1315616 - Give extensions access to cached favicon URLs

Status: NEW

Description

[Stephan Sokolow]

User Agent: Mozilla/5.0 (Windows NT 6.3; WOW64; rv:37.0) Gecko/20100101 Firefox/37.0
Build ID: 20161017194958

Steps to reproduce:

Tried to write an extension that uses tab titles, urls, and favicons to produce an analogue to the backup and export options in the bookmark manager.


Actual results:

To resolve tabs.Tab.favIconUrl, I had to grant the addon "<all_urls>" permission and I've spent a whole day (and counting) trying to write suitably non-fragile fetch() code when all I want is already retrieved and staring me in the face to the left of each Tab.title.


Expected results:

Given that favicons serve a similar role to tab titles and have similar privacy and permissions implications, there should be a simple API to retrieve the already-in-memory data using only the "tabs" permission and without worrying about cache misses.

In line with the naming scheme already in place, I propose tabs.Tab.favIconBlob.

Comment 1

[Caitlin Neiman (http://pronoun.is/she)]

To be discussed at January 24 WebExtensions Triage mtg. 

Agenda: https://docs.google.com/document/d/1add-6FL8mzksvzbyB83HUmEkVmKERd-nt740AYr-4PE/edit#

Comment 2

[Kris Maglione [:kmag] (busy; behind on reviews)]

We talked about this, and decided that we want to support this use case, but that we should do it by giving extensions access to URLs backed by our favicon cache rather than by handing them image blobs.

Comment 3

[Stephan Sokolow]

(In reply to Kris Maglione [:kmag] from comment #2)
> We talked about this, and decided that we want to support this use case, but

That's good to hear.

> that we should do it by giving extensions access to URLs backed by our
> favicon cache rather than by handing them image blobs.

Is the rationale documented anywhere I could read? I'm curious about what makes cache URLs easier to support than blobs in this situation.

Comment 5

[Kris Maglione [:kmag] (busy; behind on reviews)]

(In reply to Stephan Sokolow from comment #3)
> Is the rationale documented anywhere I could read? I'm curious about what
> makes cache URLs easier to support than blobs in this situation.

In the case of blobs, we would need to fetch, decode, and store them in memory for every tab, and there would be additional overhead involved in displaying them as well. Providing access to favicon cache URLs has better performance characteristics and a simpler implementation, and still allows extensions to fetch blobs if and when they actually need them.

Comment 6

[Stephan Sokolow]

...oh yeah! e10s is a thing now!

I was still in a mindset that it'd be cheaper to just reference the existing decoded blob used to render the tab.

(Because I don't know of a way to display an arewee10syet-style report for just the ~30 extensions I have installed and because I don't want to risk my privacy extensions silently failing, I decided to just disable e10s in my Aurora and wait until I'm forced to migrate onto it... despite my loadout and tab use being pathologically unsuited to single-process operation.)

Comment 7

[Tomislav Jovanovic :zombie]

(In reply to Kris Maglione [:kmag] from comment #2)
> We talked about this, and decided that we want to support this use case, but
> that we should do it by giving extensions access to URLs backed by our
> favicon cache rather than by handing them image blobs.

Was the idea to have a tab.faviconUrl property, or some API that would return a (cached) favicon URI for any domain?  And if it's the latter, does it make sense to make it part of the MozURLUtils WebIDL from bug 1315558 comment 4?

Comment 8

[Kris Maglione [:kmag] (busy; behind on reviews)]

My thought was that faviconUrl would point to a URL backed by the favicon cache, and then we'd have to give extensions access to those URLs.

Comment 9

[Jonathan Kingston [:jkt]]

Some ideas/issues regarding this:

- Apps that serve different favicons for logged in users won't work for container tabs (EG WhatsApp does this)
- Querying for a future page load rather than an existing tab would permit use cases like:
  https://github.com/mozilla/testpilot-containers/issues/500
- In the near/distant future we might permit different icons like PWA icon, mask-icon
  - perhaps other files are relevant here too like manifest, feature policy etc

Would it make sense to permit an api similar to:

browser.cache.icons({url: "example.com", cookieStoreId: 'blah-12'});

Comment 10

[Blake Winton (:bwinton) (:☕️)]

Relatedly, Whimsy would like the user to be able to choose to show the thumbnails of sites instead of gifs on the overridden newtab page, but we have no way of getting them.  A similar api (or an extension to this api) would be very helpful.