topology_description.ts

import { EJSON, type ObjectId } from '../bson';
import * as WIRE_CONSTANTS from '../cmap/wire_protocol/constants';
import { type MongoError, MongoRuntimeError } from '../error';
import { compareObjectId, shuffle } from '../utils';
import { ServerType, TopologyType } from './common';
import { ServerDescription } from './server_description';
import type { SrvPollingEvent } from './srv_polling';

// constants related to compatibility 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;

const MONGOS_OR_UNKNOWN = new Set<ServerType>([ServerType.Mongos, ServerType.Unknown]);
const MONGOS_OR_STANDALONE = new Set<ServerType>([ServerType.Mongos, ServerType.Standalone]);
const NON_PRIMARY_RS_MEMBERS = new Set<ServerType>([
  ServerType.RSSecondary,
  ServerType.RSArbiter,
  ServerType.RSOther
]);

/** @public */
export interface TopologyDescriptionOptions {
  heartbeatFrequencyMS?: number;
  localThresholdMS?: number;
}

/**
 * Representation of a deployment of servers
 * @public
 */
export class TopologyDescription {
  type: TopologyType;
  setName: string | null;
  maxSetVersion: number | null;
  maxElectionId: ObjectId | null;
  servers: Map<string, ServerDescription>;
  stale: boolean;
  compatible: boolean;
  compatibilityError?: string;
  logicalSessionTimeoutMinutes: number | null;
  heartbeatFrequencyMS: number;
  localThresholdMS: number;
  commonWireVersion: number;

  /**
   * Create a TopologyDescription
   */
  constructor(
    topologyType: TopologyType,
    serverDescriptions: Map<string, ServerDescription> | null = null,
    setName: string | null = null,
    maxSetVersion: number | null = null,
    maxElectionId: ObjectId | null = null,
    commonWireVersion: number | null = null,
    options: TopologyDescriptionOptions | null = null
  ) {
    options = options ?? {};

    this.type = topologyType ?? TopologyType.Unknown;
    this.servers = serverDescriptions ?? new Map();
    this.stale = false;
    this.compatible = true;
    this.heartbeatFrequencyMS = options.heartbeatFrequencyMS ?? 0;
    this.localThresholdMS = options.localThresholdMS ?? 15;
    this.setName = setName ?? null;
    this.maxElectionId = maxElectionId ?? null;
    this.maxSetVersion = maxSetVersion ?? null;
    this.commonWireVersion = commonWireVersion ?? 0;

    // determine server compatibility
    for (const serverDescription of this.servers.values()) {
      // Load balancer mode is always compatible.
      if (
        serverDescription.type === ServerType.Unknown ||
        serverDescription.type === ServerType.LoadBalancer
      ) {
        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 a hello 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.
    this.logicalSessionTimeoutMinutes = null;
    for (const [, server] of this.servers) {
      if (server.isReadable) {
        if (server.logicalSessionTimeoutMinutes == null) {
          // If any of the servers have a null logicalSessionsTimeout, then the whole topology does
          this.logicalSessionTimeoutMinutes = null;
          break;
        }

        if (this.logicalSessionTimeoutMinutes == null) {
          // First server with a non null logicalSessionsTimeout
          this.logicalSessionTimeoutMinutes = server.logicalSessionTimeoutMinutes;
          continue;
        }

        // Always select the smaller of the:
        // current server logicalSessionsTimeout and the topologies logicalSessionsTimeout
        this.logicalSessionTimeoutMinutes = Math.min(
          this.logicalSessionTimeoutMinutes,
          server.logicalSessionTimeoutMinutes
        );
      }
    }
  }

  /**
   * Returns a new TopologyDescription based on the SrvPollingEvent
   * @internal
   */
  updateFromSrvPollingEvent(ev: SrvPollingEvent, srvMaxHosts = 0): TopologyDescription {
    /** The SRV addresses defines the set of addresses we should be using */
    const incomingHostnames = ev.hostnames();
    const currentHostnames = new Set(this.servers.keys());

    const hostnamesToAdd = new Set<string>(incomingHostnames);
    const hostnamesToRemove = new Set<string>();
    for (const hostname of currentHostnames) {
      // filter hostnamesToAdd (made from incomingHostnames) down to what is *not* present in currentHostnames
      hostnamesToAdd.delete(hostname);
      if (!incomingHostnames.has(hostname)) {
        // If the SRV Records no longer include this hostname
        // we have to stop using it
        hostnamesToRemove.add(hostname);
      }
    }

    if (hostnamesToAdd.size === 0 && hostnamesToRemove.size === 0) {
      // No new hosts to add and none to remove
      return this;
    }

    const serverDescriptions = new Map(this.servers);
    for (const removedHost of hostnamesToRemove) {
      serverDescriptions.delete(removedHost);
    }

    if (hostnamesToAdd.size > 0) {
      if (srvMaxHosts === 0) {
        // Add all!
        for (const hostToAdd of hostnamesToAdd) {
          serverDescriptions.set(hostToAdd, new ServerDescription(hostToAdd));
        }
      } else if (serverDescriptions.size < srvMaxHosts) {
        // Add only the amount needed to get us back to srvMaxHosts
        const selectedHosts = shuffle(hostnamesToAdd, srvMaxHosts - serverDescriptions.size);
        for (const selectedHostToAdd of selectedHosts) {
          serverDescriptions.set(selectedHostToAdd, new ServerDescription(selectedHostToAdd));
        }
      }
    }

    return new TopologyDescription(
      this.type,
      serverDescriptions,
      this.setName,
      this.maxSetVersion,
      this.maxElectionId,
      this.commonWireVersion,
      { heartbeatFrequencyMS: this.heartbeatFrequencyMS, localThresholdMS: this.localThresholdMS }
    );
  }

  /**
   * Returns a copy of this description updated with a given ServerDescription
   * @internal
   */
  update(serverDescription: ServerDescription): TopologyDescription {
    const address = serverDescription.address;

    // potentially mutated values
    let { type: topologyType, setName, maxSetVersion, maxElectionId, commonWireVersion } = this;

    const serverType = serverDescription.type;
    const 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);
      }
    }

    if (
      typeof serverDescription.setName === 'string' &&
      typeof setName === 'string' &&
      serverDescription.setName !== setName
    ) {
      if (topologyType === TopologyType.Single) {
        // "Single" Topology with setName mismatch is direct connection usage, mark unknown do not remove
        serverDescription = new ServerDescription(address);
      } else {
        serverDescriptions.delete(address);
      }
    }

    // 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,
        { heartbeatFrequencyMS: this.heartbeatFrequencyMS, localThresholdMS: this.localThresholdMS }
      );
    }

    if (topologyType === TopologyType.Unknown) {
      if (serverType === ServerType.Standalone && this.servers.size !== 1) {
        serverDescriptions.delete(address);
      } else {
        topologyType = topologyTypeForServerType(serverType);
      }
    }

    if (topologyType === TopologyType.Sharded) {
      if (!MONGOS_OR_UNKNOWN.has(serverType)) {
        serverDescriptions.delete(address);
      }
    }

    if (topologyType === TopologyType.ReplicaSetNoPrimary) {
      if (MONGOS_OR_STANDALONE.has(serverType)) {
        serverDescriptions.delete(address);
      }

      if (serverType === ServerType.RSPrimary) {
        const result = updateRsFromPrimary(
          serverDescriptions,
          serverDescription,
          setName,
          maxSetVersion,
          maxElectionId
        );

        topologyType = result[0];
        setName = result[1];
        maxSetVersion = result[2];
        maxElectionId = result[3];
      } else if (NON_PRIMARY_RS_MEMBERS.has(serverType)) {
        const result = updateRsNoPrimaryFromMember(serverDescriptions, serverDescription, setName);
        topologyType = result[0];
        setName = result[1];
      }
    }

    if (topologyType === TopologyType.ReplicaSetWithPrimary) {
      if (MONGOS_OR_STANDALONE.has(serverType)) {
        serverDescriptions.delete(address);
        topologyType = checkHasPrimary(serverDescriptions);
      } else if (serverType === ServerType.RSPrimary) {
        const result = updateRsFromPrimary(
          serverDescriptions,
          serverDescription,
          setName,
          maxSetVersion,
          maxElectionId
        );

        topologyType = result[0];
        setName = result[1];
        maxSetVersion = result[2];
        maxElectionId = result[3];
      } else if (NON_PRIMARY_RS_MEMBERS.has(serverType)) {
        topologyType = updateRsWithPrimaryFromMember(
          serverDescriptions,
          serverDescription,
          setName
        );
      } else {
        topologyType = checkHasPrimary(serverDescriptions);
      }
    }

    return new TopologyDescription(
      topologyType,
      serverDescriptions,
      setName,
      maxSetVersion,
      maxElectionId,
      commonWireVersion,
      { heartbeatFrequencyMS: this.heartbeatFrequencyMS, localThresholdMS: this.localThresholdMS }
    );
  }

  get error(): MongoError | null {
    const descriptionsWithError = Array.from(this.servers.values()).filter(
      (sd: ServerDescription) => sd.error
    );

    if (descriptionsWithError.length > 0) {
      return descriptionsWithError[0].error;
    }

    return null;
  }

  /**
   * Determines if the topology description has any known servers
   */
  get hasKnownServers(): boolean {
    return Array.from(this.servers.values()).some(
      (sd: ServerDescription) => sd.type !== ServerType.Unknown
    );
  }

  /**
   * Determines if this topology description has a data-bearing server available.
   */
  get hasDataBearingServers(): boolean {
    return Array.from(this.servers.values()).some((sd: ServerDescription) => sd.isDataBearing);
  }

  /**
   * Determines if the topology has a definition for the provided address
   * @internal
   */
  hasServer(address: string): boolean {
    return this.servers.has(address);
  }

  toJSON() {
    return EJSON.serialize(this);
  }
}

function topologyTypeForServerType(serverType: ServerType): TopologyType {
  switch (serverType) {
    case ServerType.Standalone:
      return TopologyType.Single;
    case ServerType.Mongos:
      return TopologyType.Sharded;
    case ServerType.RSPrimary:
      return TopologyType.ReplicaSetWithPrimary;
    case ServerType.RSOther:
    case ServerType.RSSecondary:
      return TopologyType.ReplicaSetNoPrimary;
    default:
      return TopologyType.Unknown;
  }
}

function updateRsFromPrimary(
  serverDescriptions: Map<string, ServerDescription>,
  serverDescription: ServerDescription,
  setName: string | null = null,
  maxSetVersion: number | null = null,
  maxElectionId: ObjectId | null = null
): [TopologyType, string | null, number | null, ObjectId | null] {
  setName = setName || serverDescription.setName;
  if (setName !== serverDescription.setName) {
    serverDescriptions.delete(serverDescription.address);
    return [checkHasPrimary(serverDescriptions), setName, maxSetVersion, maxElectionId];
  }

  if (serverDescription.maxWireVersion >= 17) {
    const electionIdComparison = compareObjectId(maxElectionId, serverDescription.electionId);
    const maxElectionIdIsEqual = electionIdComparison === 0;
    const maxElectionIdIsLess = electionIdComparison === -1;
    const maxSetVersionIsLessOrEqual =
      (maxSetVersion ?? -1) <= (serverDescription.setVersion ?? -1);

    if (maxElectionIdIsLess || (maxElectionIdIsEqual && maxSetVersionIsLessOrEqual)) {
      // The reported electionId was greater
      // or the electionId was equal and reported setVersion was greater
      // Always update both values, they are a tuple
      maxElectionId = serverDescription.electionId;
      maxSetVersion = serverDescription.setVersion;
    } else {
      // Stale primary
      // replace serverDescription with a default ServerDescription of type "Unknown"
      serverDescriptions.set(
        serverDescription.address,
        new ServerDescription(serverDescription.address)
      );

      return [checkHasPrimary(serverDescriptions), setName, maxSetVersion, maxElectionId];
    }
  } else {
    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, server] of serverDescriptions) {
    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: string) => {
    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: string) => responseAddresses.indexOf(addr) === -1)
    .forEach((address: string) => {
      serverDescriptions.delete(address);
    });

  return [checkHasPrimary(serverDescriptions), setName, maxSetVersion, maxElectionId];
}

function updateRsWithPrimaryFromMember(
  serverDescriptions: Map<string, ServerDescription>,
  serverDescription: ServerDescription,
  setName: string | null = null
): TopologyType {
  if (setName == null) {
    // TODO(NODE-3483): should be an appropriate runtime error
    throw new MongoRuntimeError('Argument "setName" is required if connected to a replica set');
  }

  if (
    setName !== serverDescription.setName ||
    (serverDescription.me && serverDescription.address !== serverDescription.me)
  ) {
    serverDescriptions.delete(serverDescription.address);
  }

  return checkHasPrimary(serverDescriptions);
}

function updateRsNoPrimaryFromMember(
  serverDescriptions: Map<string, ServerDescription>,
  serverDescription: ServerDescription,
  setName: string | null = null
): [TopologyType, string | null] {
  const topologyType = TopologyType.ReplicaSetNoPrimary;
  setName = setName ?? serverDescription.setName;
  if (setName !== serverDescription.setName) {
    serverDescriptions.delete(serverDescription.address);
    return [topologyType, setName];
  }

  serverDescription.allHosts.forEach((address: string) => {
    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: Map<string, ServerDescription>): TopologyType {
  for (const serverDescription of serverDescriptions.values()) {
    if (serverDescription.type === ServerType.RSPrimary) {
      return TopologyType.ReplicaSetWithPrimary;
    }
  }

  return TopologyType.ReplicaSetNoPrimary;
}