Serverless Worker Function for ASN prefix parsing for OPNsense and pfSense

asn.js

/***
 * Worker Function for ASN prefix parsing
 * Will query the BigIP API for a given ASN and return a plain-text representation of the ASN prefixes 
 * (IP ranges) that can be used in either OPNsense or pfSense URL Tables (Firewall alias).
 * 
 * See https://docs.opnsense.org/manual/aliases.html (OPNsense) and https://docs.netgate.com/pfsense/en/latest/firewall/aliases.html (pfSense) for details of their use.
 *
 * You can deploy this worker for example on the free tier of CloudFlare (Up to 100'000 requests a day) or 
 * any other serverless platform that supports JavaScript 
 *
 * See https://workers.cloudflare.com/
 * 
 * Inspired by http://asn.blawk.net/
 * Use: https://my-asn-worker.example.com/?asn=2906
 */

async function handleRequest(request) {
  const init = {
    headers: {
      'content-type': 'text/plain;charset=UTF-8',
    },
  }

  const url = request.url
  const bgpViewUrl = "https://api.bgpview.io/asn/" // API: https://bgpview.docs.apiary.io/
  
	// Function to parse query strings
	function getParameterByName(name) {
		name = name.replace(/[\[\]]/g, '\\$&')
		name = name.replace(/\//g, '')
		var regex = new RegExp('[?&]' + name + '(=([^&#]*)|&|#|$)'),
			results = regex.exec(url)

		if (!results) return null
		else if (!results[2]) return ''
		else if (results[2]) {
			results[2] = results[2].replace(/\//g, '')
		}
		
		return decodeURIComponent(results[2].replace(/\+/g, ' '));
	}

	// Usage example 
	var asn = getParameterByName('asn')
	
  if(asn) {
    const response = await fetch(bgpViewUrl + asn + "/prefixes", init);
    const results = await gatherResponse(response);

    if(results.status == "ok" ) {
            var prefixes = "; BGP View Sources list of ASN prefixes\n; https://bgpview.io\n; Generated by CloudFlare Worker " + url + "\n; Last-Modified: " + new Date();
      results.data.ipv4_prefixes.forEach(obj => {
        prefixes = prefixes + "\n" + obj.prefix + " ; " + obj.description + "(" + obj.country_code + ")"
      });
      return new Response(prefixes, init)
    } else {
      return new Response("ASN Prefix Error.\nPlease verify your ASN is correct.\nParsed ASN: " + asn, {status: 500})
    }
    
  } else {
    return new Response('', init)
  }

}
addEventListener('fetch', event => {
  return event.respondWith(handleRequest(event.request))
})
/**
 * gatherResponse awaits and returns a response body as a string.
 * Use await gatherResponse(..) in an async function to get the response body
 * @param {Response} response
 */
async function gatherResponse(response) {
  const { headers } = response
  const contentType = headers.get('content-type')
  if (contentType.includes('application/json')) {
    return await response.json()
  } else if (contentType.includes('application/text')) {
    return await response.text()
  } else if (contentType.includes('text/html')) {
    return await response.text()
  } else {
    return await response.text()
  }
}