This month in Servo: faster fonts, fetches, and flexbox!

Servo now supports ‘mix-blend-mode: plus-lighter’ (@mrobinson, #34057) and ‘transition-behavior: allow-discrete’ (@Loirooriol, #33991), including in the ‘transition’ shorthand (@Loirooriol, #34005), along with the fetch metadata request headers ‘Sec-Fetch-Site’, ‘Sec-Fetch-Mode’, ‘Sec-Fetch-User’, and ‘Sec-Fetch-Dest’ (@simonwuelker, #33830).

We now have partial support for the CSS size keywords ‘min-content’, ‘max-content’, ‘fit-content’, and ‘stretch’ (@Loirooriol, #33558, #33659, #33854, #33951), including in floats (@Loirooriol, #33666), atomic inlines (@Loirooriol, #33737), and elements with ‘position: absolute’ or ‘fixed’ (@Loirooriol, #33950).

We’re implementing the SubtleCrypto API, starting with full support for crypto.subtle.digest() (@simonwuelker, #34034), partial support for generateKey() with AES-CBC and AES-CTR (@msub2, #33628, #33963), and partial support for encrypt(), and decrypt() with AES-CBC (@msub2, #33795).

More engine changes

Servo’s architecture is improving, with a new cross-process compositor API that reduces memory copy overhead for video (@mrobinson, @crbrz, #33619, #33660, #33817). We’ve also started phasing out our old OpenGL bindings (gleam and sparkle) in favour of glow, which should reduce Servo’s complexity and binary size (@sagudev, @mrobinson, surfman#318, webxr#248, #33538, #33910, #33911).

We’ve updated to Stylo 2024-10-04 (@Loirooriol, #33767) and wgpu 23 (@sagudev, #34073, #33819, #33635). The new version of wgpu includes several patches from @sagudev, adding support for const_assert, as well as accessing const arrays with runtime index values. We’ve also reworked WebGPU canvas presentation to ensure that we never use old buffers by mistake (@sagudev, #33613).

We’ve also landed a bunch of improvements to our DOM geometry APIs, with DOMMatrix now supporting toString() (@simonwuelker, #33792) and updating is2D on mutation (@simonwuelker, #33796), support for DOMRect.fromRect() (@simonwuelker, #33798), and getBounds() on DOMQuad now handling NaN correctly (@simonwuelker, #33794).

We now correctly handle non-ASCII characters in <img srcset> (@evuez, #33873), correctly handle data: URLs in more situations (@webbeef, #33500), and no longer throw an uncaught exception when pages try to use IntersectionObserver (@mrobinson, #33989).

Outreachy contributors are doing great work in Servo again, helping us land many of this month’s improvements to GC static analysis (@taniishkaa, @webbeef, @chickenleaf, @jdm, @jahielkomu, @wulanseruniati, @lauwwulan, #33692, #33706, #33800, #33774, #33816, #33808, #33827, #33822, #33820, #33828, #33852, #33843, #33836, #33865, #33862, #33891, #33888, #33880, #33902, #33892, #33893, #33895, #33931, #33924, #33917, #33921, #33958, #33920, #33973, #33960, #33928, #33985, #33984, #33978, #33975, #34003, #34002) and code health (@chickenleaf, @DileepReddyP, @taniishkaa, @mercybassey, @jahielkomu, @cashall-0, @tony-nyagah, @lwz23, @Noble14477, #33959, #33713, #33804, #33618, #33625, #33631, #33632, #33633, #33643, #33643, #33646, #33648, #33653, #33664, #33685, #33686, #33689, #33686, #33690, #33705, #33707, #33724, #33727, #33728, #33729, #33730, #33740, #33744, #33757, #33771, #33757, #33782, #33790, #33809, #33818, #33821, #33835, #33840, #33853, #33849, #33860, #33878, #33881, #33894, #33935, #33936, #33943).

Performance improvements

Our font system is faster now, with reduced latency when loading system fonts (@mrobinson, #33638), layout no longer blocking on sending font data to WebRender (@mrobinson, #33600), and memory mapped system fonts on macOS and FreeType platforms like Linux (@mrobinson, @mukilan, #33747).

Servo now has a dedicated fetch thread (@mrobinson, #33863). This greatly reduces the number of IPC channels we create for individual requests, and should fix crashes related to file descriptor exhaustion on some platforms. Brotli-compressed responses are also handled more efficiently, such that we run the parser with up to 8 KiB of decompressed data at a time, rather than only 10 bytes of compressed data at a time (@crbrz, #33611).

Flexbox layout now uses caching to avoid doing unnecessary work (@mrobinson, @Loirooriol, #33964, #33967), and now has experimental tracing-based profiling support (@mrobinson, #33647), which in turn no longer spams RUST_LOG=info when not enabled (@delan, #33845). We’ve also landed optimisations in table layout (@Loirooriol, #33575) and in our layout engine as a whole (@Loirooriol, #33806).

Work continues on making our massive script crate build faster, with improved incremental builds (@sagudev, @mrobinson, #33502) and further patches towards splitting script into smaller crates (@sagudev, @jdm, #33627, #33665).

We’ve also fixed several crashes, including when initiating a WebXR session on macOS (@jdm, #33962), when laying out replaced elements (@Loirooriol, #34006), when running JavaScript modules (@jdm, #33938), and in many situations when garbage collection occurs (@chickenleaf, @taniishkaa, @Loirooriol, @jdm, #33857, #33875, #33904, #33929, #33942, #33976, #34019, #34020, #33965, #33937).

servoshell, embedding, and devtools

Devtools support (--devtools 6080) is now compatible with Firefox 131+ (@eerii, #33661), and no longer lists iframes as if they were inspectable tabs (@eerii, #34032).

Servo-the-browser now avoids unnecessary redraws (@webbeef, #34008), massively reducing its CPU usage, and no longer scrolls too slowly on HiDPI systems (@nicoburns, #34063). We now update the location bar when redirects happen (@rwakulszowa, #34004), and these updates are sent to all embedders of Servo, not just servoshell.

We’ve added a new --unminify-css option (@Taym95, #33919), allowing you to dump the CSS used by a page like you can for JavaScript. This will pave the way for allowing you to modify that CSS for debugging site compat issues, which is not yet implemented.

We’ve also added a new --screen-size option that can help with testing mobile websites (@mrobinson, #34038), renaming the old --resolution option to --window-size, and we’ve removed --no-minibrowser mode (@Taym95, #33677).

We now publish nightly builds for OpenHarmony on servo.org (@mukilan, #33801). When running servoshell on OpenHarmony, we now display toasts when pages load or panic (@jschwe, #33621), and you can now pass certain Servo options via hdc shell aa start or a test app (@jschwe, #33588).

Donations

Thanks again for your generous support! We are now receiving 4201 USD/month (+1.3% over September) in recurring donations. We are no longer accepting donations on LFX — if you were donating there, please move your recurring donations to GitHub or Open Collective.

Servo is also on thanks.dev, and already ten GitHub users that depend on Servo are sponsoring us there. If you use Servo libraries like url, html5ever, selectors, or cssparser, signing up for thanks.dev could be a good way for you (or your employer) to give back to the community.

With this money, we’ve been able to pay for a second Outreachy intern in this upcoming round, plus our web hosting and self-hosted CI runners for Windows and Linux builds. When the time comes, we’ll also be able to afford macOS runners and perf bots! As always, use of these funds will be decided transparently in the Technical Steering Committee. For more details, head to our Sponsorship page.

Conference talks

• Servo project update — Manuel Rego spoke at the LF Europe Member Summit about the status and long-term vision of the Servo project
• Servo: Building a Browser Rendering Engine in Rust (slides) — Rakhi Sharma spoke at the Ubuntu Summit about Servo’s recent work in embedding, layout, and benchmarking