A simple Worker to display Cloudflare headers

This post shows how to create a simple worker that displays Cloudflare headers.

1. Create a new project using wrangler wrangler init cf-header.

2. Using your preferred code editor, modify ./src/index.ts as follows.

   Note: The Cloudflare Request interface is documented here: Request.

    /**
     * Welcome to Cloudflare Workers! This is your first worker.
    *
    * - Run `wrangler dev src/index.ts` in your terminal to start a development server
    * - Open a browser tab at http://localhost:8787/ to see your worker in action
    * - Run `wrangler publish src/index.ts --name my-worker` to publish your worker
    *
    * Learn more at https://developers.cloudflare.com/workers/
    */
   
    export default {
      async fetch(request: Request): Promise<Response> {
        // Cloudflare Properties
        const CfProperties = request.cf
   
        // Request Headers
        var reqHeaders: any = {}
        for (const key of request.headers.keys()) {
          let a = key.toString()
          reqHeaders[key] = request.headers.get(key)
        }
   
        return new Response(JSON.stringify({
          "CfProperties": CfProperties,
          "RequestHeaders": reqHeaders
        }, null, 2));
      },
    };
   

3. Test and Publish your worker using wrangler dev and wrangler publish.

4. To see all Cloudflare headers, you need to add a custom domain to the Worker. You do this in the Cloudflare dashboard > Account Home > Workers > your Worker > Triggers > Custom Domains.

5. Navigate to the worker cf-header.yourdomain. The output will look like the following.

    {
      "CfProperties": {
        "clientTcpRtt": 7,
        "longitude": "<redacted>",
        "latitude": "<redacted>",
        "tlsCipher": "AEAD-AES128-GCM-SHA256",
        "continent": "OC",
        "asn": "<redacted>",
        "clientAcceptEncoding": "gzip, deflate, br",
        "country": "AU",
        "tlsClientAuth": {
          "certIssuerDNLegacy": "",
          "certIssuerSKI": "",
          "certSubjectDNRFC2253": "",
          "certSubjectDNLegacy": "",
          "certFingerprintSHA256": "",
          "certNotBefore": "",
          "certSKI": "",
          "certSerial": "",
          "certIssuerDN": "",
          "certVerified": "NONE",
          "certNotAfter": "",
          "certSubjectDN": "",
          "certPresented": "0",
          "certRevoked": "0",
          "certIssuerSerial": "",
          "certIssuerDNRFC2253": "",
          "certFingerprintSHA1": ""
        },
        "tlsExportedAuthenticator": {
          "clientFinished": "80da6df49bf69e60c64e9ec5ccacc6ea8e0f607918b4d1245561074da70fda15",
          "clientHandshake": "a74a7f73f879d5235ba754e9732f6d5acdc7fb1fce50c16c1d60a3b27dbe85a1",
          "serverHandshake": "0eea3a4aacf97bd0cef7c0a6a693b691d8c03de44ae0d526ee66c182ea38d1c6",
          "serverFinished": "078ce079e5bc5b4349fc51cdbb218d53097b5dc1c9cdda15645e951bf5c4d3f1"
        },
        "tlsVersion": "TLSv1.3",
        "colo": "SYD",
        "timezone": "Australia/Sydney",
        "city": "<redacted>",
        "httpProtocol": "HTTP/2",
        "edgeRequestKeepAliveStatus": 1,
        "requestPriority": "weight=256;exclusive=1",
        "botManagement": {
          "corporateProxy": false,
          "verifiedBot": false,
          "ja3Hash": "cd08e31494f9531f560d64c695473da9",
          "staticResource": false,
          "score": 99
        },
        "clientTrustScore": 99,
        "region": "<redacted>",
        "regionCode": "<redacted>",
        "asOrganization": "<redacted>",
        "postalCode": "<redacted>"
      },
      "RequestHeaders": {
        "accept": "text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,image/apng,*/*;q=0.8,application/signed-exchange;v=b3;q=0.9",
        "accept-encoding": "gzip",
        "accept-language": "en-US,en;q=0.9",
        "cf-connecting-ip": "<redacted>",
        "cf-ipcountry": "AU",
        "cf-ray": "7638d33dbc15a894",
        "cf-visitor": "{\"scheme\":\"https\"}",
        "connection": "Keep-Alive",
        "cookie": "__cf_bm=mmJ0FiLNxEKkKnwCBFcTwzeEyLxiV56m4ox4mqCNaIg-1667348698-0-ARj47UomevLNr4fnqvMYKwHAUJmdkrmwdtbi3tyHBmx3Q6FnLaoElIZDR73IXfHp9toaW34oDqtl8OnO8k2bphDyhjluTfI/KfqwT/qYkts4GRcJKnpY7aNZHWsaIF4GhaIvVZn2F+NK0KDQXpwfES7tiwLN8/WpUcqQJ0ZlcRQl",
        "host": "cf-headers.<redacted>",
        "sec-ch-ua": "\"Chromium\";v=\"106\", \"Google Chrome\";v=\"106\", \"Not;A=Brand\";v=\"99\"",
        "sec-ch-ua-mobile": "?0",
        "sec-ch-ua-platform": "\"macOS\"",
        "sec-fetch-dest": "document",
        "sec-fetch-mode": "navigate",
        "sec-fetch-site": "none",
        "sec-fetch-user": "?1",
        "upgrade-insecure-requests": "1",
        "user-agent": "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/106.0.0.0 Safari/537.36",
        "x-forwarded-proto": "https",
        "x-real-ip": "<redacted>"
      }
    }