[webkit-help] Content Blocker - blocked requests should not seem successful to requester

[Andrey Meshkov]

As I've never got answered on this list, I've filed a bug report:
https://bugs.webkit.org/show_bug.cgi?id=151649

--
wbr, Andrey Meshkov
skype: aymeshkov
cell: +7 903 534 9643

2015-11-30 2:46 GMT+03:00 Andrey Meshkov <am at adguard.com>:

> Hi!
>
> There is an issue with the way content blockers present blocked requests
> to the requesters.
>
> Usually (e.g. for all other browsers) when request is blocked by add-on or
> extension it looks like an error to the page code. For instance, "onerror"
> is called for XMLHttpRequest and "element.onerror" callback is called for
> the DOM element if it's load is blocked by the ad blocker.
>
> This is a common behavior and it's handled by web developers.
>
> In case of Safari content blocker "onerror" event is not raised and it may
> seem that request is successful while it is not.
>
> Here is an example.
>
> This is a rule blocking access to visualwebsiteoptimizer.com domain.
> This domain is a known tracker so you can see this rule in all "privacy"
> related filter lists like EasyPrivacy and such.
> [
> {
> "trigger": {
> "url-filter": "^https?://[^.]+\\.?visualwebsiteoptimizer\\.com[/:&?]?",
> "load-type": [
> "third-party"
> ]
> },
> "action": {
> "type": "block"
> }
> }
> ]
>
> But it can't be used in Safari because the "silent" blocking breaks entire
> website which use visualwebsiteoptimizer.com. Examples of such websites:
> http://info.singtel.com
> http://www.harveynorman.com.au
>
> Here is a code used by them:
> http://pastebin.com/awYa9s95
>
> As you can see they handle "onerror" callback, but it's not fired in
> Safari so the "body" element remains hidden.
>
> Btw, this issue also causes significant delays when ads are blocked on
> Youtube. They also are waiting for "onerror" callback to fire, but as it is
> not fired, video does not start until "ontimeout" is fired.
>
> --
> wbr, Andrey Meshkov
>
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