Filtering CUPS redundent events

cups_notify/listener.py

@@ -1,6 +1,9 @@
 # -*- coding: utf-8 -*-
 
+import socket
 import threading
+import os.path as osp
+from contextlib import closing
 from xml.etree import ElementTree
 try:
     from http.server import HTTPServer, BaseHTTPRequestHandler
@@ -13,6 +16,13 @@
 from cups_notify import event
 
 
+def find_free_port():
+    with closing(socket.socket(socket.AF_INET, socket.SOCK_STREAM)) as sock:
+        sock.bind(('', 0))
+        sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
+        return sock.getsockname()[1]
+
+
 class NotificationHandler(BaseHTTPRequestHandler):
 
     def get_chunk_size(self):
@@ -49,10 +59,15 @@ def do_PUT(self):
         else:
             chunk_data = self.get_chunk_data(chunk_size)
             root = ElementTree.fromstring(chunk_data.decode('utf-8'))
+
+            evts = []
             for channel in root.iterfind('channel'):
                 for item in reversed([e for e in channel.iterfind('item')]):
-                    txt = ElementTree.tostring(item, encoding='utf8')
-                    self.server.callback(dict((elem.tag, elem.text) for elem in item.iter() if elem.text.strip()))
+                    data = dict((elem.tag, elem.text) for elem in item.iter() if elem.text.strip())
+                    evts.append(event.CupsEvent(data))
+
+            if evts:
+                self.server.notify(evts)
 
         self.send_response(200)
         self.end_headers()
@@ -61,13 +76,13 @@ def do_PUT(self):
 class NotificationListerner(HTTPServer):
 
     def __init__(self, cups_conn, callback, filters=None, address='localhost'):
-        HTTPServer.__init__(self, (address, 9988), NotificationHandler)
+        HTTPServer.__init__(self, (address, find_free_port()), NotificationHandler)
         self._conn = cups_conn
         self._thread = None
         self._filters = filters or [event.CUPS_EVT_ALL]
         self._rss_uri = 'rss://{}:{}'.format(self.server_address[0], self.server_address[1])
-
-        self.callback = callback
+        self._last_guid = -1
+        self._callback = callback
 
     def start(self):
         """Start the notification server.
@@ -81,7 +96,11 @@ def start(self):
         self.cancel_subscriptions()
 
         # Renew notifications subscription
-        cups_uri = "ipp://localhost:{}".format(cups.getPort())
+        if osp.exists(cups.getServer()):
+            hostname = 'localhost'
+        else:
+            hostname = cups.getServer()
+        cups_uri = "ipp://{}:{}".format(hostname, cups.getPort())
         self._conn.createSubscription(cups_uri,
                                       recipient_uri=self._rss_uri,
                                       events=self._filters)
@@ -93,6 +112,17 @@ def is_running(self):
             return self._thread.is_alive()
         return False
 
+    def notify(self, evts):
+        """Notify the subscriber for new events. Events are filtered
+        because CUPS server re-sends all previously sent events.
+        """
+        valid_evts = []
+        for evt in evts:
+            if evt.guid > self._last_guid:
+                valid_evts.append(evt.guid)
+                self._callback(evt)
+        self._last_guid = max(valid_evts)
+
     def cancel_subscriptions(self):
         """Cancel all subscriptions related to the server URI.
         """