cli - Dave's Blog


GoBack/GoForward in Win10 UWP WebView

2018 Oct 23, 9:18

The GoBack and GoForward methods on the UWP WebView (x-ms-webview in HTML, Windows.UI.Xaml.Controls.WebView in XAML, and Windows.Web.UI.Interop.WebViewControl in Win32) act the same as the Back and Forward buttons in the Edge browser. They don't necessarily change the top level document of the WebView. If inside the webview an iframe navigates then that navigation will be recorded in the forward/back history and the GoBack / GoForward call may result in navigating that iframe. This makes sense as an end user using the Edge browser since if I click a link to navigate one place and then hit Back I expect to sort of undo that most recent navigation regardless of if that navigation happened in an iframe or the top level document.

If that doesn't make sense for your application and you want to navigate forward or back ignoring iframe navigates, unfortunately there's no perfect workaround.

One workaround could be to try calling GoBack and then checking if a FrameNavigationStarting event fires or a NavigationStarting event fires. If a frame navigates then try calling GoBack again. There could be async races in this case since other navigates could come in and send you the wrong signal and interrupt your multi step GoBack operation.

You could also try keeping track of all top level document navigations and manually navigate back to the URIs you care about. However, GoBack and GoForward also restore some amount of user state (form fills etc) in addition to navigating. Manually calling navigate will not give this same behavior.

PermalinkCommentsuri uwp webview

Tiny browser features: JSBrowser zoom

2018 May 10, 3:49

JSBrowser is a basic browser built as a Win10 JavaScript UWP app around the WebView HTML element. Its fun and relatively simple to implement tiny browser features in JavaScript and in this post I'm implementing zoom.

My plan to implement zoom is to add a zoom slider to the settings div that controls the scale of the WebView element via CSS transform. My resulting zoom change is in git and you can try the whole thing out in my JSBrowser fork.


I can implement the zoom settings slider as a range type input HTML element. This conveniently provides me a min, max, and step property and suits exactly my purposes. I chose some values that I thought would be reasonable so the browser can scale between half to 3x by increments of one quarter. This is a tiny browser feature after all so there's no custom zoom entry.

<a><label for="webviewZoom">Zoom</label><input type="range" min="50" max="300" step="25" value="100" id="webviewZoom" /></a>

To let the user know this slider is for controlling zoom, I make a label HTML element that says Zoom. The label HTML element has a for attribute which takes the id of another HTML element. This lets the browser know what the label is labelling and lets the browser do things like when the label is clicked to put focus on the slider.


There are no explicit scale APIs for WebView so to change the size of the content in the WebView we use CSS.

        this.applyWebviewZoom = state => {
const minValue = this.webviewZoom.getAttribute("min");
const maxValue = this.webviewZoom.getAttribute("max");
const scaleValue = Math.max(Math.min(parseInt(this.webviewZoom.value, 10), maxValue), minValue) / 100;

// Use setAttribute so they all change together to avoid weird visual glitches
this.webview.setAttribute("style", [
["width", (100 / scaleValue) + "%"],
["height", "calc(" + (-40 / scaleValue) + "px + " + (100 / scaleValue) + "%)"],
["transform", "scale(" + scaleValue + ")"]
].map(pair => pair[0] + ": " + pair[1]).join("; "));

Because the user changes the scale at runtime I accordingly replace the static CSS for the WebView element with the script above to programmatically modify the style of the WebView. I change the style with one setAttribute call to do my best to avoid the browser performing unnecessary work or displaying the WebView in an intermediate and incomplete state. Applying the scale to the element is as simple as adding 'transform: scale(X)' but then there are two interesting problems.

The first is that the size of the WebView is also scaled not just the content within it. To keep the WebView the same effective size so that it still fits properly into our browser UI, we must compensate for the scale in the WebView width and height. Accordingly, you can see that we scale up by scaleValue and then in width and height we divide by the scaleValue.

transform-origin: 0% 0%;

The other issue is that by default the scale transform's origin is the center of the WebView element. This means when scaled up all sides of the WebView would expand out. But when modifying the width and height those apply relative to the upper left of the element so our inverse scale application to the width and height above aren't quite enough. We also have to change the origin of the scale transform to match the origin of the changes to the width and height.

PermalinkCommentsbrowser css-transform javascript JS jsbrowser uwp webview win10

Application Content URI Rule effects

2017 Jun 30, 3:01

Previously I described Application Content URI Rules (ACUR) parsing and ACUR ordering. This post describes what you get from putting a URI in ACUR.

URIs in the ACUR gain the following which is otherwise unavailable:

  • Geoloc API usage
  • Audio and video capture API usage
  • Pointer lock API usage
  • Web notifications API usage
  • IndexedDB API usage
  • Clipboard API usage
  • window.external.notify access from within webview
  • window.close the primary window
  • Top level navigation in the primary window
  • Cross origin XHR and fetch to ms-appx(-web) scheme URIs
  • Cross origin dirtied canvas read access if dirtied by ms-appx(-web) scheme URIs
  • Cross origin text track for video element for tracks from ms-appx(-web) scheme URIs

URIs in the ACUR that also have full WinRT access additionally gain the following:

  • Cross origin XHR and fetch
  • Cross origin dirtied canvas read access
  • Cross origin text track for video element
  • Local audio and video WinRT plugins work with media elements
PermalinkCommentsapplication-content-uri-rules coding javascript programming windows-store

Tweet from NASA Planetquest

2017 Jan 26, 10:25
See another solar system! These are real images of a 4-planet system ~130 light-years from . Read about it: 

Tweet from David Rousset

2016 Dec 6, 8:45
Creating an extension for all browsers: , , , & : 

Tweet from Jen Gentleman 🌺

2016 Nov 4, 8:39
If you ever see a dialog box in this style & need to record what it said, instead of typing it out, just CTRL+C ➡📋

Tweet from Liz Kreutz

2016 Oct 13, 6:46
For those interested: Clinton said gifs with a hard "G"

Tweet from Hillary Clinton

2016 Oct 9, 1:44
RT this if you're proud to have Hillary's back tonight. 

Tweet from Jen Gentleman 🌺

2016 Oct 8, 2:19
In case you were wondering: Yes, the new address bar that was added to RegEdit supports Alt+D to set keyboard focus 😊

Tweet from Clickbait Robot

2016 Sep 26, 12:53
18 Screwdrivers That Look Like Matt LeBlanc

Tweet from ClickHole

2016 Sep 7, 8:00
Silencing Dissent: Donald Trump Threw An Elderly Version Of Himself Out Of His Rally For Shouting ‘Beware Hubris!’ 

Tweet from Mike Birbiglia

2016 Aug 24, 11:12
When people hack someone's shit you have a responsibility as a decent person to not look at it. You're better than that.

Tweet from Garrett Serack

2016 Aug 18, 2:57
For the record, yes you can run on Linux in Bash on Windows (aka ) /cc @bitcrazed @bradwilson

WPAD Server Fiddler Extension Source

2016 Aug 5, 3:18

I've put my WPAD Fiddler extension source and the installer on GitHub.

Six years ago I made a WPAD DHCP server Fiddler extension (described previously and previously). The extension runs a WPAD DHCP server telling any clients that connect to connect to the running Fiddler instance. I've finally got around to putting the source on GitHub. I haven't touched it in five or so years so this is either for posterity or education or something.

PermalinkCommentsdhcp fiddler network security wpad

Tweet from Buzz Aldrin

2016 Jul 26, 12:25
47 years ago I submitted my travel voucher reimbursement for my trip to the moon.

WinRT Toast from PowerShell

2016 Jun 15, 3:54

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:

$toast = New-Object Windows.UI.Notifications.ToastNotification -ArgumentList $xml;
And here I call the static method CreateToastNotifier on the ToastNotificationManager class:
$notifier = [Windows.UI.Notifications.ToastNotificationManager]::CreateToastNotifier($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;
} c# powershell toast winrt

Tweet from Jen Gentleman

2016 May 13, 3:51
You can use the curser controller just by flicking it 😉 📱

Tweet from Bobak Ferdowsi

2016 Apr 22, 4:40
Hi, you may know me from space, but did you know Earth is my favorite planet? Love it & each other.

Tweet from Kumail Nanjiani

2016 Apr 5, 11:22
Terrified that the will reveal I never beat Dragon Age: Inquisition.

Retweet of FakeUnicode

2016 Feb 12, 7:25
> typeof NaN 'number' > (╯°□°)╯︵ ┻━┻) ...
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