jarle/Bun Upload files via HTTP using FormData
skills/bun-guides-http-file-uploads/SKILL.md
Upload files via HTTP using FormData
$ install --global
skillsauthnpx skillsauth add jarle/bun-skills Bun Upload files via HTTP using FormDataInstall this skill globally with one command. Works with Claude Code, Cursor, and Windsurf.
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SKILL.md
- name:
- Bun Upload files via HTTP using FormData
- description:
- Upload files via HTTP using FormData
Upload files via HTTP using FormData
To upload files via HTTP with Bun, use the FormData API. Let's start with a HTTP server that serves a simple HTML web form.
const server = Bun.serve({
port: 4000,
async fetch(req) {
const url = new URL(req.url);
// return index.html for root path
if (url.pathname === "/")
return new Response(Bun.file("index.html"), {
headers: {
"Content-Type": "text/html",
},
});
return new Response("Not Found", { status: 404 });
},
});
console.log(`Listening on http://localhost:${server.port}`);
We can define our HTML form in another file, index.html.
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8" />
<title>Form</title>
</head>
<body>
<form action="/action" method="post" enctype="multipart/form-data">
<input type="text" name="name" placeholder="Name" />
<input type="file" name="profilePicture" />
<input type="submit" value="Submit" />
</form>
</body>
</html>
At this point, we can run the server and visit localhost:4000 to see our form.
bun run index.ts
Listening on http://localhost:4000
Our form will send a POST request to the /action endpoint with the form data. Let's handle that request in our server.
First we use the .formData() method on the incoming Request to asynchronously parse its contents to a FormData instance. Then we can use the .get() method to extract the value of the name and profilePicture fields. Here name corresponds to a string and profilePicture is a Blob.
Finally, we write the Blob to disk using Bun.write().
const server = Bun.serve({
port: 4000,
async fetch(req) {
const url = new URL(req.url);
// return index.html for root path
if (url.pathname === "/")
return new Response(Bun.file("index.html"), {
headers: {
"Content-Type": "text/html",
},
});
// parse formdata at /action // [!code ++]
if (url.pathname === "/action") { // [!code ++]
const formdata = await req.formData(); // [!code ++]
const name = formdata.get("name"); // [!code ++]
const profilePicture = formdata.get("profilePicture"); // [!code ++]
if (!profilePicture) throw new Error("Must upload a profile picture."); // [!code ++]
// write profilePicture to disk // [!code ++]
await Bun.write("profilePicture.png", profilePicture); // [!code ++]
return new Response("Success"); // [!code ++]
} // [!code ++]
return new Response("Not Found", { status: 404 });
},
});
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