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const childProcess = require('child_process');
const path = require('path');
const makeError = require('../util/MakeError');
const makePlainError = require('../util/MakePlainError');
/**
* Represents a Shard spawned by the ShardingManager.
*/
class Shard {
/**
* @param {ShardingManager} manager The sharding manager
* @param {number} id The ID of this shard
* @param {Array} [args=[]] Command line arguments to pass to the script
*/
constructor(manager, id, args = []) {
/**
* Manager that created the shard
* @type {ShardingManager}
*/
this.manager = manager;
/**
* ID of the shard
* @type {number}
*/
this.id = id;
/**
* The environment variables for the shard
* @type {Object}
*/
this.env = Object.assign({}, process.env, {
SHARD_ID: this.id,
SHARD_COUNT: this.manager.totalShards,
CLIENT_TOKEN: this.manager.token,
});
/**
* Process of the shard
* @type {ChildProcess}
*/
this.process = childProcess.fork(path.resolve(this.manager.file), args, {
env: this.env,
});
this.process.on('message', this._handleMessage.bind(this));
this.process.once('exit', () => {
if (this.manager.respawn) this.manager.createShard(this.id);
});
this._evals = new Map();
this._fetches = new Map();
}
/**
* Sends a message to the shard's process.
* @param {*} message Message to send to the shard
* @returns {Promise<Shard>}
*/
send(message) {
return new Promise((resolve, reject) => {
const sent = this.process.send(message, err => {
if (err) reject(err); else resolve(this);
});
if (!sent) throw new Error('Failed to send message to shard\'s process.');
});
}
/**
* Fetches a Client property value of the shard.
* @param {string} prop Name of the Client property to get, using periods for nesting
* @returns {Promise<*>}
* @example
* shard.fetchClientValue('guilds.size').then(count => {
* console.log(`${count} guilds in shard ${shard.id}`);
* }).catch(console.error);
*/
fetchClientValue(prop) {
if (this._fetches.has(prop)) return this._fetches.get(prop);
const promise = new Promise((resolve, reject) => {
const listener = message => {
if (!message || message._fetchProp !== prop) return;
this.process.removeListener('message', listener);
this._fetches.delete(prop);
resolve(message._result);
};
this.process.on('message', listener);
this.send({ _fetchProp: prop }).catch(err => {
this.process.removeListener('message', listener);
this._fetches.delete(prop);
reject(err);
});
});
this._fetches.set(prop, promise);
return promise;
}
/**
* Evaluates a script on the shard, in the context of the Client.
* @param {string} script JavaScript to run on the shard
* @returns {Promise<*>} Result of the script execution
*/
eval(script) {
if (this._evals.has(script)) return this._evals.get(script);
const promise = new Promise((resolve, reject) => {
const listener = message => {
if (!message || message._eval !== script) return;
this.process.removeListener('message', listener);
this._evals.delete(script);
if (!message._error) resolve(message._result); else reject(makeError(message._error));
};
this.process.on('message', listener);
this.send({ _eval: script }).catch(err => {
this.process.removeListener('message', listener);
this._evals.delete(script);
reject(err);
});
});
this._evals.set(script, promise);
return promise;
}
/**
* Handles an IPC message
* @param {*} message Message received
* @private
*/
_handleMessage(message) {
if (message) {
// Shard is requesting a property fetch
if (message._sFetchProp) {
this.manager.fetchClientValues(message._sFetchProp).then(
results => this.send({ _sFetchProp: message._sFetchProp, _result: results }),
err => this.send({ _sFetchProp: message._sFetchProp, _error: makePlainError(err) })
);
return;
}
// Shard is requesting an eval broadcast
if (message._sEval) {
this.manager.broadcastEval(message._sEval).then(
results => this.send({ _sEval: message._sEval, _result: results }),
err => this.send({ _sEval: message._sEval, _error: makePlainError(err) })
);
return;
}
}
/**
* Emitted upon recieving a message from a shard
* @event ShardingManager#message
* @param {Shard} shard Shard that sent the message
* @param {*} message Message that was received
*/
this.manager.emit('message', this, message);
}
}
module.exports = Shard;
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