typescript 42 lines · 8 steps

Request-scoped context service in NestJS

A request-scoped provider snapshots per-request metadata once at construction and exposes it safely to the rest of the app.

Explained by highlit
NestJS Intermediate dependency-injection request-scope immutability context-propagation
1import { Injectable, Scope, Inject } from '@nestjs/common';
2import { REQUEST } from '@nestjs/core';
3import { Request } from 'express';
4 
5export interface RequestContext {
6 requestId: string;
7 userId: string | null;
8 tenantId: string | null;
9 ip: string;
10}
11 
12@Injectable({ scope: Scope.REQUEST })
13export class RequestContextService {
14 private readonly context: RequestContext;
15 
16 constructor(@Inject(REQUEST) private readonly request: Request) {
17 const user = (request as Request & { user?: { id: string; tenantId?: string } }).user;
18 
19 this.context = {
20 requestId:
21 (request.headers['x-request-id'] as string) ?? crypto.randomUUID(),
22 userId: user?.id ?? null,
23 tenantId: user?.tenantId ?? (request.headers['x-tenant-id'] as string) ?? null,
24 ip: request.ip ?? request.socket.remoteAddress ?? 'unknown',
25 };
26 }
27 
28 get requestId(): string {
29 return this.context.requestId;
30 }
31 
32 requireTenantId(): string {
33 if (!this.context.tenantId) {
34 throw new Error('No tenant bound to the current request');
35 }
36 return this.context.tenantId;
37 }
38 
39 snapshot(): Readonly<RequestContext> {
40 return { ...this.context };
41 }
42}
01 / 01
STEP 01

Walkthrough

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Three takeaways
  1. 1Request-scoped providers give each HTTP request its own instance, so you can capture per-request state without threading it through every function.
  2. 2Computing derived context once in the constructor keeps reads cheap and guarantees a stable snapshot for the request's lifetime.
  3. 3Returning copies and requiring mandatory values guards callers from mutating shared state or silently proceeding with missing data.

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