simple cf worker to proxy jellyfin plugin repository

worker.js

export default {
  async fetch(request, env, ctx) {
    ctx.passThroughOnException();
    const url = new URL(request.url);
    const uri = url.pathname.slice(1);
    if (request.method != "GET" || uri.length < 3 || uri.indexOf('.') == -1 || uri == "favicon.ico" || uri == "robots.txt") {
      return new Response('', { status: 405 })
    } else {
      if (!uri.startsWith('http')) uri = 'https://' + uri;
      if (uri.endsWith('/manifest.json')) {
        return proxyJson(uri, request);
      } else {
        return proxyRequest(uri, request)
      }
    }
  }
}
async function proxyRequest(url, request) {
  let init = {
    method: request.method,
    headers: {}
  };
  // Only pass through a subset of headers
  const proxyHeaders = ["Accept",
                        "Accept-Encoding",
                        "Accept-Language",
                        "Referer",
                        "User-Agent"];
  for (let name of proxyHeaders) {
    let value = request.headers.get(name);
    if (value) {
      init.headers[name] = value;
    }
  }
  // Add an X-Forwarded-For with the client IP
  const clientAddr = request.headers.get('cf-connecting-ip');
  if (clientAddr) {
    init.headers['X-Forwarded-For'] = clientAddr;
  }

  const response = await fetch(url, init);
  if (response) {
    const responseHeaders = ["Content-Type",
                             "Cache-Control",
                             "Expires",
                             "Accept-Ranges",
                             "Date",
                             "Last-Modified",
                             "ETag"];
    // Only include a strict subset of response headers
    let responseInit = {status: response.status,
                        statusText: response.statusText,
                        headers: {}};
    for (let name of responseHeaders) {
      let value = response.headers.get(name);
      if (value) {
        responseInit.headers[name] = value;
      }
    }
    // Add some security headers to make sure there isn't scriptable content
    // being proxied.
    responseInit.headers['X-Content-Type-Options'] = "nosniff";
    const newResponse = new Response(response.body, responseInit);
    return newResponse;
  }

  return response;
}
async function proxyJson(url, request) {
  let manifest = await fetchCSS(url, request)
  if (manifest) {
    const responseInit = {headers: {
      "Content-Type": "text/json; charset=utf-8",
      "Cache-Control": "private, max-age=86400, stale-while-revalidate=604800"
    }};
    const newResponse = new Response(manifest, responseInit);
    return newResponse;
  } else {
    // Do a straight-through proxy as fallback
    return proxyRequest(url, request);
  }
}
async function fetchCSS(url, request) {
  let jsonText = "";
  let headers = {'Referer': request.url};
  const clientAddr = request.headers.get('cf-connecting-ip');
  if (clientAddr) {
    headers['X-Forwarded-For'] = clientAddr;
  }
  headers['User-Agent'] = request.headers.get('user-agent') ?? "Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 6.0; Trident/4.0)";

  try {
    const response = await fetch(url, {headers: headers});
    if (response && response.status === 200) {
      jsonText = await response.text();

      jsonText = jsonText.replace(/(?<![\/:])(https?:)?\/\/([a-z]+\.)?github[a-z]*\.com\//mgi, 'https://mirror.ghproxy.com/$&');
    }
  } catch(e) {
    // Ignore the exception
  }
  return jsonText;
}