abinpaul1/gsoc22.md

## gsoc22.md

      
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              gsoc22.md
            
          
    Render-blocking status in Resource Timing API

Abin K Paul (abin.paul1@gmail.com)
Mentors


Yoav Weiss
Hao Liu

Intro

Introduce a new field renderBlockingStatus to PerformanceResourceTiming which would be an enum highlighting the render blocking nature of stylesheets and scripts. The project involved taking the feature through the Blink shipping process which includes adding changes to the Fetch and Resource Timing specifications, adding necessary Web Platform Tests and an implementation of the feature in Chromium.
Initial proposal

https://docs.google.com/document/d/1J0WlKFKxDDWCMHEXtO-vUdgJonbHRQSNDsYUBAwhguY
Feature work


An issue for the feature was available in the repository for Resource-Timing : w3c/resource-timing#262


As part of the blink process, the first step was to create a new entry for the feature in Chrome Status Dashboard to track its status throughout the process : https://chromestatus.com/feature/5166965277589504


An explainer is put together to describe the proposed change to developers : https://github.com/w3c/resource-timing/blob/gh-pages/Explainers/Render_Blocking_Status.md


Since in this case the new feature is added to Resource Timing, the feature proposal is presented to the Web Performance Working group to gather feedback on the same.

Recording of the presentation is available online : Recording Link
Discussion after the presentation is captured in the meeting minutes : Minutes Link


Once the working group is on board, the proposed spec changes are made

Resource Timing : w3c/resource-timing#327
Fetch : whatwg/fetch#1449


Along with the spec changes, it is necessary to add Web platform tests for the feature. These are tests that run in all browsers to ensure compatibility between browsers. These were added as part of the chromium CL and are automatically merged into the WPT repo when the chromium CL is merged.
At this stage the feature is behind a flag (namely enable-experimental-web-platform-features). Before we check in this code behind the flag, we send out an Intent to Prototype mail to blink-dev to notify folks about the feature being developed.

Intent to Prototype : https://groups.google.com/a/chromium.org/g/blink-dev/c/KD_Z1mObs_8/m/4ZHGrH20AAAJ
Chromium CL : https://chromium-review.googlesource.com/c/chromium/src/+/3709521


To gauge interest from other browser vendors requests for positions are filed in respective repositories. Before a feature can be added to the web platform, at least two implementers must be interested.

Safari - WebKit/standards-positions#17
Firefox - mozilla/standards-positions#662


To get a wider review we file for a review from the W3C TAG. Initially the new field was proposed as a string field. It was changed into an enum as per suggestion from TAG.

Issue : w3ctag/design-reviews#753
CL to convert to enum: https://chromium-review.googlesource.com/c/chromium/src/+/3812241


Once TAG review is done and we have interest from a second browser vendor and no major opposition, we are good to land the spec changes and enable the feature by default. We send out an Intent to Ship mail to blink-dev which will be signed off by 3 Blink API owners before we can enable the feature by default.

Intent to Ship : https://groups.google.com/a/chromium.org/g/blink-dev/c/0Md9xYf53gs/m/VFbwQmVpAwAJ
CL to enable feature by default : https://chromium-review.googlesource.com/c/chromium/src/+/3843756


Parallely worked on adding documentation for the feature to MDN Docs : https://developer.mozilla.org/en-US/docs/Web/API/PerformanceResourceTiming/renderBlockingStatus  (PR: mdn/content#19325)


Further work

Response Status Code in Resource Timing (Shipping in Chrome 109)

Adding a new field responseStatus to PerformanceResourceTiming which would be an integer corresponding to HTTP status code returned when fetching the resource.
Explainer : https://github.com/w3c/resource-timing/blob/gh-pages/Explainers/Response_Status_Code.md
Spec Changes

Resource Timing PR : w3c/resource-timing#335
Fetch PR : whatwg/fetch#1468
HTML PR: whatwg/html#8405

Chromium CLs

https://chromium-review.googlesource.com/c/chromium/src/+/3754923
https://chromium-review.googlesource.com/c/chromium/src/+/3958184

Content-type in Resource Timing (Work in progress)

Adding a new field contentType to PerformanceResourceTiming which would hold a string corresponding to the content type of the fetched resource.
Explainer : https://github.com/abinpaul1/resource-timing/blob/explainer-content-type/Explainers/Content-Type.md
Spec Changes

Resource Timing PR : w3c/resource-timing#341
Fetch PR : whatwg/fetch#1481

Chromium CL : https://chromium-review.googlesource.com/c/chromium/src/+/3916841