X-Git-Url: https://git.arvados.org/arvados.git/blobdiff_plain/1e2e0e4f14a730ba1bbea6a4ced5d87ea2766c35..83562734c781379665e3a337bce5b548afc88681:/sdk/python/arvados/events.py

diff --git a/sdk/python/arvados/events.py b/sdk/python/arvados/events.py
index fc86cb46d4..09f2a871a9 100644
--- a/sdk/python/arvados/events.py
+++ b/sdk/python/arvados/events.py
@@ -1,13 +1,15 @@
-from ws4py.client.threadedclient import WebSocketClient
-import threading
+import arvados
+import config
+import errors
+
+import logging
 import json
-import os
+import threading
 import time
-import ssl
+import os
 import re
-import config
-import logging
-import arvados
+import ssl
+from ws4py.client.threadedclient import WebSocketClient
 
 _logger = logging.getLogger('arvados.events')
 
@@ -22,6 +24,11 @@ class EventClient(WebSocketClient):
             ssl_options['cert_reqs'] = ssl.CERT_NONE
         else:
             ssl_options['cert_reqs'] = ssl.CERT_REQUIRED
+
+        # Warning: If the host part of url resolves to both IPv6 and
+        # IPv4 addresses (common with "localhost"), only one of them
+        # will be attempted -- and it might not be the right one. See
+        # ws4py's WebSocketBaseClient.__init__.
         super(EventClient, self).__init__(url, ssl_options=ssl_options)
         self.filters = filters
         self.on_event = on_event
@@ -58,6 +65,7 @@ class PollClient(threading.Thread):
             self.filters = [[]]
         self.on_event = on_event
         self.poll_time = poll_time
+        self.daemon = True
         self.stop = threading.Event()
 
     def run(self):
@@ -105,29 +113,41 @@ class PollClient(threading.Thread):
         del self.filters[self.filters.index(filters)]
 
 
+def _subscribe_websocket(api, filters, on_event):
+    endpoint = api._rootDesc.get('websocketUrl', None)
+    if not endpoint:
+        raise errors.FeatureNotEnabledError(
+            "Server does not advertise a websocket endpoint")
+    uri_with_token = "{}?api_token={}".format(endpoint, api.api_token)
+    client = EventClient(uri_with_token, filters, on_event)
+    ok = False
+    try:
+        client.connect()
+        ok = True
+        return client
+    finally:
+        if not ok:
+            client.close_connection()
+
 def subscribe(api, filters, on_event, poll_fallback=15):
-    '''
-    api: a client object retrieved from arvados.api(). The caller should not use this client object for anything else after calling subscribe().
-    filters: Initial subscription filters.
-    on_event: The callback when a message is received.
-    poll_fallback: If websockets are not available, fall back to polling every N seconds.  If poll_fallback=False, this will return None if websockets are not available.
-    '''
-    ws = None
-    if 'websocketUrl' in api._rootDesc:
-        try:
-            url = "{}?api_token={}".format(api._rootDesc['websocketUrl'], api.api_token)
-            ws = EventClient(url, filters, on_event)
-            ws.connect()
-            return ws
-        except Exception as e:
-            _logger.warn("Got exception %s trying to connect to websockets at %s" % (e, api._rootDesc['websocketUrl']))
-            if ws:
-                ws.close_connection()
-    if poll_fallback:
-        _logger.warn("Websockets not available, falling back to log table polling")
-        p = PollClient(api, filters, on_event, poll_fallback)
-        p.start()
-        return p
-    else:
-        _logger.error("Websockets not available")
-        return None
+    """
+    :api:
+      a client object retrieved from arvados.api(). The caller should not use this client object for anything else after calling subscribe().
+    :filters:
+      Initial subscription filters.
+    :on_event:
+      The callback when a message is received.
+    :poll_fallback:
+      If websockets are not available, fall back to polling every N seconds.  If poll_fallback=False, this will return None if websockets are not available.
+    """
+
+    if not poll_fallback:
+        return _subscribe_websocket(api, filters, on_event)
+
+    try:
+        return _subscribe_websocket(api, filters, on_event)
+    except Exception as e:
+        _logger.warn("Falling back to polling after websocket error: %s" % e)
+    p = PollClient(api, filters, on_event, poll_fallback)
+    p.start()
+    return p