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Changing the User Agent string in UWP WebView

2018 Oct 23, 9:32

There's no perfect way to change the user agent string for the UWP WebView (x-ms-webview in HTML, Windows.UI.Xaml.Controls.WebView in XAML, and Windows.Web.UI.Interop.WebViewControl in Win32) but there are two imperfect methods folks end up using.

The first is to call UrlMkSetSessionOption. This is an old public API that allows you to configure various arcane options including one that is the default user agent string for requests running through urlmon. This API is allowed by the Microsoft Store for UWP apps. The change it applies is process wide which has two potential drawbacks. If you want to be able to have different UA strings set for different requests from a WebView that's not really possible with this solution. The other drawback is if you're using out of process WebView, you need to ensure you're calling into UrlMkSetSessionOption in the WebView's process. You'll need to write third party WinRT that calls UrlMkSetSessionOption, create the out of proc WebView, navigate it to some trusted local page, use AddWebAllowedObject or provide that URI WinRT access, and call into your third party WinRT. You'll need to do that for any new WebView process you create.

The second less generally applicable solution is to use NavigateWithHttpRequestMessage and set the User-Agent HTTP header. In this case you get to control the scope of the user agent string changes but has the limitations that not all sub resource downloads will use this user agent string and for navigations you don't initiate you have to manually intercept and re-request being careful to transfer over all POST body state and HTTP headers correctly. That last part is not actually possible for iframes.

PermalinkCommentsuser-agent uwp webview

Tiny browser features: JSBrowser crash resistance

2018 May 13, 4:59

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 crash resistance.

The normal DOM mechanisms for creating an HTML WebView create an in-process WebView, in which the WebView runs on a unique UI thread. But we can use the MSWebView constructor instead to create an out-of-process WebView in which the WebView runs in its own distinct WebView process. Unlike an in-process WebView, Web content running in an out-of-process WebView can only crash the WebView process and not the app process.

        this.replaceWebView = () => {
let webview = document.querySelector("#WebView");
// Cannot access webview.src - anything that would need to communicate with the webview process may fail
let oldSrc = browser.currentUrl;
const webviewParent = webview.parentElement;
webview = new MSWebView();
Object.assign(this, {
"webview": webview
webview.setAttribute("id", "WebView");

// During startup our currentUrl field is blank. If the WebView has crashed
// and we were on a URI then we may obtain it from this property.
if (browser.currentUrl && browser.currentUrl != "") {

I run replaceWebView during startup to replace the in-process WebView created via HTML markup with an out-of-process WebView. I could be doing more to dynamically copy styles, attributes, etc but I know what I need to set on the WebView and just do that.

When a WebView process crashes the corresponding WebView object is no longer useful and a new WebView element must be created. In fact if the old WebView object is used it may throw and will no longer have valid state. Accordingly when the WebView crashes I run replaceWebView again. Additionally, I need to store the last URI we've navigated to (browser.currentUrl in the above) since the crashed WebView object won't know what URI it is on after it crashes.

            webview.addEventListener("MSWebViewProcessExited", () => { 
if (browser.currentUrl === browser.lastCrashUrl) { ++browser.lastCrashUrlCrashCount;
else {
browser.lastCrashUrl = browser.currentUrl;
browser.lastCrashUrlCrashCount = 1;
// If we crash again and again on the same URI, maybe stop trying to load that URI.
if (browser.lastCrashUrlCrashCount >= 3) {
browser.lastCrashUrl = "";
browser.lastCrashUrlCrashCount = 0;
browser.currentUrl = browser.startPage;

I also keep track of the last URI that we recovered and how many times we've recovered that same URI. If the same URI crashes more than 3 times in a row then I assume that it will keep happening and I navigate to the start URI instead.

PermalinkCommentsbrowser javascript jsbrowser uwp webview win10

Tweet from NASA Planetquest

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See another solar system! These are real images of a 4-planet system ~130 light-years from . Read about it: http://go.nasa.gov/2kySSt1 

Tweet from David Risney

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The band name alone is worth it. Mariachi Entertainment System's Mariachi Medley https://youtu.be/JpKVXBk_6r0 

Tweet from David Risney

2016 Dec 7, 2:19
I'm going to pretend that The Circle is a sequel to Antitrust http://kottke.org/16/12/trailer-for-the-circle 

Tweet from David Rousset

2016 Dec 6, 8:45
Creating an extension for all browsers: , , , & : https://www.davrous.com/2016/12/07/creating-an-extension-for-all-browsers-edge-chrome-firefox-opera-brave/ 

Tweet from Andy Baio

2016 Dec 6, 2:30
OH. MY. GOD. @SethBling MADE AN ATARI 2600 EMULATOR IN MINECRAFT. https://youtu.be/5nViIUfDMJg 

Tweet from emma jane

2016 Dec 2, 2:07
XSS: the game http://buff.ly/2gGghdI 

Tweet from The Atlantic

2016 Nov 28, 10:07
The lasting damage done by Tump's 'voter fraud' allegations: http://theatln.tc/2gczqDz 

Tweet from Richard Rudge

2016 Nov 28, 6:19
This is best piece of Superman art I've seen in a long time, made by Brakken http://brakken.tumblr.com 

Tweet from kottke.org

2016 Nov 20, 10:41
A free album of Beastie Boys remixes using Daft Punk samples http://kottke.org/16/11/beastie-boys-daft-punk-mashup 

Tweet from David Risney

2016 Nov 20, 2:47
Just fun: draw a sketch and see how fast a Google neural net takes to figure out what it is https://quickdraw.withgoogle.com/# 

Tweet from Šime Vidas

2016 Nov 17, 3:14
Chrome Canary has enabled scroll anchoring which prevents “jumps” when the layout above the viewport changes (demo: https://output.jsbin.com/parujo/quiet#heading2 )

Tweet from David Risney

2016 Nov 4, 4:08
@David_Risney Example graph https://raw.githubusercontent.com/david-risney/WinMDGraph/master/examples/3/3.dot.png  of the Windows .Services.Maps namespace

Tweet from David Risney

2016 Nov 4, 4:05
WinMDGraph graphs relationships between WinRT APIs https://github.com/david-risney/WinMDGraph/ . My initial version is up.

Tweet from David Risney

2016 Nov 3, 3:57
@FakeUnicode At least some of that is from https://tools.ietf.org/html/rfc3986 . For unreserved characters (a-z0-9._-~) normal form is decoded.

Tweet from David Risney

2016 Nov 2, 9:30
Parsing WinRT metadata (winmd files) is much easier than last time I tried. There's support in .NET reflection APIs https://deletethis.net/dave/2016-11/Parsing+WinMD+with+.NET+reflection+APIs 

Tweet from Chris Heilmann

2016 Nov 2, 4:57
The static on TV is referred to as “hangyafoci” by Hungarians, which translates to “ant soccer” https://en.wikipedia.org/wiki/Noise_(video) 

Tweet from Open Culture

2016 Nov 2, 4:31
Read the CIA’s Simple Sabotage Field Manual. How to Subvert Organizations with “Purposeful Stupidity” (1944) http://bit.ly/2dbnooU 

Tweet from David Risney

2016 Oct 23, 4:18
Only Child written by @hodgman is amazing & hilarious. Although also showed me various ways in which I'm not special http://www.maximumfun.org/dead-pilots-society/episode-2-only-child-written-john-hodgman 
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