Bun mime middleware

mime.ts

import mimes from "mime";

type RequestHandler = (req: Request) => Promise<Response>;

export function middleware(fetch: RequestHandler): RequestHandler {
  return async (req) => {
    if (req.method !== "GET") {
      return fetch(req);
    }

    const response = await fetch(req);

    if (response.status !== 200) {
      return response;
    }

    const contentTypeAlereadySet =
      response.headers.get("Content-Type") !== null;
    if (contentTypeAlereadySet) {
      return response;
    }

    const path = new URL(req.url).pathname;
    const extension = path.split(".").at(-1);
    if (extension === undefined) {
      return response;
    }

    const mimeType = mimes.getType(extension);
    if (mimeType === null) {
      return response;
    }

    response.headers.set("Content-Type", mimeType);

    return response;
  };
}