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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.
/icons/typescript.svgindex.ts
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.
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().
/icons/typescript.svgindex.ts
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
		if (url.pathname === '/action') {
			const formdata = await req.formData(); 
			const name = formdata.get('name'); 
			const profilePicture = formdata.get('profilePicture'); 
			if (!profilePicture) throw new Error('Must upload a profile picture.'); 
			// write profilePicture to disk
			await Bun.write('profilePicture.png', profilePicture); 
			return new Response('Success'); 
		} 

		return new Response('Not Found', {status: 404});
	},
});
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