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Prevent page caches from storing content-negotiation redirect #31

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Prevent page caches from storing content-negotiation redirect #31

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16 changes: 16 additions & 0 deletions src/Router/RewriteHandler.php
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Original file line number Diff line number Diff line change
Expand Up @@ -372,6 +372,22 @@ public function handle_accept_negotiation(): void {
return;
}

// Prevent shared caches (CDNs, reverse proxies) that don't honour
// Vary from storing this content-negotiation redirect and serving
// the 303 to every visitor regardless of their Accept header.
header('Cache-Control: private');

// Many WordPress page-cache plugins cache at the PHP level and may
// not vary by the Accept request header. Tell them explicitly not to
// cache this response. Sites with Vary-aware caching can disable this:
// add_filter( 'markdown_alternate_disable_page_cache_on_redirect', '__return_false' );
if ( apply_filters( 'markdown_alternate_disable_page_cache_on_redirect', true ) ) {
if ( ! defined( 'DONOTCACHEPAGE' ) ) {
define( 'DONOTCACHEPAGE', true );
}
do_action( 'litespeed_control_set_nocache', 'Content negotiation redirect' );
}

// 303 See Other: redirect to markdown URL with Vary for cache correctness.
header('Vary: Accept');
wp_safe_redirect($md_url, 303);
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