Implement support for IPv6 listener

Implement support for IPv6 listener via Python selectors module to
monitor multiple listening sockets

lib/nntp/tiny/server.py

@@ -1,10 +1,12 @@
 import enum
-import socket
-import ssl
 import threading
+import socket
+import selectors
+import ssl
 
 from configparser import ConfigParser
 
+from nntp.tiny.config    import ConfigException
 from nntp.tiny.db        import Database
 from nntp.tiny.newsgroup import Newsgroup
 from nntp.tiny.session   import Session
@@ -37,28 +39,52 @@ class Server():
         for newsgroup in db.query(Newsgroup).each():
             self.newsgroups[newsgroup.name.casefold()] = newsgroup
 
-    def run(self):
-        host = self.config['listen']['host']
-        port = int(self.config['listen']['port'])
-
-        listener = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
+    def listen(self, host: str, port: int, af: int):
+        listener = socket.socket(af, socket.SOCK_STREAM)
         listener.bind((host, port))
         listener.listen()
 
         if self.sslctx:
-            listener = self.sslctx.wrap_socket(listener, server_side=True)
+            return self.sslctx.wrap_socket(listener, server_side=True)
+
+        return listener
+
+    def accept(self, listener):
+        try:
+            sock, addr = listener.accept()
+
+            def spawn():
+                session = Session(self, sock)
+                session.handle()
+
+            thread = threading.Thread(target=spawn)
+            thread.start()
+        except ssl.SSLEOFError as e:
+            pass
+
+    def run(self):
+        port = int(self.config['listen']['port'])
+
+        listeners = list()
+
+        if self.config.has_option('listen', 'host_inet'):
+            host = self.config.get('listen', 'host_inet')
+            listeners.append(self.listen(host, port, socket.AF_INET))
+
+        if self.config.has_option('listen', 'host_inet6'):
+            host = self.config.get('listen', 'host_inet6')
+            listeners.append(self.listen(host, port, socket.AF_INET6))
+
+        if len(listeners) == 0:
+            raise ConfigException("No listener hosts specified")
+
+        sel = selectors.DefaultSelector()
+
+        for listener in listeners:
+            sel.register(listener, selectors.EVENT_READ)
 
         while True:
-            try:
-                sock, addr = listener.accept()
+            events = sel.select()
 
-                def spawn():
-                    session = Session(self, sock)
-                    session.handle()
-
-                thread = threading.Thread(target=spawn)
-                thread.start()
-            except ssl.SSLEOFError as e:
-                pass
-
-        listener.close()
+            for key, ev in events:
+                self.accept(key.fileobj)