fix(handlers): create burst handler for interaction callbacks (#8996)

* fix(handlers): create burst handler for interaction callbacks

* docs: use remarks instead of info block

Co-Authored-By: Almeida <almeidx@pm.me>

* refactor: move code duplication to shared handler

Co-authored-by: Jiralite <33201955+Jiralite@users.noreply.github.com>

* Update packages/rest/src/lib/handlers/BurstHandler.ts

---------

Co-authored-by: Almeida <almeidx@pm.me>
Co-authored-by: Jiralite <33201955+Jiralite@users.noreply.github.com>
Co-authored-by: Vlad Frangu <kingdgrizzle@gmail.com>
Co-authored-by: Aura Román <kyradiscord@gmail.com>

packages/rest/__tests__/BurstHandler.test.ts

@@ -0,0 +1,139 @@
+/* eslint-disable id-length */
+/* eslint-disable promise/prefer-await-to-then */
+import { performance } from 'node:perf_hooks';
+import { MockAgent, setGlobalDispatcher } from 'undici';
+import type { Interceptable, MockInterceptor } from 'undici/types/mock-interceptor';
+import { beforeEach, afterEach, test, expect, vitest } from 'vitest';
+import { DiscordAPIError, HTTPError, RateLimitError, REST, BurstHandlerMajorIdKey } from '../src/index.js';
+import { BurstHandler } from '../src/lib/handlers/BurstHandler.js';
+import { genPath } from './util.js';
+
+const callbackKey = `Global(POST:/interactions/:id/:token/callback):${BurstHandlerMajorIdKey}`;
+const callbackPath = new RegExp(genPath('/interactions/[0-9]{17,19}/.+/callback'));
+
+const api = new REST();
+
+let mockAgent: MockAgent;
+let mockPool: Interceptable;
+
+beforeEach(() => {
+	mockAgent = new MockAgent();
+	mockAgent.disableNetConnect();
+	setGlobalDispatcher(mockAgent);
+
+	mockPool = mockAgent.get('https://discord.com');
+	api.setAgent(mockAgent);
+});
+
+afterEach(async () => {
+	await mockAgent.close();
+});
+
+// @discordjs/rest uses the `content-type` header to detect whether to parse
+// the response as JSON or as an ArrayBuffer.
+const responseOptions: MockInterceptor.MockResponseOptions = {
+	headers: {
+		'content-type': 'application/json',
+	},
+};
+
+test('Interaction callback creates burst handler', async () => {
+	mockPool.intercept({ path: callbackPath, method: 'POST' }).reply(200);
+
+	expect(api.requestManager.handlers.get(callbackKey)).toBe(undefined);
+	expect(
+		await api.post('/interactions/1234567890123456789/totallyarealtoken/callback', {
+			auth: false,
+			body: { type: 4, data: { content: 'Reply' } },
+		}),
+	).toBeInstanceOf(Uint8Array);
+	expect(api.requestManager.handlers.get(callbackKey)).toBeInstanceOf(BurstHandler);
+});
+
+test('Requests are handled in bursts', async () => {
+	mockPool.intercept({ path: callbackPath, method: 'POST' }).reply(200).delay(100).times(3);
+
+	// Return the current time on these results as their response does not indicate anything
+	const [a, b, c] = await Promise.all([
+		api
+			.post('/interactions/1234567890123456789/totallyarealtoken/callback', {
+				auth: false,
+				body: { type: 4, data: { content: 'Reply1' } },
+			})
+			.then(() => performance.now()),
+		api
+			.post('/interactions/2345678901234567890/anotherveryrealtoken/callback', {
+				auth: false,
+				body: { type: 4, data: { content: 'Reply2' } },
+			})
+			.then(() => performance.now()),
+		api
+			.post('/interactions/3456789012345678901/nowaytheresanotherone/callback', {
+				auth: false,
+				body: { type: 4, data: { content: 'Reply3' } },
+			})
+			.then(() => performance.now()),
+	]);
+
+	expect(b - a).toBeLessThan(10);
+	expect(c - a).toBeLessThan(10);
+});
+
+test('Handle 404', async () => {
+	mockPool
+		.intercept({ path: callbackPath, method: 'POST' })
+		.reply(404, { message: 'Unknown interaction', code: 10_062 }, responseOptions);
+
+	const promise = api.post('/interactions/1234567890123456788/definitelynotarealinteraction/callback', {
+		auth: false,
+		body: { type: 4, data: { content: 'Malicious' } },
+	});
+	await expect(promise).rejects.toThrowError('Unknown interaction');
+	await expect(promise).rejects.toBeInstanceOf(DiscordAPIError);
+});
+
+let unexpected429 = true;
+test('Handle unexpected 429', async () => {
+	mockPool
+		.intercept({
+			path: callbackPath,
+			method: 'POST',
+		})
+		.reply(() => {
+			if (unexpected429) {
+				unexpected429 = false;
+				return {
+					statusCode: 429,
+					data: '',
+					responseOptions: {
+						headers: {
+							'retry-after': '1',
+							via: '1.1 google',
+						},
+					},
+				};
+			}
+
+			return {
+				statusCode: 200,
+				data: { test: true },
+				responseOptions,
+			};
+		})
+		.times(2);
+
+	const previous = performance.now();
+	let firstResolvedTime: number;
+	const unexpectedLimit = api
+		.post('/interactions/1234567890123456789/totallyarealtoken/callback', {
+			auth: false,
+			body: { type: 4, data: { content: 'Reply' } },
+		})
+		.then((res) => {
+			firstResolvedTime = performance.now();
+			return res;
+		});
+
+	expect(await unexpectedLimit).toStrictEqual({ test: true });
+	expect(performance.now()).toBeGreaterThanOrEqual(previous + 1_000);
+});