Bug 1638509 - Enable the limited PostUpdate to update the WDBA task. r=agashlin,bytesized

This also requires removing the registry value cleanup from the unregister-task
command and adding a new uninstall command which removes both the task and the
registry values, because this patch now runs unregister-task during updates to
remove the task before re-adding it, and that needs to leave the registry alone.

Differential Revision: https://phabricator.services.mozilla.com/D76354

browser/installer/windows/nsis/shared.nsh

@@ -193,8 +193,12 @@ ${If} $TmpVal == "HKCU"
                     "DidRegisterDefaultBrowserAgent"
   ${If} $0 != 0
   ${OrIf} ${Errors}
-    Exec '"$INSTDIR\default-browser-agent.exe" update-task $AppUserModelID'
+    Exec '"$INSTDIR\default-browser-agent.exe" register-task $AppUserModelID'
   ${EndIf}
+${ElseIf} $TmpVal == "HKLM"
+  ; If we're the privileged PostUpdate, make sure that the unprivileged one
+  ; will have permission to create a task by clearing out the old one first.
+  Exec '"$INSTDIR\default-browser-agent.exe" unregister-task $AppUserModelID'
 ${EndIf}
 !endif
 

browser/installer/windows/nsis/uninstaller.nsi

@@ -464,7 +464,7 @@ Section "Uninstall"
 
   ; Uninstall the default browser agent scheduled task.
   ; This also removes the registry entries it creates.
-  ExecWait '"$INSTDIR\default-browser-agent.exe" unregister-task $AppUserModelID'
+  ExecWait '"$INSTDIR\default-browser-agent.exe" uninstall $AppUserModelID'
 
   ${un.RemovePrecompleteEntries} "false"
 

toolkit/mozapps/defaultagent/docs/index.rst

@@ -10,7 +10,7 @@ For information about the specific data that the agent sends, see :doc:`the ping
 Scheduled Task
 ==============
 
-The agent runs as a `Windows scheduled task <https://docs.microsoft.com/en-us/windows/win32/taskschd/about-the-task-scheduler>`_. The scheduled task executes all of the agent's primary functions; all of its other functions relate to managing the task. The Windows installer is responsible for creating (and the uninstaller for removing) the agent's task entry, but the code for actually doing this resides in the agent itself, and the installers simply call it using dedicated command line parameters (``register-task`` and ``unregister-task``). The :doc:`PostUpdate </browser/installer/windows/installer/Helper>` code also calls the agent with ``update-task`` to update any properties of an existing task registration that need to be updated, or to create one during an application update if none exists.
+The agent runs as a `Windows scheduled task <https://docs.microsoft.com/en-us/windows/win32/taskschd/about-the-task-scheduler>`_. The scheduled task executes all of the agent's primary functions; all of its other functions relate to managing the task. The Windows installer is responsible for creating (and the uninstaller for removing) the agent's task entry, but the code for actually doing this resides in the agent itself, and the installers simply call it using dedicated command line parameters (``register-task`` and ``uninstall``). The :doc:`PostUpdate </browser/installer/windows/installer/Helper>` code also calls the agent to update any properties of an existing task registration that need to be updated, or to create one during an application update if none exists.
 
 The tasks are normal entries in the Windows Task Scheduler, managed using `its Win32 API <https://docs.microsoft.com/en-us/windows/win32/api/_taskschd/>`_. They're created in a tasks folder called "Mozilla" (or whatever the application's vendor name is), and there's one for each installation of Firefox (or other Mozilla application). The task is set to run automatically every 24 hours starting at the time it's registered (with the first run being 24 hours after that), or the nearest time after that the computer is awake. The task is configured with one action, which is to run the agent binary with the command line parameter ``do-task``, the command that invokes the actual agent functionality.
 

toolkit/mozapps/defaultagent/main.cpp

@@ -101,7 +101,10 @@ static void RemoveAllRegistryEntries() {
 //   token argument is required and should be the same one that was passed in
 //   when the task was registered.
 // unregister-task [unique-token]
-//   Removes the previously created task along with any registry entries that
+//   Removes the previously created task. The unique token argument is required
+//   and should be the same one that was passed in when the task was registered.
+// uninstall [unique-token]
+//   Removes the previously created task, and also removes all registry entries
 //   running the task may have created. The unique token argument is required
 //   and should be the same one that was passed in when the task was registered.
 // do-task
@@ -121,13 +124,16 @@ int wmain(int argc, wchar_t** argv) {
     ~ComUninitializer() { CoUninitialize(); }
   } kCUi;
 
-  // The remove-task command is allowed even if the policy disabling the task
-  // is set, mainly so that the uninstaller will work.
-  if (!wcscmp(argv[1], L"unregister-task")) {
+  // The uninstall and unregister commands are allowed even if the policy
+  // disabling the task is set, so that uninstalls and updates always work.
+  if (!wcscmp(argv[1], L"uninstall") || !wcscmp(argv[1], L"unregister-task")) {
     if (argc < 3 || !argv[2]) {
       return E_INVALIDARG;
     }
-    RemoveAllRegistryEntries();
+
+    if (!wcscmp(argv[1], L"uninstall")) {
+      RemoveAllRegistryEntries();
+    }
     return RemoveTask(argv[2]);
   }