FS#4140 - umdns does not respect legacy queries (not from port 5353)

[openwrt-bot]

kirelagin:

According to [[https://datatracker.ietf.org/doc/html/rfc6762#section-6.7|Section 6.7 of the RFC]], if the query was sent not from port 5353, the responder MUST respond over unicast and, most importantly, to the same port that the query was sent from.

This is what currently prevents

dig -p 5353 @224.0.0.251

from working, since dig is expecting the response on the random port it sent its query from, but umdns, contrary to the specifiation, always sends to port 5353.

[openwrt-bot]

kirelagin:

I made a patch (untested!) that will ensure the response goes to the right address/port.

However, there are additional requirements that, IIUC, are currently not satisfied:

This unicast response MUST be a
conventional unicast response as would be generated by a conventional
Unicast DNS server; for example, it MUST repeat the query ID and the
question given in the query message. In addition, the cache-flush
bit described in Section 10.2, "Announcements to Flush Outdated Cache
Entries", MUST NOT be set in legacy unicast responses.

[rthakur33]

pull request #12 resolves this issue