[RFC PATCH v1 2/2] dts: Remove XML-RPC server for Scapy TG and instead us ScapyShell

[jspewock@iol.unh.edu]

From: Jeremy Spewock <jspewock@iol.unh.edu>

Previously all scapy commands were handled using an XML-RPC server that
ran on the TGNode. This unnecessarily enforces a minimum Python version
of 3.10 on the server that is being used as a traffic generator and
complicates the implementation of scapy methods. This patch removes the
XML-RPC server completely and instead uses a ScapyShell to handle all
Scapy interactions.

Bugzilla ID: 1374
depends-on: series-32014 ("Improve interactive shell output gathering
and logging")

Signed-off-by: Jeremy Spewock <jspewock@iol.unh.edu>
---
 .../testbed_model/traffic_generator/scapy.py  | 284 +-----------------
 1 file changed, 14 insertions(+), 270 deletions(-)

diff --git a/dts/framework/testbed_model/traffic_generator/scapy.py b/dts/framework/testbed_model/traffic_generator/scapy.py
index 5676235119..2b299ad02f 100644
--- a/dts/framework/testbed_model/traffic_generator/scapy.py
+++ b/dts/framework/testbed_model/traffic_generator/scapy.py
@@ -13,20 +13,11 @@
 with a local server proxy from the :mod:`xmlrpc.client` module.
 """
 
-import inspect
-import marshal
-import time
-import types
-import xmlrpc.client
-from xmlrpc.server import SimpleXMLRPCServer
 
-import scapy.all  # type: ignore[import]
-from scapy.layers.l2 import Ether  # type: ignore[import]
 from scapy.packet import Packet  # type: ignore[import]
 
 from framework.config import OS, ScapyTrafficGeneratorConfig
-from framework.remote_session import PythonShell
-from framework.settings import SETTINGS
+from framework.remote_session import ScapyShell
 from framework.testbed_model.node import Node
 from framework.testbed_model.port import Port
 
@@ -36,220 +27,29 @@
     _get_default_capture_name,
 )
 
-"""
-========= BEGIN RPC FUNCTIONS =========
-
-All of the functions in this section are intended to be exported to a python
-shell which runs a scapy RPC server. These functions are made available via that
-RPC server to the packet generator. To add a new function to the RPC server,
-first write the function in this section. Then, if you need any imports, make sure to
-add them to SCAPY_RPC_SERVER_IMPORTS as well. After that, add the function to the list
-in EXPORTED_FUNCTIONS. Note that kwargs (keyword arguments) do not work via xmlrpc,
-so you may need to construct wrapper functions around many scapy types.
-"""
-
-"""
-Add the line needed to import something in a normal python environment
-as an entry to this array. It will be imported before any functions are
-sent to the server.
-"""
-SCAPY_RPC_SERVER_IMPORTS = [
-    "from scapy.all import *",
-    "import xmlrpc",
-    "import sys",
-    "from xmlrpc.server import SimpleXMLRPCServer",
-    "import marshal",
-    "import pickle",
-    "import types",
-    "import time",
-]
-
-
-def scapy_send_packets_and_capture(
-    xmlrpc_packets: list[xmlrpc.client.Binary],
-    send_iface: str,
-    recv_iface: str,
-    duration: float,
-    sniff_filter: str,
-) -> list[bytes]:
-    """The RPC function to send and capture packets.
-
-    This function is meant to be executed on the remote TG node via the server proxy.
-
-    Args:
-        xmlrpc_packets: The packets to send. These need to be converted to
-            :class:`~xmlrpc.client.Binary` objects before sending to the remote server.
-        send_iface: The logical name of the egress interface.
-        recv_iface: The logical name of the ingress interface.
-        duration: Capture for this amount of time, in seconds.
-
-    Returns:
-        A list of bytes. Each item in the list represents one packet, which needs
-        to be converted back upon transfer from the remote node.
-    """
-    scapy_packets = [scapy.all.Packet(packet.data) for packet in xmlrpc_packets]
-    sniffer = scapy.all.AsyncSniffer(
-        iface=recv_iface,
-        store=True,
-        started_callback=lambda *args: scapy.all.sendp(scapy_packets, iface=send_iface),
-        filter=sniff_filter,
-    )
-    sniffer.start()
-    time.sleep(duration)
-    return [scapy_packet.build() for scapy_packet in sniffer.stop(join=True)]
-
-
-def scapy_send_packets(xmlrpc_packets: list[xmlrpc.client.Binary], send_iface: str) -> None:
-    """The RPC function to send packets.
-
-    This function is meant to be executed on the remote TG node via the server proxy.
-    It only sends `xmlrpc_packets`, without capturing them.
-
-    Args:
-        xmlrpc_packets: The packets to send. These need to be converted to
-            :class:`~xmlrpc.client.Binary` objects before sending to the remote server.
-        send_iface: The logical name of the egress interface.
-    """
-    scapy_packets = [scapy.all.Packet(packet.data) for packet in xmlrpc_packets]
-    scapy.all.sendp(scapy_packets, iface=send_iface, realtime=True, verbose=True)
-
-
-"""
-Functions to be exposed by the scapy RPC server.
-"""
-RPC_FUNCTIONS = [
-    scapy_send_packets,
-    scapy_send_packets_and_capture,
-]
-
-"""
-========= END RPC FUNCTIONS =========
-"""
-
-
-class QuittableXMLRPCServer(SimpleXMLRPCServer):
-    r"""Basic XML-RPC server.
-
-    The server may be augmented by functions serializable by the :mod:`marshal` module.
-
-    Example:
-        ::
-
-            def hello_world():
-                # to be sent to the XML-RPC server
-                print("Hello World!")
-
-            # start the XML-RPC server on the remote node
-            # the example assumes you're already connect to a tg_node
-            # this is done by starting a Python shell on the remote node
-            from framework.remote_session import PythonShell
-            session = tg_node.create_interactive_shell(PythonShell, timeout=5, privileged=True)
-
-            # then importing the modules needed to run the server
-            # and the modules for any functions later added to the server
-            session.send_command("import xmlrpc")
-            session.send_command("from xmlrpc.server import SimpleXMLRPCServer")
-
-            # sending the source code of this class to the Python shell
-            from xmlrpc.server import SimpleXMLRPCServer
-            src = inspect.getsource(QuittableXMLRPCServer)
-            src = "\n".join([l for l in src.splitlines() if not l.isspace() and l != ""])
-            spacing = "\n" * 4
-            session.send_command(spacing + src + spacing)
-
-            # then starting the server with:
-            command = "s = QuittableXMLRPCServer(('0.0.0.0', {listen_port}));s.serve_forever()"
-            session.send_command(command, "XMLRPC OK")
-
-            # now the server is running on the remote node and we can add functions to it
-            # first connect to the server from the execution node
-            import xmlrpc.client
-            server_url = f"http://{tg_node.config.hostname}:8000"
-            rpc_server_proxy = xmlrpc.client.ServerProxy(server_url)
-
-            # get the function bytes to send
-            import marshal
-            function_bytes = marshal.dumps(hello_world.__code__)
-            rpc_server_proxy.add_rpc_function(hello_world.__name__, function_bytes)
-
-            # now we can execute the function on the server
-            xmlrpc_binary_recv: xmlrpc.client.Binary = rpc_server_proxy.hello_world()
-            print(str(xmlrpc_binary_recv))
-    """
-
-    def __init__(self, *args, **kwargs):
-        """Extend the XML-RPC server initialization.
-
-        Args:
-            args: The positional arguments that will be passed to the superclass's constructor.
-            kwargs: The keyword arguments that will be passed to the superclass's constructor.
-                The `allow_none` argument will be set to :data:`True`.
-        """
-        kwargs["allow_none"] = True
-        super().__init__(*args, **kwargs)
-        self.register_introspection_functions()
-        self.register_function(self.quit)
-        self.register_function(self.add_rpc_function)
-
-    def quit(self) -> None:
-        """Quit the server."""
-        self._BaseServer__shutdown_request = True
-        return None
-
-    def add_rpc_function(self, name: str, function_bytes: xmlrpc.client.Binary) -> None:
-        """Add a function to the server from the local server proxy.
-
-        Args:
-              name: The name of the function.
-              function_bytes: The code of the function.
-        """
-        function_code = marshal.loads(function_bytes.data)
-        function = types.FunctionType(function_code, globals(), name)
-        self.register_function(function)
-
-    def serve_forever(self, poll_interval: float = 0.5) -> None:
-        """Extend the superclass method with an additional print.
-
-        Once executed in the local server proxy, the print gives us a clear string to expect
-        when starting the server. The print means this function was executed on the XML-RPC server.
-        """
-        print("XMLRPC OK")
-        super().serve_forever(poll_interval)
-
 
 class ScapyTrafficGenerator(CapturingTrafficGenerator):
-    """Provides access to scapy functions via an RPC interface.
+    """Provides access to scapy functions on a traffic generator.
 
     This class extends the base with remote execution of scapy functions.
 
-    Any packets sent to the remote server are first converted to bytes. They are received as
-    :class:`~xmlrpc.client.Binary` objects on the server side. When the server sends the packets
-    back, they are also received as :class:`~xmlrpc.client.Binary` objects on the client side, are
-    converted back to :class:`~scapy.packet.Packet` objects and only then returned from the methods.
+    All processing of packets is handled via an instance of a
+    :class:`framework.remote_session.scapy_shell.ScapyShell` that runs on the underlying
+    :class:`framework.testbed_model.tg_node.TGNode`.
 
     Attributes:
         session: The exclusive interactive remote session created by the Scapy
-            traffic generator where the XML-RPC server runs.
-        rpc_server_proxy: The object used by clients to execute functions
-            on the XML-RPC server.
+            traffic generator.
     """
 
-    session: PythonShell
-    rpc_server_proxy: xmlrpc.client.ServerProxy
+    session: ScapyShell
     _config: ScapyTrafficGeneratorConfig
 
     def __init__(self, tg_node: Node, config: ScapyTrafficGeneratorConfig):
         """Extend the constructor with Scapy TG specifics.
 
-        The traffic generator first starts an XML-RPC on the remote `tg_node`.
-        Then it populates the server with functions which use the Scapy library
-        to send/receive traffic:
-
-            * :func:`scapy_send_packets_and_capture`
-            * :func:`scapy_send_packets`
-
-        To enable verbose logging from the xmlrpc client, use the :option:`--verbose`
-        command line argument or the :envvar:`DTS_VERBOSE` environment variable.
+        The traffic generator starts an underlying session that handles scapy interactions
+        that it will use in its provided methods.
 
         Args:
             tg_node: The node where the traffic generator resides.
@@ -262,50 +62,11 @@ def __init__(self, tg_node: Node, config: ScapyTrafficGeneratorConfig):
         ), "Linux is the only supported OS for scapy traffic generation"
 
         self.session = self._tg_node.create_interactive_shell(
-            PythonShell, timeout=5, privileged=True, name="ScapyXMLRPCServer"
-        )
-
-        # import libs in remote python console
-        for import_statement in SCAPY_RPC_SERVER_IMPORTS:
-            self.session.send_command(import_statement)
-
-        # start the server
-        xmlrpc_server_listen_port = 8000
-        self._start_xmlrpc_server_in_remote_python(xmlrpc_server_listen_port)
-
-        # connect to the server
-        server_url = f"http://{self._tg_node.config.hostname}:{xmlrpc_server_listen_port}"
-        self.rpc_server_proxy = xmlrpc.client.ServerProxy(
-            server_url, allow_none=True, verbose=SETTINGS.verbose
-        )
-
-        # add functions to the server
-        for function in RPC_FUNCTIONS:
-            # A slightly hacky way to move a function to the remote server.
-            # It is constructed from the name and code on the other side.
-            # Pickle cannot handle functions, nor can any of the other serialization
-            # frameworks aside from the libraries used to generate pyc files, which
-            # are even more messy to work with.
-            function_bytes = marshal.dumps(function.__code__)
-            self.rpc_server_proxy.add_rpc_function(function.__name__, function_bytes)
-
-    def _start_xmlrpc_server_in_remote_python(self, listen_port: int) -> None:
-        # load the source of the function
-        src = inspect.getsource(QuittableXMLRPCServer)
-        # Lines with only whitespace break the repl if in the middle of a function
-        # or class, so strip all lines containing only whitespace
-        src = "\n".join([line for line in src.splitlines() if not line.isspace() and line != ""])
-
-        # execute it in the python terminal
-        self.session.send_command(src + "\n")
-        self.session.send_command(
-            f"server = QuittableXMLRPCServer(('0.0.0.0', {listen_port}));server.serve_forever()",
-            "XMLRPC OK",
+            ScapyShell, timeout=5, privileged=True
         )
 
     def _send_packets(self, packets: list[Packet], port: Port) -> None:
-        packets = [packet.build() for packet in packets]
-        self.rpc_server_proxy.scapy_send_packets(packets, port.logical_name)
+        self.session.send_packets(packets, port)
 
     def _create_packet_filter(self, filter_config: PacketFilteringConfig) -> str:
         """Combines filter settings from `filter_config` into a BPF that scapy can use.
@@ -338,27 +99,10 @@ def _send_packets_and_capture(
         duration: float,
         capture_name: str = _get_default_capture_name(),
     ) -> list[Packet]:
-        binary_packets = [packet.build() for packet in packets]
-
-        xmlrpc_packets: list[
-            xmlrpc.client.Binary
-        ] = self.rpc_server_proxy.scapy_send_packets_and_capture(
-            binary_packets,
-            send_port.logical_name,
-            receive_port.logical_name,
-            duration,
-            self._create_packet_filter(filter_config),
-        )  # type: ignore[assignment]
-
-        scapy_packets = [Ether(packet.data) for packet in xmlrpc_packets]
-        return scapy_packets
+        return self.session.send_packets_and_capture(
+            packets, send_port, receive_port, self._create_packet_filter(filter_config), duration
+        )
 
     def close(self) -> None:
         """Close the traffic generator."""
-        try:
-            self.rpc_server_proxy.quit()
-        except ConnectionRefusedError:
-            # Because the python instance closes, we get no RPC response.
-            # Thus, this error is expected
-            pass
         self.session.close()
-- 
2.45.1