Use gethostbyname when using aiodns

Slixmpp behaves differently when resolving host names, whether aiodns
is used or not. With aiodns only DNS is used, while without
`asyncio.loop.getaddrinfo()` is used instead, which utilizes the Name
Service Switch (NSS) to resolve host names by other means (hosts-file,
mDNS, ...) as well.

To unify the behavior, this replaces the use of
`aiodns.DNSResolver().query()` with
`aiodns.DNSResolver().gethostbyname()`. This makes the behavior
resolving host names more consistent between using aiodns or not, as
both now honor the NSS configuration and removes the need for the
previously existing workaround to resolve localhost.

slixmpp/xmlstream/resolver.py

@@ -15,7 +15,13 @@ from slixmpp.types import Protocol
 log = logging.getLogger(__name__)
 
 
-class AnswerProtocol(Protocol):
+class GetHostByNameAnswerProtocol(Protocol):
+    name: str
+    aliases: List[str]
+    addresses: List[str]
+
+
+class QueryAnswerProtocol(Protocol):
     host: str
     priority: int
     weight: int
@@ -23,6 +29,9 @@ class AnswerProtocol(Protocol):
 
 
 class ResolverProtocol(Protocol):
+    def gethostbyname(self, host: str, socket_family: socket.AddressFamily) -> Future:
+        ...
+
     def query(self, query: str, querytype: str) -> Future:
         ...
 
@@ -147,11 +156,6 @@ async def resolve(host: str, port: int, *, loop: AbstractEventLoop,
 
     results = []
     for host, port in hosts:
-        if host == 'localhost':
-            if use_ipv6:
-                results.append((host, '::1', port))
-            results.append((host, '127.0.0.1', port))
-
         if use_ipv6:
             aaaa = await get_AAAA(host, resolver=resolver,
                                        use_aiodns=use_aiodns, loop=loop)
@@ -201,13 +205,13 @@ async def get_A(host: str, *, loop: AbstractEventLoop,
             return []
 
     # Using aiodns:
-    future = resolver.query(host, 'A')
+    future = resolver.gethostbyname(host, socket.AF_INET)
     try:
-        recs = cast(Iterable[AnswerProtocol], await future)
+        recs = cast(GetHostByNameAnswerProtocol, await future)
     except Exception as e:
         log.debug('DNS: Exception while querying for %s A records: %s', host, e)
-        recs = []
+        return []
-    return [rec.host for rec in recs]
+    return [addr for addr in recs.addresses]
 
 
 async def get_AAAA(host: str, *, loop: AbstractEventLoop,
@@ -249,13 +253,13 @@ async def get_AAAA(host: str, *, loop: AbstractEventLoop,
             return []
 
     # Using aiodns:
-    future = resolver.query(host, 'AAAA')
+    future = resolver.gethostbyname(host, socket.AF_INET6)
     try:
-        recs = cast(Iterable[AnswerProtocol], await future)
+        recs = cast(GetHostByNameAnswerProtocol, await future)
     except Exception as e:
         log.debug('DNS: Exception while querying for %s AAAA records: %s', host, e)
-        recs = []
+        return []
-    return [rec.host for rec in recs]
+    return [addr for addr in recs.addresses]
 
 
 async def get_SRV(host: str, port: int, service: str,
@@ -295,12 +299,12 @@ async def get_SRV(host: str, port: int, service: str,
     try:
         future = resolver.query('_%s._%s.%s' % (service, proto, host),
                                 'SRV')
-        recs = cast(Iterable[AnswerProtocol], await future)
+        recs = cast(Iterable[QueryAnswerProtocol], await future)
     except Exception as e:
         log.debug('DNS: Exception while querying for %s SRV records: %s', host, e)
         return []
 
-    answers: Dict[int, List[AnswerProtocol]] = {}
+    answers: Dict[int, List[QueryAnswerProtocol]] = {}
     for rec in recs:
         if rec.priority not in answers:
             answers[rec.priority] = []