2016 Brotli Update

Windows 10 Build 14986 adds support for Brotli compression to the Edge browser (but, somewhat surprisingly, not IE11). So at the end of 2016, we now have support for this improved compression algorithm in Chrome, Firefox, Edge, Opera, Brave, Vivaldi, and the long tail of browsers based on Chromium. Of modern browsers, only Apple is a holdout, with a “Radar” feature request logged against Safari but no public announcements.

Unfortunately, behavior across browsers varies at the edges:

  • Edge advertises support for and decodes Brotli compression on both HTTP and HTTPS requests.
  • Chrome advertises Brotli for HTTPS connections but will decode Brotli for both HTTPS and HTTP responses.
  • Firefox advertises Brotli for HTTPS connections and will not decode Brotli responses on HTTP responses.

There’s nothing horribly broken here: sites can safely serve Brotli content to clients that ask for it and those clients will probably decode it. The exception is when the request goes over HTTP… the reason Firefox and Chrome limit their request for Brotli to HTTPS is that, historically, middleboxes (like proxies and gateway filters) have been known to corrupt compression schemes other than gzip and deflate. This proved to be such a big problem in the rollout of SDCH (a now defunct compression algorithm Chrome supported), that the Brotli implementers decided to try to avoid the issue by requiring a secure transport.

-Eric

PS: Major sites, including Facebook and Google, have started deploying Brotli in production– if your site pulls fonts from Google Fonts, you’re already using Brotli today! In unrelated news, the 2016 Performance Calendar includes a post on serving Brotli from CDNs that don’t explicitly support it yet. Another recent post shows how to pair maximal compression for static files with fast compression for dynamically generated responses.

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