NestJS Swagger Multipart File Upload Issue with Zod

Question

I'm developing a NestJS application and using the nestjs-zod library for validation and swagger documentation. However, I'm facing an issue when trying to upload files in a multipart form-data request.

The problem is that zod, which I use for validation, doesn't have a specific File type, and Swagger doesn't recognize it as a file input because it lacks the @ApiProperty({ format: 'binary' }) decoration. I'm looking for a solution to properly document and validate multipart file uploads using zod And in the same time I want to keep up using my Dtos that i am doing

dto.ts

import { createZodDto } from 'nestjs-zod/dto';
import * as z from 'nestjs-zod/z';

export const schema = z.object({
  field: z.string().optional(),
  requiredFile: z
    .string()
    .refine((str: any): str is Buffer => Buffer.isBuffer(Buffer.from(str))),
  optionalFile: z
    .string()
    .refine((str: any): str is Buffer => Buffer.isBuffer(Buffer.from(str)))
    .optional(),
});

export class Dto extends createZodDto(schema) {}

controller.ts

@Post()
@UseInterceptors(
  FileFieldsInterceptor(
    [{ name: 'requiredFile' }, { name: 'optionalFile' }],
    multerLimits,
  ),
)
@ApiConsumes('multipart/form-data')
async create(
  @Body() dto: CreateStoreDto,
  @UploadedFiles()
  files,
) {
  // Handle the request...
}

I tried also using zod-to-openapi package but nothing changed!

dto2.ts

import { createZodDto } from 'nestjs-zod/dto';
import { z as z2 } from 'nestjs-zod/z';
import { extendZodWithOpenApi } from '@asteasolutions/zod-to-openapi';

extendZodWithOpenApi(z2);

export const schema = z2.object({
  optionalFile: z2
    .custom<Express.Multer.File>()
    .openapi({ format: 'binary', type: 'string' }),
  requiredFile: z2
    .string()
    .refine((str: any): str is Buffer => Buffer.isBuffer(Buffer.from(str)))
    .openapi({ type: 'string', format: 'binary' }),
});

export class Dto extends createZodDto(schema) {}

I also tried

  file3: z2.string().openapi({ type: 'string', format: 'binary' }),

but that didnt work also

Here is the github repo you can fork and try to PR to fix the issue: https://github.com/mohrazzak/nodejs