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Param Dekoratörleriyle İstek Bağlamını Okuma

createParamDecorator ve ExecutionContext kullanarak özel @CurrentUser ve @ClientIp param dekoratörleri oluşturun.

Param Dekoratörleriyle İstek Bağlamını Okuma, CoddyKit'te ücretsiz bir NestJS Enterprise Backend APIs dersidir. Bu, 4 dersinin 1. dersidir. Aşağıdan dersin tamamını ücretsiz okuyabilir, sonra tarayıcıda yerleşik kod editörü ve 7/24 yapay zeka koçu ile uygulamalı olarak pratik yapabilirsin. Bu, NestJS Enterprise Backend APIs öğrenme yolunun bir parçasıdır ve ilerlemeniz web ve CoddyKit uygulaması arasında senkronize olur. NestJS Enterprise Backend APIs kursu toplamda 4 dersten oluşur.

Bu dersin bazı bölümleri henüz çevrilmemiş olup İngilizce olarak gösterilmektedir.

Why Param Decorators?

In NestJS controllers, you often need to pull the same piece of data out of the request over and over: the authenticated user, the client IP, a tenant id from a header. Doing this with @Req() and digging into request.user in every handler is repetitive and leaks framework details into your business logic.

Custom param decorators let you encapsulate that extraction once and reuse it everywhere:

  • @CurrentUser() instead of req.user
  • @ClientIp() instead of parsing x-forwarded-for

The result is cleaner, more testable, and more declarative controller code.

The Repetitive Way

Here is what you usually start with: grabbing the whole request object and reaching into it manually. It works, but every handler repeats the same lines, and the controller now knows about request.user, which is an implementation detail of your auth guard.

Notice how the actual route logic is buried under plumbing. This is exactly what a param decorator removes.

import { Controller, Get, Req } from '@nestjs/common';
import { Request } from 'express';

@Controller('profile')
export class ProfileController {
  @Get()
  getProfile(@Req() request: Request) {
    const user = (request as any).user;
    return { id: user.id, email: user.email };
  }
}

createParamDecorator

NestJS exposes the factory createParamDecorator from @nestjs/common. You give it a function that receives two arguments and returns whatever value you want injected into the handler parameter.

  • data — the optional argument passed when the decorator is used, e.g. @CurrentUser('email').
  • ctx: ExecutionContext — a wrapper around the current request context, independent of the transport (HTTP, RPC, WebSocket).

The returned value becomes the parameter's value at call time.

import { createParamDecorator, ExecutionContext } from '@nestjs/common';

export const Example = createParamDecorator(
  (data: unknown, ctx: ExecutionContext) => {
    // return any value -> it gets injected into the param
    return 'hello';
  },
);

Getting the HTTP Request

For HTTP apps you convert the generic ExecutionContext into an HTTP-specific argument host and read the request from it:

  • ctx.switchToHttp() returns an HttpArgumentsHost.
  • .getRequest() gives you the underlying request (Express or Fastify).

Using switchToHttp() keeps the decorator explicit about which transport it targets. The same context could also be switched to RPC or WS for other protocols.

import { createParamDecorator, ExecutionContext } from '@nestjs/common';
import { Request } from 'express';

export const RawRequest = createParamDecorator(
  (data: unknown, ctx: ExecutionContext): Request => {
    return ctx.switchToHttp().getRequest<Request>();
  },
);

Building @CurrentUser

Assume an auth guard (e.g. a JWT strategy) has already attached the authenticated user to request.user. The @CurrentUser() decorator simply returns it.

This is the canonical pattern in enterprise NestJS apps: the guard does authentication, and the decorator gives ergonomic access to the result without exposing the request object.

import { createParamDecorator, ExecutionContext } from '@nestjs/common';

export interface AuthUser {
  id: string;
  email: string;
  roles: string[];
}

export const CurrentUser = createParamDecorator(
  (data: unknown, ctx: ExecutionContext): AuthUser => {
    const request = ctx.switchToHttp().getRequest();
    return request.user;
  },
);

Using the data Argument

The first parameter, data, is what the caller passes inside the decorator's parentheses. You can use it to return a single property instead of the whole object:

  • @CurrentUser() returns the full user.
  • @CurrentUser('email') returns just the email.

Type the data argument as keyof AuthUser so the caller gets autocomplete and compile-time safety on the property name.

import { createParamDecorator, ExecutionContext } from '@nestjs/common';
import { AuthUser } from './auth-user.interface';

export const CurrentUser = createParamDecorator(
  (data: keyof AuthUser | undefined, ctx: ExecutionContext) => {
    const request = ctx.switchToHttp().getRequest();
    const user: AuthUser = request.user;
    return data ? user?.[data] : user;
  },
);

Consuming @CurrentUser in a Controller

Now the controller reads beautifully. The guard guarantees the user exists; the decorator injects exactly what each handler needs. No @Req(), no manual property digging.

This separation is what makes the handler easy to unit-test: you just call the method with a plain user object.

import { Controller, Get, UseGuards } from '@nestjs/common';
import { JwtAuthGuard } from './jwt-auth.guard';
import { CurrentUser } from './current-user.decorator';
import { AuthUser } from './auth-user.interface';

@UseGuards(JwtAuthGuard)
@Controller('me')
export class MeController {
  @Get()
  getMe(@CurrentUser() user: AuthUser) {
    return user;
  }

  @Get('email')
  getEmail(@CurrentUser('email') email: string) {
    return { email };
  }
}

Building @ClientIp

Behind a load balancer or reverse proxy, the real client IP is not request.ip but the first entry of the x-forwarded-for header. A @ClientIp() decorator centralizes this logic so every handler reads the correct address.

Important: only trust x-forwarded-for when you actually run behind a trusted proxy, and enable Express's trust proxy setting. Otherwise clients can spoof the header.

import { createParamDecorator, ExecutionContext } from '@nestjs/common';
import { Request } from 'express';

export const ClientIp = createParamDecorator(
  (data: unknown, ctx: ExecutionContext): string => {
    const request = ctx.switchToHttp().getRequest<Request>();
    const forwarded = request.headers['x-forwarded-for'];
    if (typeof forwarded === 'string' && forwarded.length > 0) {
      return forwarded.split(',')[0].trim();
    }
    return request.ip ?? '';
  },
);

Pure Extraction Logic Is Testable

The valuable part of a param decorator is its pure extraction logic. You can lift that into a plain function, unit-test it with a fake request, and call it from the decorator. Here is the IP-parsing logic as a standalone, runnable program.

This demonstrates the rule for choosing the first forwarded address and the fallback behavior — no NestJS or server required to verify it.

function extractClientIp(headers: Record<string, string>, fallbackIp: string): string {
  const forwarded = headers['x-forwarded-for'];
  if (typeof forwarded === 'string' && forwarded.length > 0) {
    return forwarded.split(',')[0].trim();
  }
  return fallbackIp;
}

console.log(extractClientIp({ 'x-forwarded-for': '203.0.113.7, 70.41.3.18' }, '10.0.0.1'));
console.log(extractClientIp({}, '10.0.0.1'));
console.log(extractClientIp({ 'x-forwarded-for': '198.51.100.5' }, '10.0.0.1'));

Combining Decorators in One Handler

Param decorators compose freely. A single handler can mix built-in decorators (@Body, @Param) with your custom ones. NestJS resolves each parameter independently by its decorator metadata.

Here an audit endpoint records who did what and from where, reading the user and IP declaratively.

import { Controller, Post, Body, UseGuards } from '@nestjs/common';
import { JwtAuthGuard } from './jwt-auth.guard';
import { CurrentUser } from './current-user.decorator';
import { ClientIp } from './client-ip.decorator';
import { AuthUser } from './auth-user.interface';

@UseGuards(JwtAuthGuard)
@Controller('audit')
export class AuditController {
  @Post('action')
  record(
    @CurrentUser('id') userId: string,
    @ClientIp() ip: string,
    @Body() body: { action: string },
  ) {
    return { userId, ip, action: body.action, at: new Date().toISOString() };
  }
}

Validation and Pipes Still Apply

A custom param decorator returns a raw value, so you can still attach pipes to it just like built-in decorators. Pass a pipe as an extra argument when using the decorator.

  • @CurrentUser('id', ParseUUIDPipe) validates that the extracted id is a UUID.
  • Pipes run after the decorator factory returns its value.

This lets you keep extraction and validation cleanly separated while still benefiting from NestJS's pipe pipeline.

import { Controller, Get, ParseUUIDPipe } from '@nestjs/common';
import { CurrentUser } from './current-user.decorator';

@Controller('orders')
export class OrdersController {
  @Get('mine')
  myOrders(@CurrentUser('id', ParseUUIDPipe) userId: string) {
    return { userId };
  }
}

Quick Check

Test your understanding of how a custom param decorator reads the request.

Recap

You learned to read request context declaratively with custom param decorators:

  • createParamDecorator((data, ctx) => ...) builds a reusable decorator; the returned value is injected into the handler parameter.
  • ctx.switchToHttp().getRequest() retrieves the HTTP request in a transport-explicit way.
  • @CurrentUser() wraps request.user (populated by your auth guard) and can return a single property via the data argument typed as keyof AuthUser.
  • @ClientIp() centralizes x-forwarded-for parsing, with a fallback to request.ip — trust the header only behind a real proxy.
  • Keep extraction logic pure so it is easy to unit-test, and remember you can still chain pipes like ParseUUIDPipe onto your custom decorators.

Sıkça Sorulan Sorular

“Param Dekoratörleriyle İstek Bağlamını Okuma” dersi ücretsiz mi?

Evet — “Param Dekoratörleriyle İstek Bağlamını Okuma” dersin tüm metni burada web'de ücretsiz olarak okunabilir. Etkileşimli olarak pratik yapmak (yerleşik kod editörü ve 7/24 yapay zeka koçu) ve NestJS Enterprise Backend APIs kursunun geri kalanını açmak için CoddyKit PRO'ya yükselt. NestJS Enterprise Backend APIs kursu toplamda 4 dersten oluşur.

“Param Dekoratörleriyle İstek Bağlamını Okuma” dersinde ne öğreneceğim?

createParamDecorator ve ExecutionContext kullanarak özel @CurrentUser ve @ClientIp param dekoratörleri oluşturun. NestJS Enterprise Backend APIs ile uygulamalı kodu tarayıcıda doğrudan çalıştırarak pratik yaparsın ve 7/24 yapay zeka koçu dersi çalışırken sorularını yanıtlar.

NestJS Enterprise Backend APIs öğrenmeye başlamak için deneyim gerekli mi?

Önceden deneyim gerekmez. CoddyKit'te NestJS Enterprise Backend APIs, başlangıçtan ileri seviyeye kadar yapılandırıldığı için buradan başlayabilir veya başından başlayıp kendi hızında ilerleme yapabilirsin. Bu, 4 dersinin 1. dersidir.

“Param Dekoratörleriyle İstek Bağlamını Okuma” dersi ne kadar sürer?

Çoğu CoddyKit dersi yaklaşık 5–10 dakika sürer. Her biri kısa ve etkileşimli olduğu için sabit ilerleme yaparsın ve web ile uygulama arasında tam olarak bıraktığın yerden devam edebilirsin.

Bu NestJS Enterprise Backend APIs dersinde kod yazıp çalıştırabilir miyim?

Evet. Her NestJS Enterprise Backend APIs dersi yerleşik bir kod editörü içerir, bu sayede tarayıcıda gerçek kod yazıp çalıştırabilir ve anlık yapay zeka geri bildirimi alırsın — yerel kurulum gerekli değildir.

Bu kursun tüm dersleri

  1. Param Dekoratörleriyle İstek Bağlamını Okuma
  2. SetMetadata ve Reflector ile Üst Veri Ekleme
  3. applyDecorators ile Dekoratörleri Birleştirme
  4. Çapraz Kesitsel Yapılandırma için Sınıf Düzeyi Dekoratörleri
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