GWT and UserAgent

[David Nouls]

Hello I read that FireFox and Chrome are deprecating the useragent string.

Is GWT depending on this and will it be impacted ?

[Thomas Broyer]

On Friday, February 18, 2022 at 6:00:24 PM UTC+1 David Nouls wrote:

Hello I read that FireFox and Chrome are deprecating the useragent string.

Not sure where you read that and what it would really mean, particularly wrt backwards compatibility: browser vendors (and spec writers) try very hard not to "break the web" (e.g. its Array.prototype.includes rather than Array.prototype.contains because many old-ish libraries monkey-patched the Array prototype with a 'contains' method) so it's very unlikely that they remove the navigator.useragent or change it in a breaking way.

What has been envisioned is to actually freeze the version in the UA string in case using a 3-digit version breaks too many websites, with Chrome relegating the major version into its "minor".

https://hacks.mozilla.org/2022/02/version-100-in-chrome-and-firefox/

 

Is GWT depending on this and will it be impacted ?

GWT does depend on the UA string, but doesn't care about the browser version, except in very few cases.

Here's the main UA-sniffing code that helps select permutations, it doesn't use the version (uses documentMode in Internet Explorer, which has since been removed and won't be in 2.10): https://github.com/gwtproject/gwt/blob/2.9.0/user/src/com/google/gwt/useragent/rebind/UserAgentPropertyGenerator.java

And here are a few cases that care about the version:

• those correctly patch all digits and won't break with 3-digit versions:
  • https://github.com/gwtproject/gwt/blob/2.9.0/user/src/com/google/gwt/user/client/ui/impl/PopupImplMozilla.java#L63
    
  • https://github.com/gwtproject/gwt/blob/2.9.0/user/src/com/google/gwt/dom/client/DOMImplMozilla.java#L33
    
  • https://github.com/gwtproject/gwt/blob/2.9.0/user/src/com/google/gwt/dom/client/DOMImplWebkit.java#L29
    
  • https://github.com/gwtproject/gwt/blob/2.9.0/user/src/com/google/gwt/user/client/ui/impl/HyperlinkImplIE.java#L40
    
• that one would likely "break" with Chrome/110–Chrome/119, but IIUC unlikely to actually break apps, only send bigger payloads because it escapes more characters: https://github.com/gwtproject/gwt/blob/2.9.0/user/src/com/google/gwt/user/client/rpc/impl/ClientSerializationStreamWriter.java#L93
  
• that one is broken since Android 10: https://github.com/gwtproject/gwt/blob/2.9.0/user/src/com/google/gwt/touch/client/TouchScroller.java#L311

All other uses of navigator.useragent seem to only care about some tokens like "safari", "chrome", "webkit", "msie", or "gecko".

[Jens]

Chrome / Safari / FireFox are all freeze their user agent string so you can not know operating system version, device type and browser build number (not the major version!) anymore. This is done to make fingerprinting more difficult.

Here is some Chrome documentation:

https://www.chromium.org/updates/ua-reduction/

If you need to access such high entropy data you need to use a new API. GWT itself should not be affected by these changes since you can still sniff if it is Chrome / Safari / Firefox and which major version it is.

-- J.