backend-patterns

Name: backend-patterns
Author: tranhieutt

69stars41forks

How to install backend-patterns?

tranhieutt/software_development_department/backend-patterns

$npx -y skills add tranhieutt/software_development_department --skill backend-patterns

Installs into the current project.

Summary

Applies production backend patterns: middleware, error handling, auth, database integration, and API design. Use when working with backend service files or when the user mentions Express, Fastify, NestJS, backend patterns, or service architecture.

Files · 1

View on GitHub

SKILL.md

1	# Backend Patterns
2
3	## Critical rules (non-obvious)
4
5	- Always handle async errors in Express: unhandled promise rejections crash the process; use `express-async-errors` or wrap every async handler
6	- Never trust `req.body` size: set `limit` on body-parser; default 100kb is too large for some, too small for others
7	- `process.env` access at import time: if accessed before `dotenv.config()`, value is undefined; call config() first in entry file
8	- Connection pool misconfiguration: default pool size (10) will exhaust under load; set `pool.max` based on `(num_cores * 2) + effective_spindle_count`
9	- `res.json()` after `res.send()`: causes "Cannot set headers after they are sent" — always `return` after sending response
10
11	## Express: production setup
12
13	```typescript
14	import express from "express";
15	import "express-async-errors"; // patches async error handling globally
16	import helmet from "helmet";
17	import { rateLimit } from "express-rate-limit";
18
19	const app = express();
20
21	app.use(helmet());
22	app.use(express.json({ limit: "10kb" }));
23	app.use(rateLimit({ windowMs: 15 * 60 * 1000, max: 100 }));
24
25	// Routes
26	app.use("/api/v1/users", userRouter);
27	app.use("/api/v1/products", productRouter);
28
29	// 404 handler — must come after all routes
30	app.use((req, res) => res.status(404).json({ error: "Not found" }));
31
32	// Global error handler — must have 4 params
33	app.use((err: Error, req: Request, res: Response, next: NextFunction) => {
34	const status = err instanceof AppError ? err.statusCode : 500;
35	res.status(status).json({ error: err.message });
36	});
37	```
38
39	## Repository pattern
40
41	```typescript
42	interface IUserRepository {
43	findById(id: string): Promise<User \| null>;
44	findByEmail(email: string): Promise<User \| null>;
45	save(user: User): Promise<User>;
46	delete(id: string): Promise<void>;
47	}
48
49	class PgUserRepository implements IUserRepository {
50	constructor(private readonly db: Pool) {}
51
52	async findById(id: string) {
53	const { rows } = await this.db.query(
54	"SELECT * FROM users WHERE id = $1 AND deleted_at IS NULL", [id]
55	);
56	return rows[0] ?? null;
57	}
58	}
59	```
60
61	## Service layer with error types
62
63	```typescript
64	class AppError extends Error {
65	constructor(public message: string, public statusCode: number) { super(message); }
66	}
67	class NotFoundError extends AppError { constructor(msg: string) { super(msg, 404); } }
68	class ForbiddenError extends AppError { constructor(msg: string) { super(msg, 403); } }
69
70	class UserService {
71	async getUser(id: string, requesterId: string): Promise<User> {
72	const user = await this.repo.findById(id);
73	if (!user) throw new NotFoundError(`User ${id} not found`);
74	if (user.id !== requesterId && !isAdmin(requesterId)) throw new ForbiddenError("Access denied");
75	return user;
76	}
77	}
78	```
79
80	## JWT middleware
81
82	```typescript
83	import jwt from "jsonwebtoken";
84
85	export function authenticate(req: Request, res: Response, next: NextFunction) {
86	const token = req.headers.authorization?.split(" ")[1];
87	if (!token) return res.status(401).json({ error: "No token" });
88	try {
89	req.user = jwt.verify(token, process.env.JWT_SECRET!) as JWTPayload;
90	next();
91	} catch {
92	res.status(401).json({ error: "Invalid token" });
93	}
94	}
95	```
96
97	## Database connection with retry
98
99	```typescript
100	import { Pool } from "pg";
101
102	const pool = new Pool({
103	connectionString: process.env.DATABASE_URL,
104	max: 20, // pool size
105	idleTimeoutMillis: 30_000,
106	connectionTimeoutMillis: 2_000,
107	});
108
109	// Test connection on startup
110	async function connectWithRetry(retries = 5, delay = 2000) {
111	for (let i = 0; i < retries; i++) {
112	try {
113	await pool.query("SELECT 1");
114	console.log("DB connected");
115	return;
116	} catch (err) {
117	if (i === retries - 1) throw err;
118	await new Promise(r => setTimeout(r, delay * (i + 1))); // exponential backoff
119	}
120	}
121	}
122	```
123
124	## Graceful shutdown
125
126	```typescript
127	const server = app.listen(PORT);
128
129	async function shutdown(signal: string) {
130	console.log(`${signal} received. Shutting down gracefully.`);
131	server.close(async () => {
132	await pool.end(); // drain DB connections
133	process.exit(0);
134	});
135	setTimeout(() => process.exit(1), 10_000); // force exit after 10s
136	}
137
138	process.on("SIGTERM", () => shutdown("SIGTERM"));
139	process.on("SIGINT", () => shutdown("SIGINT"));
140	```
141
142	## Common pitfalls
143
144	\| Pitfall \| Fix \|
145	\|---\|---\|
146	\| Async handler without try/catch \| Use `express-async

People who liked this also viewed

6 picks

Type

backend-patterns

69stars41forks

View on GitHub

How to install backend-patterns?

tranhieutt/software_development_department/backend-patterns

$npx -y skills add tranhieutt/software_development_department --skill backend-patterns

Installs into the current project.

Summary

Files · 1

View on GitHub

SKILL.md

1	# Backend Patterns
2
3	## Critical rules (non-obvious)
4
5	- Always handle async errors in Express: unhandled promise rejections crash the process; use `express-async-errors` or wrap every async handler
6	- Never trust `req.body` size: set `limit` on body-parser; default 100kb is too large for some, too small for others
7	- `process.env` access at import time: if accessed before `dotenv.config()`, value is undefined; call config() first in entry file
8	- Connection pool misconfiguration: default pool size (10) will exhaust under load; set `pool.max` based on `(num_cores * 2) + effective_spindle_count`
9	- `res.json()` after `res.send()`: causes "Cannot set headers after they are sent" — always `return` after sending response
10
11	## Express: production setup
12
13	```typescript
14	import express from "express";
15	import "express-async-errors"; // patches async error handling globally
16	import helmet from "helmet";
17	import { rateLimit } from "express-rate-limit";
18
19	const app = express();
20
21	app.use(helmet());
22	app.use(express.json({ limit: "10kb" }));
23	app.use(rateLimit({ windowMs: 15 * 60 * 1000, max: 100 }));
24
25	// Routes
26	app.use("/api/v1/users", userRouter);
27	app.use("/api/v1/products", productRouter);
28
29	// 404 handler — must come after all routes
30	app.use((req, res) => res.status(404).json({ error: "Not found" }));
31
32	// Global error handler — must have 4 params
33	app.use((err: Error, req: Request, res: Response, next: NextFunction) => {
34	const status = err instanceof AppError ? err.statusCode : 500;
35	res.status(status).json({ error: err.message });
36	});
37	```
38
39	## Repository pattern
40
41	```typescript
42	interface IUserRepository {
43	findById(id: string): Promise<User \| null>;
44	findByEmail(email: string): Promise<User \| null>;
45	save(user: User): Promise<User>;
46	delete(id: string): Promise<void>;
47	}
48
49	class PgUserRepository implements IUserRepository {
50	constructor(private readonly db: Pool) {}
51
52	async findById(id: string) {
53	const { rows } = await this.db.query(
54	"SELECT * FROM users WHERE id = $1 AND deleted_at IS NULL", [id]
55	);
56	return rows[0] ?? null;
57	}
58	}
59	```
60
61	## Service layer with error types
62
63	```typescript
64	class AppError extends Error {
65	constructor(public message: string, public statusCode: number) { super(message); }
66	}
67	class NotFoundError extends AppError { constructor(msg: string) { super(msg, 404); } }
68	class ForbiddenError extends AppError { constructor(msg: string) { super(msg, 403); } }
69
70	class UserService {
71	async getUser(id: string, requesterId: string): Promise<User> {
72	const user = await this.repo.findById(id);
73	if (!user) throw new NotFoundError(`User ${id} not found`);
74	if (user.id !== requesterId && !isAdmin(requesterId)) throw new ForbiddenError("Access denied");
75	return user;
76	}
77	}
78	```
79
80	## JWT middleware
81
82	```typescript
83	import jwt from "jsonwebtoken";
84
85	export function authenticate(req: Request, res: Response, next: NextFunction) {
86	const token = req.headers.authorization?.split(" ")[1];
87	if (!token) return res.status(401).json({ error: "No token" });
88	try {
89	req.user = jwt.verify(token, process.env.JWT_SECRET!) as JWTPayload;
90	next();
91	} catch {
92	res.status(401).json({ error: "Invalid token" });
93	}
94	}
95	```
96
97	## Database connection with retry
98
99	```typescript
100	import { Pool } from "pg";
101
102	const pool = new Pool({
103	connectionString: process.env.DATABASE_URL,
104	max: 20, // pool size
105	idleTimeoutMillis: 30_000,
106	connectionTimeoutMillis: 2_000,
107	});
108
109	// Test connection on startup
110	async function connectWithRetry(retries = 5, delay = 2000) {
111	for (let i = 0; i < retries; i++) {
112	try {
113	await pool.query("SELECT 1");
114	console.log("DB connected");
115	return;
116	} catch (err) {
117	if (i === retries - 1) throw err;
118	await new Promise(r => setTimeout(r, delay * (i + 1))); // exponential backoff
119	}
120	}
121	}
122	```
123
124	## Graceful shutdown
125
126	```typescript
127	const server = app.listen(PORT);
128
129	async function shutdown(signal: string) {
130	console.log(`${signal} received. Shutting down gracefully.`);
131	server.close(async () => {
132	await pool.end(); // drain DB connections
133	process.exit(0);
134	});
135	setTimeout(() => process.exit(1), 10_000); // force exit after 10s
136	}
137
138	process.on("SIGTERM", () => shutdown("SIGTERM"));
139	process.on("SIGINT", () => shutdown("SIGINT"));
140	```
141
142	## Common pitfalls
143
144	\| Pitfall \| Fix \|
145	\|---\|---\|
146	\| Async handler without try/catch \| Use `express-async

People who liked this also viewed

6 picks

Type