ansible: raise AnsibleConnectionFailure on connection failure; closes #183

Before:

    $ ANSIBLE_STRATEGY=mitogen ansible -i derp, derp -m setup
    An exception occurred during task execution. To see the full traceback, use -vvv. The error was:     (''.join(bits)[-300:],)
    derp | FAILED! => {
        "msg": "Unexpected failure during module execution.",
        "stdout": ""
    }

After:

    $ ANSIBLE_STRATEGY=mitogen ansible -i derp, derp -m setup
    derp | UNREACHABLE! => {
        "changed": false,
        "msg": "EOF on stream; last 300 bytes received: 'ssh: Could not resolve hostname derp: nodename nor servname provided, or not known\\r\\n'",
        "unreachable": true
    }

ansible_mitogen/connection.py

@@ -37,7 +37,7 @@ import ansible.errors
 import ansible.plugins.connection
 
 import mitogen.unix
-from mitogen.utils import cast
+import mitogen.utils
 
 import ansible_mitogen.helpers
 import ansible_mitogen.process
@@ -137,25 +137,34 @@ class Connection(ansible.plugins.connection.ConnectionBase):
     def connected(self):
         return self.broker is not None
 
+    def _wrap_connect(self, args):
+        dct = mitogen.service.call(
+            context=self.parent,
+            handle=ContextService.handle,
+            obj=mitogen.utils.cast(args),
+        )
+
+        if dct['msg']:
+            raise ansible.errors.AnsibleConnectionFailure(dct['msg'])
+
+        return dct['context'], dct['home_dir']
+
     def _connect_local(self):
         """
         Fetch a reference to the local() Context from ContextService in the
         master process.
         """
-        return mitogen.service.call(self.parent, ContextService.handle, cast({
+        return self._wrap_connect({
             'method': 'local',
             'python_path': self.python_path,
-        }))
+        })
 
     def _connect_ssh(self):
         """
         Fetch a reference to an SSH Context matching the play context from
         ContextService in the master process.
         """
-        return mitogen.service.call(
+        return self._wrap_connect({
-            self.parent,
-            ContextService.handle,
-            cast({
             'method': 'ssh',
             'check_host_keys': False,  # TODO
             'hostname': self._play_context.remote_addr,
@@ -177,19 +186,14 @@ class Connection(ansible.plugins.connection.ConnectionBase):
                 for term in shlex.split(s or '')
             ]
         })
-        )
 
     def _connect_docker(self):
-        return mitogen.service.call(
+        return self._wrap_connect({
-            self.parent,
-            ContextService.handle,
-            cast({
             'method': 'docker',
             'container': self._play_context.remote_addr,
             'python_path': self.python_path,
             'connect_timeout': self._play_context.timeout,
         })
-        )
 
     def _connect_sudo(self, via=None, python_path=None):
         """
@@ -200,10 +204,7 @@ class Connection(ansible.plugins.connection.ConnectionBase):
             Parent Context of the sudo Context. For Ansible, this should always
             be a Context returned by _connect_ssh().
         """
-        return mitogen.service.call(
+        return self._wrap_connect({
-            self.parent,
-            ContextService.handle,
-            cast({
             'method': 'sudo',
             'username': self._play_context.become_user,
             'password': self._play_context.become_pass,
@@ -216,7 +217,6 @@ class Connection(ansible.plugins.connection.ConnectionBase):
                 self._play_context.become_flags or ''
             ),
         })
-        )
 
     def _connect(self):
         """
@@ -318,8 +318,8 @@ class Connection(ansible.plugins.connection.ConnectionBase):
         emulate_tty = (not in_data and sudoable)
         rc, stdout, stderr = self.call(
             ansible_mitogen.helpers.exec_command,
-            cmd=cast(cmd),
+            cmd=mitogen.utils.cast(cmd),
-            in_data=cast(in_data),
+            in_data=mitogen.utils.cast(in_data),
             chdir=mitogen_chdir,
             emulate_tty=emulate_tty,
         )
@@ -341,7 +341,7 @@ class Connection(ansible.plugins.connection.ConnectionBase):
             Local filesystem path to write.
         """
         output = self.call(ansible_mitogen.helpers.read_path,
-                           cast(in_path))
+                           mitogen.utils.cast(in_path))
         ansible_mitogen.helpers.write_path(out_path, output)
 
     def put_data(self, out_path, data):
@@ -355,7 +355,8 @@ class Connection(ansible.plugins.connection.ConnectionBase):
             Remote filesystem path to write.
         """
         self.call(ansible_mitogen.helpers.write_path,
-                  cast(out_path), cast(data))
+                  mitogen.utils.cast(out_path),
+                  mitogen.utils.cast(data))
 
     def put_file(self, in_path, out_path):
         """

ansible_mitogen/services.py

@@ -81,9 +81,21 @@ class ContextService(mitogen.service.DeduplicatingService):
     def get_response(self, args):
         args.pop('discriminator', None)
         method = getattr(self.router, args.pop('method'))
+        try:
             context = method(**args)
+        except mitogen.core.StreamError as e:
+            return {
+                'context': None,
+                'home_dir': None,
+                'msg': str(e),
+            }
+
         home_dir = context.call(os.path.expanduser, '~')
-        return context, home_dir
+        return {
+            'context': context,
+            'home_dir': home_dir,
+            'msg': None,
+        }
 
 
 class FileService(mitogen.service.Service):