thebushidocollective NestJS Guards and Interceptors
Master NestJS guards and interceptors for implementing authentication, authorization, logging, and request/response transformation.
Guards Fundamentals
Understanding CanActivate and ExecutionContext.
import { Injectable, CanActivate, ExecutionContext } from '@nestjs/common';
import { Observable } from 'rxjs';
@Injectable()
export class BasicGuard implements CanActivate {
canActivate(
context: ExecutionContext,
): boolean | Promise<boolean> | Observable<boolean> {
const request = context.switchToHttp().getRequest();
return this.validateRequest(request);
}
private validateRequest(request: any): boolean {
// Simple validation logic
return !!request.headers.authorization;
}
}
// ExecutionContext provides context about current request
@Injectable()
export class ContextAwareGuard implements CanActivate {
canActivate(context: ExecutionContext): boolean {
// Get HTTP context
const httpContext = context.switchToHttp();
const request = httpContext.getRequest();
const response = httpContext.getResponse();
// Get handler and class information
const handler = context.getHandler();
const controller = context.getClass();
console.log(`Handler: ${handler.name}`);
console.log(`Controller: ${controller.name}`);
return true;
}
}
// Usage in controller
import { Controller, Get, UseGuards } from '@nestjs/common';
@Controller('users')
@UseGuards(BasicGuard)
export class UserController {
@Get()
findAll() {
return [];
}
@Get('profile')
@UseGuards(ContextAwareGuard) // Method-level guard
getProfile() {
return { name: 'John' };
}
}
Authentication Guards
JWT, session, and API key authentication patterns.
import { Injectable, UnauthorizedException } from '@nestjs/common';
import { JwtService } from '@nestjs/jwt';
@Injectable()
export class JwtAuthGuard implements CanActivate {
constructor(private jwtService: JwtService) {}
async canActivate(context: ExecutionContext): Promise<boolean> {
const request = context.switchToHttp().getRequest();
const token = this.extractTokenFromHeader(request);
if (!token) {
throw new UnauthorizedException('No token provided');
}
try {
const payload = await this.jwtService.verifyAsync(token, {
secret: process.env.JWT_SECRET,
});
// Attach user to request
request['user'] = payload;
} catch {
throw new UnauthorizedException('Invalid token');
}
return true;
}
private extractTokenFromHeader(request: any): string | undefined {
const [type, token] = request.headers.authorization?.split(' ') ?? [];
return type === 'Bearer' ? token : undefined;
}
}
// Session-based authentication
@Injectable()
export class SessionAuthGuard implements CanActivate {
canActivate(context: ExecutionContext): boolean {
const request = context.switchToHttp().getRequest();
if (!request.session || !request.session.userId) {
throw new UnauthorizedException('Not authenticated');
}
return true;
}
}
// API Key authentication
@Injectable()
export class ApiKeyGuard implements CanActivate {
constructor(private configService: ConfigService) {}
canActivate(context: ExecutionContext): boolean {
const request = context.switchToHttp().getRequest();
const apiKey = request.headers['x-api-key'];
if (!apiKey) {
throw new UnauthorizedException('API key required');
}
const validApiKey = this.configService.get('API_KEY');
if (apiKey !== validApiKey) {
throw new UnauthorizedException('Invalid API key');
}
return true;
}
}
// Multiple auth strategies
@Injectable()
export class MultiAuthGuard implements CanActivate {
constructor(
private jwtService: JwtService,
private configService: ConfigService,
) {}
async canActivate(context: ExecutionContext): Promise<boolean> {
const request = context.switchToHttp().getRequest();
// Try JWT first
const token = this.extractTokenFromHeader(request);
if (token) {
try {
const payload = await this.jwtService.verifyAsync(token);
request['user'] = payload;
return true;
} catch {}
}
// Fall back to API key
const apiKey = request.headers['x-api-key'];
if (apiKey === this.configService.get('API_KEY')) {
return true;
}
throw new UnauthorizedException();
}
private extractTokenFromHeader(request: any): string | undefined {
const [type, token] = request.headers.authorization?.split(' ') ?? [];
return type === 'Bearer' ? token : undefined;
}
}
Role-Based Authorization Guards
RBAC patterns with decorators.
import { SetMetadata } from '@nestjs/common';
import { Reflector } from '@nestjs/core';
// Define roles
export enum Role {
USER = 'user',
ADMIN = 'admin',
MODERATOR = 'moderator',
}
// Roles decorator
export const ROLES_KEY = 'roles';
export const Roles = (...roles: Role[]) => SetMetadata(ROLES_KEY, roles);
// Roles guard
@Injectable()
export class RolesGuard implements CanActivate {
constructor(private reflector: Reflector) {}
canActivate(context: ExecutionContext): boolean {
const requiredRoles = this.reflector.getAllAndOverride<Role[]>(ROLES_KEY, [
context.getHandler(),
context.getClass(),
]);
if (!requiredRoles) {
return true; // No roles required
}
const request = context.switchToHttp().getRequest();
const user = request.user;
if (!user) {
throw new UnauthorizedException('User not authenticated');
}
const hasRole = requiredRoles.some((role) => user.roles?.includes(role));
if (!hasRole) {
throw new ForbiddenException('Insufficient permissions');
}
return true;
}
}
// Usage
@Controller('admin')
@UseGuards(JwtAuthGuard, RolesGuard)
export class AdminController {
@Get('users')
@Roles(Role.ADMIN)
getAllUsers() {
return [];
}
@Get('moderate')
@Roles(Role.ADMIN, Role.MODERATOR)
moderateContent() {
return { message: 'Moderation tools' };
}
}
// Permission-based authorization
export const PERMISSIONS_KEY = 'permissions';
export const RequirePermissions = (...permissions: string[]) =>
SetMetadata(PERMISSIONS_KEY, permissions);
@Injectable()
export class PermissionsGuard implements CanActivate {
constructor(private reflector: Reflector) {}
canActivate(context: ExecutionContext): boolean {
const requiredPermissions = this.reflector.getAllAndOverride<string[]>(
PERMISSIONS_KEY,
[context.getHandler(), context.getClass()],
);
if (!requiredPermissions) {
return true;
}
const request = context.switchToHttp().getRequest();
const user = request.user;
const hasPermission = requiredPermissions.every((permission) =>
user.permissions?.includes(permission),
);
if (!hasPermission) {
throw new ForbiddenException('Missing required permissions');
}
return true;
}
}
// Resource ownership guard
@Injectable()
export class ResourceOwnerGuard implements CanActivate {
constructor(private usersService: UsersService) {}
async canActivate(context: ExecutionContext): Promise<boolean> {
const request = context.switchToHttp().getRequest();
const user = request.user;
const resourceId = request.params.id;
const resource = await this.usersService.findOne(resourceId);
if (!resource) {
throw new NotFoundException('Resource not found');
}
if (resource.userId !== user.id && !user.roles.includes(Role.ADMIN)) {
throw new ForbiddenException('You do not own this resource');
}
// Attach resource to request for later use
request['resource'] = resource;
return true;
}
}
Interceptors Fundamentals
NestInterceptor and response transformation.
import {
Injectable,
NestInterceptor,
ExecutionContext,
CallHandler,
} from '@nestjs/common';
import { Observable } from 'rxjs';
import { map, tap } from 'rxjs/operators';
// Basic interceptor
@Injectable()
export class LoggingInterceptor implements NestInterceptor {
intercept(context: ExecutionContext, next: CallHandler): Observable<any> {
console.log('Before...');
const now = Date.now();
return next
.handle()
.pipe(tap(() => console.log(`After... ${Date.now() - now}ms`)));
}
}
// Transform response
@Injectable()
export class TransformInterceptor<T> implements NestInterceptor<T, Response<T>> {
intercept(
context: ExecutionContext,
next: CallHandler,
): Observable<Response<T>> {
return next.handle().pipe(
map((data) => ({
data,
timestamp: new Date().toISOString(),
path: context.switchToHttp().getRequest().url,
})),
);
}
}
interface Response<T> {
data: T;
timestamp: string;
path: string;
}
// Error handling in interceptor
@Injectable()
export class ErrorsInterceptor implements NestInterceptor {
intercept(context: ExecutionContext, next: CallHandler): Observable<any> {
return next.handle().pipe(
catchError((err) => {
console.error('Error caught in interceptor:', err);
throw new InternalServerErrorException('Something went wrong');
}),
);
}
}
// Usage
@Controller('users')
@UseInterceptors(LoggingInterceptor)
export class UserController {
@Get()
@UseInterceptors(TransformInterceptor)
findAll() {
return [{ id: 1, name: 'John' }];
}
}
Logging Interceptors
Advanced logging patterns.
import { Logger } from '@nestjs/common';
@Injectable()
export class RequestLoggingInterceptor implements NestInterceptor {
private readonly logger = new Logger(RequestLoggingInterceptor.name);
intercept(context: ExecutionContext, next: CallHandler): Observable<any> {
const request = context.switchToHttp().getRequest();
const { method, url, body } = request;
const userAgent = request.get('user-agent') || '';
this.logger.log(`Incoming Request: ${method} ${url}`);
this.logger.debug(`User Agent: ${userAgent}`);
this.logger.debug(`Body: ${JSON.stringify(body)}`);
const now = Date.now();
return next.handle().pipe(
tap({
next: (data) => {
const response = context.switchToHttp().getResponse();
this.logger.log(
`Response: ${method} ${url} ${response.statusCode} - ${Date.now() - now}ms`,
);
},
error: (err) => {
this.logger.error(
`Error: ${method} ${url} - ${err.message}`,
err.stack,
);
},
}),
);
}
}
// Performance monitoring
@Injectable()
export class PerformanceInterceptor implements NestInterceptor {
private readonly logger = new Logger(PerformanceInterceptor.name);
intercept(context: ExecutionContext, next: CallHandler): Observable<any> {
const request = context.switchToHttp().getRequest();
const { method, url } = request;
const startTime = Date.now();
return next.handle().pipe(
tap(() => {
const duration = Date.now() - startTime;
if (duration > 1000) {
this.logger.warn(`Slow request: ${method} ${url} - ${duration}ms`);
} else {
this.logger.log(`${method} ${url} - ${duration}ms`);
}
}),
);
}
}
Response Transformation Interceptors
Shaping API responses consistently.
// Wrap all responses
@Injectable()
export class ResponseWrapperInterceptor implements NestInterceptor {
intercept(context: ExecutionContext, next: CallHandler): Observable<any> {
return next.handle().pipe(
map((data) => {
const response = context.switchToHttp().getResponse();
return {
statusCode: response.statusCode,
message: 'Success',
data,
};
}),
);
}
}
// Pagination wrapper
interface PaginatedResponse<T> {
items: T[];
total: number;
page: number;
pageSize: number;
totalPages: number;
}
@Injectable()
export class PaginationInterceptor implements NestInterceptor {
intercept(context: ExecutionContext, next: CallHandler): Observable<any> {
return next.handle().pipe(
map((data) => {
if (data && typeof data === 'object' && 'items' in data) {
const { items, total } = data;
const request = context.switchToHttp().getRequest();
const page = parseInt(request.query.page) || 1;
const pageSize = parseInt(request.query.pageSize) || 10;
return {
items,
total,
page,
pageSize,
totalPages: Math.ceil(total / pageSize),
};
}
return data;
}),
);
}
}
// Exclude null fields
@Injectable()
export class ExcludeNullInterceptor implements NestInterceptor {
intercept(context: ExecutionContext, next: CallHandler): Observable<any> {
return next.handle().pipe(
map((data) => {
return this.removeNullValues(data);
}),
);
}
private removeNullValues(obj: any): any {
if (Array.isArray(obj)) {
return obj.map((item) => this.removeNullValues(item));
}
if (obj !== null && typeof obj === 'object') {
return Object.entries(obj).reduce((acc, [key, value]) => {
if (value !== null) {
acc[key] = this.removeNullValues(value);
}
return acc;
}, {});
}
return obj;
}
}
Caching Interceptors
Implementing caching strategies.
import { CACHE_MANAGER } from '@nestjs/cache-manager';
import { Cache } from 'cache-manager';
@Injectable()
export class CacheInterceptor implements NestInterceptor {
constructor(@Inject(CACHE_MANAGER) private cacheManager: Cache) {}
async intercept(
context: ExecutionContext,
next: CallHandler,
): Promise<Observable<any>> {
const request = context.switchToHttp().getRequest();
const cacheKey = `${request.method}:${request.url}`;
// Check cache
const cachedResponse = await this.cacheManager.get(cacheKey);
if (cachedResponse) {
return of(cachedResponse);
}
// Execute handler and cache result
return next.handle().pipe(
tap(async (response) => {
await this.cacheManager.set(cacheKey, response, 60000); // 60s TTL
}),
);
}
}
// Conditional caching
export const CACHE_KEY_METADATA = 'cache_key';
export const CacheKey = (key: string) => SetMetadata(CACHE_KEY_METADATA, key);
@Injectable()
export class SmartCacheInterceptor implements NestInterceptor {
constructor(
@Inject(CACHE_MANAGER) private cacheManager: Cache,
private reflector: Reflector,
) {}
async intercept(
context: ExecutionContext,
next: CallHandler,
): Promise<Observable<any>> {
const cacheKey = this.reflector.get(CACHE_KEY_METADATA, context.getHandler());
if (!cacheKey) {
return next.handle();
}
const cached = await this.cacheManager.get(cacheKey);
if (cached) {
return of(cached);
}
return next.handle().pipe(
tap(async (response) => {
await this.cacheManager.set(cacheKey, response);
}),
);
}
}
// Usage
@Controller('products')
export class ProductsController {
@Get()
@CacheKey('all-products')
findAll() {
return this.productsService.findAll();
}
}
Timeout Interceptors
Handling request timeouts.
import { timeout, catchError } from 'rxjs/operators';
import { throwError, TimeoutError } from 'rxjs';
@Injectable()
export class TimeoutInterceptor implements NestInterceptor {
intercept(context: ExecutionContext, next: CallHandler): Observable<any> {
return next.handle().pipe(
timeout(5000), // 5 second timeout
catchError((err) => {
if (err instanceof TimeoutError) {
return throwError(() => new RequestTimeoutException());
}
return throwError(() => err);
}),
);
}
}
// Dynamic timeout based on endpoint
export const TIMEOUT_METADATA = 'timeout';
export const Timeout = (milliseconds: number) =>
SetMetadata(TIMEOUT_METADATA, milliseconds);
@Injectable()
export class DynamicTimeoutInterceptor implements NestInterceptor {
constructor(private reflector: Reflector) {}
intercept(context: ExecutionContext, next: CallHandler): Observable<any> {
const timeoutValue =
this.reflector.get(TIMEOUT_METADATA, context.getHandler()) || 5000;
return next.handle().pipe(
timeout(timeoutValue),
catchError((err) => {
if (err instanceof TimeoutError) {
return throwError(() => new RequestTimeoutException());
}
return throwError(() => err);
}),
);
}
}
// Usage
@Controller('reports')
export class ReportsController {
@Get('generate')
@Timeout(30000) // 30 second timeout for long-running report
generateReport() {
return this.reportsService.generate();
}
}
Pipes
Validation and transformation pipes.
import { PipeTransform, Injectable, ArgumentMetadata, BadRequestException } from '@nestjs/common';
import { validate } from 'class-validator';
import { plainToInstance } from 'class-transformer';
// Built-in validation pipe
import { ValidationPipe } from '@nestjs/common';
@Controller('users')
export class UserController {
@Post()
create(@Body(new ValidationPipe()) createUserDto: CreateUserDto) {
return this.usersService.create(createUserDto);
}
}
// Custom validation pipe
@Injectable()
export class CustomValidationPipe implements PipeTransform<any> {
async transform(value: any, { metatype }: ArgumentMetadata) {
if (!metatype || !this.toValidate(metatype)) {
return value;
}
const object = plainToInstance(metatype, value);
const errors = await validate(object);
if (errors.length > 0) {
const messages = errors.map((err) => ({
property: err.property,
constraints: err.constraints,
}));
throw new BadRequestException({ errors: messages });
}
return value;
}
private toValidate(metatype: Function): boolean {
const types: Function[] = [String, Boolean, Number, Array, Object];
return !types.includes(metatype);
}
}
// Transformation pipes
@Injectable()
export class ParseIntPipe implements PipeTransform<string, number> {
transform(value: string, metadata: ArgumentMetadata): number {
const val = parseInt(value, 10);
if (isNaN(val)) {
throw new BadRequestException('Validation failed (numeric string expected)');
}
return val;
}
}
// Built-in pipes usage
@Get(':id')
findOne(@Param('id', ParseIntPipe) id: number) {
return this.usersService.findOne(id);
}
// Strip fields pipe
@Injectable()
export class StripFieldsPipe implements PipeTransform {
constructor(private readonly fieldsToStrip: string[]) {}
transform(value: any) {
if (typeof value !== 'object' || value === null) {
return value;
}
const result = { ...value };
this.fieldsToStrip.forEach((field) => {
delete result[field];
});
return result;
}
}
// Default value pipe
@Injectable()
export class DefaultValuePipe implements PipeTransform {
constructor(private readonly defaultValue: any) {}
transform(value: any) {
return value !== undefined && value !== null ? value : this.defaultValue;
}
}
Exception Filters
Custom exception handling.
import {
ExceptionFilter,
Catch,
ArgumentsHost,
HttpException,
HttpStatus,
} from '@nestjs/common';
import { Request, Response } from 'express';
// HTTP exception filter
@Catch(HttpException)
export class HttpExceptionFilter implements ExceptionFilter {
catch(exception: HttpException, host: ArgumentsHost) {
const ctx = host.switchToHttp();
const response = ctx.getResponse<Response>();
const request = ctx.getRequest<Request>();
const status = exception.getStatus();
response.status(status).json({
statusCode: status,
timestamp: new Date().toISOString(),
path: request.url,
message: exception.message,
});
}
}
// All exceptions filter
@Catch()
export class AllExceptionsFilter implements ExceptionFilter {
private readonly logger = new Logger(AllExceptionsFilter.name);
catch(exception: unknown, host: ArgumentsHost) {
const ctx = host.switchToHttp();
const response = ctx.getResponse<Response>();
const request = ctx.getRequest<Request>();
const status =
exception instanceof HttpException
? exception.getStatus()
: HttpStatus.INTERNAL_SERVER_ERROR;
const message =
exception instanceof HttpException
? exception.message
: 'Internal server error';
this.logger.error(
`${request.method} ${request.url}`,
exception instanceof Error ? exception.stack : 'Unknown error',
);
response.status(status).json({
statusCode: status,
timestamp: new Date().toISOString(),
path: request.url,
message,
});
}
}
// Validation exception filter
@Catch(BadRequestException)
export class ValidationExceptionFilter implements ExceptionFilter {
catch(exception: BadRequestException, host: ArgumentsHost) {
const ctx = host.switchToHttp();
const response = ctx.getResponse<Response>();
const request = ctx.getRequest<Request>();
const exceptionResponse = exception.getResponse();
const errors =
typeof exceptionResponse === 'object' && 'message' in exceptionResponse
? exceptionResponse['message']
: exceptionResponse;
response.status(HttpStatus.BAD_REQUEST).json({
statusCode: HttpStatus.BAD_REQUEST,
timestamp: new Date().toISOString(),
path: request.url,
errors,
});
}
}
// Usage
@Controller('users')
@UseFilters(new HttpExceptionFilter())
export class UserController {}
// Global filter
async function bootstrap() {
const app = await NestFactory.create(AppModule);
app.useGlobalFilters(new AllExceptionsFilter());
await app.listen(3000);
}
Middleware
Function and class middleware.
import { Injectable, NestMiddleware } from '@nestjs/common';
import { Request, Response, NextFunction } from 'express';
// Class middleware
@Injectable()
export class LoggerMiddleware implements NestMiddleware {
private logger = new Logger('HTTP');
use(req: Request, res: Response, next: NextFunction) {
const { method, originalUrl } = req;
const startTime = Date.now();
res.on('finish', () => {
const { statusCode } = res;
const duration = Date.now() - startTime;
this.logger.log(`${method} ${originalUrl} ${statusCode} - ${duration}ms`);
});
next();
}
}
// Function middleware
export function logger(req: Request, res: Response, next: NextFunction) {
console.log(`Request: ${req.method} ${req.url}`);
next();
}
// Authentication middleware
@Injectable()
export class AuthMiddleware implements NestMiddleware {
constructor(private authService: AuthService) {}
async use(req: Request, res: Response, next: NextFunction) {
const token = req.headers.authorization?.split(' ')[1];
if (!token) {
throw new UnauthorizedException('No token provided');
}
try {
const user = await this.authService.validateToken(token);
req['user'] = user;
next();
} catch (error) {
throw new UnauthorizedException('Invalid token');
}
}
}
// CORS middleware
@Injectable()
export class CorsMiddleware implements NestMiddleware {
use(req: Request, res: Response, next: NextFunction) {
res.header('Access-Control-Allow-Origin', '*');
res.header('Access-Control-Allow-Methods', 'GET,PUT,POST,DELETE');
res.header('Access-Control-Allow-Headers', 'Content-Type, Authorization');
if (req.method === 'OPTIONS') {
res.sendStatus(200);
} else {
next();
}
}
}
// Apply middleware in module
import { Module, MiddlewareConsumer, RequestMethod } from '@nestjs/common';
@Module({
imports: [],
controllers: [UserController],
})
export class AppModule {
configure(consumer: MiddlewareConsumer) {
consumer
.apply(LoggerMiddleware)
.forRoutes('*');
consumer
.apply(AuthMiddleware)
.exclude(
{ path: 'auth/login', method: RequestMethod.POST },
{ path: 'health', method: RequestMethod.GET },
)
.forRoutes('*');
}
}
Request Lifecycle and Execution Order
Understanding the order of execution.
// Order of execution:
// 1. Middleware
// 2. Guards
// 3. Interceptors (before)
// 4. Pipes
// 5. Controller method
// 6. Interceptors (after)
// 7. Exception filters
@Controller('demo')
export class DemoController {
private readonly logger = new Logger(DemoController.name);
@Post()
@UseGuards(DemoGuard)
@UseInterceptors(DemoInterceptor)
@UsePipes(DemoPipe)
create(@Body() data: any) {
this.logger.log('5. Controller method executed');
return data;
}
}
@Injectable()
export class DemoGuard implements CanActivate {
private readonly logger = new Logger(DemoGuard.name);
canActivate(context: ExecutionContext): boolean {
this.logger.log('2. Guard executed');
return true;
}
}
@Injectable()
export class DemoInterceptor implements NestInterceptor {
private readonly logger = new Logger(DemoInterceptor.name);
intercept(context: ExecutionContext, next: CallHandler): Observable<any> {
this.logger.log('3. Interceptor before');
return next.handle().pipe(
tap(() => this.logger.log('6. Interceptor after')),
);
}
}
@Injectable()
export class DemoPipe implements PipeTransform {
private readonly logger = new Logger(DemoPipe.name);
transform(value: any) {
this.logger.log('4. Pipe executed');
return value;
}
}
Testing Guards and Interceptors
Unit testing patterns.
import { Test, TestingModule } from '@nestjs/testing';
import { ExecutionContext } from '@nestjs/common';
describe('JwtAuthGuard', () => {
let guard: JwtAuthGuard;
let jwtService: JwtService;
beforeEach(async () => {
const module: TestingModule = await Test.createTestingModule({
providers: [
JwtAuthGuard,
{
provide: JwtService,
useValue: {
verifyAsync: jest.fn(),
},
},
],
}).compile();
guard = module.get<JwtAuthGuard>(JwtAuthGuard);
jwtService = module.get<JwtService>(JwtService);
});
it('should allow valid token', async () => {
const mockContext = {
switchToHttp: () => ({
getRequest: () => ({
headers: { authorization: 'Bearer valid-token' },
}),
}),
} as ExecutionContext;
jest.spyOn(jwtService, 'verifyAsync').mockResolvedValue({ userId: 1 });
const result = await guard.canActivate(mockContext);
expect(result).toBe(true);
});
it('should reject invalid token', async () => {
const mockContext = {
switchToHttp: () => ({
getRequest: () => ({
headers: { authorization: 'Bearer invalid-token' },
}),
}),
} as ExecutionContext;
jest.spyOn(jwtService, 'verifyAsync').mockRejectedValue(new Error());
await expect(guard.canActivate(mockContext)).rejects.toThrow(
UnauthorizedException,
);
});
});
describe('TransformInterceptor', () => {
let interceptor: TransformInterceptor;
beforeEach(() => {
interceptor = new TransformInterceptor();
});
it('should transform response', (done) => {
const mockContext = {
switchToHttp: () => ({
getRequest: () => ({ url: '/test' }),
}),
} as ExecutionContext;
const mockCallHandler = {
handle: () => of({ name: 'Test' }),
};
interceptor.intercept(mockContext, mockCallHandler).subscribe((result) => {
expect(result).toHaveProperty('data');
expect(result).toHaveProperty('timestamp');
expect(result).toHaveProperty('path');
expect(result.data).toEqual({ name: 'Test' });
done();
});
});
});
When to Use This Skill
Use nestjs-guards-interceptors when:
- Implementing authentication and authorization
- Adding logging and monitoring to your application
- Transforming request/response data consistently
- Implementing caching strategies
- Adding timeouts to requests
- Handling cross-cutting concerns
- Building middleware for request processing
- Creating reusable validation logic
- Implementing RBAC or ABAC patterns
- Adding performance monitoring
NestJS Guards and Interceptors Best Practices
- Single responsibility - Each guard/interceptor should have one clear purpose
- Use metadata - Leverage decorators and Reflector for configuration
- Chain appropriately - Understand execution order when combining multiple guards/interceptors
- Error handling - Always handle errors gracefully in guards and interceptors
- Async operations - Use async/await for database calls in guards
- Global vs local - Apply guards/interceptors at appropriate scope (global, controller, method)
- Test thoroughly - Write unit tests for all guards and interceptors
- Performance - Keep guards and interceptors lightweight
- Logging - Use Logger service instead of console.log
- Type safety - Use TypeScript generics for type-safe interceptors
NestJS Guards and Interceptors Common Pitfalls
- Wrong execution order - Not understanding middleware → guards → interceptors → pipes flow
- Forgetting async - Not using async when guards perform database operations
- Missing error handling - Guards that don't throw appropriate exceptions
- Interceptor mutation - Mutating data in interceptors instead of transforming
- Circular dependencies - Guards that create circular dependency chains
- Global scope issues - Applying too many global guards/interceptors hurts performance
- Missing metadata - Forgetting to use Reflector to read custom metadata
- Pipe placement - Using pipes in wrong order with validation
- Exception filter scope - Not understanding filter precedence
- Memory leaks - Not properly cleaning up subscriptions in interceptors