Implement Sequential Rate Limiting

src/client/rest/RequestHandlers/Sequential.js

@@ -0,0 +1,71 @@
+const RequestHandler = require('./RequestHandler');
+
+/**
+ * Handles API Requests sequentially, i.e. we wait until the current request is finished before moving onto
+ * the next. This plays a _lot_ nicer in terms of avoiding 429's when there is more than one session of the account,
+ * but it can be slower.
+ * @extends {RequestHandler}
+ */
+module.exports = class SequentialRequestHandler extends RequestHandler {
+
+  constructor(restManager) {
+    super(restManager);
+
+    /**
+     * Whether this rate limiter is waiting for a response from a request
+     * @type {Boolean}
+     */
+    this.waiting = false;
+  }
+
+  push(request) {
+    super.push(request);
+    this.handle();
+  }
+
+  /**
+   * Performs a request then resolves a promise to indicate its readiness for a new request
+   * @param {APIRequest} item the item to execute
+   * @returns {Promise<Object, Error>}
+   */
+  execute(item) {
+    return new Promise((resolve, reject) => {
+      item.request.gen().end((err, res) => {
+        if (res && res.headers) {
+          this.requestLimit = res.headers['x-ratelimit-limit'];
+          this.requestResetTime = Number(res.headers['x-ratelimit-reset']) * 1000;
+          this.requestRemaining = Number(res.headers['x-ratelimit-remaining']);
+        }
+        if (err) {
+          this.waiting = false;
+          item.reject(err);
+          reject(err);
+        } else {
+          this.queue.shift();
+          const data = res && res.body ? res.body : {};
+          item.resolve(data);
+          if (this.requestRemaining === 0) {
+            setTimeout(() => {
+              this.waiting = false;
+              resolve(data);
+            }, (this.requestResetTime - Date.now()) + 4000);
+          } else {
+            this.waiting = false;
+            resolve(data);
+          }
+        }
+      });
+    });
+  }
+
+  handle() {
+    super.handle();
+    if (this.waiting || this.queue.length === 0) {
+      return;
+    }
+    this.waiting = true;
+
+    const item = this.queue[0];
+    this.execute(item).then(() => this.handle()).catch(console.log);
+  }
+};