Module: Abqari::SpeculationRulesGuard

Defined in:: lib/abqari/speculation_rules_guard.rb

Overview

Tiny inline <script> that respects user opt-outs from background prefetching/prerendering. Reads three signals; if any is on, the <script type="speculationrules"> block in the head gets removed before the browser acts on it:

1. `prefers-reduced-data: reduce` — CSS media query (Chrome
 supports it; Safari doesn't but treats it as no-match).
2. `navigator.connection.saveData` — JS flag set when the user
 has Save-Data on in their browser data settings.
3. (Implicit) `navigator.connection.effectiveType === 'slow-2g'`
 or `'2g'` — very slow connections get the same opt-out.

Stable single-line string so the SHA256 hash is constant across builds; HeadersFile adds the hash to the CSP script-src list so strict CSP still allows this one inline script.

Constant Summary collapse

SCRIPT =

"(function(){try{var c=navigator.connection;var saveData=c&&c.saveData;var slow=c&&(c.effectiveType==='slow-2g'||c.effectiveType==='2g');var reducedData=window.matchMedia&&window.matchMedia('(prefers-reduced-data: reduce)').matches;if(saveData||slow||reducedData){var s=document.getElementById('abqari-spec-rules');if(s)s.remove()}}catch(e){}})()"

SHA256 =

"sha256-#{Base64.strict_encode64(Digest::SHA256.digest(SCRIPT))}"