middlewares

Middlewares

Note: The middlewares folder is purely an organizational grouping. It contains NestJS Guards, Interceptors, and Filters — each with distinct roles in the request lifecycle. The choice to group them under a single folder was made solely for project organization purposes.

Request Lifecycle

Request → Guards → Interceptors (before) → Handler → Interceptors (after) → Filters (on error) → Response

Type	Purpose	When Runs
Guards	Authorization, access control	Before handler
Interceptors	Transform request/response, logging, tracing	Before & after handler
Filters	Error handling, exception formatting	On exceptions

Guards

Guide	Implementation	Description
Authorization Guard	authorization.guard.ts	RBAC permission checking via @Permission decorator

Interceptors

Guide	Implementation	Description
Tracing Interceptor	tracing.interceptor.ts	Distributed tracing with OpenTelemetry, auto traceid propagation
HTTP Logger Interceptor	http-logger.interceptor.ts	TraceId generation and context assignment for logs
Metrics Interceptor	metrics.interceptor.ts	HTTP metrics collection for Prometheus/Grafana
Request Timeout Interceptor	request-timeout.interceptor.ts	Per-route timeout control
Exception Handler Interceptor	exception-handler.interceptor.ts	Error catching and tracing finalization

Filters

Guide	Implementation	Description
Exception Handler Filter	exception-handler.filter.ts	Standardizes and sanitizes all API error responses

Middlewares (NestJS)

Guide	Implementation	Description
Authentication Middleware	authentication.middleware.ts	JWT token validation and user injection