Use FormData in an HTTP Response in Deno/Oak

I know that I can create a FormData in the client and send it to the server (in this case I'm using Deno/Oak), and read it from there.

But is this possible vice versa?

If I have a route in Oak, and I want it to send a multipart response (with one or more blobs, and with one or more strings), how can I do it?

Oak's automatic response body handling supports FormData so you can set context.response.body to an instance of FormData and Oak will take care of the rest. e.g.:

import { Application } from "https://deno.land/x/oak@v9.0.0/mod.ts";

const app = new Application();

app.use((ctx) => {
  const data = new FormData();
  data.append("string1", "Hi");
  data.append("string2", "Bye");
  data.append("blob1", new Blob(['<a id="a">Hi</a>'], { type: "text/xml" }));
  data.append("blob2", new Blob(['<b id="b">Bye</b>'], { type: "text/xml" }));
  ctx.response.body = data;
});

await app.listen({ port: 8000 });

% curl localhost:8000
------7115155097707325061106360125
Content-Disposition: form-data; name="string1"

Hi
------7115155097707325061106360125
Content-Disposition: form-data; name="string2"

Bye
------7115155097707325061106360125
Content-Disposition: form-data; name="blob1"; filename="blob"
Content-Type: text/xml

<a id="a">Hi</a>
------7115155097707325061106360125
Content-Disposition: form-data; name="blob2"; filename="blob"
Content-Type: text/xml

<b id="b">Bye</b>
------7115155097707325061106360125--

The same can be done directly in Deno without any additional framework:

const server = Deno.listen({ port: 8000 });

for await (const conn of server) serveHttp(conn);

async function serveHttp(conn: Deno.Conn) {
  const httpConn = Deno.serveHttp(conn);
  for await (const requestEvent of httpConn) {
    const data = new FormData();
    data.append("string1", "Hi");
    data.append("string2", "Bye");
    data.append("blob1", new Blob(['<a id="a">Hi</a>'], { type: "text/xml" }));
    data.append("blob2", new Blob(['<b id="b">Bye</b>'], { type: "text/xml" }));
    requestEvent.respondWith(new Response(data));
  }
}