ERR_SPDY_PROTOCOL_ERROR and Brotli Content-Encoding

Hello, we are using Cloudflare as a cdn for our static assets origined in Amazon S3, for more than 5 months now.

Until now we didin’t have any issues. Since last Friday (13/7), a static js file we serve through cloudlare started showing ERR_SPDY_PROTOCOL_ERROR in chrome console. We noticed that on Monday. That event caused us a huge drop to our metrics and serving features!

We tried various solutions - as those mentioned here - but we din’t have any result.

We noticed that this error was caused only from https (secure) sites calling our js library. Our library is gziped and stored in origin (Amazon S3) with the Content-Encoding: gzip header. We have concluded that our js library was served by CF with Brotli header although we have set the gzip header.

Why CF was serving our files with br encoding, instead of the gzip? This was the reason that our library couldn’t be properly decoded and run in the browser.

We checked the Brotli settings (throught the API) in our zone and was set to “on”. Is this the default? and why until now we didn’t have any similar issue on https sites that use our library?

When we change the zone Brotli settings to “off” the library was being served with the gzip encoding and stopped showing the ERR_SPDY_PROTOCOL_ERROR

There were any update from your side, that changed something, because we were using the default free plan for our account without any custom changes?

What other check we can do in order to be safe not to have any issues again?

And one final question, if there was a change from your site, is there any way of getting updates on your service changes?


Hi there,

This sounds unusual - would you mind dropping a line in to Support with the URL where you were seeing this? You can e-mail them via [email protected] and reference this thread if you prefer.


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