From 12b51be8633689763080f2eb1e0b13487e3e71e1 Mon Sep 17 00:00:00 2001
From: Alexander Bokovoy <ab@samba.org>
Date: Sat, 24 Oct 2020 12:17:44 +0300
Subject: [PATCH] DNS Resolver: support both dnspython before and after 2.0.0

`dnspython` 2.0.0 has many changes and several deprecations like:

```
> dns.resolver.resolve() has been added, allowing control of whether
search lists are used. dns.resolver.query() is retained for backwards
compatibility, but deprecated. The default for search list behavior can
be set at in the resolver object with the use_search_by_default
parameter. The default is False.

> dns.resolver.resolve_address() has been added, allowing easy
address-to-name lookups.
```

The new class `DNSResolver`:
- provides the compatibility layer
- defaults the previous behavior (the search list configured in the
  system's resolver configuration is used for relative names)
- defaults lifetime to 15sec (determines the number of seconds
  to spend trying to get an answer to the question)

The compatibility shim was developed by Stanislav Levin for FreeIPA and
adopted for Samba by Alexander Bokovoy.

Signed-off-by: Stanislav Levin <slev@altlinux.org>
Signed-off-by: Alexander Bokovoy <ab@samba.org>
---
 python/samba/dnsresolver.py           | 68 +++++++++++++++++++++++++++
 source4/scripting/bin/samba_dnsupdate |  5 +-
 2 files changed, 71 insertions(+), 2 deletions(-)
 create mode 100644 python/samba/dnsresolver.py

diff --git a/python/samba/dnsresolver.py b/python/samba/dnsresolver.py
new file mode 100644
index 00000000000..a627555a855
--- /dev/null
+++ b/python/samba/dnsresolver.py
@@ -0,0 +1,68 @@
+# Samba wrapper for DNS resolvers
+#
+# Copyright (C) Stanislav Levin <slev@altlinux.org>
+# Copyright (C) Alexander Bokovoy <ab@samba.org>
+#
+# 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 dns.resolver
+import dns.rdatatype
+import dns.reversename
+
+class DNSResolver(dns.resolver.Resolver):
+    """DNS stub resolver compatible with both dnspython < 2.0.0
+    and dnspython >= 2.0.0.
+
+    Set `use_search_by_default` attribute to `True`, which
+    determines the default for whether the search list configured
+    in the system's resolver configuration is used for relative
+    names, and whether the resolver's domain may be added to relative
+    names.
+
+    Increase the default lifetime which determines the number of seconds
+    to spend trying to get an answer to the question. dnspython 2.0.0
+    changes this to 5sec, while the previous one was 30sec.
+    """
+    def __init__(self, *args, **kwargs):
+        super().__init__(*args, **kwargs)
+        self.reset_defaults()
+        self.resolve = getattr(super(), "resolve", self.query)
+        self.resolve_address = getattr(
+            super(),
+            "resolve_address",
+            self._resolve_address
+        )
+
+    def reset_defaults(self):
+        self.use_search_by_default = True
+        # the default is 5sec
+        self.lifetime = 15
+
+    def reset(self):
+        super().reset()
+        self.reset_defaults()
+
+    def _resolve_address(self, ip_address, *args, **kwargs):
+        """Query nameservers for PTR records.
+
+        :param ip_address: IPv4 or IPv6 address
+        :type ip_address: str
+        """
+        return self.resolve(
+            dns.reversename.from_address(ip_address),
+            rdtype=dns.rdatatype.PTR,
+            *args,
+            **kwargs,
+        )
diff --git a/source4/scripting/bin/samba_dnsupdate b/source4/scripting/bin/samba_dnsupdate
index 44eb1cadd27..fe04ce71338 100755
--- a/source4/scripting/bin/samba_dnsupdate
+++ b/source4/scripting/bin/samba_dnsupdate
@@ -53,6 +53,7 @@ from samba.compat import get_string
 from samba.compat import text_type
 import ldb
 
+from samba.dnsresolver import DNSResolver
 import dns.resolver
 import dns.exception
 
@@ -259,7 +260,7 @@ def hostname_match(h1, h2):
 
 def get_resolver(d=None):
     resolv_conf = os.getenv('RESOLV_CONF', default='/etc/resolv.conf')
-    resolver = dns.resolver.Resolver(filename=resolv_conf, configure=True)
+    resolver = DNSResolver(filename=resolv_conf, configure=True)
 
     if d is not None and d.nameservers != []:
         resolver.nameservers = d.nameservers
@@ -271,7 +272,7 @@ def check_one_dns_name(name, name_type, d=None):
     if d and not d.nameservers:
         d.nameservers = resolver.nameservers
     # dns.resolver.Answer
-    return resolver.query(name, name_type)
+    return resolver.resolve(name, name_type)
 
 def check_dns_name(d):
     """check that a DNS entry exists."""
-- 
2.28.0