Little gist providing two functions to parse a form from an incoming message and also validate it immediately using a given Zod schema.

formidableZodParse.ts

import formidable from 'formidable';
import { IncomingMessage } from 'http';
import { z, ZodObject, ZodType } from 'zod';

export type KnownFormFields = Record<string, ZodType>;

export type FormParseResult<TFields, TFiles> = {
  error?: Error;
  fields?: TFields;
  files?: TFiles;
};

export async function parseIncomingForm<TFields = any, TFiles = any>(
  request: IncomingMessage
): Promise<FormParseResult<TFields, TFiles>> {
  return await new Promise((resolve, reject) => {
    formidable().parse(request, (error: any, fields: any, files: any) => {
      if (error) reject({ error });
      resolve({ error, fields, files });
    });
  });
}

/**
 * Parses the form fields potentially given in the request using given schema
 * and throws an error if the fields do not match the expectations.
 *
 * @example
 * const { name } = validateIncomingFields(request, z.object({ name: z.string() }));
 *
 * @param request - the incoming message (often the to be handled API request)
 * @param schema - the schema used to parse given request's form data
 */
export async function validateIncomingFields<
  TFields extends KnownFormFields,
  TObject extends ZodObject<TFields>
>(request: IncomingMessage, schema: TObject): Promise<z.infer<TObject>> {
  const data = await parseIncomingForm<TFields>(request);
  if (!data.error) return schema.parse(data.fields);
  return Promise.reject(data.error);
}

  "dependencies": {
    "@types/formidable": "^2.0.5",
    "formidable": "^2.1.1",
    "typescript": "4.9.5",
    "zod": "^3.20.6"
  }