Beware: GZIP + Brotli

[goaround]

Some client (Google Search Console + Google Crawler probably) have problems decoding with Brotli compressed gzip-files. If Brotli is active on the server.

At the moment the rocket-nginx.conf just checks if the client accept gzip and than serves the _gzip-file which will compressed again with Brotli:
# Is GZIP accepted by client ?
if ($http_accept_encoding ~ gzip) {
set $rocket_encryption "_gzip";
}

For this reason I check if the client accept Brotli and unset $rocket_encryption:
# Is Brotli accepted by client ?
if ($http_accept_encoding ~ br) {
set $rocket_encryption "";
}

[maximejobin]

Do you know what is the priority order and how it's set when both gzip and Brotli are active?

Thank you for letting me know.

[goaround]

Nginx takes the gzip-file and compresses it again with Brotli on the fly.
That works with modern browsers nevertheless but some google tools and I guess the google bot, too have problems with it.

[maximejobin]

My understanding was that it was an alternative to GZIP. Not that it used the GZIP file and used Brotli after it. I did not see that in the documentation.

Can you educate me on your sources? That way, I can code it properly.

[goaround]

It is an alternative to GZIP.
I think the problem is, rocket-nginx serves the gzip-file and Nginx don't know that the the file is gzip-compressed and compresses it again with Brotli.

With $http_accept_encoding ~ gzip you only check if the client accept gzip but it can accept br, too.

I let Google render a few pages without the check if the client accept br :

He took the gzip-file and the "Content-Encoding" says br

[maximejobin]

Ok, I get what you mean.

My main concern now is: when GZIP and BR are acceptable encoding, how do I ask Nginx (via the configuration file I made) what is the encoding that it will use ? Then, if it's "BR", the code suggestion you did make sense. If it's GZIP, we can use the code as is.

The question remains: when both are available, how can I know which one did Nginx pick ?

This is what I need to figure.

[goaround]

I think if Brotli is active and the client accept it, it will take brotli.

[maximejobin]

I understand. Now, I need a confirmation of that behaviour. :-)