feat(Rest): optional ratelimit errors

src/client/Client.js

@@ -492,6 +492,12 @@ class Client extends BaseClient {
     if (typeof options.retryLimit !== 'number' || isNaN(options.retryLimit)) {
       throw new TypeError('CLIENT_INVALID_OPTION', 'retryLimit', 'a number');
     }
+    if (
+      typeof options.rejectOnRateLimit !== 'undefined' &&
+      !(typeof options.rejectOnRateLimit === 'function' || Array.isArray(options.rejectOnRateLimit))
+    ) {
+      throw new TypeError('CLIENT_INVALID_OPTION', 'rejectOnRateLimit', 'an array or a function');
+    }
   }
 }
 

src/index.js

@@ -21,6 +21,7 @@ module.exports = {
   BaseManager: require('./managers/BaseManager'),
   DiscordAPIError: require('./rest/DiscordAPIError'),
   HTTPError: require('./rest/HTTPError'),
+  RateLimitError: require('./rest/RateLimitError'),
   MessageFlags: require('./util/MessageFlags'),
   Intents: require('./util/Intents'),
   Permissions: require('./util/Permissions'),

src/rest/RateLimitError.js

@@ -0,0 +1,55 @@
+'use strict';
+
+/**
+ * Represents a RateLimit error from a request.
+ * @extends Error
+ */
+class RateLimitError extends Error {
+  constructor({ timeout, limit, method, path, route, global }) {
+    super(`A ${global ? 'global ' : ''}rate limit was hit on route ${route}`);
+
+    /**
+     * The name of the error
+     * @type {string}
+     */
+    this.name = 'RateLimitError';
+
+    /**
+     * Time until this rate limit ends, in ms
+     * @type {number}
+     */
+    this.timeout = timeout;
+
+    /**
+     * The HTTP method used for the request
+     * @type {string}
+     */
+    this.method = method;
+
+    /**
+     * The path of the request relative to the HTTP endpoint
+     * @type {string}
+     */
+    this.path = path;
+
+    /**
+     * The route of the request relative to the HTTP endpoint
+     * @type {string}
+     */
+    this.route = route;
+
+    /**
+     * Whether this rate limit is global
+     * @type {boolean}
+     */
+    this.global = global;
+
+    /**
+     * The maximum amount of requests of this end point
+     * @type {number}
+     */
+    this.limit = limit;
+  }
+}
+
+module.exports = RateLimitError;

src/rest/RequestHandler.js

@@ -3,6 +3,7 @@
 const AsyncQueue = require('./AsyncQueue');
 const DiscordAPIError = require('./DiscordAPIError');
 const HTTPError = require('./HTTPError');
+const RateLimitError = require('./RateLimitError');
 const {
   Events: { RATE_LIMIT, INVALID_REQUEST_WARNING },
 } = require('../util/Constants');
@@ -77,6 +78,30 @@ class RequestHandler {
     });
   }
 
+  /*
+   * Determines whether the request should be queued or whether a RateLimitError should be thrown
+   */
+  async onRateLimit(request, limit, timeout, isGlobal) {
+    const { options } = this.manager.client;
+    if (!options.rejectOnRateLimit) return;
+
+    const rateLimitData = {
+      timeout,
+      limit,
+      method: request.method,
+      path: request.path,
+      route: request.route,
+      global: isGlobal,
+    };
+    const shouldThrow =
+      typeof options.rejectOnRateLimit === 'function'
+        ? await options.rejectOnRateLimit(rateLimitData)
+        : options.rejectOnRateLimit.some(route => rateLimitData.route.startsWith(route.toLowerCase()));
+    if (shouldThrow) {
+      throw new RateLimitError(rateLimitData);
+    }
+  }
+
   async execute(request) {
     /*
      * After calculations have been done, pre-emptively stop further requests
@@ -90,17 +115,10 @@ class RequestHandler {
         // Set the variables based on the global rate limit
         limit = this.manager.globalLimit;
         timeout = this.manager.globalReset + this.manager.client.options.restTimeOffset - Date.now();
-        // If this is the first task to reach the global timeout, set the global delay
-        if (!this.manager.globalDelay) {
-          // The global delay function should clear the global delay state when it is resolved
-          this.manager.globalDelay = this.globalDelayFor(timeout);
-        }
-        delayPromise = this.manager.globalDelay;
       } else {
         // Set the variables based on the route-specific rate limit
         limit = this.limit;
         timeout = this.reset + this.manager.client.options.restTimeOffset - Date.now();
-        delayPromise = Util.delayFor(timeout);
       }
 
       if (this.manager.client.listenerCount(RATE_LIMIT)) {
@@ -125,6 +143,20 @@ class RequestHandler {
         });
       }
 
+      // Determine whether a RateLimitError should be thrown
+      await this.onRateLimit(request, limit, timeout, isGlobal); // eslint-disable-line no-await-in-loop
+
+      if (isGlobal) {
+        // If this is the first task to reach the global timeout, set the global delay
+        if (!this.manager.globalDelay) {
+          // The global delay function should clear the global delay state when it is resolved
+          this.manager.globalDelay = this.globalDelayFor(timeout);
+        }
+        delayPromise = this.manager.globalDelay;
+      } else {
+        delayPromise = Util.delayFor(timeout);
+      }
+
       // Wait for the timeout to expire in order to avoid an actual 429
       await delayPromise; // eslint-disable-line no-await-in-loop
     }
@@ -225,6 +257,20 @@ class RequestHandler {
       if (res.status === 429) {
         // A ratelimit was hit - this should never happen
         this.manager.client.emit('debug', `429 hit on route ${request.route}${sublimitTimeout ? ' for sublimit' : ''}`);
+
+        const isGlobal = this.globalLimited;
+        let limit, timeout;
+        if (isGlobal) {
+          // Set the variables based on the global rate limit
+          limit = this.manager.globalLimit;
+          timeout = this.manager.globalReset + this.manager.client.options.restTimeOffset - Date.now();
+        } else {
+          // Set the variables based on the route-specific rate limit
+          limit = this.limit;
+          timeout = this.reset + this.manager.client.options.restTimeOffset - Date.now();
+        }
+        await this.onRateLimit(request, limit, timeout, isGlobal);
+
         // If caused by a sublimit, wait it out here so other requests on the route can be handled
         if (sublimitTimeout) {
           await Util.delayFor(sublimitTimeout);

src/util/Constants.js

@@ -3,6 +3,24 @@
 const Package = (exports.Package = require('../../package.json'));
 const { Error, RangeError } = require('../errors');
 
+/**
+ * Rate limit data
+ * @typedef {Object} RateLimitData
+ * @property {number} timeout Time until this rate limit ends, in ms
+ * @property {number} limit The maximum amount of requests of this endpoint
+ * @property {string} method The http method of this request
+ * @property {string} path The path of the request relative to the HTTP endpoint
+ * @property {string} route The route of the request relative to the HTTP endpoint
+ * @property {boolean} global Whether this is a global rate limit
+ */
+
+/**
+ * Whether this rate limit should throw an Error
+ * @typedef {Function} RateLimitQueueFilter
+ * @param {RateLimitData} rateLimitData The data of this rate limit
+ * @returns {boolean|Promise<boolean>}
+ */
+
 /**
  * Options for a client.
  * @typedef {Object} ClientOptions
@@ -34,6 +52,10 @@ const { Error, RangeError } = require('../errors');
  * (or 0 for never)
  * @property {number} [restGlobalRateLimit=0] How many requests to allow sending per second (0 for unlimited, 50 for
  * the standard global limit used by Discord)
+ * @property {string[]|RateLimitQueueFilter} [rejectOnRateLimit] Decides how rate limits and pre-emptive throttles
+ * should be handled. If this option is an array containing the prefix of the request route (e.g. /channels to match any
+ * route starting with /channels, such as /channels/222197033908436994/messages) or a function returning true, a
+ * {@link RateLimitError} will be thrown. Otherwise the request will be queued for later
  * @property {number} [retryLimit=1] How many times to retry on 5XX errors (Infinity for indefinite amount of retries)
  * @property {PresenceData} [presence={}] Presence data to use upon login
  * @property {IntentsResolvable} intents Intents to enable for this connection

typings/index.d.ts

@@ -461,9 +461,7 @@ declare module 'discord.js' {
     Endpoints: {
       botGateway: string;
       invite: (root: string, code: string) => string;
-      CDN: (
-        root: string,
-      ) => {
+      CDN: (root: string) => {
         Asset: (name: string) => string;
         DefaultAvatar: (id: string | number) => string;
         Emoji: (emojiID: string, format: 'png' | 'gif') => string;
@@ -1022,6 +1020,13 @@ declare module 'discord.js' {
     public path: string;
   }
 
+  // tslint:disable-next-line:no-empty-interface - Merge RateLimitData into RateLimitError to not have to type it again
+  interface RateLimitError extends RateLimitData {}
+  export class RateLimitError extends Error {
+    constructor(data: RateLimitData);
+    public name: 'RateLimitError';
+  }
+
   export class Integration extends Base {
     constructor(client: Client, data: object, guild: Guild);
     public account: IntegrationAccount;
@@ -2659,6 +2664,7 @@ declare module 'discord.js' {
     intents: BitFieldResolvable<IntentsString, number>;
     ws?: WebSocketOptions;
     http?: HTTPOptions;
+    rejectOnRateLimit?: string[] | ((data: RateLimitData) => boolean | Promise<boolean>);
   }
 
   type ClientPresenceStatus = 'online' | 'idle' | 'dnd';