addons: add AddonHalt exception

This can be raised from an addon handler to stop further processing of a flow.

Use this to prevent further handling of web app requests.

mitmproxy/addons.py

@@ -86,4 +86,7 @@ class Addons:
 
     def __call__(self, name, *args, **kwargs):
         for i in self.chain:
+            try:
                 self.invoke(i, name, *args, **kwargs)
+            except exceptions.AddonHalt:
+                return

mitmproxy/builtins/wsgiapp.py

@@ -1,4 +1,5 @@
 from mitmproxy import ctx
+from mitmproxy import exceptions
 
 from netlib import wsgi
 from netlib import version
@@ -30,6 +31,7 @@ class WSGIApp:
         if err:
             ctx.log.warn("Error in wsgi app. %s" % err, "error")
         flow.reply.kill()
+        raise exceptions.AddonHalt()
 
     def request(self, f):
         if (f.request.pretty_host, f.request.port) == (self.host, self.port):

mitmproxy/console/master.py

@@ -224,7 +224,6 @@ class ConsoleMaster(flow.FlowMaster):
     def __init__(self, server, options):
         flow.FlowMaster.__init__(self, options, server)
         self.state = ConsoleState()
-        self.addons.add(self.state)
         self.stream_path = None
         # This line is just for type hinting
         self.options = self.options  # type: Options
@@ -252,6 +251,7 @@ class ConsoleMaster(flow.FlowMaster):
         signals.push_view_state.connect(self.sig_push_view_state)
         signals.sig_add_log.connect(self.sig_add_log)
         self.addons.add(*builtins.default_addons())
+        self.addons.add(self.state)
 
     def __setattr__(self, name, value):
         self.__dict__[name] = value

mitmproxy/exceptions.py

@@ -96,3 +96,7 @@ class OptionsError(Exception):
 
 class AddonError(Exception):
     pass
+
+
+class AddonHalt(Exception):
+    pass

mitmproxy/web/master.py

@@ -135,8 +135,8 @@ class WebMaster(flow.FlowMaster):
     def __init__(self, server, options):
         super().__init__(options, server)
         self.state = WebState()
-        self.addons.add(self.state)
         self.addons.add(*builtins.default_addons())
+        self.addons.add(self.state)
         self.app = app.Application(
             self, self.options.wdebug, self.options.wauthenticator
         )