Formidable V2 Filter issue

[Deval Patel]

Support plan

• Which support plan is this issue covered by? (Community, Sponsor, Enterprise): Free
• Currently blocking your project/work? (yes/no): Yes
• Affecting a production system? (yes/no): no

Context

• Node.js version:16.20.0
• Release Line of Formidable (Legacy, Current, Next): https://www.npmjs.com/package/formidable/v/2.1.2
• Formidable exact version:2.1.2
• Environment (node, browser, native, OS): node
• Used with (popular names of modules): NextJS13

What are you trying to achieve or the steps to reproduce?

When I attached a file as png or another type. The formidable filter option returns false. In this false case formidable.parse() method does not give the form error invalid file type. variable formError always return null or undefined even if filter is false.

 const allowedMimeTypes = ['application/pdf', 'application/msword', 'application/vnd.openxmlformats-officedocument.wordprocessingml.document'];

                const formData = new formidable.IncomingForm({
                    keepExtensions: true,
                    allowEmptyFiles: false,
                    multiples: false,
                    filter(part) {
                        if (part && part.mimetype) {
                            return allowedMimeTypes.includes(part.mimetype);
                        }
                        return false;
                    },
                    uploadDir: "uploads/resume",
                    filename(name, ext, part, form) {
                        var currentTimeStamp = Math.floor(Date.now() / 1000);
                        return `resume_${currentTimeStamp}${ext}`;
                    },
                });

return new Promise((accept, reject) => {

                    formData.parse(req, (fromError, fields, files) => {
                        try {
                            if (fromError) {
                                const { resume } = files;

                                if ((resume as unknown as PersistentFile)) {
                                    const fileDetail = JSON.parse(JSON.stringify(resume));
                                    if (fileDetail) {
                                        fs.rmSync(fileDetail.filepath, { force: true });
                                    }
                                }

                                const response: ApiResponse<undefined | null> = { status: false, message: fromError, data: null };
                                return reject(res.status(500).json(response));
                            }

                            const response: ApiResponse<undefined | null> = { status: true, message: "Success", data: null };
                            return accept(res.status(200).json(response));

                        } catch (exception) {
                            const { resume } = files;
                            if ((resume as unknown as PersistentFile)) {
                                const fileDetails = JSON.parse(JSON.stringify(resume));
                                if (fileDetails.lenght > 0) {
                                    fs.rmSync(fileDetails[0].filepath, { force: true });
                                }
                            }
                            // console.error(exception);
                            const response: ApiResponse<undefined | null> = { status: false, message: `${exception}`, data: null };
                            return reject(res.status(500).json(response));
                        }

                    });
                });

What was the result you got?

formData.parse(req, (fromError, fields, files) => {})

fromError always return null or undefined even if formData filter option returns false.

What result did you expect?

fromError returns a valid file type filter error.

[GrosSacASacs]

Behaves like Array.filter: Returning false will simply ignore the file and go to the next.

use form.emit('error') inside filter to make form.parse error (formData.emit('error') in your case)

[GrosSacASacs]

I also recommend you to slugify ext as it is user input and may contain invalid characters

                    return `resume_${currentTimeStamp}${slugify(ext)}`;