Intent to Ship: Spec-compliant JSON MIME type detection

[Issack John]

Contact emails

issac...@microsoft.com, dan...@microsoft.com

Explainer

None

Specification

https://mimesniff.spec.whatwg.org/#json-mime-type

Summary

Chromium now recognizes all valid JSON MIME types as defined by the WHATWG mimesniff specification. This includes any MIME type whose subtype ends with “+json”, in addition to the traditional application/json and text/json. This change ensures that web APIs and features relying on JSON detection behave consistently with the web platform standard and other browsers. A key motivation for this change is to fix JSON module import behavior, where previously valid JSON MIME types like text/html+json and image/svg+json would fail to load as modules. Draft CL: https://chromium-review.googlesource.com/c/chromium/src/+/6525687 Related Issues: https://github.com/whatwg/mimesniff/issues/112. The consensus was to retain the broad definition of JSON MIME types—including all */*+json.

Blink component

Blink>Network

Search tags

json, mime, sniffing, spec-compliance, interoperability

TAG review

None; this is a small change to match an existing spec and behavior of other browsers.

TAG review status

Not applicable

Risks

Interoperability and Compatibility

Interoperability risk is low. This change brings Chromium into alignment with the WHATWG MIME Sniffing Standard §4.6, which defines a JSON MIME type as any MIME type whose subtype ends with +json (e.g., text/html+json, image/svg+json), or is exactly application/json or text/json. Firefox and Safari already match this behavior, and the change improves interoperability for web developers. https://wpt.fyi/results/html/semantics/scripting-1/the-script-element/json-module/valid-content-type.html A specific compatibility consequence is that JSON module imports (both static and dynamic) of files with */*+json MIME types would previously have produced an error but will now succeed. This seems low risk.

Gecko: Shipped/Shipping

WebKit: Shipped/Shipping

Web developers: No signals

Other signals:

Ergonomics

None expected

WebView application risks

Does this intent deprecate or change behavior of existing APIs, such that it has potentially high risk for Android WebView-based applications?

None

Debuggability

None

Will this feature be supported on all six Blink platforms (Windows, Mac, Linux, ChromeOS, Android, and Android WebView)?

Yes

Is this feature fully tested by web-platform-tests?

Yes

Test: https://wpt.fyi/results/html/semantics/scripting-1/the-script-element/json-module/valid-content-type.html

Flag name on about://flags

None

Finch feature name

SpecCompliantJsonMimeTypes

Rollout plan

Will ship enabled for all users

Requires code in //chrome?

False

Estimated milestones

Shipping on desktop	138
Shipping on Android	138
Shipping on WebView	138

Anticipated spec changes

Open questions about a feature may be a source of future web compat or interop issues. Please list open issues (e.g. links to known github issues in the project for the feature specification) whose resolution may introduce web compat/interop risk (e.g., changing to naming or structure of the API in a non-backward-compatible way).

None

Link to entry on the Chrome Platform Status

https://chromestatus.com/feature/5470594816278528?gate=6275763980206080

This intent message was generated by Chrome Platform Status.

[Issack John]

We plan to deploy the feature as an enabled-by-default base::Feature, primarily to act as an emergency shutoff valve rather than going through a formal feature rollout. This approach aligns with the consensus-based standards section, which doesn’t call for a gradual rollout, and given the low risk, we believe a full rollout process isn’t necessary.

That said, we’re calling this out here to give an opportunity to raise any concerns about deploying it in this way.

[Domenic Denicola]

LGTM1. This is a nice focused interop and spec-compliance change that should have approximately zero compat impact. I agree with the plan of shipping enabled-by-default and using Finch as an emergency kill switch if something (very) unexpected happens.

--
You received this message because you are subscribed to the Google Groups "blink-dev" group.
To unsubscribe from this group and stop receiving emails from it, send an email to blink-dev+...@chromium.org.
To view this discussion visit https://groups.google.com/a/chromium.org/d/msgid/blink-dev/52cec510-3355-4452-b961-b9f5fe1cb323n%40chromium.org.

[Yoav Weiss (@Shopify)]

LGTM2

To view this discussion visit https://groups.google.com/a/chromium.org/d/msgid/blink-dev/CAM0wra-KjjfbSyesFiXTxAsWhCkX%2B1CCtT%3DwiippOLKmoXiqXQ%40mail.gmail.com.

[Yoav Weiss (@Shopify)]

Can you flip the testing review bit in chromestatus.com? That would ensure the testing folks take a look at this.

[Daniel Bratell]

LGTM3

/Daniel

To view this discussion visit https://groups.google.com/a/chromium.org/d/msgid/blink-dev/CAOmohSL6xAgTpm%3Dh0csiONCe8%2BQVCivGQZ6JOzCLFXr%3D6TtOuw%40mail.gmail.com.

[Issack John]

Thanks for the reviews! I’ve just requested the testing review on chromestatus.com so it’s on their radar now.