Allow customizing dns.resolver.Resolver class attributes (#823)

CHANGELOG.md

@@ -3,6 +3,7 @@ Change Log
 
 HEAD
 ----
+-   Allow overriding `dns.resolver.Resolver` class attributes via `Autodiscovery.DNS_RESOLVER_ATTRS`.
 
 
 3.3.0

docs/index.md

@@ -154,8 +154,14 @@ account = Account(primary_smtp_address='[email protected]', credentials=credentia
 # different 'access_type':
 account = Account(primary_smtp_address='[email protected]', credentials=credentials,
                   autodiscover=True, access_type=IMPERSONATION)
+
+# Autodiscover needs to make some DNS queries. We use the dnspython package for that. Here's
+# an example of customizing the way the dns.resolver.Resolver object is created:
+from exchangelib.autodiscover import Autodiscovery
+Autodiscovery.DNS_RESOLVER_ATTRS['edns'] = False  # Disable EDNS queries
 ```
 
+
 ### Optimizing connections
 ```python
 from exchangelib import DELEGATE, Account, Configuration, Credentials, NTLM, Build, Version

exchangelib/autodiscover/discovery.py

@@ -75,6 +75,9 @@ class Autodiscovery:
     INITIAL_RETRY_POLICY = FailFast()
     RETRY_WAIT = 10  # Seconds to wait before retry on connection errors
     MAX_REDIRECTS = 10  # Maximum number of URL redirects before we give up
+    DNS_RESOLVER_ATTRS = {
+        'timeout': AutodiscoverProtocol.TIMEOUT,
+    }
 
     def __init__(self, email, credentials=None, auth_type=None, retry_policy=None):
         """
@@ -149,7 +152,8 @@ def _cache_key(self):
     @threaded_cached_property
     def resolver(self):
         resolver = dns.resolver.Resolver()
-        resolver.timeout = AutodiscoverProtocol.TIMEOUT
+        for k, v in self.DNS_RESOLVER_ATTRS.items():
+            setattr(resolver, k, v)
         return resolver
 
     def _build_response(self, ad_response):