debug.py

"""
Logging and debuging facility
-----------------------------

Levels:

  DEBUG
    Detailed information, typically of interest only when diagnosing problems.
  INFO
    Confirmation that things are working as expected.
  WARNING
    An indication that something unexpected happened, or indicative of
    some problem in the near future (e.g. 'disk space low'). The software
    is still working as expected.
  ERROR
    Due to a more serious problem, the software has not been able to
    perform some function.
  CRITICAL
    A serious error, indicating that the program itself may be unable to
    continue running.

There are three loggers by default: `console_only`, `file_only` and `both`.
You can configure logging in the logging.dat in the appdata dir.
It's format is described in the :func:`logging.config.fileConfig` doc.

Use:

>>> import logging
>>> logger = logging.getLogger('default')

The old form: ``from debug import logger`` is also may be used,
but only in the top level modules.

Logging is thread-safe so you don't have to worry about locks,
just import and log.
"""

import logging
import logging.config
import os
import sys

from six.moves import configparser

import helper_startup
import state

helper_startup.loadConfig()

# Now can be overriden from a config file, which uses standard python
# logging.config.fileConfig interface
# examples are here:
# https://web.archive.org/web/20170712122006/https://bitmessage.org/forum/index.php/topic,4820.msg11163.html#msg11163
log_level = 'WARNING'


def log_uncaught_exceptions(ex_cls, ex, tb):
    """The last resort logging function used for sys.excepthook"""
    logging.critical('Unhandled exception', exc_info=(ex_cls, ex, tb))


def configureLogging():
    """
    Configure logging,
    using either logging.dat file in the state.appdata dir
    or dictionary with hardcoded settings.
    """
    sys.excepthook = log_uncaught_exceptions
    fail_msg = ''
    try:
        logging_config = os.path.join(state.appdata, 'logging.dat')
        logging.config.fileConfig(
            logging_config, disable_existing_loggers=False)
        return (
            False,
            'Loaded logger configuration from %s' % logging_config
        )
    except (OSError, configparser.NoSectionError, KeyError):
        if os.path.isfile(logging_config):
            fail_msg = \
                'Failed to load logger configuration from %s, using default' \
                ' logging config\n%s' % \
                (logging_config, sys.exc_info())
        else:
            # no need to confuse the user if the logger config
            # is missing entirely
            fail_msg = 'Using default logger configuration'

    logging_config = {
        'version': 1,
        'formatters': {
            'default': {
                'format': u'%(asctime)s - %(levelname)s - %(message)s',
            },
        },
        'handlers': {
            'console': {
                'class': 'logging.StreamHandler',
                'formatter': 'default',
                'level': log_level,
                'stream': 'ext://sys.stderr'
            },
            'file': {
                'class': 'logging.handlers.RotatingFileHandler',
                'formatter': 'default',
                'level': log_level,
                'filename': os.path.join(state.appdata, 'debug.log'),
                'maxBytes': 2097152,  # 2 MiB
                'backupCount': 1,
                'encoding': 'UTF-8',
            }
        },
        'loggers': {
            'console_only': {
                'handlers': ['console'],
                'propagate': 0
            },
            'file_only': {
                'handlers': ['file'],
                'propagate': 0
            },
            'both': {
                'handlers': ['console', 'file'],
                'propagate': 0
            },
        },
        'root': {
            'level': log_level,
            'handlers': ['console'],
        },
    }

    logging_config['loggers']['default'] = logging_config['loggers'][
        'file_only' if '-c' in sys.argv else 'both']
    logging.config.dictConfig(logging_config)

    return True, fail_msg


def resetLogging():
    """Reconfigure logging in runtime when state.appdata dir changed"""
    # pylint: disable=global-statement, used-before-assignment
    global logger
    for i in logger.handlers:
        logger.removeHandler(i)
        i.flush()
        i.close()
    configureLogging()
    logger = logging.getLogger('default')


# !

preconfigured, msg = configureLogging()
logger = logging.getLogger('default')
if msg:
    logger.log(logging.WARNING if preconfigured else logging.INFO, msg)