NestJS File Upload Multiple File Type Verification

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I had this problem limiting the types of files going to the backend using Nestjs.

So I built a custom validator, here’s how it looks:

import {BadRequestException, Injectable, PipeTransform} from '@nestjs/common';
import {extname} from 'path';

export function getFileValidator(): PipeTransform {
 return new ParseFilePipeDocument();
}

@Injectable()
export class ParseFilePipeDocument implements PipeTransform {
 private readonly allowedExtensions = [ '.png', '.pdf', '.jpeg', '.jpg'];
 
 transform(value: Express.Multer.File): Express.Multer.File {
  const extension = extname(value.originalname);
  if(!this.allowedExtensions.includes(extension)) {
   throw new BadRequestException(`File type ${extension} not supported`);
  }
  return value;
 }

}

And here’s how I use it in my Controller class:

@Controller("path-to-controller")
export class ExampleController {
 constructor(
  private readonly exampleService: ExampleService
 ) {}

 @Post('documents/upload')
 async createDocument(
  @Body() createDocDto: CreateDocumentDTO,
  @UploadedFile(getFileValidator()) document: Express.Multer.File
 ) {
  return this.exampleService.uploadDocument(document);
 }
}

Pretty neat hm?

Originally published at https://lucas-schiavini.com on March 8, 2023.