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EXPERIMENTAL: preconnect and dns-prefetch resource hints for CDN domains (#26215)

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Why this change?

In https://web.dev/articles/preconnect-and-dns-prefetch, it describes
how hinting to the browser to preconnect to domains which we will
eventually use the connection for can help improve the time it takes to
load a page.

We are putting this behind an experimental flag so that we can test and
profile this in a production environment.

What does this change introduce?

Introduce a hidden experimental `experimental_preconnect_link_header`
site setting which when enabled will add the `preconnect` and
`dns-prefetch` resource hints to the response headers for full page load
requests.
This commit is contained in:
Alan Guo Xiang Tan
2024-03-18 13:45:41 +08:00
committed by GitHub
parent d5b944f1de
commit 36cdb1444c
4 changed files with 58 additions and 8 deletions
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27
app/controllers/application_controller.rb
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@ -53,7 +53,7 @@ class ApplicationController < ActionController::Base
after_action :add_noindex_header_to_non_canonical, if: :spa_boot_request?
after_action :set_cross_origin_opener_policy_header, if: :spa_boot_request?
after_action :clean_xml, if: :is_feed_response?
around_action :link_preload, if: -> { spa_boot_request? && GlobalSetting.preload_link_header }
around_action :add_link_header, if: -> { spa_boot_request? }
HONEYPOT_KEY ||= "HONEYPOT_KEY"
CHALLENGE_KEY ||= "CHALLENGE_KEY"
@ -1096,10 +1096,29 @@ class ApplicationController < ActionController::Base
result
end
def link_preload
@links_to_preload = []
def add_link_header
@links_to_preload = [] if GlobalSetting.preload_link_header
yield
response.headers["Link"] = @links_to_preload.join(", ") if !@links_to_preload.empty?
links = []
if SiteSetting.experimental_preconnect_link_header
[GlobalSetting.cdn_url, SiteSetting.s3_cdn_url].each do |url|
next if url.blank?
base_url = URI.join(url, "/").to_s.chomp("/")
links.push("<#{base_url}>; rel=preconnect;")
# Not all browsers support the preconnect resource hint so we are adding dns-prefetch as the fallback
links.push("<#{base_url}>; rel=dns-prefetch;")
end
end
if GlobalSetting.preload_link_header && !@links_to_preload.empty?
links = links.concat(@links_to_preload)
end
response.headers["Link"] = links.join(", ") if links.present?
end
def spa_boot_request?