Rip out client sharding logic into its own class

src/client/Client.js

@@ -10,6 +10,7 @@ const WebSocketManager = require('./websocket/WebSocketManager');
 const ActionsManager = require('./actions/ActionsManager');
 const Collection = require('../util/Collection');
 const Presence = require('../structures/Presence').Presence;
+const ShardUtil = require('../sharding/ShardUtil');
 
 /**
  * The starting point for making a Discord Bot.
@@ -85,6 +86,13 @@ class Client extends EventEmitter {
      */
     this.voice = new ClientVoiceManager(this);
 
+    /**
+     * The shard helpers for the client (only if the process was spawned as a child, such as from a ShardingManager)
+     * @type {?ShardUtil}
+     */
+    this.shard = process.send ? ShardUtil.singleton(this) : null;
+    if (this.shard) process.on('message', this.shard._handleMessage.bind(this.shard));
+
     /**
      * A Collection of the Client's stored users
      * @type {Collection<string, User>}
@@ -146,24 +154,6 @@ class Client extends EventEmitter {
     if (this.options.message_sweep_interval > 0) {
       this.setInterval(this.sweepMessages.bind(this), this.options.message_sweep_interval * 1000);
     }
-
-    if (process.send) {
-      process.on('message', message => {
-        if (!message) return;
-        if (message._eval) {
-          try {
-            process.send({ _evalResult: eval(message._eval) });
-          } catch (err) {
-            process.send({ _evalError: err });
-          }
-        } else if (message._fetchProp) {
-          const props = message._fetchProp.split('.');
-          let value = this; // eslint-disable-line consistent-this
-          for (const prop of props) value = value[prop];
-          process.send({ _fetchProp: message._fetchProp, _fetchPropValue: value });
-        }
-      });
-    }
   }
 
   /**

src/sharding/ShardUtil.js

@@ -0,0 +1,47 @@
+/**
+ * Helper class for sharded clients
+ */
+class ShardUtil {
+  /**
+   * @param {Client} client Client of the current shard
+   */
+  constructor(client) {
+    this.client = client;
+  }
+
+  /**
+   * Handles an IPC message
+   * @param {*} message Message received
+   */
+  _handleMessage(message) {
+    if (!message) return;
+    if (message._eval) {
+      try {
+        process.send({ _evalResult: eval(message._eval) });
+      } catch (err) {
+        process.send({ _evalError: err });
+      }
+    } else if (message._fetchProp) {
+      const props = message._fetchProp.split('.');
+      let value = this; // eslint-disable-line consistent-this
+      for (const prop of props) value = value[prop];
+      process.send({ _fetchProp: message._fetchProp, _fetchPropValue: value });
+    }
+  }
+
+  /**
+   * Creates/gets the singleton of this class
+   * @param {Client} client Client to use
+   * @returns {ShardUtil}
+   */
+  static singleton(client) {
+    if (!this._singleton) {
+      this._singleton = new this(client);
+    } else {
+      client.emit('error', 'Multiple clients created in child process; only the first will handle sharding helpers.');
+    }
+    return this._singleton;
+  }
+}
+
+module.exports = ShardUtil;