'use strict';
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const ServerDescription = require('./server_description').ServerDescription;
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const calculateDurationInMs = require('../utils').calculateDurationInMs;
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/**
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* Published when server description changes, but does NOT include changes to the RTT.
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*
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* @property {Object} topologyId A unique identifier for the topology
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* @property {ServerAddress} address The address (host/port pair) of the server
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* @property {ServerDescription} previousDescription The previous server description
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* @property {ServerDescription} newDescription The new server description
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*/
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class ServerDescriptionChangedEvent {
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constructor(topologyId, address, previousDescription, newDescription) {
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Object.assign(this, { topologyId, address, previousDescription, newDescription });
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}
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}
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/**
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* Published when server is initialized.
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*
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* @property {Object} topologyId A unique identifier for the topology
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* @property {ServerAddress} address The address (host/port pair) of the server
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*/
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class ServerOpeningEvent {
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constructor(topologyId, address) {
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Object.assign(this, { topologyId, address });
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}
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}
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/**
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* Published when server is closed.
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*
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* @property {ServerAddress} address The address (host/port pair) of the server
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* @property {Object} topologyId A unique identifier for the topology
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*/
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class ServerClosedEvent {
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constructor(topologyId, address) {
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Object.assign(this, { topologyId, address });
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}
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}
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/**
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* Published when topology description changes.
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*
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* @property {Object} topologyId
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* @property {TopologyDescription} previousDescription The old topology description
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* @property {TopologyDescription} newDescription The new topology description
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*/
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class TopologyDescriptionChangedEvent {
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constructor(topologyId, previousDescription, newDescription) {
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Object.assign(this, { topologyId, previousDescription, newDescription });
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}
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}
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/**
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* Published when topology is initialized.
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*
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* @param {Object} topologyId A unique identifier for the topology
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*/
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class TopologyOpeningEvent {
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constructor(topologyId) {
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Object.assign(this, { topologyId });
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}
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}
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/**
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* Published when topology is closed.
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*
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* @param {Object} topologyId A unique identifier for the topology
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*/
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class TopologyClosedEvent {
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constructor(topologyId) {
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Object.assign(this, { topologyId });
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}
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}
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/**
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* Fired when the server monitor’s ismaster command is started - immediately before
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* the ismaster command is serialized into raw BSON and written to the socket.
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*
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* @property {Object} connectionId The connection id for the command
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*/
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class ServerHeartbeatStartedEvent {
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constructor(connectionId) {
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Object.assign(this, { connectionId });
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}
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}
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/**
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* Fired when the server monitor’s ismaster succeeds.
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*
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* @param {Number} duration The execution time of the event in ms
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* @param {Object} reply The command reply
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* @param {Object} connectionId The connection id for the command
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*/
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class ServerHeartbeatSucceededEvent {
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constructor(duration, reply, connectionId) {
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Object.assign(this, { duration, reply, connectionId });
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}
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}
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/**
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* Fired when the server monitor’s ismaster fails, either with an “ok: 0” or a socket exception.
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*
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* @param {Number} duration The execution time of the event in ms
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* @param {MongoError|Object} failure The command failure
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* @param {Object} connectionId The connection id for the command
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*/
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class ServerHeartbeatFailedEvent {
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constructor(duration, failure, connectionId) {
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Object.assign(this, { duration, failure, connectionId });
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}
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}
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/**
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* Performs a server check as described by the SDAM spec.
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*
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* NOTE: This method automatically reschedules itself, so that there is always an active
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* monitoring process
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*
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* @param {Server} server The server to monitor
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*/
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function monitorServer(server, options) {
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options = options || {};
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const heartbeatFrequencyMS = options.heartbeatFrequencyMS || 10000;
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if (options.initial === true) {
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server.s.monitorId = setTimeout(() => monitorServer(server), heartbeatFrequencyMS);
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return;
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}
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// executes a single check of a server
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const checkServer = callback => {
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let start = process.hrtime();
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// emit a signal indicating we have started the heartbeat
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server.emit('serverHeartbeatStarted', new ServerHeartbeatStartedEvent(server.name));
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// NOTE: legacy monitoring event
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process.nextTick(() => server.emit('monitoring', server));
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server.command(
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'admin.$cmd',
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{ ismaster: true },
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{
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monitoring: true,
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socketTimeout: server.s.options.connectionTimeout || 2000
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},
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(err, result) => {
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let duration = calculateDurationInMs(start);
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if (err) {
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server.emit(
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'serverHeartbeatFailed',
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new ServerHeartbeatFailedEvent(duration, err, server.name)
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);
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return callback(err, null);
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}
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const isMaster = result.result;
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server.emit(
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'serverHeartbeatSucceded',
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new ServerHeartbeatSucceededEvent(duration, isMaster, server.name)
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);
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return callback(null, isMaster);
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}
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);
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};
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const successHandler = isMaster => {
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server.s.monitoring = false;
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// emit an event indicating that our description has changed
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server.emit('descriptionReceived', new ServerDescription(server.description.address, isMaster));
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// schedule the next monitoring process
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server.s.monitorId = setTimeout(() => monitorServer(server), heartbeatFrequencyMS);
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};
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// run the actual monitoring loop
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server.s.monitoring = true;
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checkServer((err, isMaster) => {
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if (!err) {
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successHandler(isMaster);
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return;
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}
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// According to the SDAM specification's "Network error during server check" section, if
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// an ismaster call fails we reset the server's pool. If a server was once connected,
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// change its type to `Unknown` only after retrying once.
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server.s.pool.reset(() => {
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// otherwise re-attempt monitoring once
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checkServer((error, isMaster) => {
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if (error) {
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server.s.monitoring = false;
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// we revert to an `Unknown` by emitting a default description with no isMaster
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server.emit(
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'descriptionReceived',
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new ServerDescription(server.description.address, null, { error })
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);
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// we do not reschedule monitoring in this case
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return;
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}
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successHandler(isMaster);
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});
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});
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});
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}
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module.exports = {
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ServerDescriptionChangedEvent,
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ServerOpeningEvent,
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ServerClosedEvent,
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TopologyDescriptionChangedEvent,
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TopologyOpeningEvent,
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TopologyClosedEvent,
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ServerHeartbeatStartedEvent,
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ServerHeartbeatSucceededEvent,
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ServerHeartbeatFailedEvent,
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monitorServer
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};
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