Add IPv6 support

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.

proxy.py

@@ -1,13 +1,14 @@
 #!/usr/bin/env python3
 
-from zeroconf import Zeroconf, ServiceBrowser, ServiceStateChange, ServiceInfo, DNSQuestion, DNSOutgoing, RecordUpdateListener
+from zeroconf import Zeroconf, ServiceBrowser, ServiceStateChange, ServiceInfo, DNSQuestion, DNSOutgoing, RecordUpdateListener, IPVersion
-from zeroconf.const import _TYPE_A, _CLASS_IN, _FLAGS_QR_QUERY
+from zeroconf.const import _TYPE_A, _TYPE_AAAA, _CLASS_IN, _FLAGS_QR_QUERY
 import sys
 import time
 from twisted.internet import reactor, defer, threads
 from twisted.names import client, dns, error, server
 from twisted.python import log
 import socket
+import ipaddress
 
 domain = sys.argv[1]
 port = int(sys.argv[2])
@@ -16,7 +17,7 @@ timeout = 2
 
 class DynamicResolver(object):
     def __init__(self):
-        self.zeroconf = Zeroconf(ip_version=4)
+        self.zeroconf = Zeroconf(ip_version=IPVersion.All)
     
     def _dynamicResponseRequired(self, query):
         if str(query.name).endswith(domain):
@@ -84,22 +85,33 @@ class DynamicResolver(object):
             answers = [dns.RRHeader(name=localname[:-6] + domain, ttl=ttl, type=dns.SRV, payload=dns.Record_SRV(
                     info.priority, info.weight, info.port, info.server[:-6] + domain
                 ))]
-            additional = [dns.RRHeader(name=info.server[:-6] + domain, ttl=ttl, type=dns.A, payload=dns.Record_A(
+            target = info.server[:-6] + domain
-                    socket.inet_ntop(socket.AF_INET, addr)
+            additional = [dns.RRHeader(name=target, ttl=ttl, type=dns.A, payload=dns.Record_A(
-                )) for addr in info.addresses]
+                    str(addr)
+                )) for addr in info.ip_addresses_by_version(IPVersion.V4Only)]
+            additional += [dns.RRHeader(name=target, ttl=ttl, type=dns.AAAA, payload=dns.Record_AAAA(
+                    str(addr)
+                )) for addr in info.ip_addresses_by_version(IPVersion.V6Only) if not addr.is_link_local]
             return answers, [], additional
         
-        def host(localname):
+        def host(localname, qtype):
+            if qtype == dns.AAAA:
+                mdns_type, addr_len, parse_addr = _TYPE_AAAA, 16, ipaddress.IPv6Address
+            else:
+                mdns_type, addr_len, parse_addr = _TYPE_A, 4, ipaddress.IPv4Address
+
             class listener(RecordUpdateListener):
                 def __init__(self):
                     self.addrs = []
                     self.time = time.time()
                 def update_record(self, zc, now, record):
-                    if record.type == _TYPE_A and len(record.address) == 4:
+                    if record.type == mdns_type and len(record.address) == addr_len:
-                        self.addrs.append(socket.inet_ntop(socket.AF_INET, record.address))
+                        addr = parse_addr(record.address)
+                        if not addr.is_link_local:
+                            self.addrs.append(str(addr))
 
             l = listener()
-            q = DNSQuestion(localname, _TYPE_A, _CLASS_IN)
+            q = DNSQuestion(localname, mdns_type, _CLASS_IN)
             self.zeroconf.add_listener(l, q)
             out = DNSOutgoing(_FLAGS_QR_QUERY)
             out.add_question(q)
@@ -108,7 +120,8 @@ class DynamicResolver(object):
                 time.sleep(0.1)
             self.zeroconf.remove_listener(l)
 
-            answers = [dns.RRHeader(name=query.name.name, ttl=ttl, type=dns.A, payload=dns.Record_A(
+            record_cls = dns.Record_AAAA if qtype == dns.AAAA else dns.Record_A
+            answers = [dns.RRHeader(name=query.name.name, ttl=ttl, type=qtype, payload=record_cls(
                     addr
                 )) for addr in l.addrs]
 
@@ -125,10 +138,10 @@ class DynamicResolver(object):
         elif query.type == dns.SRV:
             d = threads.deferToThread(srv, localname)
             return d
-        elif query.type == dns.A:
+        elif query.type in (dns.A, dns.AAAA):
-            d = threads.deferToThread(host, localname)
+            d = threads.deferToThread(host, localname, query.type)
             return d
-        elif query.type != dns.AAAA:
+        else:
             print("Unsupported request", query)
         d.callback(([], [], []))
         return d