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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;
webviewParent.removeChild(webview);
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 != "") {
this.trigger("newWebview");
this.navigateTo(browser.currentUrl);
}
webviewParent.appendChild(webview);

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;
}
this.replaceWebView();
});

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 David Risney

2017 Jan 13, 12:54
Free startup idea: Legally binding "but you have to survive a night in a haunted house" clauses and infrastructure for hillarious wills.
PermalinkComments

Tweet from Gimlet

2016 Aug 29, 11:40
So there's also this...📺 https://twitter.com/podcaststartup/status/770430060448714752 
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Guardian - Secrets, lies and Snowden’s email: why I was...

2014 May 21, 2:11


Guardian - Secrets, lies and Snowden’s email: why I was forced to shut down Lavabit

"For the first time, the founder of an encrypted email startup that was supposed to insure privacy for all reveals how the FBI and the US legal system made sure we don’t have the right to much privacy in the first place"

PermalinkCommentslaw legal encryption technical

(via Parody Tech Startup Explainer Video for Vooza)

2012 Jun 7, 3:04


(via Parody Tech Startup Explainer Video for Vooza)

PermalinkCommentshumor startup buzzword vooza video web

Native x86 Android runtime will enable Android apps on Windows

2011 May 26, 1:28This was on my todo list. I'll scratch it off knowing far more funded folks are doing this: "A startup called BlueStacks has developed an Android runtime environment for the Windows operating system. It will enable users to run Android applications alongside conventional Windows software on Microsoft's operating system." "One example would be a convertible netbook tablet that normally runs Windows but switches to an Android interface for greater touch-friendliness when the screen is flipped.
Such a product would offer the full power and multitasking capabilities of Windows but also benefit from having access to Android's broad touch-enabled software ecosystem."PermalinkCommentswindows programming android java technical

Kempa.com » Absolutely surreal excerpt from a New Yorker profile of Vampire Weekend

2010 Jan 6, 1:58Tom DeLonge tries to sell Vampire Weekend a website. "...this whole thing reads like a scene from a modern-day Spinal Tap. Weird music industry insanity crossed with internet startup hucksterism with a dash of awkward standoffishness. I love it. All of this is heightened by the fact that BOTH parties are being followed by separate documentary film crews, who are filming the insanity. How weird is that?"PermalinkCommentsinternet music vampire-weekend band documentary via:waxy

Opera Speed Dial Code-less Hack for IE7

2007 Apr 17, 11:45Opera (the fifth most popular web browser) has a new feature named Speed Dial (video of it in action). Whenever you open a new tab you get your Speed Dial view which consists of nine thumbnails of user-settable pages. Its like a quick-favorites that appears every time you open a new tab. I think this is a neat idea and was considering how I might do that in IE7. The following is my hack-y and ugly but no coding required version of Speed Dial for IE7. I like my hack and I'm about to expound upon it in unnecessary detail so skip to the last paragraph if you're afraid of losing interest.

By default in IE7, whenever you open a new tab you navigate to 'about:Tabs'. As noted in wikipedia the result of navigation to 'about:Tabs' is determined by values in the registry. Specifically, values in the key in "HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Internet Explorer\AboutURLs". Usually this fact is exploited by malicious software to hijack "about:blank" and show you ads but we can hijack it too in order to display our Speed Dial-ish page.

Of course since this is a code-less hack we've got limited options on what to change 'about:Tabs' to display. It should have the following requirements.
  1. Something local so that our 'about:Tabs' doesn't disappear when we go offline and so that its relatively fast.
  2. The user should be able to modify its content.
  3. Show links that the user uses.
  4. Show thumbnails of those links
  5. Provide easy to use drag and drop interaction and generally look cool.
Now, I use del.icio.us which allows me to store all of my favorites online and which provides RSS feeds that list my saved links. New in IE7 is an RSS platform that will, among other things, cache RSS feeds locally. So, by pointing about:Tabs to my del.icio.us feed 'http://del.icio.us/rss/sequelguy/quickreference' I get (1) from IE7's RSS support, and (2) and (3) from del.icio.us. Of course requirements (4) and (5) are missing but hey, I said this was ugly.

In summary, if you change the registry value "HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Internet Explorer\AboutURLs!Tabs" to point to an RSS feed of your favorites you can get a hack-y version of Opera's Speed Dial. I should note that although its referenced on pages such as wikipedia changing your 'about:Tabs' URI in the manner I describe is not documented and not supported by Microsoft. There could be all kinds of horrible repercussions from this change of which I'm not aware. Yeah, actually you know what? Forget I said any of this. Pretend I never wrote it...PermalinkCommentsbrowser technical hack
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