Initial commit

node_modules/mongodb/lib/core/sdam/common.js

@@ -0,0 +1,67 @@
+'use strict';
+
+// shared state names
+const STATE_CLOSING = 'closing';
+const STATE_CLOSED = 'closed';
+const STATE_CONNECTING = 'connecting';
+const STATE_CONNECTED = 'connected';
+
+// An enumeration of topology types we know about
+const TopologyType = {
+  Single: 'Single',
+  ReplicaSetNoPrimary: 'ReplicaSetNoPrimary',
+  ReplicaSetWithPrimary: 'ReplicaSetWithPrimary',
+  Sharded: 'Sharded',
+  Unknown: 'Unknown'
+};
+
+// An enumeration of server types we know about
+const ServerType = {
+  Standalone: 'Standalone',
+  Mongos: 'Mongos',
+  PossiblePrimary: 'PossiblePrimary',
+  RSPrimary: 'RSPrimary',
+  RSSecondary: 'RSSecondary',
+  RSArbiter: 'RSArbiter',
+  RSOther: 'RSOther',
+  RSGhost: 'RSGhost',
+  Unknown: 'Unknown'
+};
+
+// helper to get a server's type that works for both legacy and unified topologies
+function serverType(server) {
+  let description = server.s.description || server.s.serverDescription;
+  if (description.topologyType === TopologyType.Single) return description.servers[0].type;
+  return description.type;
+}
+
+const TOPOLOGY_DEFAULTS = {
+  useUnifiedTopology: true,
+  localThresholdMS: 15,
+  serverSelectionTimeoutMS: 30000,
+  heartbeatFrequencyMS: 10000,
+  minHeartbeatFrequencyMS: 500
+};
+
+function drainTimerQueue(queue) {
+  queue.forEach(clearTimeout);
+  queue.clear();
+}
+
+function clearAndRemoveTimerFrom(timer, timers) {
+  clearTimeout(timer);
+  return timers.delete(timer);
+}
+
+module.exports = {
+  STATE_CLOSING,
+  STATE_CLOSED,
+  STATE_CONNECTING,
+  STATE_CONNECTED,
+  TOPOLOGY_DEFAULTS,
+  TopologyType,
+  ServerType,
+  serverType,
+  drainTimerQueue,
+  clearAndRemoveTimerFrom
+};

node_modules/mongodb/lib/core/sdam/events.js

@@ -0,0 +1,124 @@
+'use strict';
+
+/**
+ * Published when server description changes, but does NOT include changes to the RTT.
+ *
+ * @property {Object} topologyId A unique identifier for the topology
+ * @property {ServerAddress} address The address (host/port pair) of the server
+ * @property {ServerDescription} previousDescription The previous server description
+ * @property {ServerDescription} newDescription The new server description
+ */
+class ServerDescriptionChangedEvent {
+  constructor(topologyId, address, previousDescription, newDescription) {
+    Object.assign(this, { topologyId, address, previousDescription, newDescription });
+  }
+}
+
+/**
+ * Published when server is initialized.
+ *
+ * @property {Object} topologyId A unique identifier for the topology
+ * @property {ServerAddress} address The address (host/port pair) of the server
+ */
+class ServerOpeningEvent {
+  constructor(topologyId, address) {
+    Object.assign(this, { topologyId, address });
+  }
+}
+
+/**
+ * Published when server is closed.
+ *
+ * @property {ServerAddress} address The address (host/port pair) of the server
+ * @property {Object} topologyId A unique identifier for the topology
+ */
+class ServerClosedEvent {
+  constructor(topologyId, address) {
+    Object.assign(this, { topologyId, address });
+  }
+}
+
+/**
+ * Published when topology description changes.
+ *
+ * @property {Object} topologyId
+ * @property {TopologyDescription} previousDescription The old topology description
+ * @property {TopologyDescription} newDescription The new topology description
+ */
+class TopologyDescriptionChangedEvent {
+  constructor(topologyId, previousDescription, newDescription) {
+    Object.assign(this, { topologyId, previousDescription, newDescription });
+  }
+}
+
+/**
+ * Published when topology is initialized.
+ *
+ * @param {Object} topologyId A unique identifier for the topology
+ */
+class TopologyOpeningEvent {
+  constructor(topologyId) {
+    Object.assign(this, { topologyId });
+  }
+}
+
+/**
+ * Published when topology is closed.
+ *
+ * @param {Object} topologyId A unique identifier for the topology
+ */
+class TopologyClosedEvent {
+  constructor(topologyId) {
+    Object.assign(this, { topologyId });
+  }
+}
+
+/**
+ * Fired when the server monitor’s ismaster command is started - immediately before
+ * the ismaster command is serialized into raw BSON and written to the socket.
+ *
+ * @property {Object} connectionId The connection id for the command
+ */
+class ServerHeartbeatStartedEvent {
+  constructor(connectionId) {
+    Object.assign(this, { connectionId });
+  }
+}
+
+/**
+ * Fired when the server monitor’s ismaster succeeds.
+ *
+ * @param {Number} duration The execution time of the event in ms
+ * @param {Object} reply The command reply
+ * @param {Object} connectionId The connection id for the command
+ */
+class ServerHeartbeatSucceededEvent {
+  constructor(duration, reply, connectionId) {
+    Object.assign(this, { connectionId, duration, reply });
+  }
+}
+
+/**
+ * Fired when the server monitor’s ismaster fails, either with an “ok: 0” or a socket exception.
+ *
+ * @param {Number} duration The execution time of the event in ms
+ * @param {MongoError|Object} failure The command failure
+ * @param {Object} connectionId The connection id for the command
+ */
+class ServerHeartbeatFailedEvent {
+  constructor(duration, failure, connectionId) {
+    Object.assign(this, { connectionId, duration, failure });
+  }
+}
+
+module.exports = {
+  ServerDescriptionChangedEvent,
+  ServerOpeningEvent,
+  ServerClosedEvent,
+  TopologyDescriptionChangedEvent,
+  TopologyOpeningEvent,
+  TopologyClosedEvent,
+  ServerHeartbeatStartedEvent,
+  ServerHeartbeatSucceededEvent,
+  ServerHeartbeatFailedEvent
+};

node_modules/mongodb/lib/core/sdam/monitor.js

@@ -0,0 +1,405 @@
+'use strict';
+
+const ServerType = require('./common').ServerType;
+const EventEmitter = require('events');
+const connect = require('../connection/connect');
+const Connection = require('../../cmap/connection').Connection;
+const common = require('./common');
+const makeStateMachine = require('../utils').makeStateMachine;
+const MongoNetworkError = require('../error').MongoNetworkError;
+const BSON = require('../connection/utils').retrieveBSON();
+const makeInterruptableAsyncInterval = require('../../utils').makeInterruptableAsyncInterval;
+const calculateDurationInMs = require('../../utils').calculateDurationInMs;
+const now = require('../../utils').now;
+
+const sdamEvents = require('./events');
+const ServerHeartbeatStartedEvent = sdamEvents.ServerHeartbeatStartedEvent;
+const ServerHeartbeatSucceededEvent = sdamEvents.ServerHeartbeatSucceededEvent;
+const ServerHeartbeatFailedEvent = sdamEvents.ServerHeartbeatFailedEvent;
+
+const kServer = Symbol('server');
+const kMonitorId = Symbol('monitorId');
+const kConnection = Symbol('connection');
+const kCancellationToken = Symbol('cancellationToken');
+const kRTTPinger = Symbol('rttPinger');
+const kRoundTripTime = Symbol('roundTripTime');
+
+const STATE_CLOSED = common.STATE_CLOSED;
+const STATE_CLOSING = common.STATE_CLOSING;
+const STATE_IDLE = 'idle';
+const STATE_MONITORING = 'monitoring';
+const stateTransition = makeStateMachine({
+  [STATE_CLOSING]: [STATE_CLOSING, STATE_IDLE, STATE_CLOSED],
+  [STATE_CLOSED]: [STATE_CLOSED, STATE_MONITORING],
+  [STATE_IDLE]: [STATE_IDLE, STATE_MONITORING, STATE_CLOSING],
+  [STATE_MONITORING]: [STATE_MONITORING, STATE_IDLE, STATE_CLOSING]
+});
+
+const INVALID_REQUEST_CHECK_STATES = new Set([STATE_CLOSING, STATE_CLOSED, STATE_MONITORING]);
+
+function isInCloseState(monitor) {
+  return monitor.s.state === STATE_CLOSED || monitor.s.state === STATE_CLOSING;
+}
+
+class Monitor extends EventEmitter {
+  constructor(server, options) {
+    super(options);
+
+    this[kServer] = server;
+    this[kConnection] = undefined;
+    this[kCancellationToken] = new EventEmitter();
+    this[kCancellationToken].setMaxListeners(Infinity);
+    this[kMonitorId] = null;
+    this.s = {
+      state: STATE_CLOSED
+    };
+
+    this.address = server.description.address;
+    this.options = Object.freeze({
+      connectTimeoutMS:
+        typeof options.connectionTimeout === 'number'
+          ? options.connectionTimeout
+          : typeof options.connectTimeoutMS === 'number'
+          ? options.connectTimeoutMS
+          : 10000,
+      heartbeatFrequencyMS:
+        typeof options.heartbeatFrequencyMS === 'number' ? options.heartbeatFrequencyMS : 10000,
+      minHeartbeatFrequencyMS:
+        typeof options.minHeartbeatFrequencyMS === 'number' ? options.minHeartbeatFrequencyMS : 500
+    });
+
+    // TODO: refactor this to pull it directly from the pool, requires new ConnectionPool integration
+    const connectOptions = Object.assign(
+      {
+        id: '<monitor>',
+        host: server.description.host,
+        port: server.description.port,
+        bson: server.s.bson,
+        connectionType: Connection
+      },
+      server.s.options,
+      this.options,
+
+      // force BSON serialization options
+      {
+        raw: false,
+        promoteLongs: true,
+        promoteValues: true,
+        promoteBuffers: true
+      }
+    );
+
+    // ensure no authentication is used for monitoring
+    delete connectOptions.credentials;
+    this.connectOptions = Object.freeze(connectOptions);
+  }
+
+  connect() {
+    if (this.s.state !== STATE_CLOSED) {
+      return;
+    }
+
+    // start
+    const heartbeatFrequencyMS = this.options.heartbeatFrequencyMS;
+    const minHeartbeatFrequencyMS = this.options.minHeartbeatFrequencyMS;
+    this[kMonitorId] = makeInterruptableAsyncInterval(monitorServer(this), {
+      interval: heartbeatFrequencyMS,
+      minInterval: minHeartbeatFrequencyMS,
+      immediate: true
+    });
+  }
+
+  requestCheck() {
+    if (INVALID_REQUEST_CHECK_STATES.has(this.s.state)) {
+      return;
+    }
+
+    this[kMonitorId].wake();
+  }
+
+  reset() {
+    if (isInCloseState(this)) {
+      return;
+    }
+
+    stateTransition(this, STATE_CLOSING);
+    resetMonitorState(this);
+
+    // restart monitor
+    stateTransition(this, STATE_IDLE);
+
+    // restart monitoring
+    const heartbeatFrequencyMS = this.options.heartbeatFrequencyMS;
+    const minHeartbeatFrequencyMS = this.options.minHeartbeatFrequencyMS;
+    this[kMonitorId] = makeInterruptableAsyncInterval(monitorServer(this), {
+      interval: heartbeatFrequencyMS,
+      minInterval: minHeartbeatFrequencyMS
+    });
+  }
+
+  close() {
+    if (isInCloseState(this)) {
+      return;
+    }
+
+    stateTransition(this, STATE_CLOSING);
+    resetMonitorState(this);
+
+    // close monitor
+    this.emit('close');
+    stateTransition(this, STATE_CLOSED);
+  }
+}
+
+function resetMonitorState(monitor) {
+  stateTransition(monitor, STATE_CLOSING);
+  if (monitor[kMonitorId]) {
+    monitor[kMonitorId].stop();
+    monitor[kMonitorId] = null;
+  }
+
+  if (monitor[kRTTPinger]) {
+    monitor[kRTTPinger].close();
+    monitor[kRTTPinger] = undefined;
+  }
+
+  monitor[kCancellationToken].emit('cancel');
+  if (monitor[kMonitorId]) {
+    clearTimeout(monitor[kMonitorId]);
+    monitor[kMonitorId] = undefined;
+  }
+
+  if (monitor[kConnection]) {
+    monitor[kConnection].destroy({ force: true });
+  }
+}
+
+function checkServer(monitor, callback) {
+  let start = now();
+  monitor.emit('serverHeartbeatStarted', new ServerHeartbeatStartedEvent(monitor.address));
+
+  function failureHandler(err) {
+    if (monitor[kConnection]) {
+      monitor[kConnection].destroy({ force: true });
+      monitor[kConnection] = undefined;
+    }
+
+    monitor.emit(
+      'serverHeartbeatFailed',
+      new ServerHeartbeatFailedEvent(calculateDurationInMs(start), err, monitor.address)
+    );
+
+    monitor.emit('resetServer', err);
+    monitor.emit('resetConnectionPool');
+    callback(err);
+  }
+
+  if (monitor[kConnection] != null && !monitor[kConnection].closed) {
+    const connectTimeoutMS = monitor.options.connectTimeoutMS;
+    const maxAwaitTimeMS = monitor.options.heartbeatFrequencyMS;
+    const topologyVersion = monitor[kServer].description.topologyVersion;
+    const isAwaitable = topologyVersion != null;
+
+    const cmd = isAwaitable
+      ? { ismaster: true, maxAwaitTimeMS, topologyVersion: makeTopologyVersion(topologyVersion) }
+      : { ismaster: true };
+
+    const options = isAwaitable
+      ? { socketTimeout: connectTimeoutMS + maxAwaitTimeMS, exhaustAllowed: true }
+      : { socketTimeout: connectTimeoutMS };
+
+    if (isAwaitable && monitor[kRTTPinger] == null) {
+      monitor[kRTTPinger] = new RTTPinger(monitor[kCancellationToken], monitor.connectOptions);
+    }
+
+    monitor[kConnection].command('admin.$cmd', cmd, options, (err, result) => {
+      if (err) {
+        failureHandler(err);
+        return;
+      }
+
+      const isMaster = result.result;
+      const duration = isAwaitable
+        ? monitor[kRTTPinger].roundTripTime
+        : calculateDurationInMs(start);
+
+      monitor.emit(
+        'serverHeartbeatSucceeded',
+        new ServerHeartbeatSucceededEvent(duration, isMaster, monitor.address)
+      );
+
+      // if we are using the streaming protocol then we immediately issue another `started`
+      // event, otherwise the "check" is complete and return to the main monitor loop
+      if (isAwaitable && isMaster.topologyVersion) {
+        monitor.emit('serverHeartbeatStarted', new ServerHeartbeatStartedEvent(monitor.address));
+        start = now();
+      } else {
+        if (monitor[kRTTPinger]) {
+          monitor[kRTTPinger].close();
+          monitor[kRTTPinger] = undefined;
+        }
+
+        callback(undefined, isMaster);
+      }
+    });
+
+    return;
+  }
+
+  // connecting does an implicit `ismaster`
+  connect(monitor.connectOptions, monitor[kCancellationToken], (err, conn) => {
+    if (conn && isInCloseState(monitor)) {
+      conn.destroy({ force: true });
+      return;
+    }
+
+    if (err) {
+      monitor[kConnection] = undefined;
+
+      // we already reset the connection pool on network errors in all cases
+      if (!(err instanceof MongoNetworkError)) {
+        monitor.emit('resetConnectionPool');
+      }
+
+      failureHandler(err);
+      return;
+    }
+
+    monitor[kConnection] = conn;
+    monitor.emit(
+      'serverHeartbeatSucceeded',
+      new ServerHeartbeatSucceededEvent(
+        calculateDurationInMs(start),
+        conn.ismaster,
+        monitor.address
+      )
+    );
+
+    callback(undefined, conn.ismaster);
+  });
+}
+
+function monitorServer(monitor) {
+  return callback => {
+    stateTransition(monitor, STATE_MONITORING);
+    function done() {
+      if (!isInCloseState(monitor)) {
+        stateTransition(monitor, STATE_IDLE);
+      }
+
+      callback();
+    }
+
+    // TODO: the next line is a legacy event, remove in v4
+    process.nextTick(() => monitor.emit('monitoring', monitor[kServer]));
+
+    checkServer(monitor, (err, isMaster) => {
+      if (err) {
+        // otherwise an error occured on initial discovery, also bail
+        if (monitor[kServer].description.type === ServerType.Unknown) {
+          monitor.emit('resetServer', err);
+          return done();
+        }
+      }
+
+      // if the check indicates streaming is supported, immediately reschedule monitoring
+      if (isMaster && isMaster.topologyVersion) {
+        setTimeout(() => {
+          if (!isInCloseState(monitor)) {
+            monitor[kMonitorId].wake();
+          }
+        });
+      }
+
+      done();
+    });
+  };
+}
+
+function makeTopologyVersion(tv) {
+  return {
+    processId: tv.processId,
+    counter: BSON.Long.fromNumber(tv.counter)
+  };
+}
+
+class RTTPinger {
+  constructor(cancellationToken, options) {
+    this[kConnection] = null;
+    this[kCancellationToken] = cancellationToken;
+    this[kRoundTripTime] = 0;
+    this.closed = false;
+
+    const heartbeatFrequencyMS = options.heartbeatFrequencyMS;
+    this[kMonitorId] = setTimeout(() => measureRoundTripTime(this, options), heartbeatFrequencyMS);
+  }
+
+  get roundTripTime() {
+    return this[kRoundTripTime];
+  }
+
+  close() {
+    this.closed = true;
+
+    clearTimeout(this[kMonitorId]);
+    this[kMonitorId] = undefined;
+
+    if (this[kConnection]) {
+      this[kConnection].destroy({ force: true });
+    }
+  }
+}
+
+function measureRoundTripTime(rttPinger, options) {
+  const start = now();
+  const cancellationToken = rttPinger[kCancellationToken];
+  const heartbeatFrequencyMS = options.heartbeatFrequencyMS;
+  if (rttPinger.closed) {
+    return;
+  }
+
+  function measureAndReschedule(conn) {
+    if (rttPinger.closed) {
+      conn.destroy({ force: true });
+      return;
+    }
+
+    if (rttPinger[kConnection] == null) {
+      rttPinger[kConnection] = conn;
+    }
+
+    rttPinger[kRoundTripTime] = calculateDurationInMs(start);
+    rttPinger[kMonitorId] = setTimeout(
+      () => measureRoundTripTime(rttPinger, options),
+      heartbeatFrequencyMS
+    );
+  }
+
+  if (rttPinger[kConnection] == null) {
+    connect(options, cancellationToken, (err, conn) => {
+      if (err) {
+        rttPinger[kConnection] = undefined;
+        rttPinger[kRoundTripTime] = 0;
+        return;
+      }
+
+      measureAndReschedule(conn);
+    });
+
+    return;
+  }
+
+  rttPinger[kConnection].command('admin.$cmd', { ismaster: 1 }, err => {
+    if (err) {
+      rttPinger[kConnection] = undefined;
+      rttPinger[kRoundTripTime] = 0;
+      return;
+    }
+
+    measureAndReschedule();
+  });
+}
+
+module.exports = {
+  Monitor
+};

node_modules/mongodb/lib/core/sdam/server.js

@@ -0,0 +1,564 @@
+'use strict';
+const EventEmitter = require('events');
+const ConnectionPool = require('../../cmap/connection_pool').ConnectionPool;
+const CMAP_EVENT_NAMES = require('../../cmap/events').CMAP_EVENT_NAMES;
+const MongoError = require('../error').MongoError;
+const relayEvents = require('../utils').relayEvents;
+const BSON = require('../connection/utils').retrieveBSON();
+const Logger = require('../connection/logger');
+const ServerDescription = require('./server_description').ServerDescription;
+const compareTopologyVersion = require('./server_description').compareTopologyVersion;
+const ReadPreference = require('../topologies/read_preference');
+const Monitor = require('./monitor').Monitor;
+const MongoNetworkError = require('../error').MongoNetworkError;
+const MongoNetworkTimeoutError = require('../error').MongoNetworkTimeoutError;
+const collationNotSupported = require('../utils').collationNotSupported;
+const debugOptions = require('../connection/utils').debugOptions;
+const isSDAMUnrecoverableError = require('../error').isSDAMUnrecoverableError;
+const isRetryableWriteError = require('../error').isRetryableWriteError;
+const isNodeShuttingDownError = require('../error').isNodeShuttingDownError;
+const isNetworkErrorBeforeHandshake = require('../error').isNetworkErrorBeforeHandshake;
+const maxWireVersion = require('../utils').maxWireVersion;
+const makeStateMachine = require('../utils').makeStateMachine;
+const common = require('./common');
+const ServerType = common.ServerType;
+const isTransactionCommand = require('../transactions').isTransactionCommand;
+
+// Used for filtering out fields for logging
+const DEBUG_FIELDS = [
+  'reconnect',
+  'reconnectTries',
+  'reconnectInterval',
+  'emitError',
+  'cursorFactory',
+  'host',
+  'port',
+  'size',
+  'keepAlive',
+  'keepAliveInitialDelay',
+  'noDelay',
+  'connectionTimeout',
+  'checkServerIdentity',
+  'socketTimeout',
+  'ssl',
+  'ca',
+  'crl',
+  'cert',
+  'key',
+  'rejectUnauthorized',
+  'promoteLongs',
+  'promoteValues',
+  'promoteBuffers',
+  'servername'
+];
+
+const STATE_CLOSING = common.STATE_CLOSING;
+const STATE_CLOSED = common.STATE_CLOSED;
+const STATE_CONNECTING = common.STATE_CONNECTING;
+const STATE_CONNECTED = common.STATE_CONNECTED;
+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]
+});
+
+const kMonitor = Symbol('monitor');
+
+/**
+ *
+ * @fires Server#serverHeartbeatStarted
+ * @fires Server#serverHeartbeatSucceeded
+ * @fires Server#serverHeartbeatFailed
+ */
+class Server extends EventEmitter {
+  /**
+   * Create a server
+   *
+   * @param {ServerDescription} description
+   * @param {Object} options
+   */
+  constructor(description, options, topology) {
+    super();
+
+    this.s = {
+      // the server description
+      description,
+      // a saved copy of the incoming options
+      options,
+      // the server logger
+      logger: Logger('Server', options),
+      // the bson parser
+      bson:
+        options.bson ||
+        new BSON([
+          BSON.Binary,
+          BSON.Code,
+          BSON.DBRef,
+          BSON.Decimal128,
+          BSON.Double,
+          BSON.Int32,
+          BSON.Long,
+          BSON.Map,
+          BSON.MaxKey,
+          BSON.MinKey,
+          BSON.ObjectId,
+          BSON.BSONRegExp,
+          BSON.Symbol,
+          BSON.Timestamp
+        ]),
+      // the server state
+      state: STATE_CLOSED,
+      credentials: options.credentials,
+      topology
+    };
+
+    // create the connection pool
+    // NOTE: this used to happen in `connect`, we supported overriding pool options there
+    const poolOptions = Object.assign(
+      { host: this.description.host, port: this.description.port, bson: this.s.bson },
+      options
+    );
+
+    this.s.pool = new ConnectionPool(poolOptions);
+    relayEvents(
+      this.s.pool,
+      this,
+      ['commandStarted', 'commandSucceeded', 'commandFailed'].concat(CMAP_EVENT_NAMES)
+    );
+
+    this.s.pool.on('clusterTimeReceived', clusterTime => {
+      this.clusterTime = clusterTime;
+    });
+
+    // create the monitor
+    this[kMonitor] = new Monitor(this, this.s.options);
+    relayEvents(this[kMonitor], this, [
+      'serverHeartbeatStarted',
+      'serverHeartbeatSucceeded',
+      'serverHeartbeatFailed',
+
+      // legacy events
+      'monitoring'
+    ]);
+
+    this[kMonitor].on('resetConnectionPool', () => {
+      this.s.pool.clear();
+    });
+
+    this[kMonitor].on('resetServer', error => markServerUnknown(this, error));
+    this[kMonitor].on('serverHeartbeatSucceeded', event => {
+      this.emit(
+        'descriptionReceived',
+        new ServerDescription(this.description.address, event.reply, {
+          roundTripTime: calculateRoundTripTime(this.description.roundTripTime, event.duration)
+        })
+      );
+
+      if (this.s.state === STATE_CONNECTING) {
+        stateTransition(this, STATE_CONNECTED);
+        this.emit('connect', this);
+      }
+    });
+  }
+
+  get description() {
+    return this.s.description;
+  }
+
+  get name() {
+    return this.s.description.address;
+  }
+
+  get autoEncrypter() {
+    if (this.s.options && this.s.options.autoEncrypter) {
+      return this.s.options.autoEncrypter;
+    }
+    return null;
+  }
+
+  /**
+   * Initiate server connect
+   */
+  connect() {
+    if (this.s.state !== STATE_CLOSED) {
+      return;
+    }
+
+    stateTransition(this, STATE_CONNECTING);
+    this[kMonitor].connect();
+  }
+
+  /**
+   * Destroy the server connection
+   *
+   * @param {object} [options] Optional settings
+   * @param {Boolean} [options.force=false] Force destroy the pool
+   */
+  destroy(options, callback) {
+    if (typeof options === 'function') (callback = options), (options = {});
+    options = Object.assign({}, { force: false }, options);
+
+    if (this.s.state === STATE_CLOSED) {
+      if (typeof callback === 'function') {
+        callback();
+      }
+
+      return;
+    }
+
+    stateTransition(this, STATE_CLOSING);
+
+    this[kMonitor].close();
+    this.s.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() {
+    this[kMonitor].requestCheck();
+  }
+
+  /**
+   * Execute a command
+   *
+   * @param {string} ns The MongoDB fully qualified namespace (ex: db1.collection1)
+   * @param {object} cmd The command hash
+   * @param {object} [options] Optional settings
+   * @param {ReadPreference} [options.readPreference] Specify read preference if command supports it
+   * @param {Boolean} [options.serializeFunctions=false] Specify if functions on an object should be serialized.
+   * @param {Boolean} [options.checkKeys=false] Specify if the bson parser should validate keys.
+   * @param {Boolean} [options.ignoreUndefined=false] Specify if the BSON serializer should ignore undefined fields.
+   * @param {Boolean} [options.fullResult=false] Return the full envelope instead of just the result document.
+   * @param {ClientSession} [options.session] Session to use for the operation
+   * @param {opResultCallback} callback A callback function
+   */
+  command(ns, cmd, options, callback) {
+    if (typeof options === 'function') {
+      (callback = options), (options = {}), (options = options || {});
+    }
+
+    if (this.s.state === STATE_CLOSING || this.s.state === STATE_CLOSED) {
+      callback(new MongoError('server is closed'));
+      return;
+    }
+
+    const error = basicReadValidations(this, options);
+    if (error) {
+      return callback(error);
+    }
+
+    // Clone the options
+    options = Object.assign({}, options, { wireProtocolCommand: false });
+
+    // Debug log
+    if (this.s.logger.isDebug()) {
+      this.s.logger.debug(
+        `executing command [${JSON.stringify({
+          ns,
+          cmd,
+          options: debugOptions(DEBUG_FIELDS, options)
+        })}] against ${this.name}`
+      );
+    }
+
+    // error if collation not supported
+    if (collationNotSupported(this, cmd)) {
+      callback(new MongoError(`server ${this.name} does not support collation`));
+      return;
+    }
+
+    this.s.pool.withConnection((err, conn, cb) => {
+      if (err) {
+        markServerUnknown(this, err);
+        return cb(err);
+      }
+
+      conn.command(ns, cmd, options, makeOperationHandler(this, conn, cmd, options, cb));
+    }, callback);
+  }
+
+  /**
+   * Execute a query against the server
+   *
+   * @param {string} ns The MongoDB fully qualified namespace (ex: db1.collection1)
+   * @param {object} cmd The command document for the query
+   * @param {object} options Optional settings
+   * @param {function} callback
+   */
+  query(ns, cmd, cursorState, options, callback) {
+    if (this.s.state === STATE_CLOSING || this.s.state === STATE_CLOSED) {
+      callback(new MongoError('server is closed'));
+      return;
+    }
+
+    this.s.pool.withConnection((err, conn, cb) => {
+      if (err) {
+        markServerUnknown(this, err);
+        return cb(err);
+      }
+
+      conn.query(ns, cmd, cursorState, options, makeOperationHandler(this, conn, cmd, options, cb));
+    }, callback);
+  }
+
+  /**
+   * Execute a `getMore` against the server
+   *
+   * @param {string} ns The MongoDB fully qualified namespace (ex: db1.collection1)
+   * @param {object} cursorState State data associated with the cursor calling this method
+   * @param {object} options Optional settings
+   * @param {function} callback
+   */
+  getMore(ns, cursorState, batchSize, options, callback) {
+    if (this.s.state === STATE_CLOSING || this.s.state === STATE_CLOSED) {
+      callback(new MongoError('server is closed'));
+      return;
+    }
+
+    this.s.pool.withConnection((err, conn, cb) => {
+      if (err) {
+        markServerUnknown(this, err);
+        return cb(err);
+      }
+
+      conn.getMore(
+        ns,
+        cursorState,
+        batchSize,
+        options,
+        makeOperationHandler(this, conn, null, options, cb)
+      );
+    }, callback);
+  }
+
+  /**
+   * Execute a `killCursors` command against the server
+   *
+   * @param {string} ns The MongoDB fully qualified namespace (ex: db1.collection1)
+   * @param {object} cursorState State data associated with the cursor calling this method
+   * @param {function} callback
+   */
+  killCursors(ns, cursorState, callback) {
+    if (this.s.state === STATE_CLOSING || this.s.state === STATE_CLOSED) {
+      if (typeof callback === 'function') {
+        callback(new MongoError('server is closed'));
+      }
+
+      return;
+    }
+
+    this.s.pool.withConnection((err, conn, cb) => {
+      if (err) {
+        markServerUnknown(this, err);
+        return cb(err);
+      }
+
+      conn.killCursors(ns, cursorState, makeOperationHandler(this, conn, null, undefined, cb));
+    }, callback);
+  }
+
+  /**
+   * Insert one or more documents
+   * @method
+   * @param {string} ns The MongoDB fully qualified namespace (ex: db1.collection1)
+   * @param {array} ops An array of documents to insert
+   * @param {boolean} [options.ordered=true] Execute in order or out of order
+   * @param {object} [options.writeConcern={}] Write concern for the operation
+   * @param {Boolean} [options.serializeFunctions=false] Specify if functions on an object should be serialized.
+   * @param {Boolean} [options.ignoreUndefined=false] Specify if the BSON serializer should ignore undefined fields.
+   * @param {ClientSession} [options.session] Session to use for the operation
+   * @param {opResultCallback} callback A callback function
+   */
+  insert(ns, ops, options, callback) {
+    executeWriteOperation({ server: this, op: 'insert', ns, ops }, options, callback);
+  }
+
+  /**
+   * Perform one or more update operations
+   * @method
+   * @param {string} ns The MongoDB fully qualified namespace (ex: db1.collection1)
+   * @param {array} ops An array of updates
+   * @param {boolean} [options.ordered=true] Execute in order or out of order
+   * @param {object} [options.writeConcern={}] Write concern for the operation
+   * @param {Boolean} [options.serializeFunctions=false] Specify if functions on an object should be serialized.
+   * @param {Boolean} [options.ignoreUndefined=false] Specify if the BSON serializer should ignore undefined fields.
+   * @param {ClientSession} [options.session] Session to use for the operation
+   * @param {opResultCallback} callback A callback function
+   */
+  update(ns, ops, options, callback) {
+    executeWriteOperation({ server: this, op: 'update', ns, ops }, options, callback);
+  }
+
+  /**
+   * Perform one or more remove operations
+   * @method
+   * @param {string} ns The MongoDB fully qualified namespace (ex: db1.collection1)
+   * @param {array} ops An array of removes
+   * @param {boolean} [options.ordered=true] Execute in order or out of order
+   * @param {object} [options.writeConcern={}] Write concern for the operation
+   * @param {Boolean} [options.serializeFunctions=false] Specify if functions on an object should be serialized.
+   * @param {Boolean} [options.ignoreUndefined=false] Specify if the BSON serializer should ignore undefined fields.
+   * @param {ClientSession} [options.session] Session to use for the operation
+   * @param {opResultCallback} callback A callback function
+   */
+  remove(ns, ops, options, callback) {
+    executeWriteOperation({ server: this, op: 'remove', ns, ops }, options, callback);
+  }
+}
+
+Object.defineProperty(Server.prototype, 'clusterTime', {
+  get: function() {
+    return this.s.topology.clusterTime;
+  },
+  set: function(clusterTime) {
+    this.s.topology.clusterTime = clusterTime;
+  }
+});
+
+function supportsRetryableWrites(server) {
+  return (
+    server.description.maxWireVersion >= 6 &&
+    server.description.logicalSessionTimeoutMinutes &&
+    server.description.type !== ServerType.Standalone
+  );
+}
+
+function calculateRoundTripTime(oldRtt, duration) {
+  if (oldRtt === -1) {
+    return duration;
+  }
+
+  const alpha = 0.2;
+  return alpha * duration + (1 - alpha) * oldRtt;
+}
+
+function basicReadValidations(server, options) {
+  if (options.readPreference && !(options.readPreference instanceof ReadPreference)) {
+    return new MongoError('readPreference must be an instance of ReadPreference');
+  }
+}
+
+function executeWriteOperation(args, options, callback) {
+  if (typeof options === 'function') (callback = options), (options = {});
+  options = options || {};
+
+  // TODO: once we drop Node 4, use destructuring either here or in arguments.
+  const server = args.server;
+  const op = args.op;
+  const ns = args.ns;
+  const ops = Array.isArray(args.ops) ? args.ops : [args.ops];
+
+  if (server.s.state === STATE_CLOSING || server.s.state === STATE_CLOSED) {
+    callback(new MongoError('server is closed'));
+    return;
+  }
+
+  if (collationNotSupported(server, options)) {
+    callback(new MongoError(`server ${server.name} does not support collation`));
+    return;
+  }
+  const unacknowledgedWrite = options.writeConcern && options.writeConcern.w === 0;
+  if (unacknowledgedWrite || maxWireVersion(server) < 5) {
+    if ((op === 'update' || op === 'remove') && ops.find(o => o.hint)) {
+      callback(new MongoError(`servers < 3.4 do not support hint on ${op}`));
+      return;
+    }
+  }
+
+  server.s.pool.withConnection((err, conn, cb) => {
+    if (err) {
+      markServerUnknown(server, err);
+      return cb(err);
+    }
+
+    conn[op](ns, ops, options, makeOperationHandler(server, conn, ops, options, cb));
+  }, callback);
+}
+
+function markServerUnknown(server, error) {
+  if (error instanceof MongoNetworkError && !(error instanceof MongoNetworkTimeoutError)) {
+    server[kMonitor].reset();
+  }
+
+  server.emit(
+    'descriptionReceived',
+    new ServerDescription(server.description.address, null, {
+      error,
+      topologyVersion:
+        error && error.topologyVersion ? error.topologyVersion : server.description.topologyVersion
+    })
+  );
+}
+
+function connectionIsStale(pool, connection) {
+  return connection.generation !== pool.generation;
+}
+
+function shouldHandleStateChangeError(server, err) {
+  const etv = err.topologyVersion;
+  const stv = server.description.topologyVersion;
+
+  return compareTopologyVersion(stv, etv) < 0;
+}
+
+function inActiveTransaction(session, cmd) {
+  return session && session.inTransaction() && !isTransactionCommand(cmd);
+}
+
+function makeOperationHandler(server, connection, cmd, options, callback) {
+  const session = options && options.session;
+
+  return function handleOperationResult(err, result) {
+    if (err && !connectionIsStale(server.s.pool, connection)) {
+      if (err instanceof MongoNetworkError) {
+        if (session && !session.hasEnded) {
+          session.serverSession.isDirty = true;
+        }
+
+        if (supportsRetryableWrites(server) && !inActiveTransaction(session, cmd)) {
+          err.addErrorLabel('RetryableWriteError');
+        }
+
+        if (!(err instanceof MongoNetworkTimeoutError) || isNetworkErrorBeforeHandshake(err)) {
+          markServerUnknown(server, err);
+          server.s.pool.clear();
+        }
+      } else {
+        // if pre-4.4 server, then add error label if its a retryable write error
+        if (
+          maxWireVersion(server) < 9 &&
+          isRetryableWriteError(err) &&
+          !inActiveTransaction(session, cmd)
+        ) {
+          err.addErrorLabel('RetryableWriteError');
+        }
+
+        if (isSDAMUnrecoverableError(err)) {
+          if (shouldHandleStateChangeError(server, err)) {
+            if (maxWireVersion(server) <= 7 || isNodeShuttingDownError(err)) {
+              server.s.pool.clear();
+            }
+
+            markServerUnknown(server, err);
+            process.nextTick(() => server.requestCheck());
+          }
+        }
+      }
+    }
+
+    callback(err, result);
+  };
+}
+
+module.exports = {
+  Server
+};

node_modules/mongodb/lib/core/sdam/server_description.js

@@ -0,0 +1,227 @@
+'use strict';
+
+const arrayStrictEqual = require('../utils').arrayStrictEqual;
+const tagsStrictEqual = require('../utils').tagsStrictEqual;
+const errorStrictEqual = require('../utils').errorStrictEqual;
+const ServerType = require('./common').ServerType;
+const now = require('../../utils').now;
+
+const WRITABLE_SERVER_TYPES = new Set([
+  ServerType.RSPrimary,
+  ServerType.Standalone,
+  ServerType.Mongos
+]);
+
+const DATA_BEARING_SERVER_TYPES = new Set([
+  ServerType.RSPrimary,
+  ServerType.RSSecondary,
+  ServerType.Mongos,
+  ServerType.Standalone
+]);
+
+const ISMASTER_FIELDS = [
+  'minWireVersion',
+  'maxWireVersion',
+  'maxBsonObjectSize',
+  'maxMessageSizeBytes',
+  'maxWriteBatchSize',
+  'compression',
+  'me',
+  'hosts',
+  'passives',
+  'arbiters',
+  'tags',
+  'setName',
+  'setVersion',
+  'electionId',
+  'primary',
+  'logicalSessionTimeoutMinutes',
+  'saslSupportedMechs',
+  '__nodejs_mock_server__',
+  '$clusterTime'
+];
+
+/**
+ * The client's view of a single server, based on the most recent ismaster outcome.
+ *
+ * Internal type, not meant to be directly instantiated
+ */
+class ServerDescription {
+  /**
+   * Create a ServerDescription
+   * @param {String} address The address of the server
+   * @param {Object} [ismaster] An optional ismaster response for this server
+   * @param {Object} [options] Optional settings
+   * @param {Number} [options.roundTripTime] The round trip time to ping this server (in ms)
+   * @param {Error} [options.error] An Error used for better reporting debugging
+   * @param {any} [options.topologyVersion] The topologyVersion
+   */
+  constructor(address, ismaster, options) {
+    options = options || {};
+    ismaster = Object.assign(
+      {
+        minWireVersion: 0,
+        maxWireVersion: 0,
+        hosts: [],
+        passives: [],
+        arbiters: [],
+        tags: []
+      },
+      ismaster
+    );
+
+    this.address = address;
+    this.error = options.error;
+    this.roundTripTime = options.roundTripTime || -1;
+    this.lastUpdateTime = now();
+    this.lastWriteDate = ismaster.lastWrite ? ismaster.lastWrite.lastWriteDate : null;
+    this.opTime = ismaster.lastWrite ? ismaster.lastWrite.opTime : null;
+    this.type = parseServerType(ismaster);
+    this.topologyVersion = options.topologyVersion || ismaster.topologyVersion;
+
+    // direct mappings
+    ISMASTER_FIELDS.forEach(field => {
+      if (typeof ismaster[field] !== 'undefined') this[field] = ismaster[field];
+    });
+
+    // normalize case for hosts
+    if (this.me) this.me = this.me.toLowerCase();
+    this.hosts = this.hosts.map(host => host.toLowerCase());
+    this.passives = this.passives.map(host => host.toLowerCase());
+    this.arbiters = this.arbiters.map(host => host.toLowerCase());
+  }
+
+  get allHosts() {
+    return this.hosts.concat(this.arbiters).concat(this.passives);
+  }
+
+  /**
+   * @return {Boolean} Is this server available for reads
+   */
+  get isReadable() {
+    return this.type === ServerType.RSSecondary || this.isWritable;
+  }
+
+  /**
+   * @return {Boolean} Is this server data bearing
+   */
+  get isDataBearing() {
+    return DATA_BEARING_SERVER_TYPES.has(this.type);
+  }
+
+  /**
+   * @return {Boolean} Is this server available for writes
+   */
+  get isWritable() {
+    return WRITABLE_SERVER_TYPES.has(this.type);
+  }
+
+  get host() {
+    const chopLength = `:${this.port}`.length;
+    return this.address.slice(0, -chopLength);
+  }
+
+  get port() {
+    const port = this.address.split(':').pop();
+    return port ? Number.parseInt(port, 10) : port;
+  }
+
+  /**
+   * Determines if another `ServerDescription` is equal to this one per the rules defined
+   * in the {@link https://github.com/mongodb/specifications/blob/master/source/server-discovery-and-monitoring/server-discovery-and-monitoring.rst#serverdescription|SDAM spec}
+   *
+   * @param {ServerDescription} other
+   * @return {Boolean}
+   */
+  equals(other) {
+    const topologyVersionsEqual =
+      this.topologyVersion === other.topologyVersion ||
+      compareTopologyVersion(this.topologyVersion, other.topologyVersion) === 0;
+
+    return (
+      other != null &&
+      errorStrictEqual(this.error, other.error) &&
+      this.type === other.type &&
+      this.minWireVersion === other.minWireVersion &&
+      this.me === other.me &&
+      arrayStrictEqual(this.hosts, other.hosts) &&
+      tagsStrictEqual(this.tags, other.tags) &&
+      this.setName === other.setName &&
+      this.setVersion === other.setVersion &&
+      (this.electionId
+        ? other.electionId && this.electionId.equals(other.electionId)
+        : this.electionId === other.electionId) &&
+      this.primary === other.primary &&
+      this.logicalSessionTimeoutMinutes === other.logicalSessionTimeoutMinutes &&
+      topologyVersionsEqual
+    );
+  }
+}
+
+/**
+ * Parses an `ismaster` message and determines the server type
+ *
+ * @param {Object} ismaster The `ismaster` message to parse
+ * @return {ServerType}
+ */
+function parseServerType(ismaster) {
+  if (!ismaster || !ismaster.ok) {
+    return ServerType.Unknown;
+  }
+
+  if (ismaster.isreplicaset) {
+    return ServerType.RSGhost;
+  }
+
+  if (ismaster.msg && ismaster.msg === 'isdbgrid') {
+    return ServerType.Mongos;
+  }
+
+  if (ismaster.setName) {
+    if (ismaster.hidden) {
+      return ServerType.RSOther;
+    } else if (ismaster.ismaster) {
+      return ServerType.RSPrimary;
+    } else if (ismaster.secondary) {
+      return ServerType.RSSecondary;
+    } else if (ismaster.arbiterOnly) {
+      return ServerType.RSArbiter;
+    } else {
+      return ServerType.RSOther;
+    }
+  }
+
+  return ServerType.Standalone;
+}
+
+/**
+ * Compares two topology versions.
+ *
+ * @param {object} lhs
+ * @param {object} rhs
+ * @returns A negative number if `lhs` is older than `rhs`; positive if `lhs` is newer than `rhs`; 0 if they are equivalent.
+ */
+function compareTopologyVersion(lhs, rhs) {
+  if (lhs == null || rhs == null) {
+    return -1;
+  }
+
+  if (lhs.processId.equals(rhs.processId)) {
+    // TODO: handle counters as Longs
+    if (lhs.counter === rhs.counter) {
+      return 0;
+    } else if (lhs.counter < rhs.counter) {
+      return -1;
+    }
+
+    return 1;
+  }
+
+  return -1;
+}
+
+module.exports = {
+  ServerDescription,
+  parseServerType,
+  compareTopologyVersion
+};

node_modules/mongodb/lib/core/sdam/server_selection.js

@@ -0,0 +1,238 @@
+'use strict';
+const ServerType = require('./common').ServerType;
+const TopologyType = require('./common').TopologyType;
+const ReadPreference = require('../topologies/read_preference');
+const MongoError = require('../error').MongoError;
+
+// max staleness constants
+const IDLE_WRITE_PERIOD = 10000;
+const SMALLEST_MAX_STALENESS_SECONDS = 90;
+
+/**
+ * Returns a server selector that selects for writable servers
+ */
+function writableServerSelector() {
+  return function(topologyDescription, servers) {
+    return latencyWindowReducer(
+      topologyDescription,
+      servers.filter(s => s.isWritable)
+    );
+  };
+}
+
+/**
+ * Reduces the passed in array of servers by the rules of the "Max Staleness" specification
+ * found here: https://github.com/mongodb/specifications/blob/master/source/max-staleness/max-staleness.rst
+ *
+ * @param {ReadPreference} readPreference The read preference providing max staleness guidance
+ * @param {topologyDescription} topologyDescription The topology description
+ * @param {ServerDescription[]} servers The list of server descriptions to be reduced
+ * @return {ServerDescription[]} The list of servers that satisfy the requirements of max staleness
+ */
+function maxStalenessReducer(readPreference, topologyDescription, servers) {
+  if (readPreference.maxStalenessSeconds == null || readPreference.maxStalenessSeconds < 0) {
+    return servers;
+  }
+
+  const maxStaleness = readPreference.maxStalenessSeconds;
+  const maxStalenessVariance =
+    (topologyDescription.heartbeatFrequencyMS + IDLE_WRITE_PERIOD) / 1000;
+  if (maxStaleness < maxStalenessVariance) {
+    throw new MongoError(`maxStalenessSeconds must be at least ${maxStalenessVariance} seconds`);
+  }
+
+  if (maxStaleness < SMALLEST_MAX_STALENESS_SECONDS) {
+    throw new MongoError(
+      `maxStalenessSeconds must be at least ${SMALLEST_MAX_STALENESS_SECONDS} seconds`
+    );
+  }
+
+  if (topologyDescription.type === TopologyType.ReplicaSetWithPrimary) {
+    const primary = Array.from(topologyDescription.servers.values()).filter(primaryFilter)[0];
+    return servers.reduce((result, server) => {
+      const stalenessMS =
+        server.lastUpdateTime -
+        server.lastWriteDate -
+        (primary.lastUpdateTime - primary.lastWriteDate) +
+        topologyDescription.heartbeatFrequencyMS;
+
+      const staleness = stalenessMS / 1000;
+      if (staleness <= readPreference.maxStalenessSeconds) result.push(server);
+      return result;
+    }, []);
+  }
+
+  if (topologyDescription.type === TopologyType.ReplicaSetNoPrimary) {
+    if (servers.length === 0) {
+      return servers;
+    }
+
+    const sMax = servers.reduce((max, s) => (s.lastWriteDate > max.lastWriteDate ? s : max));
+    return servers.reduce((result, server) => {
+      const stalenessMS =
+        sMax.lastWriteDate - server.lastWriteDate + topologyDescription.heartbeatFrequencyMS;
+
+      const staleness = stalenessMS / 1000;
+      if (staleness <= readPreference.maxStalenessSeconds) result.push(server);
+      return result;
+    }, []);
+  }
+
+  return servers;
+}
+
+/**
+ * Determines whether a server's tags match a given set of tags
+ *
+ * @param {String[]} tagSet The requested tag set to match
+ * @param {String[]} serverTags The server's tags
+ */
+function tagSetMatch(tagSet, serverTags) {
+  const keys = Object.keys(tagSet);
+  const serverTagKeys = Object.keys(serverTags);
+  for (let i = 0; i < keys.length; ++i) {
+    const key = keys[i];
+    if (serverTagKeys.indexOf(key) === -1 || serverTags[key] !== tagSet[key]) {
+      return false;
+    }
+  }
+
+  return true;
+}
+
+/**
+ * Reduces a set of server descriptions based on tags requested by the read preference
+ *
+ * @param {ReadPreference} readPreference The read preference providing the requested tags
+ * @param {ServerDescription[]} servers The list of server descriptions to reduce
+ * @return {ServerDescription[]} The list of servers matching the requested tags
+ */
+function tagSetReducer(readPreference, servers) {
+  if (
+    readPreference.tags == null ||
+    (Array.isArray(readPreference.tags) && readPreference.tags.length === 0)
+  ) {
+    return servers;
+  }
+
+  for (let i = 0; i < readPreference.tags.length; ++i) {
+    const tagSet = readPreference.tags[i];
+    const serversMatchingTagset = servers.reduce((matched, server) => {
+      if (tagSetMatch(tagSet, server.tags)) matched.push(server);
+      return matched;
+    }, []);
+
+    if (serversMatchingTagset.length) {
+      return serversMatchingTagset;
+    }
+  }
+
+  return [];
+}
+
+/**
+ * Reduces a list of servers to ensure they fall within an acceptable latency window. This is
+ * further specified in the "Server Selection" specification, found here:
+ * https://github.com/mongodb/specifications/blob/master/source/server-selection/server-selection.rst
+ *
+ * @param {topologyDescription} topologyDescription The topology description
+ * @param {ServerDescription[]} servers The list of servers to reduce
+ * @returns {ServerDescription[]} The servers which fall within an acceptable latency window
+ */
+function latencyWindowReducer(topologyDescription, servers) {
+  const low = servers.reduce(
+    (min, server) => (min === -1 ? server.roundTripTime : Math.min(server.roundTripTime, min)),
+    -1
+  );
+
+  const high = low + topologyDescription.localThresholdMS;
+
+  return servers.reduce((result, server) => {
+    if (server.roundTripTime <= high && server.roundTripTime >= low) result.push(server);
+    return result;
+  }, []);
+}
+
+// filters
+function primaryFilter(server) {
+  return server.type === ServerType.RSPrimary;
+}
+
+function secondaryFilter(server) {
+  return server.type === ServerType.RSSecondary;
+}
+
+function nearestFilter(server) {
+  return server.type === ServerType.RSSecondary || server.type === ServerType.RSPrimary;
+}
+
+function knownFilter(server) {
+  return server.type !== ServerType.Unknown;
+}
+
+/**
+ * Returns a function which selects servers based on a provided read preference
+ *
+ * @param {ReadPreference} readPreference The read preference to select with
+ */
+function readPreferenceServerSelector(readPreference) {
+  if (!readPreference.isValid()) {
+    throw new TypeError('Invalid read preference specified');
+  }
+
+  return function(topologyDescription, servers) {
+    const commonWireVersion = topologyDescription.commonWireVersion;
+    if (
+      commonWireVersion &&
+      readPreference.minWireVersion &&
+      readPreference.minWireVersion > commonWireVersion
+    ) {
+      throw new MongoError(
+        `Minimum wire version '${readPreference.minWireVersion}' required, but found '${commonWireVersion}'`
+      );
+    }
+
+    if (topologyDescription.type === TopologyType.Unknown) {
+      return [];
+    }
+
+    if (
+      topologyDescription.type === TopologyType.Single ||
+      topologyDescription.type === TopologyType.Sharded
+    ) {
+      return latencyWindowReducer(topologyDescription, servers.filter(knownFilter));
+    }
+
+    const mode = readPreference.mode;
+    if (mode === ReadPreference.PRIMARY) {
+      return servers.filter(primaryFilter);
+    }
+
+    if (mode === ReadPreference.PRIMARY_PREFERRED) {
+      const result = servers.filter(primaryFilter);
+      if (result.length) {
+        return result;
+      }
+    }
+
+    const filter = mode === ReadPreference.NEAREST ? nearestFilter : secondaryFilter;
+    const selectedServers = latencyWindowReducer(
+      topologyDescription,
+      tagSetReducer(
+        readPreference,
+        maxStalenessReducer(readPreference, topologyDescription, servers.filter(filter))
+      )
+    );
+
+    if (mode === ReadPreference.SECONDARY_PREFERRED && selectedServers.length === 0) {
+      return servers.filter(primaryFilter);
+    }
+
+    return selectedServers;
+  };
+}
+
+module.exports = {
+  writableServerSelector,
+  readPreferenceServerSelector
+};

node_modules/mongodb/lib/core/sdam/srv_polling.js

@@ -0,0 +1,135 @@
+'use strict';
+
+const Logger = require('../connection/logger');
+const EventEmitter = require('events').EventEmitter;
+const dns = require('dns');
+/**
+ * Determines whether a provided address matches the provided parent domain in order
+ * to avoid certain attack vectors.
+ *
+ * @param {String} srvAddress The address to check against a domain
+ * @param {String} parentDomain The domain to check the provided address against
+ * @return {Boolean} Whether the provided address matches the parent domain
+ */
+function matchesParentDomain(srvAddress, parentDomain) {
+  const regex = /^.*?\./;
+  const srv = `.${srvAddress.replace(regex, '')}`;
+  const parent = `.${parentDomain.replace(regex, '')}`;
+  return srv.endsWith(parent);
+}
+
+class SrvPollingEvent {
+  constructor(srvRecords) {
+    this.srvRecords = srvRecords;
+  }
+
+  addresses() {
+    return new Set(this.srvRecords.map(record => `${record.name}:${record.port}`));
+  }
+}
+
+class SrvPoller extends EventEmitter {
+  /**
+   * @param {object} options
+   * @param {string} options.srvHost
+   * @param {number} [options.heartbeatFrequencyMS]
+   * @param {function} [options.logger]
+   * @param {string} [options.loggerLevel]
+   */
+  constructor(options) {
+    super();
+
+    if (!options || !options.srvHost) {
+      throw new TypeError('options for SrvPoller must exist and include srvHost');
+    }
+
+    this.srvHost = options.srvHost;
+    this.rescanSrvIntervalMS = 60000;
+    this.heartbeatFrequencyMS = options.heartbeatFrequencyMS || 10000;
+    this.logger = Logger('srvPoller', options);
+
+    this.haMode = false;
+    this.generation = 0;
+
+    this._timeout = null;
+  }
+
+  get srvAddress() {
+    return `_mongodb._tcp.${this.srvHost}`;
+  }
+
+  get intervalMS() {
+    return this.haMode ? this.heartbeatFrequencyMS : this.rescanSrvIntervalMS;
+  }
+
+  start() {
+    if (!this._timeout) {
+      this.schedule();
+    }
+  }
+
+  stop() {
+    if (this._timeout) {
+      clearTimeout(this._timeout);
+      this.generation += 1;
+      this._timeout = null;
+    }
+  }
+
+  schedule() {
+    clearTimeout(this._timeout);
+    this._timeout = setTimeout(() => this._poll(), this.intervalMS);
+  }
+
+  success(srvRecords) {
+    this.haMode = false;
+    this.schedule();
+    this.emit('srvRecordDiscovery', new SrvPollingEvent(srvRecords));
+  }
+
+  failure(message, obj) {
+    this.logger.warn(message, obj);
+    this.haMode = true;
+    this.schedule();
+  }
+
+  parentDomainMismatch(srvRecord) {
+    this.logger.warn(
+      `parent domain mismatch on SRV record (${srvRecord.name}:${srvRecord.port})`,
+      srvRecord
+    );
+  }
+
+  _poll() {
+    const generation = this.generation;
+    dns.resolveSrv(this.srvAddress, (err, srvRecords) => {
+      if (generation !== this.generation) {
+        return;
+      }
+
+      if (err) {
+        this.failure('DNS error', err);
+        return;
+      }
+
+      const finalAddresses = [];
+      srvRecords.forEach(record => {
+        if (matchesParentDomain(record.name, this.srvHost)) {
+          finalAddresses.push(record);
+        } else {
+          this.parentDomainMismatch(record);
+        }
+      });
+
+      if (!finalAddresses.length) {
+        this.failure('No valid addresses found at host');
+        return;
+      }
+
+      this.success(finalAddresses);
+    });
+  }
+}
+
+module.exports.SrvPollingEvent = SrvPollingEvent;
+module.exports.SrvPoller = SrvPoller;

node_modules/mongodb/lib/core/sdam/topology_description.js

@@ -0,0 +1,441 @@
+'use strict';
+const ServerType = require('./common').ServerType;
+const ServerDescription = require('./server_description').ServerDescription;
+const WIRE_CONSTANTS = require('../wireprotocol/constants');
+const TopologyType = require('./common').TopologyType;
+
+// contstants related to compatability checks
+const MIN_SUPPORTED_SERVER_VERSION = WIRE_CONSTANTS.MIN_SUPPORTED_SERVER_VERSION;
+const MAX_SUPPORTED_SERVER_VERSION = WIRE_CONSTANTS.MAX_SUPPORTED_SERVER_VERSION;
+const MIN_SUPPORTED_WIRE_VERSION = WIRE_CONSTANTS.MIN_SUPPORTED_WIRE_VERSION;
+const MAX_SUPPORTED_WIRE_VERSION = WIRE_CONSTANTS.MAX_SUPPORTED_WIRE_VERSION;
+
+// Representation of a deployment of servers
+class TopologyDescription {
+  /**
+   * Create a TopologyDescription
+   *
+   * @param {string} topologyType
+   * @param {Map<string, ServerDescription>} serverDescriptions the a map of address to ServerDescription
+   * @param {string} setName
+   * @param {number} maxSetVersion
+   * @param {ObjectId} maxElectionId
+   */
+  constructor(
+    topologyType,
+    serverDescriptions,
+    setName,
+    maxSetVersion,
+    maxElectionId,
+    commonWireVersion,
+    options
+  ) {
+    options = options || {};
+
+    // TODO: consider assigning all these values to a temporary value `s` which
+    //       we use `Object.freeze` on, ensuring the internal state of this type
+    //       is immutable.
+    this.type = topologyType || TopologyType.Unknown;
+    this.setName = setName || null;
+    this.maxSetVersion = maxSetVersion || null;
+    this.maxElectionId = maxElectionId || null;
+    this.servers = serverDescriptions || new Map();
+    this.stale = false;
+    this.compatible = true;
+    this.compatibilityError = null;
+    this.logicalSessionTimeoutMinutes = null;
+    this.heartbeatFrequencyMS = options.heartbeatFrequencyMS || 0;
+    this.localThresholdMS = options.localThresholdMS || 0;
+    this.commonWireVersion = commonWireVersion || null;
+
+    // save this locally, but don't display when printing the instance out
+    Object.defineProperty(this, 'options', { value: options, enumberable: false });
+
+    // determine server compatibility
+    for (const serverDescription of this.servers.values()) {
+      if (serverDescription.type === ServerType.Unknown) continue;
+
+      if (serverDescription.minWireVersion > MAX_SUPPORTED_WIRE_VERSION) {
+        this.compatible = false;
+        this.compatibilityError = `Server at ${serverDescription.address} requires wire version ${serverDescription.minWireVersion}, but this version of the driver only supports up to ${MAX_SUPPORTED_WIRE_VERSION} (MongoDB ${MAX_SUPPORTED_SERVER_VERSION})`;
+      }
+
+      if (serverDescription.maxWireVersion < MIN_SUPPORTED_WIRE_VERSION) {
+        this.compatible = false;
+        this.compatibilityError = `Server at ${serverDescription.address} reports wire version ${serverDescription.maxWireVersion}, but this version of the driver requires at least ${MIN_SUPPORTED_WIRE_VERSION} (MongoDB ${MIN_SUPPORTED_SERVER_VERSION}).`;
+        break;
+      }
+    }
+
+    // Whenever a client updates the TopologyDescription from an ismaster response, it MUST set
+    // TopologyDescription.logicalSessionTimeoutMinutes to the smallest logicalSessionTimeoutMinutes
+    // value among ServerDescriptions of all data-bearing server types. If any have a null
+    // logicalSessionTimeoutMinutes, then TopologyDescription.logicalSessionTimeoutMinutes MUST be
+    // set to null.
+    const readableServers = Array.from(this.servers.values()).filter(s => s.isReadable);
+    this.logicalSessionTimeoutMinutes = readableServers.reduce((result, server) => {
+      if (server.logicalSessionTimeoutMinutes == null) return null;
+      if (result == null) return server.logicalSessionTimeoutMinutes;
+      return Math.min(result, server.logicalSessionTimeoutMinutes);
+    }, null);
+  }
+
+  /**
+   * Returns a new TopologyDescription based on the SrvPollingEvent
+   * @param {SrvPollingEvent} ev The event
+   */
+  updateFromSrvPollingEvent(ev) {
+    const newAddresses = ev.addresses();
+    const serverDescriptions = new Map(this.servers);
+    for (const server of this.servers) {
+      if (newAddresses.has(server[0])) {
+        newAddresses.delete(server[0]);
+      } else {
+        serverDescriptions.delete(server[0]);
+      }
+    }
+
+    if (serverDescriptions.size === this.servers.size && newAddresses.size === 0) {
+      return this;
+    }
+
+    for (const address of newAddresses) {
+      serverDescriptions.set(address, new ServerDescription(address));
+    }
+
+    return new TopologyDescription(
+      this.type,
+      serverDescriptions,
+      this.setName,
+      this.maxSetVersion,
+      this.maxElectionId,
+      this.commonWireVersion,
+      this.options,
+      null
+    );
+  }
+
+  /**
+   * Returns a copy of this description updated with a given ServerDescription
+   *
+   * @param {ServerDescription} serverDescription
+   */
+  update(serverDescription) {
+    const address = serverDescription.address;
+    // NOTE: there are a number of prime targets for refactoring here
+    //       once we support destructuring assignments
+
+    // potentially mutated values
+    let topologyType = this.type;
+    let setName = this.setName;
+    let maxSetVersion = this.maxSetVersion;
+    let maxElectionId = this.maxElectionId;
+    let commonWireVersion = this.commonWireVersion;
+
+    if (serverDescription.setName && setName && serverDescription.setName !== setName) {
+      serverDescription = new ServerDescription(address, null);
+    }
+
+    const serverType = serverDescription.type;
+    let serverDescriptions = new Map(this.servers);
+
+    // update common wire version
+    if (serverDescription.maxWireVersion !== 0) {
+      if (commonWireVersion == null) {
+        commonWireVersion = serverDescription.maxWireVersion;
+      } else {
+        commonWireVersion = Math.min(commonWireVersion, serverDescription.maxWireVersion);
+      }
+    }
+
+    // update the actual server description
+    serverDescriptions.set(address, serverDescription);
+
+    if (topologyType === TopologyType.Single) {
+      // once we are defined as single, that never changes
+      return new TopologyDescription(
+        TopologyType.Single,
+        serverDescriptions,
+        setName,
+        maxSetVersion,
+        maxElectionId,
+        commonWireVersion,
+        this.options
+      );
+    }
+
+    if (topologyType === TopologyType.Unknown) {
+      if (serverType === ServerType.Standalone && this.servers.size !== 1) {
+        serverDescriptions.delete(address);
+      } else {
+        topologyType = topologyTypeForServerType(serverType);
+      }
+    }
+
+    if (topologyType === TopologyType.Sharded) {
+      if ([ServerType.Mongos, ServerType.Unknown].indexOf(serverType) === -1) {
+        serverDescriptions.delete(address);
+      }
+    }
+
+    if (topologyType === TopologyType.ReplicaSetNoPrimary) {
+      if ([ServerType.Standalone, ServerType.Mongos].indexOf(serverType) >= 0) {
+        serverDescriptions.delete(address);
+      }
+
+      if (serverType === ServerType.RSPrimary) {
+        const result = updateRsFromPrimary(
+          serverDescriptions,
+          setName,
+          serverDescription,
+          maxSetVersion,
+          maxElectionId
+        );
+
+        (topologyType = result[0]),
+          (setName = result[1]),
+          (maxSetVersion = result[2]),
+          (maxElectionId = result[3]);
+      } else if (
+        [ServerType.RSSecondary, ServerType.RSArbiter, ServerType.RSOther].indexOf(serverType) >= 0
+      ) {
+        const result = updateRsNoPrimaryFromMember(serverDescriptions, setName, serverDescription);
+        (topologyType = result[0]), (setName = result[1]);
+      }
+    }
+
+    if (topologyType === TopologyType.ReplicaSetWithPrimary) {
+      if ([ServerType.Standalone, ServerType.Mongos].indexOf(serverType) >= 0) {
+        serverDescriptions.delete(address);
+        topologyType = checkHasPrimary(serverDescriptions);
+      } else if (serverType === ServerType.RSPrimary) {
+        const result = updateRsFromPrimary(
+          serverDescriptions,
+          setName,
+          serverDescription,
+          maxSetVersion,
+          maxElectionId
+        );
+
+        (topologyType = result[0]),
+          (setName = result[1]),
+          (maxSetVersion = result[2]),
+          (maxElectionId = result[3]);
+      } else if (
+        [ServerType.RSSecondary, ServerType.RSArbiter, ServerType.RSOther].indexOf(serverType) >= 0
+      ) {
+        topologyType = updateRsWithPrimaryFromMember(
+          serverDescriptions,
+          setName,
+          serverDescription
+        );
+      } else {
+        topologyType = checkHasPrimary(serverDescriptions);
+      }
+    }
+
+    return new TopologyDescription(
+      topologyType,
+      serverDescriptions,
+      setName,
+      maxSetVersion,
+      maxElectionId,
+      commonWireVersion,
+      this.options
+    );
+  }
+
+  get error() {
+    const descriptionsWithError = Array.from(this.servers.values()).filter(sd => sd.error);
+    if (descriptionsWithError.length > 0) {
+      return descriptionsWithError[0].error;
+    }
+  }
+
+  /**
+   * Determines if the topology description has any known servers
+   */
+  get hasKnownServers() {
+    return Array.from(this.servers.values()).some(sd => sd.type !== ServerType.Unknown);
+  }
+
+  /**
+   * Determines if this topology description has a data-bearing server available.
+   */
+  get hasDataBearingServers() {
+    return Array.from(this.servers.values()).some(sd => sd.isDataBearing);
+  }
+
+  /**
+   * Determines if the topology has a definition for the provided address
+   *
+   * @param {String} address
+   * @return {Boolean} Whether the topology knows about this server
+   */
+  hasServer(address) {
+    return this.servers.has(address);
+  }
+}
+
+function topologyTypeForServerType(serverType) {
+  if (serverType === ServerType.Standalone) {
+    return TopologyType.Single;
+  }
+
+  if (serverType === ServerType.Mongos) {
+    return TopologyType.Sharded;
+  }
+
+  if (serverType === ServerType.RSPrimary) {
+    return TopologyType.ReplicaSetWithPrimary;
+  }
+
+  if (serverType === ServerType.RSGhost || serverType === ServerType.Unknown) {
+    return TopologyType.Unknown;
+  }
+
+  return TopologyType.ReplicaSetNoPrimary;
+}
+
+function compareObjectId(oid1, oid2) {
+  if (oid1 == null) {
+    return -1;
+  }
+
+  if (oid2 == null) {
+    return 1;
+  }
+
+  if (oid1.id instanceof Buffer && oid2.id instanceof Buffer) {
+    const oid1Buffer = oid1.id;
+    const oid2Buffer = oid2.id;
+    return oid1Buffer.compare(oid2Buffer);
+  }
+
+  const oid1String = oid1.toString();
+  const oid2String = oid2.toString();
+  return oid1String.localeCompare(oid2String);
+}
+
+function updateRsFromPrimary(
+  serverDescriptions,
+  setName,
+  serverDescription,
+  maxSetVersion,
+  maxElectionId
+) {
+  setName = setName || serverDescription.setName;
+  if (setName !== serverDescription.setName) {
+    serverDescriptions.delete(serverDescription.address);
+    return [checkHasPrimary(serverDescriptions), setName, maxSetVersion, maxElectionId];
+  }
+
+  const electionId = serverDescription.electionId ? serverDescription.electionId : null;
+  if (serverDescription.setVersion && electionId) {
+    if (maxSetVersion && maxElectionId) {
+      if (
+        maxSetVersion > serverDescription.setVersion ||
+        compareObjectId(maxElectionId, electionId) > 0
+      ) {
+        // this primary is stale, we must remove it
+        serverDescriptions.set(
+          serverDescription.address,
+          new ServerDescription(serverDescription.address)
+        );
+
+        return [checkHasPrimary(serverDescriptions), setName, maxSetVersion, maxElectionId];
+      }
+    }
+
+    maxElectionId = serverDescription.electionId;
+  }
+
+  if (
+    serverDescription.setVersion != null &&
+    (maxSetVersion == null || serverDescription.setVersion > maxSetVersion)
+  ) {
+    maxSetVersion = serverDescription.setVersion;
+  }
+
+  // We've heard from the primary. Is it the same primary as before?
+  for (const address of serverDescriptions.keys()) {
+    const server = serverDescriptions.get(address);
+
+    if (server.type === ServerType.RSPrimary && server.address !== serverDescription.address) {
+      // Reset old primary's type to Unknown.
+      serverDescriptions.set(address, new ServerDescription(server.address));
+
+      // There can only be one primary
+      break;
+    }
+  }
+
+  // Discover new hosts from this primary's response.
+  serverDescription.allHosts.forEach(address => {
+    if (!serverDescriptions.has(address)) {
+      serverDescriptions.set(address, new ServerDescription(address));
+    }
+  });
+
+  // Remove hosts not in the response.
+  const currentAddresses = Array.from(serverDescriptions.keys());
+  const responseAddresses = serverDescription.allHosts;
+  currentAddresses
+    .filter(addr => responseAddresses.indexOf(addr) === -1)
+    .forEach(address => {
+      serverDescriptions.delete(address);
+    });
+
+  return [checkHasPrimary(serverDescriptions), setName, maxSetVersion, maxElectionId];
+}
+
+function updateRsWithPrimaryFromMember(serverDescriptions, setName, serverDescription) {
+  if (setName == null) {
+    throw new TypeError('setName is required');
+  }
+
+  if (
+    setName !== serverDescription.setName ||
+    (serverDescription.me && serverDescription.address !== serverDescription.me)
+  ) {
+    serverDescriptions.delete(serverDescription.address);
+  }
+
+  return checkHasPrimary(serverDescriptions);
+}
+
+function updateRsNoPrimaryFromMember(serverDescriptions, setName, serverDescription) {
+  let topologyType = TopologyType.ReplicaSetNoPrimary;
+
+  setName = setName || serverDescription.setName;
+  if (setName !== serverDescription.setName) {
+    serverDescriptions.delete(serverDescription.address);
+    return [topologyType, setName];
+  }
+
+  serverDescription.allHosts.forEach(address => {
+    if (!serverDescriptions.has(address)) {
+      serverDescriptions.set(address, new ServerDescription(address));
+    }
+  });
+
+  if (serverDescription.me && serverDescription.address !== serverDescription.me) {
+    serverDescriptions.delete(serverDescription.address);
+  }
+
+  return [topologyType, setName];
+}
+
+function checkHasPrimary(serverDescriptions) {
+  for (const addr of serverDescriptions.keys()) {
+    if (serverDescriptions.get(addr).type === ServerType.RSPrimary) {
+      return TopologyType.ReplicaSetWithPrimary;
+    }
+  }
+
+  return TopologyType.ReplicaSetNoPrimary;
+}
+
+module.exports = {
+  TopologyDescription
+};