Refactor ControllableAsyncDnsServer setup

When this class was introduced, the constructor of its base class had no
parameters. This was changed in the meantime and these parameters were
not accessible by users of the subclass.

Don't override the constructor.
Move command setup to methods.
Move subclass-specific storage to cached properties.
Take instances of Command instead of the classes themselves for
symmetry with install_response_handler.

(cherry picked from commit a0970f3d04)

bin/tests/system/chain/ans4/ans.py

@@ -473,7 +473,8 @@ class ChainResponseHandler(DomainHandler):
 
 
 def main() -> None:
-    server = ControllableAsyncDnsServer(commands=[ChainSetupCommand])
+    server = ControllableAsyncDnsServer()
+    server.install_control_command(ChainSetupCommand())
     server.run()
 
 

bin/tests/system/fetchlimit/ans4/ans.py

@@ -39,7 +39,8 @@ class MaybeDelayedAddressAnswerHandler(ResponseHandler):
 
 
 def main() -> None:
-    server = ControllableAsyncDnsServer([ToggleResponsesCommand])
+    server = ControllableAsyncDnsServer()
+    server.install_control_command(ToggleResponsesCommand())
     server.install_response_handler(MaybeDelayedAddressAnswerHandler())
     server.run()
 

bin/tests/system/forward/ans11/ans.py

@@ -49,7 +49,8 @@ class ExtraAnswersHandler(DomainHandler):
 
 
 def main() -> None:
-    server = ControllableAsyncDnsServer(commands=[ToggleResponsesCommand])
+    server = ControllableAsyncDnsServer()
+    server.install_control_command(ToggleResponsesCommand())
     server.install_response_handler(ExtraAnswersHandler())
     server.run()
 

bin/tests/system/forward/ans6/ans.py

@@ -72,7 +72,8 @@ class ChaseDsHandler(ResponseHandler):
 
 
 def main() -> None:
-    server = ControllableAsyncDnsServer([ToggleResponsesCommand])
+    server = ControllableAsyncDnsServer()
+    server.install_control_command(ToggleResponsesCommand())
     server.install_response_handler(ChaseDsHandler())
     server.run()
 

bin/tests/system/isctest/asyncserver.py

@@ -21,7 +21,6 @@ from typing import (
     List,
     Optional,
     Tuple,
-    Type,
     Union,
     cast,
 )
@@ -1281,22 +1280,29 @@ class ControllableAsyncDnsServer(AsyncDnsServer):
 
     _CONTROL_DOMAIN = "_control."
 
-    def __init__(self, commands: List[Type["ControlCommand"]]):
-        super().__init__()
-        self._control_domain = dns.name.from_text(self._CONTROL_DOMAIN)
-        self._commands: Dict[dns.name.Name, "ControlCommand"] = {}
-        for command_class in commands:
-            command = command_class()
-            command_subdomain = dns.name.Name([command.control_subdomain])
-            control_subdomain = command_subdomain.concatenate(self._control_domain)
-            try:
-                existing_command = self._commands[control_subdomain]
-            except KeyError:
-                self._commands[control_subdomain] = command
-            else:
-                raise RuntimeError(
-                    f"{control_subdomain} already handled by {existing_command}"
-                )
+    @functools.cached_property
+    def _control_domain(self) -> dns.name.Name:
+        return dns.name.from_text(self._CONTROL_DOMAIN)
+
+    @functools.cached_property
+    def _commands(self) -> Dict[dns.name.Name, "ControlCommand"]:
+        return {}
+
+    def install_control_commands(self, commands: List["ControlCommand"]) -> None:
+        for command in commands:
+            self.install_control_command(command)
+
+    def install_control_command(self, command: "ControlCommand") -> None:
+        command_subdomain = dns.name.Name([command.control_subdomain])
+        control_subdomain = command_subdomain.concatenate(self._control_domain)
+        try:
+            existing_command = self._commands[control_subdomain]
+        except KeyError:
+            self._commands[control_subdomain] = command
+        else:
+            raise RuntimeError(
+                f"{control_subdomain} already handled by {existing_command}"
+            )
 
     async def _prepare_responses(
         self, qctx: QueryContext

bin/tests/system/xfer/ans9/ans.py

@@ -106,6 +106,7 @@ class AXFRServer(DomainHandler):
 
 
 if __name__ == "__main__":
-    server = ControllableAsyncDnsServer([ToggleResponsesCommand])
+    server = ControllableAsyncDnsServer()
+    server.install_control_command(ToggleResponsesCommand())
     server.install_response_handler(AXFRServer())
     server.run()