fix Flow.kill behaviour

This now just sets a kill reply instead of committing directly.
First, this seems like the more sane thing to do.
Second, we have an iffy race condition where we call Reply.commit()
before the addonmanager finishes its invocation, the proxy thread then progresses
and sets a new flow.reply attribute, and the addonmanager then gets confused
when finishing. This commit doesn't fix that, but mitigates it for Flow.kill
which is now committed by the addonmanager.

4 files changed, 15 insertions, 18 deletions

diff --git a/mitmproxy/addonmanager.py b/mitmproxy/addonmanager.py
index 70cfda30..37c501ee 100644
--- a/mitmproxy/addonmanager.py
+++ b/mitmproxy/addonmanager.py
@@ -230,7 +230,7 @@ class AddonManager:
 
         self.trigger(name, message)
 
-        if message.reply.state != "taken":
+        if message.reply.state == "start":
             message.reply.take()
             if not message.reply.has_message:
                 message.reply.ack()
diff --git a/mitmproxy/controller.py b/mitmproxy/controller.py
index 63117ef0..f39c1b24 100644
--- a/mitmproxy/controller.py
+++ b/mitmproxy/controller.py
@@ -105,16 +105,16 @@ class Reply:
         self.q.put(self.value)
 
     def ack(self, force=False):
-        if self.state not in {"start", "taken"}:
-            raise exceptions.ControlException(
-                "Reply is {}, but expected it to be start or taken.".format(self.state)
-            )
         self.send(self.obj, force)
 
     def kill(self, force=False):
         self.send(exceptions.Kill, force)
 
     def send(self, msg, force=False):
+        if self.state not in {"start", "taken"}:
+            raise exceptions.ControlException(
+                "Reply is {}, but expected it to be start or taken.".format(self.state)
+            )
         if self.has_message and not force:
             raise exceptions.ControlException("There is already a reply message.")
         self.value = msg
diff --git a/mitmproxy/flow.py b/mitmproxy/flow.py
index 111566b8..944c032d 100644
--- a/mitmproxy/flow.py
+++ b/mitmproxy/flow.py
@@ -1,13 +1,12 @@
 import time
+import typing  # noqa
 import uuid
 
-from mitmproxy import controller  # noqa
-from mitmproxy import stateobject
 from mitmproxy import connections
+from mitmproxy import controller, exceptions  # noqa
+from mitmproxy import stateobject
 from mitmproxy import version
 
-import typing  # noqa
-
 
 class Error(stateobject.StateObject):
 
@@ -145,7 +144,11 @@ class Flow(stateobject.StateObject):
 
     @property
     def killable(self):
-        return self.reply and self.reply.state == "taken"
+        return (
+            self.reply and
+            self.reply.state in {"start", "taken"} and
+            self.reply.value != exceptions.Kill
+        )
 
     def kill(self):
         """
@@ -153,13 +156,7 @@ class Flow(stateobject.StateObject):
         """
         self.error = Error("Connection killed")
         self.intercepted = False
-
-        # reply.state should be "taken" here, or .take() will raise an
-        # exception.
-        if self.reply.state != "taken":
-            self.reply.take()
         self.reply.kill(force=True)
-        self.reply.commit()
         self.live = False
 
     def intercept(self):
diff --git a/test/mitmproxy/proxy/protocol/test_websocket.py b/test/mitmproxy/proxy/protocol/test_websocket.py
index 490d31a0..d9389faf 100644
--- a/test/mitmproxy/proxy/protocol/test_websocket.py
+++ b/test/mitmproxy/proxy/protocol/test_websocket.py
@@ -236,8 +236,8 @@ class TestKillFlow(_WebSocketTest):
         self.master.addons.add(KillFlow())
         self.setup_connection()
 
-        frame = websockets.Frame.from_file(self.client.rfile)
-        assert frame.payload == b'foo'
+        with pytest.raises(exceptions.TcpDisconnect):
+            websockets.Frame.from_file(self.client.rfile)
 
 
 class TestSimpleTLS(_WebSocketTest):