| commit | 05e83c2ea5c6ccd05517d8b788e6b547976b7961 | [log] [tgz] |
|---|---|---|
| author | Dominic Farolino <dom@chromium.org> | Tue Jan 31 19:09:40 2023 |
| committer | Blink WPT Bot <blink-w3c-test-autoroller@chromium.org> | Tue Jan 31 19:27:04 2023 |
| tree | 385896780b0159d063075a86fd1d42d9f0b82df6 | |
| parent | ae74e9c26b40d0b81a137b7a7d1004b078ee3e93 [diff] |
Image Loading: Remove `last_base_element_url_` `blink::ImageLoader::last_base_element_url_` stores a snapshot of the Document's base URL during UpdateFromElement() [1]. However, this snapshot is not actually used to resolve the URL of the image request after the microtask checkpoint in DoUpdateFromElement(); rather, relative URL resolution always happens with the Document's live base URL mechanism [2] (more on this later). Instead, the member exists solely to detect, at image insertion time [3], if the Document's base URL has changed since the last time UpdateFromElement() was called. The rationale for this used to be to detect if a document's base URL changed before the image loading microtask (DoUpdateFromElement()) was run, so that we could protect against fetching the wrong image with a stale URL; see [4]. This was important because at the time, (before crrev.com/c/2103987) ImageLoader used to store a snapshot of the resolved image URL in the microtask state computed in UpdateFromElement(), so it was possible to wind up in DoUpdateFromElement() with an image request URL that is stale compared to the live Document's base URL (this was intentional, see crbug.com/569760 & https://codereview.chromium.org/2105283002). The solution [5] at the time was to detect, only during insertion, if the ImageLoader's last known snapshot of the Document base URL is stale, so that the image processing model can be re-entered, and the final DoUpdateFromElement() call is made with an up-to-date URL. This protects against the very specific issue of: 1. Creating an image (thus scheduling the microtask) 2. Changing the Document's base URL 3. The microtask that finally runs fetches an image with a stale URL However, I have no idea how this could protect against the original bug filed [4]; see https://chromium-review.googlesource.com/c/chromium/src/+/3311225/comments/5ab9c13f_9c553169 where there is some discussion about how the original bug could have behaved. In any case, since then, crrev.com/c/2103987 has landed which ensures that DoUpdateElement() always resolves relative URLs with the live Document's base URL, so it is impossible for DoUpdateElement() to fetch an outdated URL. This leaves us with the `last_base_element_url_` member that is used as a discriminator to re-invoke the image processing model upon insertion due to this member being stale compared to the Document's base URL. This results in Chromium sometimes fetching the same exact image twice (3-step scenario listed above), which makes this member entirely obsolete dead weight. Furthermore, the HTML Standard does not define general image insertion as a "relevant mutation" [6] that would invoke #update-the-image-data, and it certainly does not capture any base-URL-specific state in the microtask machinery. After some discussion on https://github.com/whatwg/html/issues/7383, we've decided to align Chromium with the specification, which prompts this CL. Testing-wise, this CL is covered by: - image-load-reset-on-new-base.html - Created in response to [4] - svg-image-load-reset-on-new-base.html - Same as above, but the SVG variant - image-base-url.html - Added/moved in crrev.com/c/2103987 - TODO: Add a test that ensures only one request is made - This test is important because while the others ensure that the final image is correct, we've discovered that some browsers are re-fetching the image due to base URLs changing before the image microtask is run, and sometimes that second fetch is using the correct URL, and sometimes it's wrong: https://github.com/whatwg/html/issues/7383#issuecomment-1408234538 [1]: https://source.chromium.org/chromium/chromium/src/+/main:third_party/blink/renderer/core/loader/image_loader.cc;l=646-647;drc=3297fb6d70a02d8c4af8db2bc9e315053744442b [2]: https://source.chromium.org/chromium/chromium/src/+/main:third_party/blink/renderer/core/loader/image_loader.cc;l=724;drc=3297fb6d70a02d8c4af8db2bc9e315053744442b [3]: https://source.chromium.org/chromium/chromium/src/+/main:third_party/blink/renderer/core/loader/image_loader.cc;l=297-302;drc=3297fb6d70a02d8c4af8db2bc9e315053744442b [4]: https://crbug.com/897545 [5]: https://crrev.com/c/1296506 [6]: https://html.spec.whatwg.org/multipage/images.html#relevant-mutations Bug: 569760,897545 Change-Id: If6a93c091bfaea2944489e3660adc695d04c3e72 Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3311225 Reviewed-by: Fredrik Söderquist <fs@opera.com> Commit-Queue: Dominic Farolino <dom@chromium.org> Cr-Commit-Position: refs/heads/main@{#1099380}
The web-platform-tests Project is a cross-browser test suite for the Web-platform stack. Writing tests in a way that allows them to be run in all browsers gives browser projects confidence that they are shipping software that is compatible with other implementations, and that later implementations will be compatible with their implementations. This in turn gives Web authors/developers confidence that they can actually rely on the Web platform to deliver on the promise of working across browsers and devices without needing extra layers of abstraction to paper over the gaps left by specification editors and implementors.
The most important sources of information and activity are:
wpt:matrix.org matrix channel; includes participants located around the world, but busiest during the European working day.If you'd like clarification about anything, don't hesitate to ask in the chat room or on the mailing list.
Clone or otherwise get https://github.com/web-platform-tests/wpt.
Note: because of the frequent creation and deletion of branches in this repo, it is recommended to “prune” stale branches when fetching updates, i.e. use git pull --prune (or git fetch -p && git merge).
See the documentation website and in particular the system setup for running tests locally.
The wpt command provides a frontend to a variety of tools for working with and running web-platform-tests. Some of the most useful commands are:
wpt serve - For starting the wpt http serverwpt run - For running tests in a browserwpt lint - For running the lint against all testswpt manifest - For updating or generating a MANIFEST.json test manifestwpt install - For installing the latest release of a browser or webdriver server on the local machine.wpt serve-wave - For starting the wpt http server and the WAVE test runner. For more details on how to use the WAVE test runner see the documentation.On Windows wpt commands must be prefixed with python or the path to the python binary (if python is not in your %PATH%).
python wpt [command]
Alternatively, you may also use Bash on Ubuntu on Windows in the Windows 10 Anniversary Update build, then access your windows partition from there to launch wpt commands.
Please make sure git and your text editor do not automatically convert line endings, as it will cause lint errors. For git, please set git config core.autocrlf false in your working tree.
The master branch is automatically synced to wpt.live and w3c-test.org.
Save the Web, Write Some Tests!
Absolutely everyone is welcome to contribute to test development. No test is too small or too simple, especially if it corresponds to something for which you've noted an interoperability bug in a browser.
The way to contribute is just as usual:
git checkout -b topic../wpt lint as described above.If you spot an issue with a test and are not comfortable providing a pull request per above to fix it, please file a new issue. Thank you!