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How-update-works.md

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Started from Help page to know how browser update works.

WebUI update modules

Help page shows update progress whether new version download is in progress or finished and relaunch button when update is ready. So that page is good start point to study about how update works on both WebUI and C++ world.

In the source code, the term about page is used instead of help page.

about_page.js and about_page.html are main resources for that page.

In about_page.html, below code shows update status.(Unrelated codes are deleted)

<div class="start padded">
  <div id="updateStatusMessage" hidden="[[!showUpdateStatus_]]">
    <div
      inner-h-t-m-l="[[getUpdateStatusMessage_(currentUpdateStatusEvent_)]]">
    </div>
  </div>
  <div class="secondary">$i18n{aboutBrowserVersion}</div>
</div>

In above code, currentUpdateStatusEvent_ variable seems data that holds current udpate status. How currentUpdateStatusEvent_ has current update status? In about_page.js, it is set by onUpdateStatusChanged() method. onUPdateStatusChanged() is bound with update-status-changed event. That event is emitted from AboutHandler::SetUpdateStatus() in c++ world.

When help page is loaded, StartListening() in about_page.js is run. Then, aboutBrowserProxy_.refreshUpdateStatus() calls AboutHandler::HandleRefreshUpdateStatus(). And platform specific VersionUpdater::CheckForUpdate() check current status and makes update at about page.

AboutHandler is initialized in MdSettingsUI ctor.

So far, I saw the WebUI-side update module briefly. Let's check how VersionUpdater is implemented on all platforms.

Native(C++) update modules

AFAICT, there are four native modules related with update in chrome.

To understand how chrome update work, we need to know about below modules.

  • VersionUpdater
  • UpgradeDetector
  • UI (Infobar, toolbar and app menu)
  • BrowserProcessImpl::StartAutoupdateTimer

VersionUpdater

VersionUpdater is interface to expose per-platform updating functionality to webui. As I wrote above, AboutHandler owns VersionUpdater. VersionUpdater::CheckForUpdate() is most important method. It begins the update process by checking for update availability from help page.

Windows

On Windows, chromium has two versions of VersionUpdater

  • VersionUpdaterWin (chrome brand)
  • VersionUpdaterBasic (non chrome brand)
VersionUpdaterWin

VersionUpdaterWin uses on google_upddate_win.h and UpdateCheckDriver seems do update works with COM class with CLSID_GoogleUpdate3WebUserClass. GoogleUpdateCore.exe includes that coclass and it is built from omaha.

UpdateCheckDriver notifies update status from GoogleUpdateCore.exe to VersionUpdaterWin via UPdateCheckDelegate. Then, about page displays update status/progress via callback passed to VersionUpdaterWin.

VersionUpdaterBasic

VersionUpdaterBasic depends on UpgradeDetector to get upgrade status only update is ready or not by checking UpgradeDetector::GetInstance()->notify_upgrade().

TODOs

We should implement brave_update_win.h that uses our own version of brave_update_idl.idl(similar to google_update_idl.idl) to replace google_update_win.h. That coclasses would be included by BraveUpdate.exe from omaha.

MacOSX

On MacOSX, VersionUpdaterMac is used to check update status with KeystoneGlue. KeystoneGlue uses KeystoneRegistration.framework. It's not open-sourced and used via NSBundle.

KeystoneRegistration.framework seems to update status via NSNotificationCenter and KeystoneGlue observers its messages(KSRegistrationXXXNotification). With those mesages, KeystoneGlue manages udpate status and propagates udpate status to chrome by sending kAutoupdateStatusNotification via noti center.

If KeystoneRegistration.framework doesn't exist on local machine, VersionUpdaterMac::CheckForUpdate do nothing. Just notify that update is disabled.

VersionUpdaterMac gets update status from kAutoupdateStatusNotification, then this update status is used by about page.

There is another client of kAutoupdateStatusNotification. It's KeystonePromotionInfoBar. It will be covered in UI section later.

TODOs

Sparkle.framework will be used for update on MacOSX. We should implement like BraveVersionUpdateMac that interact with SparkleGlue.

Linux

On Linux, VersionUpdateBasic is included. See above VersionUpdaterBasic section.

UpgradeDetector(Impl)

UpgradeDetector monitors whether new version is installed in background. It periodically checkes whether new version is installed on machine by comparing current running version and installed version by UpgradeDetectorImpl::DetectUpgradeTask. When it detects, notifies upgrade recommendation to observers.(see below the observer list)

The way to detect installed version varies on platform.

On windows, register key/value (by InstallUtil::GetChromeVersion) is used to detect.

On MacOSX, the value of CFBundleShortVersionString in Info.plist is used. (See keystone_glue::CurrentlyInstalledVersion())

On Posix(Linux), new version is obtained by creating new browser process instance with switches::kProductVersion. (See base::GetAppOutput()).

If detect interval isn't specified in cmdline, default interval (in upgrade_detector_impl.cc) is 2 hours. constexpr base::TimeDelta kCheckForUpgrade = base::TimeDelta::FromHours(2)

So, UpgradeDetector detects whether Update module/process(such as GoogleUpdateCore.exe(Win), Keystone(MacOSX) or package manager(Linux?)) downloads new version or not and notifies based on upgrade severity.

There are many UpgradeObservers.

  • ServiceProcessControl propagate update status to service processes
  • AppMenuIconController controls whether show update icon over appmenu
  • RelaunchNotificationController controls relaunch bubble ui based on annoyance level.
  • ToolbarView controls whether update bubble notification shows or not
  • AboutHandler triggers update check when help page is visible
TODOs

We can use most of existing logics except checking installed version. We might use different register key on Win and use SparkleGlue to check installed version on MacOSX.

UI

I found that there are three UIs related with update.

  • KeystonePromotionInfobar (show info bar when promotion is enabled)
  • ToolbarVew (notification bubble)
  • App menu (update menu entry with icon)
  • App menu icon (app menu button shows update status icon)
TODOs

I think most of UIs can be reused except KeystonePromotionInfobar

BrowserProcessImpl::StartAutoupdateTimer

This timer trigger restarts when upgrade is ready and chromium is running in background.

Brief summary

Chromium uses different external modules(GoogleUpdateCore.exe, Keystone and package manager) to install new version.

Chromium detects upgrade by checking installed version vs running version.

When chromium determines to recommand upgrade to user, infobar, app menu and notification bubble are used.

Also, when user opens help page, it triggers update check.