Don't send webp to CriOS when there is no accept:image/webp

[jmarantz]

The latest Chrome on iOS, based on WKWebView, cannot render webp images, but mod_pagespeed sends them.

See http://blog.chromium.org/2016/01/a-faster-more-stable-chrome-on-ios.html

I confirmed that this browser also does not send accept:image/webp. If, in the future, webp is re-enabled in CriOS, it will likely send accept:image/webp again.

This is a workaround:

SetEnvIf User-Agent CriOS mps_disable_webp
RequestHeader set ModPagespeedFilters -convert_jpeg_to_webp env=mps_disable_webp

[jmarantz]

Note: a similar issue was found in #969

[jeffkaufman]

At this point maybe we should switch to a simple "send webp if and only if we get accept:webp"?

[jmarantz]

I agree with that, but that's a larger change (assuming we still want to send webp to Android 4.0) and want to do that in a follow-up.

[huibaolin]

Android browser supports WebP since 4.0 but doesn't have WebP header. It
still has ~11% market share totally in mobile and tablet [1]. It's not
clear what is the portion of 4.0+ in this 11%, however most likely it's not
trivial.

[1]
https://www.netmarketshare.com/browser-market-share.aspx?qprid=2&qpcustomd=1

On Thu, Jan 28, 2016 at 10:41 AM, Joshua Marantz notifications@github.com
wrote:

I agree with that, but that's a larger change (assuming we still want to
send webp to Android 4.0) and want to do that in a follow-up.

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Reply to this email directly or view it on GitHub
#1256 (comment)
.

[jmarantz]

It turns out we need to separately disable webp-lossless and webp-animated, so the full workaround is:

SetEnvIf User-Agent CriOS mps_disable_webp
RequestHeader set ModPagespeedFilters -convert_jpeg_to_webp,-convert_to_webp_lossless,-convert_to_webp_animated env=mps_disable_webp

[jmarantz]

More detailed workaround information for nginx and apache. None of this will be needed once we have 23947d0 in a release.

Apache & mod_pagespeed 1.10:
# Temporary workaround for
# #1256
SetEnvIf User-Agent CriOS mps_disable_webp
RequestHeader set ModPagespeedFilters -convert_jpeg_to_webp,-convert_to_webp_lossless,-convert_to_webp_animated env=mps_disable_webp

Nginx & ngx_pagespeed 1.10:
http {
pagespeed ProcessScriptVariables on;
server {
set $disable_filters "";
if ($http_user_agent ~ CriOS) {
set $disable_filters "convert_jpeg_to_webp,convert_to_webp_lossless,convert_to_webp_animated";
}
pagespeed DisableFilters "$disable_filters";
}
}

In 1.9, there is no convert_to_webp_animated filter, and the nginx variable support is not present in PageSpeed so you have to completely disable webp until we get you a patch.

Apache & mod_pagespeed 1.9:
# Temporary workaround for
# #1256
SetEnvIf User-Agent CriOS mps_disable_webp
RequestHeader set ModPagespeedFilters -convert_jpeg_to_webp,-convert_to_webp_lossless env=mps_disable_webp

Nginx & ngx_pagespeed 1.9:
http {
pagespeed DisableFilters "convert_jpeg_to_webp,convert_to_webp_lossless";
}