Next.js API route hangs (stays in pending state) when multer encounters a validation error

[abdullah-manafikhi]

Summary

Using multer for file uploads in a Next.js API route with bodyParser: false
When multer validation fails, the API call gets stuck in a pending state
The server logs show errors being caught, but responses aren't making it back to the client

// Configure multer for file uploads with image file type restrictions
const upload = multer({
  storage: multer.diskStorage({
    destination: imagesPath,
    filename: (req, file, cb) => {
      const uniqueSuffix = Date.now() + '-' + Math.round(Math.random() * 1e9);
      cb(null, file.fieldname + '-' + uniqueSuffix + path.extname(file.originalname));
    },
  }),
  fileFilter: (req, file, cb) => {
    // Only allow image file types
    const allowedFileTypes = ['image/jpeg', 'image/png', 'image/gif', 'image/webp', 'image/svg+xml'];

    if (allowedFileTypes.includes(file.mimetype)) {
      cb(null, true);
    } else {
      cb(new Error('File type not allowed. Only images (JPEG, PNG, GIF, WEBP, SVG) are permitted.'), false);
    }
  },
  limits: {
    fileSize: 5 * 1024 * 1024, // 5MB max image size
  },
});

export const config = {
  api: {
    bodyParser: false,
  },
};

export default async function handler(req, res) {
  // Using multer with Promise wrapper
  const multerUpload = () => {
    return new Promise((resolve, reject) => {
      upload.single('image')(req, res, function(err) {
        if (err) {
          console.error('Multer error:', err.message);
          // This response never makes it back to the client when multer fails
          return res.status(400).json({ error: 'Error message' });
        }
        resolve();
      });
    });
  };
  
  await multerUpload();
  // Rest of handler logic...
 
  return res.status(201).json(result);
}

Additional information

Looking for a reliable way to handle multer errors in Next.js API routes that properly sends responses back to the client and doesn't leave requests hanging in a pending state.

Example

No response