Re-use the same IP if server still has active threads

To avoid problems when re-connecting after for example a timeout. 

Closes #733

sabnzbd/downloader.py

@@ -98,26 +98,40 @@ class Server(object):
 
     @property
     def hostip(self):
-        """ based on value of load_balancing() and self.info:
-            0: return the host name itself (so: do nothing)
-            1 and self.info has more than 1 entry (read: IP address): Return a random entry from the possible IPs
-            2 and self.info has more than 1 entry (read: IP address): Return the quickest IP based on the happyeyeballs algorithm
+        """ In case a server still has active connections, we use the same IP again
+            If new connection then based on value of load_balancing() and self.info:
+            0 - return the first entry, so all threads use the same IP
+            1 - and self.info has more than 1 entry (read: IP address): Return a random entry from the possible IPs
+            2 - and self.info has more than 1 entry (read: IP address): Return the quickest IP based on the happyeyeballs algorithm
             In case of problems: return the host name itself
         """
-        if cfg.load_balancing() == 1 and self.info and len(self.info) > 1:
+        # Check if already a succesfull ongoing connection
+        if self.busy_threads and self.busy_threads[0].nntp:
+            # Re-use that IP
+            logging.debug('%s: Re-using address %s', self.host, self.busy_threads[0].nntp.host)
+            return self.busy_threads[0].nntp.host
+
+        # Determine new IP
+        if cfg.load_balancing() == 0 and self.info:
+            # Just return the first one, so all next threads use the same IP
+            ip = self.info[0][4][0]
+            logging.debug('%s: Connecting to address %s', self.host, ip)
+
+        elif cfg.load_balancing() == 1 and self.info and len(self.info) > 1:
             # Return a random entry from the possible IPs
             rnd = random.randint(0, len(self.info) - 1)
             ip = self.info[rnd][4][0]
-            logging.debug('For server %s, using IP %s', self.host, ip)
+            logging.debug('%s: Connecting to address %s', self.host, ip)
+
         elif cfg.load_balancing() == 2 and self.info and len(self.info) > 1:
             # RFC6555 / Happy Eyeballs:
             ip = happyeyeballs(self.host, port=self.port, ssl=self.ssl)
             if ip:
-                logging.debug('For server %s, using IP %s as server', self.host, ip)
+                logging.debug('%s: Connecting to address %s', self.host, ip)
             else:
                 # nothing returned, so there was a connection problem
                 ip = self.host
-                logging.debug('For server %s, no successful IP connection possible', self.host)
+                logging.debug('%s: No successful IP connection was possible', self.host)
         else:
             ip = self.host
         return ip