Add check_output function and tests.

certbot-postfix/certbot_postfix/util.py

@@ -0,0 +1,49 @@
+"""Utility functions for use in the Postfix installer."""
+
+import logging
+import subprocess
+
+
+logger = logging.getLogger(__name__)
+
+
+def check_output(*args, **kwargs):
+    """Backported version of subprocess.check_output for Python 2.6+.
+
+    This is the same as subprocess.check_output from newer versions of
+    Python, except:
+
+    1. The return value is a string rather than a byte string. To
+    accomplish this, the caller cannot set the parameter
+    universal_newlines.
+    2. If the command exits with a nonzero status, output is not
+    included in the raised subprocess.CalledProcessError because
+    subprocess.CalledProcessError on Python 2.6 does not support this.
+    Instead, the failure including the output is logged.
+
+    :param tuple args: positional arguments for Popen
+    :param dict kwargs: keyword arguments for Popen
+
+    :returns: data printed to stdout
+    :rtype: str
+
+    """
+    for keyword in ('stdout', 'universal_newlines',):
+        if keyword in kwargs:
+            raise ValueError(
+                keyword + ' argument not allowed, it will be overridden.')
+
+    kwargs['stdout'] = subprocess.PIPE
+    kwargs['universal_newlines'] = True
+
+    process = subprocess.Popen(*args, **kwargs)
+    output, unused_err = process.communicate()
+    retcode = process.poll()
+    if retcode:
+        cmd = kwargs.get('args')
+        if cmd is None:
+            cmd = args[0]
+        logger.debug(
+            "'%s' exited with %d. Output was:\n%s", cmd, retcode, output)
+        raise subprocess.CalledProcessError(retcode, cmd)
+    return output

certbot-postfix/certbot_postfix/util_test.py

@@ -0,0 +1,50 @@
+"""Tests for certbot_postfix.util."""
+
+import subprocess
+import unittest
+
+import mock
+
+class CheckOutputTest(unittest.TestCase):
+    """Tests for certbot_postfix.util.check_output."""
+
+    @classmethod
+    def _call(cls, *args, **kwargs):
+        from certbot_postfix.util import check_output
+        return check_output(*args, **kwargs)
+
+    @mock.patch('certbot_postfix.util.logger')
+    @mock.patch('certbot_postfix.util.subprocess.Popen')
+    def test_command_error(self, mock_popen, mock_logger):
+        command = 'foo'
+        retcode = 42
+        output = 'bar'
+
+        mock_popen().communicate.return_value = (output, '')
+        mock_popen().poll.return_value = 42
+
+        self.assertRaises(subprocess.CalledProcessError, self._call, command)
+
+        log_args = mock_logger.debug.call_args[0]
+        self.assertTrue(command in log_args)
+        self.assertTrue(retcode in log_args)
+        self.assertTrue(output in log_args)
+
+    @mock.patch('certbot_postfix.util.subprocess.Popen')
+    def test_success(self, mock_popen):
+        command = 'foo'
+        output = 'bar'
+        mock_popen().communicate.return_value = (output, '')
+        mock_popen().poll.return_value = 0
+
+        self.assertEqual(self._call(command), output)
+
+    def test_stdout_error(self):
+        self.assertRaises(ValueError, self._call, stdout=None)
+
+    def test_universal_newlines_error(self):
+        self.assertRaises(ValueError, self._call, universal_newlines=False)
+
+
+if __name__ == '__main__':  # pragma: no cover
+    unittest.main()