Contact emails
miketa...@chromium.org, jadekess...@chromium.org
Explainer
https://github.com/WICG/ua-client-hints#explainer-reducing-user-agent-granularity
Specification
https://wicg.github.io/ua-client-hints/#sec-ch-ua-wow64
Summary
The Sec-CH-UA-WoW64 Client Hint is a backwards compatible shim for sites
relying on "WoW64-ness" (32-bit app running in 64-bit Windows) as they
transition from the User-Agent string to UA-CH. It returns a boolean value.
Blink component
Blink>Network>ClientHints
<https://bugs.chromium.org/p/chromium/issues/list?q=component:Blink%3ENetwork%3EClientHints>
Motivation
We would like to provide a seamless transition from User-Agent-based use
cases to UA-CH. The "WoW64" bit is the last missing piece to accomplish
this goal.
Initial public proposal
https://github.com/WICG/ua-client-hints/issues/217
Search tags
wow, wow64, ua-ch, uach
TAG review
https://github.com/w3ctag/design-reviews/issues/640 - still open, but
issues have been addressed. I'll ping the existing issue with this
addition so folks are aware, but I don't expect it to change TAG's
stance of UA-CH as a feature.
TAG review status
Issues addressed
Risks
We don’t anticipate any risk here, we’re just moving this bit from one
API to another as a shim.
Interoperability and Compatibility
Interop: Not all browsers expose wow64-ness in the UA string today, so
sites should not treat a false value as meaningful (the spec allows for
always returning false).
Compat: This hint can be thought of as a compatibility shim for sites
migrating from User-Agent to UA-CH, otherwise N/A.
Gecko: Non-harmful on UA-CH, but were they to implement UA-CH I would
not expect them to add this hint (as they don’t expose this bit in their
UA string anymore).
WebKit: No signal. I would also not expect Apple to implement this one,
were they to implmement UA-CH.
Web developers: Mixed signals
(https://github.com/WICG/ua-client-hints/issues/217) We know of at least
one site (Meet) that uses wow64 to prevent sending a 7MB wasm binary to
users were performance is known to be lousy .
Debuggability
Nothing special needed.
Is this feature fully tested by web-platform-tests?
We'll add some.
Flag name
None.
Requires code in //chrome?
False
Estimated milestones
M100
Tracking Bug
https://bugs.chromium.org/p/chromium/issues/detail?id=1288837
Link to entry on the Chrome Platform Status
https://chromestatus.com/feature/5682026601512960
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