saibotsivad/fiddle-worker-stream-trailing-header

Attempting some trailing-header magic with HTTP 1.1 in Cloudflare Worker.

Trailing Headers

I had an idea that I could add some spicy functionality to an API if I could have the API send "headers" after all the body data was sent.

Dubious idea, but apparently in HTTP/3 you can have "trailing header frames" https://http3-explained.haxx.se/en/h3/h3-streams#http-response

After I found that, I was able to track down a similar idea in HTTP/1.1 https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Trailer

With that new-found knowledge, I wanted to make a little demo so I could see how it works in browsers and other CLI tools, e.g. cURL, and in particular I wanted to see how I could make it work in a Cloudflare Worker.

Summary

👎🚨⚠️ As far as I can tell Cloudflare is dropping the Trailer header, so this won't work.

Deploy

Copy the configuration example to your own file:

cp configuration.example.sh configuration.sh

Then go to the Cloudflare dashboard to generate a token, and set it in your configuration.sh file.

Finally, simply run npm run deploy

Cloudflare Setup

For a subdomain, you'll need to add an AAAA DNS record pointing to 100:: (the reserved IPv6 discard prefix).

That comes from the Cloudflare docs:

Subdomains must have a DNS Record

All subdomains must have a DNS record to be proxied on Cloudflare and used to invoke a Worker. For example, if you want to put a worker on myname.example.com, and you've added example.com to Cloudflare but have not added any DNS records for example.com, any request to myname.example.com will result in the error ERR_NAME_NOT_RESOLVED.

To support this, you should use the Cloudflare dashboard to add an AAAA record for myname to example.com, pointing to 100:: (the reserved IPv6 discard prefix).