How to limit total size of uploaded files in NestJS using multer?

Question

I am developing an app where user can upload multiple files which will then be added to an email as attachment. I can limit the file size of each file using multer options. However I cannot set a limit for the total number of fields.

What is the best practice for limiting the total size of files?

Here is how I parse incoming files:

@Post('send')
@UseInterceptors(
AnyFilesInterceptor({ limits: { fileSize: 2 \* 1024 \* 1024 } }),
)
sendEmailWithAttachment(
@Body() sendEmailPayload: SendEmailPayload,
@UploadedFiles() files: Array\<Express.Multer.File\>,
) {

I added 2mb limit for demonstration purposes.

I could write a function on the service level that checks the sum of the file sizes, but it did not seem very feasible.

Answer 1

You can use a Nest Guard to do this logic, for Example:

@Injectable()
export class FileSizeGuard implements CanActivate {
  constructor(private readonly maxTotalSize: number) {}

  canActivate(
    context: ExecutionContext,
  ): boolean | Promise<boolean> | Observable<boolean> {
    const request = context.switchToHttp().getRequest();
    const files: Express.Multer.File[] = request.files;
    const totalSize = files.reduce((acc, file) => acc + file.size, 0);
    if (totalSize > this.maxTotalSize) {
      return false;
    }
    return true;
  }
}

then use this guard above your controller endpoint:

@Post('send')
@UseGuards(new FileSizeGuard(10 * 1024 * 1024)) // limit total size to 10MB
...