--- title: "How to Parse Multipart Form Data with Netlify Functions" description: "In this post, we‘ll cover learned what multipart/form-data is, how it can be parsed using busboy, and how that ties in to Netlify Functions." source: "https://www.netlify.com/blog/2021/07/29/how-to-process-multipart-form-data-with-a-netlify-function/" last_updated: "2026-07-10T19:44:12.000Z" --- If you’ve ever built a file upload into your website, you might have come across the `multipart/form-data` encoding. It’s the encoding browsers use for forms with file inputs in them, and it’s also notoriously uncomfortable to work with. Netlify gives you speedy access to [built in form handling](https://www.netlify.com/products/forms/). But you can also have your forms submit to serverless functions, which can be helpful when working with backend services. This post will help you understand a related area of complexity: multi-part form data, and how to process it inside a [Netlify Function](https://www.netlify.com/products/functions/). ## What’s `multipart/form-data`, anyway? Most forms are well-suited by the `urlencoded` encoding. You may have come across it, it’s the one with where form fields are separated by `?` and `&`: ``` ?favourite_food=sushi&preorder_for=tonight&guests=4 ``` This doesn’t work well for file uploads though, since a file need some more context: The filename, its mime type and the actual contents. If we add a file upload field to our form and change the encoding to `multipart/form-data` , this is how the payload looks: ``` ------WebKitFormBoundary8TPJmPk86DOKFN5aContent-Disposition: form-data; name="favourite_food" sushi------WebKitFormBoundary8TPJmPk86DOKFN5aContent-Disposition: form-data; name="preorder_for" tonight------WebKitFormBoundary8TPJmPk86DOKFN5aContent-Disposition: form-data; name="guests" 4------WebKitFormBoundary8TPJmPk86DOKFN5aContent-Disposition: form-data; name="company_logo"; filename="some_logo.svg"Content-Type: image/svg+xml ------WebKitFormBoundary8TPJmPk86DOKFN5a-- ``` As you can see, every form field is transferred individually, separated by the `----WebKitFormBoundaryzt0ANlA4AJJAzE3w` boundary. You can also see that the part with our file contains some additional information: The filename and the file type! 🎉 There’s some performance considerations between `multipart/form-data` and `urlencoded` that are elaborated on [in this RFC](https://www.rfc-editor.org/rfc/rfc2388#section-5.2). Just know that generally, you should use `multipart/form-data` for forms with file inputs and `urlencoded` for everything else. ## Parsing `multipart/form-data` inside a Netlify Function While you certainly could build a parser for the above format yourself, this is the kind of task that’s better left to a well-optimised library. We like to use [busboy](https://github.com/mscdex/busboy), which is a high-performance parser that’s also used internally by popular Express package `multer`. Here’s a snippet that implements the parsing logic: ``` import * as Busboy from "busboy" function parseMultipartForm(event) { return new Promise((resolve) => { // we'll store all form fields inside of this const fields = {}; // let's instantiate our busboy instance! const busboy = new Busboy({ // it uses request headers // to extract the form boundary value (the ----WebKitFormBoundary thing) headers: event.headers }); // before parsing anything, we need to set up some handlers. // whenever busboy comes across a file ... busboy.on( "file", (fieldname, filestream, filename, transferEncoding, mimeType) => { // ... we take a look at the file's data ... filestream.on("data", (data) => { // ... and write the file's name, type and content into `fields`. fields[fieldname] = { filename, type: mimeType, content: data, }; }); } ); // whenever busboy comes across a normal field ... busboy.on("field", (fieldName, value) => { // ... we write its value into `fields`. fields[fieldName] = value; }); // once busboy is finished, we resolve the promise with the resulted fields. busboy.on("finish", () => { resolve(fields) }); // now that all handlers are set up, we can finally start processing our request! busboy.write(event.body); });} ``` This snippet is not the easiest thing in the world, and if you don’t get everything that’s going on - no worries. This uses Node.js Streams, which is super fast (even when used outside of Netlify Functions), and that it returns a promise of your form values. To use it, call it with your Netlify Function Event: ``` // netlify/functions/restaurantReservationEndpointmodule.exports.handler = async (event, context) => { const fields = await parseMultipartForm(event) fields.favourite_food // "sushi" fields.company_logo // { filename: "some_logo.svg", type: "image/svg+xml", content: Buffer([...]) } ...} ``` Now that you have the file, you can do whatever you want with it! Do image processing, write into a database, send it to another API … the possibilities are endless. ## Conclusion In this post, you learned what `multipart/form-data` is, how it can be parsed using busboy, and how that ties in to Netlify Functions. Got more questions? Come on over to [answers.netlify.com](https://answers.netlify.com)! ### Share - [X (fka Twitter)](https://twitter.com/intent/tweet?text=How to Process Multipart Form Data with a Netlify Function&url=https://www.netlify.com/blog/2021/07/29/how-to-process-multipart-form-data-with-a-netlify-function//) - [LinkedIn](https://www.linkedin.com/shareArticle?mini=true&url=https%3A%2F%2Fwww.netlify.com%2Fblog%2F2021%2F07%2F29%2Fhow-to-process-multipart-form-data-with-a-netlify-function%2F%2F) - [Facebook](https://www.facebook.com/sharer.php?u=https://www.netlify.com/blog/2021/07/29/how-to-process-multipart-form-data-with-a-netlify-function//) - [Bluesky](https://bsky.app/intent/compose?text=How to Process Multipart Form Data with a Netlify Function+https://www.netlify.com/blog/2021/07/29/how-to-process-multipart-form-data-with-a-netlify-function//) * * * ### Tags - [Forms](/blog/tags/forms/) - [Netlify forms](/blog/tags/netlify-forms/) - [guide](/blog/tags/guide/) - [Functions](/blog/tags/functions/) - [Netlify Functions](/blog/tags/netlify-functions/) ## Keep reading ![](/images/blog-fallback-thumbnail.svg) Guides & Tutorials September 14, 2018 [ ### Forms and Functions ](/blog/2018/09/14/forms-and-functions/) - ![Profile picture of Netlify team](/_astro/2ded7a52db41c7613be0baa648ac9bf9c1e8a985-300x300_DNhVu.svg) Netlify team ![](/images/blog-fallback-thumbnail.svg) Guides & Tutorials July 21, 2021 [ ### How to use event-triggered Netlify Functions ](/blog/2021/07/21/how-to-use-event-triggered-netlify-functions/) - ![Profile picture of Charlie Gerard](/_astro/62135565aa5522e47233c7bfac5d3c145ed33056-80x80_ZHxG3a.webp) Charlie Gerard ## Recent posts News & Announcements June 25, 2026 [ ### Netlify Functions, designed for Agent Experience ](/blog/netlify-functions-designed-for-agent-experience) - ![Profile picture of Eduardo Bouças](/_astro/52958f21e8450baf6d8e60302341a984e220c0cd-512x512_13VDlu.webp) Eduardo Bouças News & Announcements June 24, 2026 [ ### How we measure Netlify’s Agent Experience ](/blog/how-we-measure-netlify-agent-experience) - ![Profile picture of Sean Roberts](/_astro/bbf2243f8171dbddd80ab2103622106cef84d125-512x512_Z1d2LKE.webp) Sean Roberts Guides & Tutorials May 15, 2026 [ ### How to build a real-time AI chatbot in minutes with Netlify Agent Runners (no backend) ](/blog/how-to-build-a-real-time-ai-chatbot-in-minutes-with-netlify-agent-runners-no-backend) - ![Profile picture of Nahrin Jalal](/_astro/f0e7c8f227a03fe58340c99ef5439d5a896c0733-272x272_Z23kDpD.webp) Nahrin Jalal ![](/_astro/3f255b372fa958df35802666ee33b4609b2d71bd-1200x1586_1VtE2D.webp) ### How do the best dev and marketing teams work together? 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