime) => {
      this.clusterTime = clusterTime;
    });

    if (this.loadBalanced) {
      this.monitor = null;
      // monitoring is disabled in load balancing mode
      return;
    }

    // create the monitor
    this.monitor = new Monitor(this, this.s.options);

    for (const event of HEARTBEAT_EVENTS) {
      this.monitor.on(event, (e: any) => this.emit(event, e));
    }

    this.monitor.on('resetServer', (error: MongoError) => markServerUnknown(this, error));
    this.monitor.on(Server.SERVER_HEARTBEAT_SUCCEEDED, (event: ServerHeartbeatSucceededEvent) => {
      this.emit(
        Server.DESCRIPTION_RECEIVED,
        new ServerDescription(this.description.hostAddress, event.reply, {
          roundTripTime: calculateRoundTripTime(this.description.roundTripTime, event.duration)
        })
      );

      if (this.s.state === STATE_CONNECTING) {
        stateTransition(this, STATE_CONNECTED);
        this.emit(Server.CONNECT, this);
      }
    });
  }

  get clusterTime(): ClusterTime | undefined {
    return this.topology.clusterTime;
  }

  set clusterTime(clusterTime: ClusterTime | undefined) {
    this.topology.clusterTime = clusterTime;
  }

  get description(): ServerDescription {
    return this.s.description;
  }

  get name(): string {
    return this.s.description.address;
  }

  get autoEncrypter(): AutoEncrypter | undefined {
    if (this.s.options && this.s.options.autoEncrypter) {
      return this.s.options.autoEncrypter;
    }
    return;
  }

  get loadBalanced(): boolean {
    return this.topology.description.type === TopologyType.LoadBalanced;
  }

  /**
   * Initiate server connect
   */
  connect(): void {
    if (this.s.state !== STATE_CLOSED) {
      return;
    }

    stateTransition(this, STATE_CONNECTING);

    // If in load balancer mode we automatically set the server to
    // a load balancer. It never transitions out of this state and
    // has no monitor.
    if (!this.loadBalanced) {
      this.monitor?.connect();
    } else {
      stateTransition(this, STATE_CONNECTED);
      this.emit(Server.CONNECT, this);
    }
  }

  /** Destroy the server connection */
  destroy(options?: DestroyOptions, callback?: Callback): void {
    if (typeof options === 'function') {
      callback = options;
      options = { force: false };
    }
    options = Object.assign({}, { force: false }, options);

    if (this.s.state === STATE_CLOSED) {
      if (typeof callback === 'function') {
        callback();
      }

      return;
    }

    stateTransition(this, STATE_CLOSING);

    if (!this.loadBalanced) {
      this.monitor?.close();
    }

    this.pool.close(options, err => {
      stateTransition(this, STATE_CLOSED);
      this.emit('closed');
      if (typeof callback === 'function') {
        callback(err);
      }
    });
  }

  /**
   * Immediately schedule monitoring of this server. If there already an attempt being made
   * this will be a no-op.
   */
  requestCheck(): void {
    if (!this.loadBalanced) {
      this.monitor?.requestCheck();
    }
  }

  /**
   * Execute a command
   * @internal
   */
  command(
    ns: MongoDBNamespace,
    cmd: Document,
    options: CommandOptions,
    callback: Callback<Document>
  ): void {
    if (callback == null) {
      throw new MongoInvalidArgumentError('Callback must be provided');
    }

    if (ns.db == null || typeof ns === 'string') {
      throw new MongoInvalidArgumentError('Namespace must not be a string');
    }

    if (this.s.state === STATE_CLOSING || this.s.state === STATE_CLOSED) {
      callback(new MongoServerClosedError());
      return;
    }

    // Clone the options
    const finalOptions = Object.assign({}, options, { wireProtocolCommand: false });

    // There are cases where we need to flag the read preference not to get sent in
    // the command, such as pre-5.0 servers attempting to perform an aggregate write
    // with a non-primary read preference. In this case the effective read preference
    // (primary) is not the same as the provided and must be removed completely.
    if (finalOptions.omitReadPreference) {
      delete finalOptions.readPreference;
    }

    const session = finalOptions.session;
    const conn = session?.pinnedConnection;

    // NOTE: This is a hack! We can't retrieve the connections used for executing an operation
    //       (and prevent them from being checked back in) at the point of operation execution.
    //       This should be considered as part of the work for NODE-2882
    // NOTE:
    //       When incrementing operation count, it's important that we increment it before we
    //       attempt to check out a connection from the pool.  This ensures that operations that
    //       are waiting for a connection are included in the operation count.  Load balanced
    //       mode will only ever have a single server, so the operation count doesn't matter.
    //       Incrementing the operation count above the logic to handle load balanced mode would
    //       require special logic to decrement it again, or would double increment (the load
    //       balanced code makes a recursive call).  Instead, we increment the count after this
    //       check.
    if (this.loadBalanced && session && conn == null && isPinnableCommand(cmd, session)) {
      this.pool.checkOut((err, checkedOut) => {
        if (err || checkedOut == null) {
          if (callback) return callback(err);
          return;
        }

        session.pin(checkedOut);
        this.command(ns, cmd, finalOptions, callback);
      });
      return;
    }

    this.incrementOperationCount();

    this.pool.withConnection(
      conn,
      (err, conn, cb) => {
        if (err || !conn) {
          this.decrementOperationCount();
          if (!err) {
            return cb(new MongoRuntimeError('Failed to create connection without error'));
          }
          if (!(err instanceof PoolClearedError)) {
            this.handleError(err);
          }
          return cb(err);
        }

        conn.command(
          ns,
          cmd,
          finalOptions,
          makeOperationHandler(this, conn, cmd, finalOptions, (error, response) => {
            this.decrementOperationCount();
            cb(error, response);
          })
        );
      },
      callback
    );
  }

  /**
   * Handle SDAM error
   * @internal
   */
  handleError(error: AnyError, connection?: Connection) {
    if (!(error instanceof MongoError)) {
      return;
    }

    const isStaleError =
      error.connectionGeneration && error.connectionGeneration < this.pool.generation;
    if (isStaleError) {
      return;
    }

    const isNetworkNonTimeoutError =
      error instanceof MongoNetworkError && !(error instanceof MongoNetworkTimeoutError);
    const isNetworkTimeoutBeforeHandshakeError = isNetworkErrorBeforeHandshake(error);
    const isAuthHandshakeError = error.hasErrorLabel(MongoErrorLabel.HandshakeError);
    if (isNetworkNonTimeoutError || isNetworkTimeoutBeforeHandshakeError || isAuthHandshakeError) {
      // In load balanced mode we never mark the server as unknown and always
      // clear for the specific service id.
      if (!this.loadBalanced) {
        error.addErrorLabel(MongoErrorLabel.ResetPool);
        markServerUnknown(this, error);
      } else if (connection) {
        this.pool.clear({ serviceId: connection.serviceId });
      }
    } else {
      if (isSDAMUnrecoverableError(error)) {
        if (shouldHandleStateChangeError(this, error)) {
          const shouldClearPool = maxWireVersion(this) <= 7 || isNodeShuttingDownError(error);
          if (this.loadBalanced && connection && shouldClearPool) {
            this.pool.clear({ serviceId: connection.serviceId });
          }

          if (!this.loadBalanced) {
            if (shouldClearPool) {
              error.addErrorLabel(MongoErrorLabel.ResetPool);
            }
            markServerUnknown(this, error);
            process.nextTick(() => this.requestCheck());
          }
        }
      }
    }
  }

  /**
   * Decrement the operation count, returning the new count.
   */
  private decrementOperationCount(): number {
    return (this.s.operationCount -= 1);
  }

  /**
   * Increment the operation count, returning the new count.
   */
  private incrementOperationCount(): number {
    return (this.s.operationCount += 1);
  }
}

function calculateRoundTripTime(oldRtt: number, duration: number): number {
  if (oldRtt === -1) {
    return duration;
  }

  const alpha = 0.2;
  return alpha * duration + (1 - alpha) * oldRtt;
}

function markServerUnknown(server: Server, error?: MongoServerError) {
  // Load balancer servers can never be marked unknown.
  if (server.loadBalanced) {
    return;
  }

  if (error instanceof MongoNetworkError && !(error instanceof MongoNetworkTimeoutError)) {
    server.monitor?.reset();
  }

  server.emit(
    Server.DESCRIPTION_RECEIVED,
    new ServerDescription(server.description.hostAddress, undefined, { error })
  );
}

function isPinnableCommand(cmd: Document, session?: ClientSession): boolean {
  if (session) {
    return (
      session.inTransaction() ||
      'aggregate' in cmd ||
      'find' in cmd ||
      'getMore' in cmd ||
      'listCollections' in cmd ||
      'listIndexes' in cmd
    );
  }

  return false;
}

function connectionIsStale(pool: ConnectionPool, connection: Connection) {
  if (connection.serviceId) {
    return (
      connection.generation !== pool.serviceGenerations.get(connection.serviceId.toHexString())
    );
  }

  return connection.generation !== pool.generation;
}

function shouldHandleStateChangeError(server: Server, err: MongoError) {
  const etv = err.topologyVersion;
  const stv = server.description.topologyVersion;
  return compareTopologyVersion(stv, etv) < 0;
}

function inActiveTransaction(session: ClientSession | undefined, cmd: Document) {
  return session && session.inTransaction() && !isTransactionCommand(cmd);
}

/** this checks the retryWrites option passed down from the client options, it
 * does not check if the server supports retryable writes */
function isRetryableWritesEnabled(topology: Topology) {
  return topology.s.options.retryWrites !== false;
}

function makeOperationHandler(
  server: Server,
  connection: Connection,
  cmd: Document,
  options: CommandOptions | GetMoreOptions | undefined,
  callback: Callback
): Callback {
  const session = options?.session;
  return function handleOperationResult(error, result) {
    // We should not swallow an error if it is present.
    if (error == null && result != null) {
      return callback(undefined, result);
    }

    if (options != null && 'noResponse' in options && options.noResponse === true) {
      return callback(undefined, null);
    }

    if (!error) {
      return callback(new MongoUnexpectedServerResponseError('Empty response with no error'));
    }

    if (!(error instanceof MongoError)) {
      // Node.js or some other error we have not special handling for
      return callback(error);
    }

    if (connectionIsStale(server.pool, connection)) {
      return callback(error);
    }

    if (error instanceof MongoNetworkError) {
      if (session && !session.hasEnded && session.serverSession) {
        session.serverSession.isDirty = true;
      }

      // inActiveTransaction check handles commit and abort.
      if (
        inActiveTransaction(session, cmd) &&
        !error.hasErrorLabel(MongoErrorLabel.TransientTransactionError)
      ) {
        error.addErrorLabel(MongoErrorLabel.TransientTransactionError);
      }

      if (
        (isRetryableWritesEnabled(server.topology) || isTransactionCommand(cmd)) &&
        supportsRetryableWrites(server) &&
        !inActiveTransaction(session, cmd)
      ) {
        error.addErrorLabel(MongoErrorLabel.RetryableWriteError);
      }
    } else {
      if (
        (isRetryableWritesEnabled(server.topology) || isTransactionCommand(cmd)) &&
        needsRetryableWriteLabel(error, maxWireVersion(server)) &&
        !inActiveTransaction(session, cmd)
      ) {
        error.addErrorLabel(MongoErrorLabel.RetryableWriteError);
      }
    }

    if (
      session &&
      session.isPinned &&
      error.hasErrorLabel(MongoErrorLabel.TransientTransactionError)
    ) {
      session.unpin({ force: true });
    }

    server.handleError(error, connection);

    return callback(error);
  };
}