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.

The other day I had to debug a JavaScript UWA that was failing when trying to use an undefined property. In a previous OS build this code would run and the property was defined. I wanted something similar to windbg/cdb's ba command that lets me set a breakpoint on read or writes to a memory location so I could see what was creating the object in the previous OS build and what that code was doing now in the current OS build. I couldn't find such a breakpoint mechanism in Visual Studio or F12 so I wrote a little script to approximate JavaScript data breakpoints.

The script creates a stub object with a getter and setter. It actually performs the get or set but also calls debugger; to break in the debugger. In order to handle my case of needing to break when window.object1.object2 was created or accessed, I further had it recursively set up such stub objects for the matching property names.

Its not perfect because it is an enumerable property and shows up in hasOwnProperty and likely other places. But for your average code that checks for the existence of a property via if (object.property) it works well.

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.

Some time back while I was working on getting the Javascript Windows Store app platform running on Windows Phone (now available on the last Windows Phone release!) I had an interesting bug that in retrospect is amusing.

I had just finished a work item to get accessibility working for JS WinPhone apps when I got a new bug: With some set of JS apps, accessibility appeared to be totally broken. At that time in development the only mechanism we had to test accessibility was a test tool that runs on the PC, connects to the phone, and dumps out the accessibility tree of whatever app is running on the phone. In this bug, the tool would spin for a while and then timeout with an error and no accessibility information.

My first thought was this was an issue in my new accessibility code. However, debugging with breakpoints on my code I could see none of my code was run nor the code that should call it. The code that called that code was a more generic messaging system that hit my breakpoints constantly.

Rather than trying to work backward from the failure point, I decided to try and narrow down the repro and work forwards from there. One thing all the apps with the bug had in common was their usage of WinJS, but not all WinJS apps demonstrated the issue. Using a binary search approach on one such app I removed unrelated app code until all that was left was the app's usage of the WinJS AppBar and the bug still occurred. I replaced the WinJS AppBar usage with direct usage of the underlying AppBar WinRT APIs and continued.

Only some calls to the AppBar WinRT object produced the issue:

        var appBar = Windows.UI.WebUI.Core.WebUICommandBar.getForCurrentView(); 
        // appBar.opacity = 1;
        // appBar.closeDisplayMode = Windows.UI.WebUI.Core.WebUICommandBarClosedDisplayMode.default;
        appBar.backgroundColor = Windows.UI.Colors.white; // Bug! 

I eventually realized that predefined WinRT color values like Windows.UI.Colors.aqua would cause the issue while JS literal based colors didn't cause the issue (Windows.UI.Color is a WinRT struct which projects in JS as a JS literal object with the struct members as JS object properties so its easy to write something like {r: 0, g: 0, b: 0, a: 0} to make a color) and I had been mixing both in my tests without realizing there would be a difference. I debugged into the backgroundColor property setter that consumed the WinRT color struct to see what was different between Windows.UI.Colors.black and {a: 1, r: 0, g: 0, b: 0} and found the two structs to be byte wise exactly the same.

On a hunch I tried my test app with only a reference to the color and otherwise no interaction with the AppBar and not doing anything with the actual reference to the color: Windows.UI.Colors.black;. This too caused the issue. I knew that the implementation for these WinRT const values live in a DLL and guessed that something in the code to create these predefined colors was causing the issue. I debugged in and no luck. Now I also have experienced crusty code that would do exciting things in its DllMain, the function that's called when a DLL is loaded into the process so I tried modifying my C++ code to simply LoadLibrary the DLL containing the WinRT color definition, windows.ui.xaml.dll and found the bug still occurred! A short lived moment of relief as the world seemed to make sense again.

Debugging into DllMain nothing interesting happened. There were interesting calls in there to be sure, but all of them behind conditions that were false. I was again stumped. On another hunch I tried renaming the DLL and only LoadLibrary'ing it and the bug went away. I took a different DLL renamed it windows.ui.xaml.dll and tried LoadLibrary'ing that and the bug came back. Just the name of the DLL was causing the issue.

I searched for the DLL name in our source code index and found hits in the accessibility tool. Grinning I opened the source to find that the accessibility tool's phone side service was trying to determine if a process belonged to a XAML app or not because XAML apps had a different accessibility contract. It did this by checking to see if windows.ui.xaml.dll was loaded in the target process.

At this point I got to fix my main issue and open several new bugs for the variety of problems I had just run into. This is a how to on writing software that is difficult to debug.

Sarah and I have been enjoying Glitch for a while now. Reviews are usually positive although occasionally biting (but mostly accurate).

I enjoy Glitch as a game of exploration: exploring the game's lands with hidden and secret rooms, and exploring the games skills and game mechanics. The issue with my enjoyment coming from exploration is that after I've explored all streets and learned all skills I've got nothing left to do. But I've found that even after that I can have fun writing client side JavaScript against Glitch's web APIs making tools (I work on the Glitch Helperator) for use in Glitch. And on a semi-regular basis they add new features reviving my interest in the game itself.

        CreateIUriBuilder(resolvedUri, 0, 0, &builder);
        builder->SetHost(host);
        builder->CreateUri(0xFFFFFFFF, 0, 0, &resolvedUri);

    ResolveHost(resolvedUri, &resolvedUri);

    operator T**()  
    {  
        T *ptrValue = mPtrValue;
        mPtrValue->Release();
        mPtrValue = NULL;
        return &ptrValue;
    }

I've made two simple command line tools related to the console window and Win7 jump lists. The source is available for both but neither is much more than the sort of samples you'd find on MSDN =).

• SetAppUserModelId
• SetJumpList

SetAppUserModelId lets you change the Application User Model ID for the current console window. The AppUserModelId is the value Win7 uses to group together icons on the task bar and is what the task bar's jump lists are associated with. The tool lets you change that as well as the icon and name that appear in the task bar for the window, and the command to launch if the user attempts to re-launch the application from its task bar icon.

SetJumpList lets you set the jump list associated with a particular AppUserModelId. You pass the AppUserModelId as the only parameter and then in its standard input you give it lines specifying items that should appear in the jump list and what to execute when those items are picked.

I put these together to make my build environment easier to deal with at work. I have to deal with multiple enlistments in many different branches and so I wrote a simple script around these two tools to group my build windows by branch name in the task bar, and to add the history of commands I've used to launch the build environment console windows to the jump list of each.