selftest: add central dns forwarder

This is a small DNS server that has hard redirects to the different domain
controllers based on domain names. This is required because future commits will
avoid calling into libresolv's code which resolv_wrapper takes care of.

Signed-off-by: Volker Lendecke <vl@samba.org>
Reviewed-by: Jeremy Allison <jra@samba.org>

python/samba/tests/dns_forwarder_helpers/dns_hub.py

@@ -0,0 +1,156 @@
+#!/usr/bin/env python
+#
+# Unix SMB/CIFS implementation.
+# Copyright (C) Volker Lendecke 2017
+#
+# 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/>.
+#
+# Based on the EchoServer example from python docs
+
+import threading
+import sys
+import os
+import select
+import socket
+from samba.dcerpc import dns
+from samba.tests.dns_base import DNSTest
+import samba.ndr as ndr
+
+if sys.version_info[0] < 3:
+    import SocketServer
+    sserver = SocketServer
+else:
+    import socketserver
+    sserver = socketserver
+
+class DnsHandler(sserver.BaseRequestHandler):
+    def dns_transaction_udp(self, packet, host):
+        "send a DNS query and read the reply"
+        s = None
+        try:
+            send_packet = ndr.ndr_pack(packet)
+            s = socket.socket(socket.AF_INET, socket.SOCK_DGRAM, 0)
+            s.settimeout(5)
+            s.connect((host, 53))
+            s.sendall(send_packet, 0)
+            recv_packet = s.recv(2048, 0)
+            return ndr.ndr_unpack(dns.name_packet, recv_packet)
+        except socket.error as err:
+            print("Error sending to host %s for name %s: %s\n" %
+                  (host, packet.questions[0].name, err.errno))
+            raise
+        finally:
+            if s is not None:
+                s.close()
+        return None
+
+    def forwarder(self, name):
+        lname = name.lower()
+
+        if lname.endswith('an-address-that-will-not-resolve'):
+            return 'ignore'
+        if lname.endswith('dsfsdfs'):
+            return 'fail'
+        if lname.endswith('adnonssdom.samba.example.com'):
+            return '127.0.0.17'
+        if lname.endswith('adnontlmdom.samba.example.com'):
+            return '127.0.0.18'
+        if lname.endswith('samba2000.example.com'):
+            return '127.0.0.25'
+        if lname.endswith('samba2003.example.com'):
+            return '127.0.0.26'
+        if lname.endswith('samba2008r2.example.com'):
+            return '127.0.0.27'
+        if lname.endswith('addom.samba.example.com'):
+            return '127.0.0.30'
+        if lname.endswith('sub.samba.example.com'):
+            return '127.0.0.31'
+        if lname.endswith('chgdcpassword.samba.example.com'):
+            return '127.0.0.32'
+        if lname.endswith('backupdom.samba.example.com'):
+            return '127.0.0.40'
+        if lname.endswith('renamedom.samba.example.com'):
+            return '127.0.0.42'
+        if lname.endswith('labdom.samba.example.com'):
+            return '127.0.0.43'
+        if lname.endswith('samba.example.com'):
+            return '127.0.0.21'
+        return None
+
+    def handle(self):
+        data, socket = self.request
+        query = ndr.ndr_unpack(dns.name_packet, data);
+        name = query.questions[0].name
+        forwarder = self.forwarder(name)
+        response = None
+
+        if forwarder is 'ignore':
+            return
+        elif forwarder is 'fail':
+            pass
+        elif forwarder is not None:
+            response = self.dns_transaction_udp(query, forwarder)
+        else:
+            response = query
+            response.operation |= dns.DNS_FLAG_REPLY
+            response.operation |= dns.DNS_FLAG_RECURSION_AVAIL
+            response.operation |= dns.DNS_RCODE_NXDOMAIN
+
+        if response is None:
+            response = query
+            response.operation |= dns.DNS_FLAG_REPLY
+            response.operation |= dns.DNS_FLAG_RECURSION_AVAIL
+            response.operation |= dns.DNS_RCODE_SERVFAIL
+
+        send_packet = ndr.ndr_pack(response)
+
+        print("dns_hub: sending %s to address %s for name %s\n" %
+            (forwarder, self.client_address, name))
+
+        try:
+            socket.sendto(send_packet, self.client_address)
+        except socket.error as err:
+            print("Error sending %s to address %s for name %s: %s\n" %
+                (forwarder, self.client_address, name, err.errno))
+        raise
+
+        socket.sendto(send_packet, self.client_address)
+
+class server_thread(threading.Thread):
+    def __init__(self, server):
+        threading.Thread.__init__(self)
+        self.server = server
+
+    def run(self):
+        self.server.serve_forever()
+        print("dns_hub: after serve_forever()")
+
+def main():
+    timeout = int(sys.argv[1])*1000
+    timeout = min(timeout, 2**31-1) # poll with 32-bit int can't take more
+    host = sys.argv[2]
+    server = sserver.UDPServer((host, int(53)), DnsHandler)
+    t = server_thread(server)
+    t.start()
+    p = select.poll()
+    stdin = sys.stdin.fileno()
+    p.register(stdin, select.POLLIN)
+    p.poll(timeout)
+    print("dns_hub: after poll()")
+    server.shutdown()
+    t.join()
+    print("dns_hub: before exit()")
+    sys.exit(0)
+
+main()