PERF: Improve `Accept` header handling for stylesheets and theme-js (#19357)

The default behavior for Rails is to vary the response of an endpoint based on the `Accept:` header, and therefore it returns a `Vary:` header on responses. This instructs browsers and intermediate proxies to key their caches based on the value of the request's `Accept` header. In some cases (e.g. Akamai), the presence of a `Vary` header is enough to prevent caching entirely.

This commit restructures the Rails route definitions so that:
1. The "format" segment of the route is 'required'
2. The "format" segment of the route is constrained to a single value (e.g. `js` or `css`)

Now that the routes are guaranteed to have a `:format` segment, Rails will always prioritize that over the `Accept` header, and will therefore omit the `Vary` header.

Request specs are also added to test this behaviour for both stylesheets and theme-javascripts.
This commit is contained in:
David Taylor 2022-12-07 15:46:35 +00:00 committed by GitHub
parent fc22790405
commit 1db3a578e4
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3 changed files with 47 additions and 4 deletions

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@ -561,11 +561,11 @@ Discourse::Application.routes.draw do
get "highlight-js/:hostname/:version.js" => "highlight_js#show", constraints: { hostname: /[\w\.-]+/, format: :js }
get "stylesheets/:name.css.map" => "stylesheets#show_source_map", constraints: { name: /[-a-z0-9_]+/ }
get "stylesheets/:name.css" => "stylesheets#show", constraints: { name: /[-a-z0-9_]+/ }
get "stylesheets/:name" => "stylesheets#show_source_map", constraints: { name: /[-a-z0-9_]+/, format: /css\.map/ }, format: true
get "stylesheets/:name" => "stylesheets#show", constraints: { name: /[-a-z0-9_]+/, format: "css" }, format: true
get "color-scheme-stylesheet/:id(/:theme_id)" => "stylesheets#color_scheme", constraints: { format: :json }
get "theme-javascripts/:digest.js" => "theme_javascripts#show", constraints: { digest: /\h{40}/ }
get "theme-javascripts/:digest.map" => "theme_javascripts#show_map", constraints: { digest: /\h{40}/ }
get "theme-javascripts/:digest" => "theme_javascripts#show", constraints: { digest: /\h{40}/, format: :js }, format: true
get "theme-javascripts/:digest" => "theme_javascripts#show_map", constraints: { digest: /\h{40}/, format: :map }, format: true
get "theme-javascripts/tests/:theme_id-:digest.js" => "theme_javascripts#show_tests"
post "uploads/lookup-metadata" => "uploads#metadata"

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@ -59,6 +59,30 @@ RSpec.describe StylesheetsController do
expect(response.status).to eq(200)
end
it 'ignores Accept header and does not include Vary header' do
StylesheetCache.destroy_all
manager = Stylesheet::Manager.new(theme_id: nil)
builder = Stylesheet::Manager::Builder.new(target: 'desktop', manager: manager, theme: nil)
builder.compile
digest = StylesheetCache.first.digest
get "/stylesheets/desktop_#{digest}.css"
expect(response.status).to eq(200)
expect(response.headers["Content-Type"]).to eq("text/css")
expect(response.headers["Vary"]).to eq(nil)
get "/stylesheets/desktop_#{digest}.css", headers: { "Accept" => "text/html" }
expect(response.status).to eq(200)
expect(response.headers["Content-Type"]).to eq("text/css")
expect(response.headers["Vary"]).to eq(nil)
get "/stylesheets/desktop_#{digest}.css", headers: { "Accept" => "invalidcontenttype" }
expect(response.status).to eq(200)
expect(response.headers["Content-Type"]).to eq("text/css")
expect(response.headers["Vary"]).to eq(nil)
end
describe "#color_scheme" do
it 'works as expected' do
scheme = ColorScheme.last

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@ -75,6 +75,25 @@ RSpec.describe ThemeJavascriptsController do
//# sourceMappingURL=#{digest}.map?__ws=test.localhost
JS
end
it "ignores Accept header and does not return Vary header" do
js_cache_url = "/theme-javascripts/#{javascript_cache.digest}.js"
get js_cache_url
expect(response.status).to eq(200)
expect(response.headers["Content-Type"]).to eq("text/javascript")
expect(response.headers["Vary"]).to eq(nil)
get js_cache_url, headers: { "Accept" => "text/html" }
expect(response.status).to eq(200)
expect(response.headers["Content-Type"]).to eq("text/javascript")
expect(response.headers["Vary"]).to eq(nil)
get js_cache_url, headers: { "Accept" => "invalidcontenttype" }
expect(response.status).to eq(200)
expect(response.headers["Content-Type"]).to eq("text/javascript")
expect(response.headers["Vary"]).to eq(nil)
end
end
describe "#show_map" do