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Folks familiar with JavaScript UWP apps in Win10 have often been confused by what PWAs in Win10 actually are. TLDR: PWAs in Win10 are simply JavaScript UWP apps. The main difference between these JS UWP Apps and our non-PWA JS UWP apps are our target end developer audience, and how we get Win10 PWAs into the Microsoft Store. See this Win10 blog post on PWAs on Win10 for related info.

Web App

On the web a subset of web sites are web apps. These are web sites that have app like behavior - that is a user might call it an app like Outlook, Maps or Gmail. And they may also have a W3C app manifest.

A subset of web apps are progressive web apps. Progressive web apps are web apps that have a W3C app manifest and a service worker. Various OSes are beginning to support PWAs as first class apps on their platform. This is true for Win10 as well in which PWAs are run as a WWA.

Windows Web App

In Win10 a WWA (Windows Web App) is an unofficial term for a JavaScript UWP app. These are UWP apps so they have an AppxManifest.xml, they are packaged in an Appx package, they run in an App Container, they use WinRT APIs, and are installed via the Microsoft Store. Specific to WWAs though, is that the AppxManifest.xml specifies a StartPage attribute identifying some HTML content to be used as the app. When the app is activated the OS will create a WWAHost.exe process that hosts the HTML content using the EdgeHtml rendering engine.

Packaged vs Hosted Web App

Within that we have a notion of a packaged web app and an HWA (hosted web app). There's no real technical distinction for the end developer between these two. The only real difference is whether the StartPage identifies remote HTML content on the web (HWA), or packaged HTML content from the app's appx package (packaged web app). An end developer may create an app that is a mix of these as well, with HTML content in the package and HTML content from the web. These terms are more like ends on a continuum and identifying two different developer scenarios since the underlying technical aspect is pretty much identical.

Win10 PWA

Win10 PWAs are simply HWAs that specify a StartPage of a URI for a PWA on the web. These are still JavaScript UWP apps with all the same behavior and abilities as other UWP apps. We have two ways of getting PWAs into the Microsoft Store as Win10 PWAs. The first is PWA Builder which is a tool that helps PWA end developers create and submit to the Microsoft Store a Win10 PWA appx package. The second is a crawler that runs over the web looking for PWAs which we convert and submit to the Store using an automated PWA Builder-like tool to create a Win10 PWA from PWAs on the web (see Welcoming PWAs to Win10 for more info). In both cases the conversion involves examining the PWAs W3C app manifest and producing a corresponding AppxManifest.xml. Not all features supported by AppxManifest.xml are also available in the W3c app manifest. But the result of PWA Builder can be a working starting point for end developers who can then update the AppxManifest.xml as they like to support features like share targets or others not available in W3C app manifests.

JavaScript Microsoft Store apps have some details related to activation that are specific to JavaScript Store apps and that are poorly documented which I’ll describe here.

StartPage syntax

The StartPage attributes in the AppxManifest.xml (Package/Applications/Application/@StartPage, Package/Applications/Extensions/Extension/@StartPage) define the HTML page entry point for that kind of activation. That is, Application/@StartPage defines the entry point for tile activation, Extension[@Category="windows.protocol"]/@StartPage defines the entry point for URI handling activation, etc. There are two kinds of supported values in StartPage attributes: relative Windows file paths and absolute URIs. If the attribute doesn’t parse as an absolute URI then it is instead interpreted as relative Windows file path.

This implies a few things that I’ll declare explicitly here. Windows file paths, unlike URIs, don’t have a query or fragment, so if you are using a relative Windows file path for your StartPage attribute you cannot include anything like ‘?param=value’ at the end. Absolute URIs use percent-encoding for reserved characters like ‘%’ and ‘#’. If you have a ‘#’ in your HTML filename then you need to percent-encode that ‘#’ for a URI and not for a relative Windows file path.

If you specify a relative Windows file path, it is turned into an ms-appx URI by changing all backslashes to forward slashes, percent-encoding reserved characters, and combining the result with a base URI of ms-appx:///. Accordingly the relative Windows file paths are relative to the root of your package. If you are using a relative Windows file path as your StartPage and need to switch to using a URI so you can include a query or fragment, you can follow the same steps above.

StartPage validity

The validity of the StartPage is not determined before activation. If the StartPage is a relative Windows file path for a file that doesn’t exist, or an absolute URI that is not in the Application Content URI Rules, or something that doesn’t parse as a Windows file path or URI, or otherwise an absolute URI that fails to resolve (404, bad hostname, etc etc) then the JavaScript app will navigate to the app’s navigation error page (perhaps more on that in a future blog post). Just to call it out explicitly because I have personally accidentally done this: StartPage URIs are not automatically included in the Application Content URI Rules and if you forget to include your StartPage in your ACUR you will always fail to navigate to that StartPage.

StartPage navigation

When your app is activated for a particular activation kind, the StartPage value from the entry in your app’s manifest that corresponds to that activation kind is used as the navigation target. If the app is not already running, the app is activated, navigated to that StartPage value and then the Windows.UI.WebUI.WebUIApplication activated event is fired (more details on the order of various events in a moment). If, however, your app is already running and an activation occurs, we navigate or don’t navigate to the corresponding StartPage depending on the current page of the app. Take the app’s current top level document’s URI and if after removing the fragment it already matches the StartPage value then we won’t navigate and will jump straight to firing the WebUIApplication activated event.

Since navigating the top-level document means destroying the current JavaScript engine instance and losing all your state, this behavior might be a problem for you. If so, you can use the MSApp.pageHandlesAllApplicationActivations(true) API to always skip navigating to the StartPage and instead always jump straight to firing the WebUIApplication activated event. This does require of course that all of your pages all handle all activation kinds about which any part of your app cares.

Application Content URI Rules (ACUR from now on) defines the bounds on the web that make up a Microsoft Store application. The previous blog post discussed the syntax of the Rule's Match attribute and this time I'll write about the interactions between the Rules elements.

Order

A single ApplicationContentUriRules element may have up to 100 Rule child elements. When determining if a navigation URI matches any of the ACUR the last Rule in the list with a matching match wildcard URI is used. If that Rule is an include rule then the navigation URI is determined to be an application content URI and if that Rule is an exclude rule then the navigation rule is not an application content URI. For example:

Rule Type='include' Match='https://example.com/'/
Rule Type='exclude' Match='https://example.com/'/

Given the above two rules in that order, the navigation URI https://example.com/ is not an application content URI because the last matching rule is the exclude rule. Reverse the order of the rules and get the opposite result.

WindowsRuntimeAccess

In addition to determining if a navigation URI is application content or not, a Rule may also confer varying levels of WinRT access via the optional WindowsRuntimeAccess attribute which may be set to 'none', 'allowForWeb', or 'all'. If a navigation URI matches multiple different include rules only the last rule is applied even as it applies to the WindowsRuntimeAccess attribute. For example:

Rule Type='include' Match='https://example.com/' WindowsRuntimeAccess='none'/
Rule Type='include' Match='https://example.com/' WindowsRuntimeAccess='all'/

Given the above two rules in that order, the navigation URI https://example.com/ will have access to all WinRT APIs because the last matching rule wins. Reverse the rule order and the navigation URI https://example.com/ will have no access to WinRT. There is no summation or combining of multiple matching rules - only the last matching rule wins.

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;
}

You can use conditional breakpoints and debugging commands in windbg and cdb that together can amount to effectively patching a binary at runtime. This can be useful if you have symbols but you can't easily rebuild the binary. Or if the patch is small and the binary requires a great deal of time to rebuild.

Skipping code

If you want to skip a chunk of code you can set a breakpoint at the start address of the code to skip and set the breakpoint's command to change the instruction pointer register to point to the address at the end of the code to skip and go. Voila you're skipping over that code now. For example:

bp 0x6dd6879b "r @eip=0x6dd687c3 ; g"

Changing parameters

You may want to modify parameters or variables and this is simple of course. In the following example a conditional breakpoint ANDs out a bit from dwFlags. Now when we run its as if no one is passing in that flag.

bp wiwi!RelativeCrack "?? dwFlags &= 0xFDFFFFFF;g"

Slightly more difficult is to modify string values. If the new string length is the same size or smaller than the previous, you may be able to modify the string value in place. But if the string is longer or the string memory isn't writable, you'll need a new chunk of memory into which to write your new string. You can use .dvalloc to allocate some memory and ezu to write a string into the newly allocated memory. In the following example I then overwrite the register containing the parameter I want to modify:

.dvalloc 100
ezu 000002a9`d4eb0000 "mfcore.dll"
r rcx = 000002a9`d4eb0000

Calling functions

You can also use .call to actually make new calls to methods or functions. Read more about that on the Old New Thing: Stupid debugger tricks: Calling functions and methods. Again, all of this can be used in a breakpoint command to effectively patch a binary.