chromium/components/browsing_topics/browsing_topics_redirect_observer.h

// Copyright 2024 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef COMPONENTS_BROWSING_TOPICS_BROWSING_TOPICS_REDIRECT_OBSERVER_H_
#define COMPONENTS_BROWSING_TOPICS_BROWSING_TOPICS_REDIRECT_OBSERVER_H_

#include "content/public/browser/web_contents_observer.h"
#include "content/public/browser/web_contents_user_data.h"

namespace browsing_topics {

// Topics API can be misused when a site gets topics and passes it to the next
// site in the URL param via client-side redirect, and repeating this process
// several times allows the cooperating sites to get all the user's topics upon
// a single page visit.
//
// This class tracks the topics usage in a chain of client-side redirects, by
// getting the previous page's redirect status, updating it, and initializing
// the next page with the updated status.
//
// The redirect chain we are tracking is the sequence of renderer, non-user
// initiated top-level navigations occurring in a single `WebContents`. If a
// navigation ends up in an existing page (in bfcache), then the page's redirect
// status won't be updated, as the page won't be able to learn new information
// (via URL params).
//
// Note that this doesn't perfectly match the misuse pattern:
// - False negative case: It doesn't link a popup page with the opener page.
//   However, as Chrome blocks automated popups by default, we can overlook this
//   exception.
// - False positive case: It may link two pages without direct navigation. For
//   example, the user is on page X, a link is clicked and opens a popup page Y,
//   and Y triggers an automated opener navigation that navigates X to Z. In
//   this case, page X and Z are considered to be in the same redirect chain,
//   although a gesture was involved in this process (from X to Y).
//
// While tracking the navigation initiator's context could help fix these
// issues, it would add complexity. We accept some inaccuracies in favor of a
// simpler approach.
class BrowsingTopicsRedirectObserver
    : public content::WebContentsObserver,
      public content::WebContentsUserData<BrowsingTopicsRedirectObserver> { … };

}  // namespace browsing_topics

#endif  // COMPONENTS_BROWSING_TOPICS_BROWSING_TOPICS_REDIRECT_OBSERVER_H_