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

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

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