[trel] require link-local for peer discovered by mDNS

[jwhui]

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[codecov]

Codecov Report

Attention: Patch coverage is 0% with 3 lines in your changes missing coverage. Please review.

Project coverage is 43.75%. Comparing base (2b41187) to head (09ea22c).
Report is 974 commits behind head on main.

Files with missing lines	Patch %	Lines
src/trel_dnssd/trel_dnssd.cpp	0.00%	3 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #2709       +/-   ##
===========================================
- Coverage   55.77%   43.75%   -12.03%     
===========================================
  Files          87      110       +23     
  Lines        6890    13426     +6536     
  Branches        0      957      +957     
===========================================
+ Hits         3843     5874     +2031     
- Misses       3047     7242     +4195     
- Partials        0      310      +310     

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[abtink]

LGTM. Thanks. 👍

[abtink]

👍

[EskoDijk]

@jwhui There could be a TREL peer using a (legacy?) mDNS stack that doesn't include any link-local address in host records if a non-LL address is available, such as Avahi.

Wouldn't this change break TREL with all such "legacy" peers?

[abtink]

@jwhui There could be a TREL peer using a (legacy?) mDNS stack that doesn't include any link-local address in host records if a non-LL address is available, such as Avahi.

Wouldn't this change break TREL with all such "legacy" peers?

@EskoDijk please check these PRs and issues related to this (which are similar to what you mention above):

• Mdns::Publisher signals resolved with the first address #2711
• [mdns-publisher] move link-local address filtering to DiscoveryProxy #2710
• [mdns-publisher] use FlagsMoreComing in Mdns::Publisher #2712

I think we should prefer link-local but if there is none then use other addresses.

[jwhui]

Wouldn't this change break TREL with all such "legacy" peers?

@EskoDijk , given the reported issues with existing "legacy" peers, maybe it is good to avoid connecting to such "legacy" peers.