configuration: add logging_levels section

Allow to configure the logging-levels of various loggers by adding a new
section `logging_levels` to the configuration file. Each entry in that
section configures the logging-level of one logger / channel.

README.md

@@ -113,6 +113,9 @@ collector_opts:
     blacklist:
       - docker0
       - lo
+logging_levels:
+  root: INFO
+  foomodule.barcollector: WARNING
 ```
 
 ### Start-up Configuration

p3.yml

@@ -9,3 +9,5 @@ collector_opts:
     blacklist:
       - docker0
       - lo
+logging_levels:
+  root: INFO

p3exporter/__init__.py

@@ -3,7 +3,7 @@
 from wsgiref.simple_server import make_server
 
 import yaml
-import logging
+import logging.config
 import os
 import signal
 import sys
@@ -13,6 +13,27 @@
 from p3exporter.web import create_app
 
 
+def setup_logging(cfg: dict):
+    """Set up logging as configured.
+
+    The configuration may optionally contain an entry `logging_levels`,
+    if it does not or if that entry is not a dict then does nothing.
+    The expected contents of the entry is logger-names as keys and
+    logging-levels as values.
+
+    :param cfg: Configuration as read from config-file.
+    :type cfg: dict
+    """
+    if not isinstance(cfg.get('logging_levels'), dict):
+        return
+    levels = cfg['logging_levels']
+    loggers = {k: {'level': v} for k, v in levels.items()}
+    logging.config.dictConfig({
+        'version': 1,
+        'loggers': loggers,
+    })
+
+
 def shutdown():
     """Shutdown the app in a clean way."""
     logging.info('Shutting down, see you next time!')
@@ -41,6 +62,7 @@ def main():
     with open(args.config, 'r') as config_file:
         cfg = yaml.load(config_file, Loader=yaml.SafeLoader)
     collector_config = CollectorConfig(**cfg)
+    setup_logging(cfg)
 
     Collector(collector_config)
 

tests/test_cases/logging_levels.py

@@ -0,0 +1,34 @@
+from p3exporter import setup_logging
+import logging
+import pytest
+
+
+@pytest.mark.parametrize("cfg_levels,expected", [
+    (None,                                   [logging.NOTSET,  logging.NOTSET, logging.NOTSET]),
+    ("Not a dict",                           [logging.NOTSET,  logging.NOTSET, logging.NOTSET]),
+    ({"": "INFO", "foo": "DEBUG"},           [logging.INFO,    logging.DEBUG,  logging.NOTSET]),
+    ({"root": "WARNING", "bar": "CRITICAL"}, [logging.WARNING, logging.NOTSET, logging.CRITICAL]),
+    ({"foo": 10, "bar": 20},                 [logging.NOTSET,  logging.DEBUG,  logging.INFO]),
+    ])
+def test_logging_levels(cfg_levels, expected):
+    loggers = ["", "foo", "bar"]
+
+    # GIVEN a clean slate of uninitialized logging-levels
+    for lg in loggers:
+        logging.getLogger(lg).setLevel(logging.NOTSET)
+
+    # AND an input config-dictionary
+    cfg = {
+        "exporter_name": "Test only",
+        "collectors": [],
+        "collector_opts": {},
+    }
+    if cfg_levels is not None:
+        cfg["logging_levels"] = cfg_levels
+
+    # WHEN calling setup_logging()
+    setup_logging(cfg)
+
+    # THEN the logging-levels should get changed to the expected
+    for i, lg in enumerate(loggers):
+        assert logging.getLogger(lg).level == expected[i]