Add python logger configuration

This adds a common usable logging configuration for DIB, that
can be used by different python tools or elements.

This change is a factored out patch from the block device
refactoring.

Change-Id: I34d44610f74030936e7c0f602340b183baec3f1b
Signed-off-by: Andreas Florath <andreas@florath.net>

diskimage_builder/logging_config.py

@@ -0,0 +1,97 @@
+# Copyright 2016 Andreas Florath (andreas@florath.net)
+#
+# 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.
+
+# Python Logging Configuration for DIB
+# Usage:
+# In the main (application) file, do an
+#   import logging_config
+#   ...
+#   logging_config.setup()
+# It is then possible to use the normal python logging interface, like
+#   logger = logging.getLogger(__name__)
+#   logger.info("Info Message")
+
+import json
+import logging
+import logging.config
+import os
+import sys
+
+
+# A simple formatter to more or less copy oslo.log's ContextFormatter
+class DibFormatter(logging.Formatter):
+
+    def __init__(self, *args, **kwargs):
+        self.fmt = kwargs['fmt']
+        self.debug_suffix = kwargs.pop('debug_suffix')
+        logging.Formatter.__init__(self, *args, **kwargs)
+
+    def format(self, record):
+        if record.levelno == logging.DEBUG:
+            fmt = self.fmt + self.debug_suffix
+        else:
+            fmt = self.fmt
+
+        if sys.version_info < (3, 2):
+            self._fmt = fmt
+        else:
+            self._style = logging.PercentStyle(fmt)
+            self._fmt = self._style._fmt
+
+        return logging.Formatter.format(self, record)
+
+
+def setup():
+    # Check for the DIB_DEBUG_TRACE environment variable
+    # If it is set to something greater then 0, use debug
+    # logging.
+    LOG_LEVEL = "DEBUG" if 'DIB_DEBUG_TRACE' in os.environ \
+                and int(os.environ['DIB_DEBUG_TRACE']) > 0 else "INFO"
+
+    # Default logging configuration which can be overwritten
+    # by a config file passed in by a user.
+    PYTHON_LOGGING_CONFIG = {
+        'version': 1,
+        'disable_existing_loggers': False,
+
+        'formatters': {
+            'standard': {
+                '()': 'diskimage_builder.logging_config.DibFormatter',
+                'datefmt': '%Y-%m-%d %H:%M:%S',
+                'fmt': '%(asctime)s.%(msecs)03d %(levelname)s '
+                '%(name)s [-] %(message)s',
+                'debug_suffix': ' %(funcName)s %(pathname)s:%(lineno)d'
+            }
+        },
+        'handlers': {
+            'default': {
+                'level': LOG_LEVEL,
+                'class': 'logging.StreamHandler',
+                'formatter': 'standard',
+            }
+        },
+        'loggers': {
+            '': {
+                'handlers': ['default'],
+                'level': LOG_LEVEL,
+                'propagate': True
+            }
+        }
+    }
+
+    if 'DIB_PYTHON_LOGGING_CONFIG_FILE' in os.environ:
+        with open(os.environ['DIB_PYTHON_LOGGING_CONFIG_FILE']) as fd:
+            PYTHON_LOGGING_CONFIG = json.load(fd)
+
+    logging.config.dictConfig(PYTHON_LOGGING_CONFIG)

diskimage_builder/tests/test_loggingconfig.py

@@ -0,0 +1,29 @@
+# Copyright 2016 Andreas Florath (andreas@florath.net)
+#
+# 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.
+
+import logging
+import testtools
+
+from diskimage_builder import logging_config
+
+
+class TestLoggingConfig(testtools.TestCase):
+
+    def test_defaults(self):
+        logging_config.setup()
+        log = logging.getLogger(__name__)
+        log.debug("Debug Message")
+        log.info("Info Message")
+        log.warning("Warning Message")
+        log.error("Error Message")