kotnik · June 6, 2013 14:51 · Jun 6, 2013
diff --git a/small-dns-server.py b/small-dns-server.py
@@ -0,0 +1,76 @@
+from collections import Mapping
+
+from twisted.names import dns, server, client, cache
+from twisted.application import service, internet
+
+
+class MapResolver(client.Resolver):
+    def __init__(self, mapping, servers):
+        client.Resolver.__init__(self, servers=servers)
+
+        self.mapping = mapping
+        self.ttl = 10
+
+    def lookupAddress(self, name, timeout = None):
+        if name in self.mapping:
+            # We know the answer.
+            value = self.mapping[name]
+            return [
+                (
+                    dns.RRHeader(
+                        name, dns.A, dns.IN, self.ttl,
+                        dns.Record_A(value, self.ttl)
+                    ),
+                ),
+                (),
+                ()
+            ]
+        else:
+            # Ask our backend server.
+            return self._lookup(name, dns.IN, dns.A, timeout)
+
+
+class CustomMapping(Mapping):
+    def __init__(self, servers):
+        self._servers = servers
+
+    def __getitem__(self, key):
+        return self._servers[key]
+
+    def __iter__(self):
+        return self._servers.iterkeys()
+
+    def __len__(self):
+        return len(self._servers)
+
+
+# Our custom resolver.
+custom_mapping = CustomMapping({"example.com": "33.33.33.33"})
+
+# Upstream DNS server.
+upstream_dns = "8.8.8.8"
+
+# Setup Twisted application.
+application = service.Application('dnsserver', 1, 1)
+simpledns = MapResolver(custom_mapping, servers=[(upstream_dns, 53)])
+
+# Create protocols.
+f = server.DNSServerFactory(caches=[cache.CacheResolver()], clients=[simpledns])
+p = dns.DNSDatagramProtocol(f)
+f.noisy = p.noisy = False
+
+# Register both TCP and UDP on port 53.
+ret = service.MultiService()
+PORT = 53
+
+# Attach services to the parent.
+for (klass, arg) in [(internet.TCPServer, f), (internet.UDPServer, p)]:
+    s = klass(PORT, arg)
+    s.setServiceParent(ret)
+
+# Run as a twistd application.
+ret.setServiceParent(service.IServiceCollection(application))
+
+if __name__ == '__main__':
+    import sys
+    print "Usage: twistd -ny %s" % sys.argv[0]
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