Gracefully handle errors in logging config files

Fixes bug #1154245

If the parameter to the --log-config option cannot be loaded by the
logging.config.fileConfig() function, you get an exception like this
raised:

  NoSectionError: No section: 'formatters'

which doesn't do much to help users understand the error.

Improve the situation by wrapping the error in a custom exception type
giving this:

 LogConfigError: Error loading logging config /etc/logging.conf: No section: 'formatters'

Also add some tests to check we raise this error under the most common
failure conditions.

Change-Id: I6ad2eb4867213b6356ce43d75da50218d1b498f6

openstack/common/log.py

@@ -29,6 +29,7 @@ It also allows setting of formatting information through conf.
 
 """
 
+import ConfigParser
 import cStringIO
 import inspect
 import itertools
@@ -323,10 +324,30 @@ def _create_logging_excepthook(product_name):
     return logging_excepthook
 
 
+class LogConfigError(Exception):
+
+    message = _('Error loading logging config %(log_config)s: %(err_msg)s')
+
+    def __init__(self, log_config, err_msg):
+        self.log_config = log_config
+        self.err_msg = err_msg
+
+    def __str__(self):
+        return self.message % dict(log_config=self.log_config,
+                                   err_msg=self.err_msg)
+
+
+def _load_log_config(log_config):
+    try:
+        logging.config.fileConfig(log_config)
+    except ConfigParser.Error, exc:
+        raise LogConfigError(log_config, str(exc))
+
+
 def setup(product_name):
     """Setup logging."""
     if CONF.log_config:
-        logging.config.fileConfig(CONF.log_config)
+        _load_log_config(CONF.log_config)
     else:
         _setup_logging_from_conf()
     sys.excepthook = _create_logging_excepthook(product_name)

tests/unit/test_log.py

@@ -1,7 +1,9 @@
 import cStringIO
 import logging
+import os
 import StringIO
 import sys
+import tempfile
 
 from oslo.config import cfg
 
@@ -377,3 +379,49 @@ class LogConfigOptsTestCase(test_utils.BaseTestCase):
         logdir = '/some/other/path/'
         CONF(['--logdir', logdir])
         self.assertEquals(CONF.log_dir, logdir)
+
+
+class LogConfigTestCase(test_utils.BaseTestCase):
+
+    minimal_config = """[loggers]
+keys=root
+
+[formatters]
+keys=
+
+[handlers]
+keys=
+
+[logger_root]
+handlers=
+"""
+
+    def _create_tempfile(self, basename, contents, ext='.conf'):
+        (fd, path) = tempfile.mkstemp(prefix=basename, suffix=ext)
+        try:
+            os.write(fd, contents)
+        finally:
+            os.close(fd)
+        return path
+
+    def test_log_config_ok(self):
+        log_config = self._create_tempfile('logging', self.minimal_config)
+        self.config(log_config=log_config)
+        log.setup('test_log_config')
+
+    def test_log_config_not_exist(self):
+        log_config = self._create_tempfile('logging', self.minimal_config)
+        os.remove(log_config)
+        self.config(log_config=log_config)
+        self.assertRaises(log.LogConfigError, log.setup, 'test_log_config')
+
+    def test_log_config_invalid(self):
+        log_config = self._create_tempfile('logging', self.minimal_config[5:])
+        self.config(log_config=log_config)
+        self.assertRaises(log.LogConfigError, log.setup, 'test_log_config')
+
+    def test_log_config_unreadable(self):
+        log_config = self._create_tempfile('logging', self.minimal_config)
+        os.chmod(log_config, 0)
+        self.config(log_config=log_config)
+        self.assertRaises(log.LogConfigError, log.setup, 'test_log_config')