feat(Rest): switch queue to AsyncQueue (#4835)

Co-authored-by: Sugden <28943913+NotSugden@users.noreply.github.com>

Author: kyranet

src/rest/APIRequest.js

@@ -15,6 +15,7 @@ class APIRequest {
     this.method = method;
     this.route = options.route;
     this.options = options;
+    this.retries = 0;
 
     let queryString = '';
     if (options.query) {

src/rest/AsyncQueue.js

@@ -0,0 +1,95 @@
+/**
+ * MIT License
+ *
+ * Copyright (c) 2020 kyranet, discord.js
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+
+'use strict';
+
+// TODO(kyranet, vladfrangu): replace this with discord.js v13's core AsyncQueue.
+
+/**
+ * An async queue that preserves the stack and prevents lock-ups.
+ * @private
+ */
+class AsyncQueue {
+  constructor() {
+    /**
+     * The promises array.
+     * @type {Array<{promise: Promise<void>, resolve: Function}>}
+     * @private
+     */
+    this.promises = [];
+  }
+
+  /**
+   * The remaining amount of queued promises
+   * @type {number}
+   */
+  get remaining() {
+    return this.promises.length;
+  }
+
+  /**
+   * Waits for last promise and queues a new one.
+   * @returns {Promise<void>}
+   * @example
+   * const queue = new AsyncQueue();
+   * async function request(url, options) {
+   *     await queue.wait();
+   *     try {
+   *         const result = await fetch(url, options);
+   *         // Do some operations with 'result'
+   *     } finally {
+   *         // Remove first entry from the queue and resolve for the next entry
+   *         queue.shift();
+   *     }
+   * }
+   *
+   * request(someUrl1, someOptions1); // Will call fetch() immediately
+   * request(someUrl2, someOptions2); // Will call fetch() after the first finished
+   * request(someUrl3, someOptions3); // Will call fetch() after the second finished
+   */
+  wait() {
+    const next = this.promises.length ? this.promises[this.promises.length - 1].promise : Promise.resolve();
+    let resolve;
+    const promise = new Promise(res => {
+      resolve = res;
+    });
+
+    this.promises.push({
+      resolve,
+      promise,
+    });
+
+    return next;
+  }
+
+  /**
+   * Frees the queue's lock for the next item to process.
+   */
+  shift() {
+    const deferred = this.promises.shift();
+    if (typeof deferred !== 'undefined') deferred.resolve();
+  }
+}
+
+module.exports = AsyncQueue;

src/rest/RESTManager.js

@@ -35,19 +35,6 @@ class RESTManager {
     return Endpoints.CDN(this.client.options.http.cdn);
   }
 
-  push(handler, apiRequest) {
-    return new Promise((resolve, reject) => {
-      handler
-        .push({
-          request: apiRequest,
-          resolve,
-          reject,
-          retries: 0,
-        })
-        .catch(reject);
-    });
-  }
-
   request(method, url, options = {}) {
     const apiRequest = new APIRequest(this, method, url, options);
     let handler = this.handlers.get(apiRequest.route);
@@ -57,7 +44,7 @@ class RESTManager {
       this.handlers.set(apiRequest.route, handler);
     }
 
-    return this.push(handler, apiRequest);
+    return handler.push(apiRequest);
   }
 
   get endpoint() {

src/rest/RequestHandler.js

@@ -1,5 +1,6 @@
 'use strict';
 
+const AsyncQueue = require('./AsyncQueue');
 const DiscordAPIError = require('./DiscordAPIError');
 const HTTPError = require('./HTTPError');
 const {
@@ -25,46 +26,31 @@ function calculateReset(reset, serverDate) {
 class RequestHandler {
   constructor(manager) {
     this.manager = manager;
-    this.busy = false;
-    this.queue = [];
+    this.queue = new AsyncQueue();
     this.reset = -1;
     this.remaining = -1;
     this.limit = -1;
     this.retryAfter = -1;
   }
 
-  push(request) {
-    if (this.busy) {
-      this.queue.push(request);
-      return this.run();
-    } else {
-      return this.execute(request);
+  async push(request) {
+    await this.queue.wait();
+    try {
+      return await this.execute(request);
+    } finally {
+      this.queue.shift();
     }
   }
 
-  run() {
-    if (this.queue.length === 0) return Promise.resolve();
-    return this.execute(this.queue.shift());
-  }
-
   get limited() {
     return Boolean(this.manager.globalTimeout) || (this.remaining <= 0 && Date.now() < this.reset);
   }
 
   get _inactive() {
-    return this.queue.length === 0 && !this.limited && this.busy !== true;
+    return this.queue.remaining === 0 && !this.limited;
   }
 
-  async execute(item) {
-    // Insert item back to the beginning if currently busy
-    if (this.busy) {
-      this.queue.unshift(item);
-      return null;
-    }
-
-    this.busy = true;
-    const { reject, request, resolve } = item;
-
+  async execute(request) {
     // After calculations and requests have been done, pre-emptively stop further requests
     if (this.limited) {
       const timeout = this.reset + this.manager.client.options.restTimeOffset - Date.now();
@@ -103,8 +89,7 @@ class RequestHandler {
       res = await request.make();
     } catch (error) {
       // NodeFetch error expected for all "operational" errors, such as 500 status code
-      this.busy = false;
-      return reject(new HTTPError(error.message, error.constructor.name, error.status, request.method, request.path));
+      throw new HTTPError(error.message, error.constructor.name, error.status, request.method, request.path);
     }
 
     if (res && res.headers) {
@@ -120,7 +105,7 @@ class RequestHandler {
       this.retryAfter = retryAfter ? Number(retryAfter) : -1;
 
       // https://github.com/discordapp/discord-api-docs/issues/182
-      if (item.request.route.includes('reactions')) {
+      if (request.route.includes('reactions')) {
         this.reset = new Date(serverDate).getTime() - getAPIOffset(serverDate) + 250;
       }
 
@@ -137,42 +122,39 @@ class RequestHandler {
       }
     }
 
-    // Finished handling headers, safe to unlock manager
-    this.busy = false;
-
     if (res.ok) {
-      const success = await parseResponse(res);
       // Nothing wrong with the request, proceed with the next one
-      resolve(success);
-      return this.run();
-    } else if (res.status === 429) {
+      return parseResponse(res);
+    }
+
+    // Handle ratelimited requests
+    if (res.status === 429) {
       // A ratelimit was hit - this should never happen
-      this.queue.unshift(item);
-      this.manager.client.emit('debug', `429 hit on route ${item.request.route}`);
+      this.manager.client.emit('debug', `429 hit on route ${request.route}`);
       await Util.delayFor(this.retryAfter);
-      return this.run();
-    } else if (res.status >= 500 && res.status < 600) {
+      return this.execute(request);
+    }
+
+    // Handle server errors
+    if (res.status >= 500 && res.status < 600) {
       // Retry the specified number of times for possible serverside issues
-      if (item.retries === this.manager.client.options.retryLimit) {
-        return reject(
-          new HTTPError(res.statusText, res.constructor.name, res.status, item.request.method, request.path),
-        );
-      } else {
-        item.retries++;
-        this.queue.unshift(item);
-        return this.run();
+      if (request.retries === this.manager.client.options.retryLimit) {
+        throw new HTTPError(res.statusText, res.constructor.name, res.status, request.method, request.path);
       }
-    } else {
-      // Handle possible malformed requests
-      try {
-        const data = await parseResponse(res);
-        if (res.status >= 400 && res.status < 500) {
-          return reject(new DiscordAPIError(request.path, data, request.method, res.status));
-        }
-        return null;
-      } catch (err) {
-        return reject(new HTTPError(err.message, err.constructor.name, err.status, request.method, request.path));
+
+      request.retries++;
+      return this.execute(request);
+    }
+
+    // Handle possible malformed requests
+    try {
+      const data = await parseResponse(res);
+      if (res.status >= 400 && res.status < 500) {
+        throw new DiscordAPIError(request.path, data, request.method, res.status);
       }
+      return null;
+    } catch (err) {
+      throw new HTTPError(err.message, err.constructor.name, err.status, request.method, request.path);
     }
   }
 }