suragu_org/tech_posts/brotli_in_openbsd_http.org

Brotli in OpenBSD's httpd

The modern web is heavy. My website is not heavy, but I still wanted to add compression because why not. Fortunately, compression algorithms exists. Some web servers send compressed versions of the file they serve, to serve bandwith, or to make the site load faster. There are other methods to serve bandwith like minimized CSS, HTML and JavaScript. But I think we can all agree that using a compression algorithm is a better way to accomplish this.

The main compression algorithm supported by browsers (and web servers) is gzip. A compression algorithm that has been with us since 1992. It's kinda old, but still serves its purpose pretty well. Especially when you use all of its power with the -9 flag. Which compresses the file way better. At the cost of slower speed of compression and decompression. But this isn't a big problem since the client isn't receiving large files, like more than 100MBs, the client is receiving HTMl, CSS and maybe JavaScript. Not binary files (compression is kinda counterproducent with binary files).

The OpenBSD httpd comes with the gzip-static option, you just add it wherever inside a server block in your httpd.conf. Then you cd to your webroot and run this command: gzip -9k *.html

-9 was explained before. And -k tells gzip not to delete the files after they have been compressed. As gzip deletes the original file. keeping only the .gz file.

This should be enough for most scenarios. gzip compresses files really well. But I wanted more. So I made some changes to the httpd source code to add brotli support.

At first. I wanted to add zstd support to httpd. And when I had everything done. curl was receiving the zstd files instead of the original files, I realized that browsers do not (yet) have zstd support. So I decided to use brotli instead. It wasn't that difficult to accomplish as I already wrote the hard part. I only had to replace "zstd" with "br".

This isn't done automatically. If you currently have gzip-static on your httpd configuration. You must replace it with br-static. And then you have to remove all the .gz files in your webroot (as they aren't needed anymore). Then you can read the brotli manpage to learn how to use brotli. But I wanted maximum compression. So this command was enough: brotli --max --keep *.xhtml.

You can download the patch here.