Check if the server is listening on either IPv4 or IPv6, avoid errors happening in dual stack configurations

syncplayServer.py

@@ -18,6 +18,28 @@ from twisted.internet.endpoints import TCP4ServerEndpoint, TCP6ServerEndpoint
 
 from syncplay.server import SyncFactory, ConfigurationGetter
 
+class ServerStatus: pass
+
+def isListening6(f):
+    ServerStatus.listening6 = True
+
+def isListening4(f):
+    ServerStatus.listening4 = True
+
+def failed6(f):
+    ServerStatus.listening6 = False
+    print(f.value)
+    print("IPv6 listening failed.")
+
+def failed4(f):
+    ServerStatus.listening4 = False
+    if ServerStatus.listening6 and "Address already in use" in str(f.value):
+        pass
+    else:
+        print(f.value)
+        print("IPv4 listening failed.")
+
+
 if __name__ == '__main__':
     argsGetter = ConfigurationGetter()
     args = argsGetter.getConfiguration()
@@ -34,8 +56,12 @@ if __name__ == '__main__':
         args.stats_db_file,
         args.tls
     )
-    endpoint4 = TCP4ServerEndpoint(reactor, int(args.port))
-    endpoint4.listen(factory)
     endpoint6 = TCP6ServerEndpoint(reactor, int(args.port))
-    endpoint6.listen(factory)
-    reactor.run()
+    endpoint6.listen(factory).addCallbacks(isListening6, failed6)
+    endpoint4 = TCP4ServerEndpoint(reactor, int(args.port))
+    endpoint4.listen(factory).addCallbacks(isListening4, failed4)
+    if ServerStatus.listening6 or ServerStatus.listening4:
+        reactor.run()
+    else:
+        print("Unable to listen using either IPv4 and IPv6 protocols. Quitting the server now.")
+        sys.exit()