Middleware and HTTP¶

HTTP handling in Node.js ranges from pure Node.js servers to framework-based approaches (Fastify, NestJS, Metarhia). Middleware implements the Chain of Responsibility pattern, and transport abstraction enables switching between HTTP and WebSocket without changing business logic.

Key Facts¶

Middleware in Express/Fastify is Chain of Responsibility: each handler decides to process or pass to next()
Transport abstraction: HTTP and WebSocket handlers share domain logic, differ only in data transport
Static file serving: always check file existence before sending (404 vs 500)
Same application implemented across Pure Node.js, Fastify, NestJS, and Metarhia shows: domain logic identical, only framework boilerplate differs

Patterns¶

Multi-Framework Comparison¶

metatech-university/
  NodeJS-Pure/         # Pure Node.js (no framework)
  NodeJS-Fastify/      # Fastify - lightweight, good DX
  NodeJS-Nest/         # NestJS - enterprise-grade, TypeScript-first
  NodeJS-Metarhia/     # Metarhia - schema-driven, transport-abstracted

All implement: user registration, authentication, session management,
messaging, file upload, room management, push notifications

Transport Config Switching¶

// config.js
module.exports = { transport: 'ws' }; // or 'http'

// main.js - load transport module dynamically
const transport = require(`./${config.transport}.js`);
// Enables: per-environment transport, A/B testing, fallback mechanisms

ESLint Shared Configuration¶

eslint-config-metarhia/     # Shared rules package
  index.js                  # Rules in JavaScript (not JSON)
  browser.js                # Browser-specific overrides
  node.js                   # Node-specific overrides

Each project extends and optionally overrides. Centralized rule management with per-repo flexibility.

Gotchas¶

Pure Node.js server is minimal code but complex to maintain at scale
Framework choice matters less than architecture quality - all frameworks can produce the same result
Pull request workflow for infrastructure libraries should stabilize structure before writing tests (avoid test churn)