res page 2 - Dave's Blog

I've made a PowerShell script to show system toast notifications with WinRT and PowerShell. Along the way I learned several interesting things.

First off calling WinRT from PowerShell involves a strange syntax. If you want to use a class you write [-Class-,-Namespace-,ContentType=WindowsRuntime] first to tell PowerShell about the type. For example here I create a ToastNotification object:

[void][Windows.UI.Notifications.ToastNotification,Windows.UI.Notifications,ContentType=WindowsRuntime];
$toast = New-Object Windows.UI.Notifications.ToastNotification -ArgumentList $xml;

And here I call the static method CreateToastNotifier on the ToastNotificationManager class:

[void][Windows.UI.Notifications.ToastNotificationManager,Windows.UI.Notifications,ContentType=WindowsRuntime];
$notifier = [Windows.UI.Notifications.ToastNotificationManager]::CreateToastNotifier($AppUserModelId);

With this I can call WinRT methods and this is enough to show a toast but to handle the click requires a little more work.

To handle the user clicking on the toast I need to listen to the Activated event on the Toast object. However Register-ObjectEvent doesn't handle WinRT events. To work around this I created a .NET event wrapper class to turn the WinRT event into a .NET event that Register-ObjectEvent can handle. This is based on Keith Hill's blog post on calling WinRT async methods in PowerShell. With the event wrapper class I can run the following to subscribe to the event:

function WrapToastEvent {
    param($target, $eventName);

    Add-Type -Path (Join-Path $myPath "PoshWinRT.dll")
    $wrapper = new-object "PoshWinRT.EventWrapper[Windows.UI.Notifications.ToastNotification,System.Object]";
    $wrapper.Register($target, $eventName);
}

[void](Register-ObjectEvent -InputObject (WrapToastEvent $toast "Activated") -EventName FireEvent -Action { 
    ...
});

To handle the Activated event I want to put focus back on the PowerShell window that created the toast. To do this I need to call the Win32 function SetForegroundWindow. Doing so from PowerShell is surprisingly easy. First you must tell PowerShell about the function:

Add-Type @"
    using System;
    using System.Runtime.InteropServices;
    public class PInvoke {
        [DllImport("user32.dll")] [return: MarshalAs(UnmanagedType.Bool)]
        public static extern bool SetForegroundWindow(IntPtr hwnd);
    }
"@

Then to call:

[PInvoke]::SetForegroundWindow((Get-Process -id $myWindowPid).MainWindowHandle);

But figuring out the HWND to give to SetForegroundWindow isn't totally straight forward. Get-Process exposes a MainWindowHandle property but if you start a cmd.exe prompt and then run PowerShell inside of that, the PowerShell process has 0 for its MainWindowHandle property. We must follow up process parents until we find one with a MainWindowHandle:

$myWindowPid = $pid;
while ($myWindowPid -gt 0 -and (Get-Process -id $myWindowPid).MainWindowHandle -eq 0) {
    $myWindowPid = (gwmi Win32_Process -filter "processid = $($myWindowPid)" | select ParentProcessId).ParentProcessId;
}

TL;DR: Web content in a JavaScript Windows Store app or WebView in a Windows Store app that has full access to WinRT also gets to use XHR unrestricted by cross origin checks.

By default web content in a WebView control in a Windows Store App has the same sort of limitations as that web content in a web browser. However, if you give the URI of that web content full access to WinRT, then the web content also gains the ability to use XMLHttpRequest unrestricted by cross origin checks. This means no CORS checks and no OPTIONS requests. This only works if the web content's URI matches a Rule in the ApplicationContentUriRules of your app's manifest and that Rule declares WindowsRuntimeAccess="all". If it declares WinRT access as 'None' or 'AllowForWebOnly' then XHR acts as it normally does.

In terms of security, if you've already given a page access to all of WinRT which includes the HttpRequest class and other networking classes that don't perform cross origin checks, then allowing XHR to skip CORS doesn't make things worse.