Refactor Popen usage to allow overrides

* Add subprocess.Popen wrapper in common
* Change bash.py and smb.py to use wrapper.

Because subprocess.Popen uses os.fork() to spawn child processes, it may
be desirable for a calling application to override subprocess.Popen with
a custom class that implements a different spawning method - such as
posix_spawn. With large-memory applications, posix_spawn may be more
desirable than os.fork() due to memory allocation behavior. This change
allows Satori to be compatible with such a workflow.

Change-Id: Ia60adea27d1a6cbf28341ea3aece5ee604a94583
Closes-Bug: #1412485

satori/bash.py

@@ -20,8 +20,8 @@ Execute commands over ssh or using the python subprocess module.
 
 import logging
 import shlex
-import subprocess
 
+from satori.common import popen
 from satori import errors
 from satori import smb
 from satori import ssh
@@ -147,11 +147,11 @@ class LocalShell(ShellMixin):
         """
         cwd = kwargs.get('cwd')
         with_exit_code = kwargs.get('with_exit_code')
-        spipe = subprocess.PIPE
+        spipe = popen.PIPE
 
         cmd = shlex.split(command)
         LOG.debug("Executing `%s` on local machine", command)
-        result = subprocess.Popen(
+        result = popen.popen(
             cmd, stdout=spipe, stderr=spipe, cwd=cwd)
         out, err = result.communicate()
         resultdict = {

satori/common/popen.py

@@ -0,0 +1,23 @@
+#    Licensed under the Apache License, Version 2.0 (the "License"); you may
+#    not use this file except in compliance with the License. You may obtain
+#    a copy of the License at
+#
+#         http://www.apache.org/licenses/LICENSE-2.0
+#
+#    Unless required by applicable law or agreed to in writing, software
+#    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+#    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+#    License for the specific language governing permissions and limitations
+#    under the License.
+
+""" Popen wrapper to allow custom patching of subprocess.Popen."""
+
+import subprocess
+
+PIPE = subprocess.PIPE
+STDOUT = subprocess.STDOUT
+
+
+def popen(*args, **kwargs):
+    """Wrap Popen to allow for higher level patching if necessary."""
+    return subprocess.Popen(*args, **kwargs)

satori/smb.py

@@ -26,9 +26,9 @@ import logging
 import os
 import re
 import shlex
-import subprocess
 import tempfile
 
+from satori.common import popen
 from satori import errors
 from satori import ssh
 from satori import tunnel
@@ -199,11 +199,11 @@ class SMBClient(object):  # pylint: disable=R0902
                 self.username,
                 self.password,
                 self.host)
-            self._process = subprocess.Popen(
+            self._process = popen.popen(
                 shlex.split(self._substituted_command),
                 stdout=self._file_write,
-                stderr=subprocess.STDOUT,
-                stdin=subprocess.PIPE,
+                stderr=popen.STDOUT,
+                stdin=popen.PIPE,
                 close_fds=True,
                 universal_newlines=True,
                 bufsize=-1)

satori/tests/test_bash.py

@@ -39,7 +39,7 @@ class TestLocalShell(TestBashModule):
 
     def setUp(self):
         super(TestLocalShell, self).setUp()
-        popen_patcher = mock.patch.object(bash.subprocess, 'Popen')
+        popen_patcher = mock.patch.object(bash.popen, 'popen')
         self.mock_popen = popen_patcher.start()
         mock_result = mock.MagicMock()
         mock_result.returncode = self.testrun.returncode

tox.ini

@@ -49,4 +49,4 @@ downloadcache = ~/cache/pip
 ignore = H102
 show-source = True
 exclude = .venv,.git,.tox,dist,doc,*openstack/common*,*lib/python*,*egg,build,tools,*satori/contrib*,*.ropeproject,*satori/tests*,setup.py
-max-complexity = 12
+max-complexity = 16