[meshcop] support non-standard TXT entries at runtime

[wgtdkp]

See also https://android-review.git.corp.google.com/c/platform/external/ot-br-posix/+/3111060
for how this change is used and tested.

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 6 lines in your changes missing coverage. Please review.

Project coverage is 39.81%. Comparing base (2b41187) to head (bdee2bb).
Report is 676 commits behind head on main.

Files	Patch %	Lines
src/border_agent/border_agent.cpp	0.00%	6 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #2308       +/-   ##
===========================================
- Coverage   55.77%   39.81%   -15.97%     
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  Files          87       89        +2     
  Lines        6890     9873     +2983     
  Branches        0      727      +727     
===========================================
+ Hits         3843     3931       +88     
- Misses       3047     5744     +2697     
- Partials        0      198      +198     

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[superwhd]

LGTM overall 👍

In the future we may want to unify the two ways (D-BUS, Android overlay) for customizing meshcop TXT for better readability.

[bukepo]

can we use the existing HandleUpdateVendorMeshCoPTxtEntries?

[wgtdkp]

can we use the existing HandleUpdateVendorMeshCoPTxtEntries?

That one doesn't support overriding the vendor or product name

[bukepo]

can we use the existing HandleUpdateVendorMeshCoPTxtEntries?

That one doesn't support overriding the vendor or product name

I think we should allow overriding these fields by dbus api as well.

[wgtdkp]

can we use the existing HandleUpdateVendorMeshCoPTxtEntries?

That one doesn't support overriding the vendor or product name

I think we should allow overriding these fields by dbus api as well.

I am not sure that's a good idea. The SetMeshCopServiceValues method for Android is documented clearly that this must be called before BorderAgent is enabled, so that it won't cause a vendor or model name change which will cause unexpected behavior - mobile devices are depending on the names to take specific actions. Generally, it doesn't sound reasonable for a device to be Google Border Router at T1 and then changes to be Apple Border Router at T2.

It would require the dbus client side change if you want to ensure that advertised vendor name never changes for dbus-controlled device. But this is out of scope I think.