feat: @discordjs/proxy (#7925)

Co-authored-by: Parbez <imranbarbhuiya.fsd@gmail.com>

packages/proxy/__tests__/proxyRequests.test.ts

@@ -0,0 +1,83 @@
+import { createServer } from 'node:http';
+import { REST } from '@discordjs/rest';
+import supertest from 'supertest';
+import { MockAgent, Interceptable, setGlobalDispatcher } from 'undici';
+import type { MockInterceptor } from 'undici/types/mock-interceptor';
+import { proxyRequests } from '../src';
+
+let mockAgent: MockAgent;
+let mockPool: Interceptable;
+
+const responseOptions: MockInterceptor.MockResponseOptions = {
+	headers: {
+		'content-type': 'application/json',
+	},
+};
+
+const api = new REST().setToken('A-Very-Fake-Token');
+// eslint-disable-next-line @typescript-eslint/no-misused-promises
+const server = createServer(proxyRequests(api));
+
+beforeEach(() => {
+	mockAgent = new MockAgent();
+	mockAgent.disableNetConnect(); // prevent actual requests to Discord
+	setGlobalDispatcher(mockAgent); // enabled the mock client to intercept requests
+
+	mockPool = mockAgent.get('https://discord.com');
+});
+
+afterEach(async () => {
+	await mockAgent.close();
+});
+
+afterAll(() => {
+	server.close();
+});
+
+test('simple GET', async () => {
+	mockPool
+		.intercept({
+			path: '/api/v10/simpleGet',
+			method: 'GET',
+		})
+		.reply(() => ({
+			data: { test: true },
+			statusCode: 200,
+			responseOptions: {
+				...responseOptions,
+				headers: {
+					...responseOptions.headers,
+					'x-ratelimit-limit': '10',
+				},
+			},
+		}));
+
+	const res = await supertest(server).get('/api/v10/simpleGet');
+	const headers = res.headers as Record<string, string>;
+
+	expect(headers['content-type']).toEqual(expect.stringMatching(/^application\/json/));
+	// Ratelimit headers should be dropped
+	expect(headers).not.toHaveProperty('x-ratelimit-limit');
+	expect(res.statusCode).toBe(200);
+	expect(res.body).toStrictEqual({ test: true });
+});
+
+test('failed request', async () => {
+	mockPool
+		.intercept({
+			path: '/api/v10/simpleGet',
+			method: 'GET',
+		})
+		.reply(() => ({
+			data: { code: 404, message: 'Not Found' },
+			statusCode: 404,
+			responseOptions,
+		}));
+
+	const res = await supertest(server).get('/api/v10/simpleGet');
+	const headers = res.headers as Record<string, string>;
+
+	expect(headers['content-type']).toEqual(expect.stringMatching(/^application\/json/));
+	expect(res.statusCode).toBe(404);
+	expect(res.body).toStrictEqual({ code: 404, message: 'Not Found' });
+});