fileUpload() Middleware

fileUpload() provides Multer-style multipart handling on top of the Web Standard request.formData() API. If you've used Multer with Express, the API will feel immediately familiar.

Basic Usage

import { fileUpload } from '@rasenganjs/futon';
 
const upload = fileUpload({ limits: { fileSize: 5 * 1024 * 1024 } }); // 5 MB
 
router.post('/avatar', upload.single('avatar'), async (ctx) => {
  const file = ctx.get('file'); // UploadedFile
  return json({ size: file.size, name: file.originalname });
});

The Uploader Methods

fileUpload(options) returns an Uploader with five methods, each producing a Middleware:

const upload = fileUpload();
 
router.post(
  '/gallery',
  upload.fields([
    { name: 'cover', maxCount: 1 },
    { name: 'photos', maxCount: 10 },
  ]),
  async (ctx) => {
    const { cover, photos } = ctx.get('files');
    return json({ cover: cover?.[0]?.originalname, count: photos?.length });
  }
);

Non-file fields in the same multipart body become ctx.body — just like Multer's req.body.

UploadOptions

const upload = fileUpload({
  fileFilter: (ctx, info) => info.mimetype.startsWith('image/'),
});

Unlike Multer, a rejected file produces an explicit 400 FILE_FILTER_REJECTED response rather than silently skipping the file.

Error Responses

Every rejection returns JSON with an error code you can match on:

{
  "error": {
    "code": "LIMIT_FILE_SIZE",
    "message": "File \"photo.png\" exceeds the 5242880 byte limit."
  }
}

Validation Order and Rollback

Every part of the multipart body is validated before anything is stored — limits, unexpected fields, and fileFilter are all checked first. If a file fails to store partway through a multi-file batch, already-stored files are rolled back via the storage engine's removeFile().