Issue 6803 - Implement readd snippet

Some websites "circumvent" ad blocking by trashing their own pages when they detect an ad blocker.

This snippet untrashes the page by adding the stylesheets back to the DOM.

Filter:

  example.com#$#readd style head; readd link[rel="stylesheet"] head

It works on some popular websites.

See #4750.

[Manish Jethani, 2018-07-20 21:54:47]

Patch Set 1

I'll file an issue on Trac, but meanwhile see the description here.

[hub, 2018-07-23 18:07:39]

https://codereview.adblockplus.org/29835561/diff/29835562/lib/content/snippet...
File lib/content/snippets.js (right):

https://codereview.adblockplus.org/29835561/diff/29835562/lib/content/snippet...
lib/content/snippets.js:264: for (let node of mutation.removedNodes || [])
if mutation.removedNodes is falsey, we could just skip the whole thing. Why not
checking it before `mutation.target.matches(parentSelector)` above?

[Manish Jethani, 2018-07-23 20:07:07]

Patch Set 2: Check for removedNodes first
Patch Set 3: Check if node is element

https://codereview.adblockplus.org/29835561/diff/29835562/lib/content/snippet...
File lib/content/snippets.js (right):

https://codereview.adblockplus.org/29835561/diff/29835562/lib/content/snippet...
lib/content/snippets.js:264: for (let node of mutation.removedNodes || [])
On 2018/07/23 18:07:39, hub wrote:
> if mutation.removedNodes is falsey, we could just skip the whole thing. Why
not
> checking it before `mutation.target.matches(parentSelector)` above?

Makes sense, done.

[hub, 2018-07-23 21:00:57]

LGTM

[Manish Jethani, 2018-07-23 22:32:31]

Patch Set 4: Add ifContains and unlessContains parameters
Patch Set 5: Add complementary remove-if-contains snippet

We have found some variations on the sites that we are testing with. In some
cases, there is a style element like so:

  <style>
    img { display: none }
  </style>

So, instead of removing any styles, they add more styles that hide all the
relevant content and make the page appear broken. In such cases, we need to do
the opposite: remove any stylesheets that match some pattern.

I have added a complementary remove-if-contains snippet to do this.

Since the untrash snippet prevents the removal of stylesheets, we need to pass
it the unlessContains parameter so it doesn't readd the stylesheet we are
removing using remove-if-contains (race condition).

[Manish Jethani, 2018-07-24 14:31:39]

Patch Set 6: Revert last two updates and rebase

This is the same as Patch Set 3, rebased.

I'm going back on the last two updates now because, based on testing, it seems
like we don't need the additional snippet for most domains. We can look at that
approach separately.

[hub, 2018-07-24 14:52:50]

LGTM

[Manish Jethani, 2018-07-24 15:44:45]

Patch Set 7: Rename snippet to "readd"

Sorry about this.

I have been thinking about how to name snippets and what each snippet's role
should be. I think each snippet should do something specific and well defined.
This one should readd any removed elements that match a CSS selector, period. If
there are other techniques for "untrashing" a document, they should be
implemented as their own snippets.

[hub, 2018-07-24 15:52:32]

LGTM