zeroconf represents a TXT attribute with no "=" (a bare boolean flag,
valid per RFC 6763 §6.4) or an empty value as properties[key] = None.
Reconstructing the TXT record blindly did b"%s=%s" % (key, None),
which raises TypeError since bytes %-formatting rejects None. The
exception propagated out of the deferToThread call and Twisted
answered with SERVFAIL instead of the TXT record, silently breaking
resolution for any service whose TXT record includes a bare key
(e.g. some _rfb._tcp/screen-sharing advertisements).
Found by diagnosing a real screen-sharing "impossible de resoudre"
failure over a WireGuard-tunneled deployment: dig showed SRV
resolving fine but TXT returning SERVFAIL for the same instance,
which is why dns-sd -L (needs both) never completed even after
flushing the client-side mDNSResponder cache.
Replace one-shot, blind-sleep mDNS lookups with a warm cache backed by
persistent background queriers:
- PTR (browse): a single ServiceBrowser tracks every service type seen
so far (recreated with the enlarged type set when a new one shows
up, rather than one browser per type), so zeroconf continuously
refreshes it in the background; answers are read straight from the
mDNS cache instead of blocking timeout seconds on every query.
- TXT/SRV: still resolved via get_service_info() (already cache-first
internally), but a background job now periodically re-primes the
cache so it doesn't go cold between queries.
- A/AAAA (bare hostnames): answers are read from the mDNS cache first;
only a first-ever query for a name blocks waiting for a response,
with a background job keeping it warm afterwards.
Periodic refresh jobs are scheduled by a single heap-based scheduler
thread and executed by a fixed pool of 4 worker threads, so the
background thread count stays constant no matter how many distinct
names/services get queried over the proxy's lifetime.
All returned TTLs now reflect the real remaining TTL of the underlying
mDNS record instead of a fixed constant, and goodbye packets (TTL=0)
are handled for free since eviction is delegated to zeroconf's own
cache.
Also add .gitignore for the project-local .venv/ and __pycache__/.
Synthesize an SOA record for the zone, return it for direct SOA
queries, and include it in the authority section of empty responses
so resolvers can negative-cache properly. RCODE stays NOERROR rather
than NXDOMAIN, since mDNS can't reliably prove non-existence.
Enable dual-stack mDNS lookups (Zeroconf ip_version was set to a value
that matched no IPVersion member), add AAAA query handling, and include
AAAA glue records for SRV targets. Link-local IPv6/IPv4 addresses are
filtered out since they aren't usable by clients off the local link.
franck
Michael Kuron