ldap: Add wrapper object to help with transient errors

Move LDAP connection and query handling to a new class. Attempt to
recover from transient LDAP errors by catching LDAPCommunicationErrors,
disconnecting, reconnecting, and retrying the search once. If that
doesn't work, give up and let the caller deal with an empty result.

Bug: #21

requirements.txt

@@ -1,6 +1,6 @@
 elasticsearch>=1.0.0,<2.0.0
 irc>=15.0.3
-ldap3
+ldap3==1.4.0
 mwclient>=0.8.2
 python-twitter>=3.1
 pyyaml

stashbot/ldap.py

@@ -0,0 +1,74 @@
+# -*- coding: utf-8 -*-
+#
+# This file is part of bd808's stashbot application
+# Copyright (C) 2016 Bryan Davis and contributors
+#
+# This program is free software: you can redistribute it and/or modify it
+# under the terms of the GNU General Public License as published by the Free
+# Software Foundation, either version 3 of the License, or (at your option)
+# any later version.
+#
+# This program is distributed in the hope that it will be useful, but WITHOUT
+# ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+# FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
+# more details.
+#
+# You should have received a copy of the GNU General Public License along with
+# this program.  If not, see <http://www.gnu.org/licenses/>.
+
+import ldap3
+
+
+class Client(object):
+    """LDAP client"""
+
+    def __init__(self, uri, logger):
+        self._uri = uri
+        self.logger = logger
+        self.conn = None
+
+    def _connect(self):
+        return ldap3.Connection(self._uri, auto_bind=True, auto_range=True)
+
+    def search(self, *args, **kwargs):
+        """A fairly thin wrapper around ldap3.Connection.search.
+
+        Rather then just returning a boolean status as
+        ldap3.Connection.search does, this method returns the fetched results
+        if the search succeeded.
+
+        We also try to handle some LDAP errors related to the connection
+        itself by discarding the current connection and possibly retrying the
+        request. Only one retry will be done. Consecutive
+        ldap3.LDAPCommunicationError exceptions will result in a raised
+        exception to the caller. If you do not want the default singel retry,
+        pass `retriable=False` as a named argument to the initial call.
+        """
+        if 'retriable' in kwargs:
+            retriable = kwargs['retriable']
+            del kwargs['retriable']
+        else:
+            retriable = True
+
+        try:
+            if self.conn is None:
+                self.conn = self._connect()
+            if self.conn.search(*args, **kwargs):
+                return self.conn.entries
+            else:
+                return False
+        except ldap3.LDAPCommunicationError:
+            self.conn = None
+            if retriable:
+                self.logger.exception(
+                    'LDAP server connection barfed; retrying')
+                return self.search(*args, retriable=False, **kwargs)
+            else:
+                raise
+        except:
+            # If anything at all goes wrong, ditch the connection out of
+            # paranoia. We really don't want to have to restart the bot for
+            # dumb things like LDAP hiccups.
+            self.conn = None
+            raise
+

stashbot/sal.py

@@ -17,12 +17,12 @@
 # this program.  If not, see <http://www.gnu.org/licenses/>.
 
 import datetime
-import ldap3
 import re
 import time
 import twitter
 
 from . import acls
+from . import ldap
 from . import mediawiki
 
 RE_PHAB = re.compile(r'\b(T\d+)\b')
@@ -38,10 +38,7 @@ def __init__(self, irc, phab, es, config, logger):
         self.config = config
         self.logger = logger
 
-        self.ldap = ldap3.Connection(
-            self.config['ldap']['uri'],
-            auto_bind=True
-        )
+        self.ldap = ldap.Client(self.config['ldap']['uri'], self.logger)
         self._cached_wikis = {}
         self._cached_twitter = {}
         self._cached_projects = None
@@ -201,12 +198,13 @@ def _get_ldap_names(self, ou):
         """Get a list of cn values from LDAP for a given ou."""
         dn = 'ou=%s,%s' % (ou, self.config['ldap']['base'])
         try:
-            if self.ldap.search(
+            res = self.ldap.search(
                 dn,
                 '(objectclass=groupofnames)',
                 attributes=['cn']
-            ):
-                return [g.cn for g in self.ldap.entries]
+            )
+            if res is not False:
+                return [g.cn for g in res]
             else:
                 self.logger.error('Failed to get LDAP data for %s', dn)
         except: