'''
This library is provided to allow standard python logging
to output log data as JSON formatted strings
'''
import logging
import json
import re
from datetime import date, datetime, time, timezone
import traceback
import importlib
from inspect import istraceback
from collections import OrderedDict
# skip natural LogRecord attributes
# http://docs.python.org/library/logging.html#logrecord-attributes
RESERVED_ATTRS = (
'args', 'asctime', 'created', 'exc_info', 'exc_text', 'filename',
'funcName', 'levelname', 'levelno', 'lineno', 'module',
'msecs', 'message', 'msg', 'name', 'pathname', 'process',
'processName', 'relativeCreated', 'stack_info', 'thread', 'threadName')
def merge_record_extra(record, target, reserved):
"""
Merges extra attributes from LogRecord object into target dictionary
:param record: logging.LogRecord
:param target: dict to update
:param reserved: dict or list with reserved keys to skip
"""
for key, value in record.__dict__.items():
# this allows to have numeric keys
if (key not in reserved
and not (hasattr(key, "startswith")
and key.startswith('_'))):
target[key] = value
return target
class JsonEncoder(json.JSONEncoder):
"""
A custom encoder extending the default JSONEncoder
"""
def default(self, obj):
if isinstance(obj, (date, datetime, time)):
return self.format_datetime_obj(obj)
elif istraceback(obj):
return ''.join(traceback.format_tb(obj)).strip()
elif type(obj) == Exception \
or isinstance(obj, Exception) \
or type(obj) == type:
return str(obj)
try:
return super(JsonEncoder, self).default(obj)
except TypeError:
try:
return str(obj)
except Exception:
return None
def format_datetime_obj(self, obj):
return obj.isoformat()
class JsonFormatter(logging.Formatter):
"""
A custom formatter to format logging records as json strings.
Extra values will be formatted as str() if not supported by
json default encoder
"""
def __init__(self, *args, **kwargs):
"""
:param json_default: a function for encoding non-standard objects
as outlined in http://docs.python.org/2/library/json.html
:param json_encoder: optional custom encoder
:param json_serializer: a :meth:`json.dumps`-compatible callable
that will be used to serialize the log record.
:param json_indent: an optional :meth:`json.dumps`-compatible numeric value
that will be used to customize the indent of the output json.
:param prefix: an optional string prefix added at the beginning of
the formatted string
:param rename_fields: an optional dict, used to rename field names in the output.
Rename message to @message: {'message': '@message'}
:param static_fields: an optional dict, used to add fields with static values to all logs
:param json_indent: indent parameter for json.dumps
:param json_ensure_ascii: ensure_ascii parameter for json.dumps
:param reserved_attrs: an optional list of fields that will be skipped when
outputting json log record. Defaults to all log record attributes:
http://docs.python.org/library/logging.html#logrecord-attributes
:param timestamp: an optional string/boolean field to add a timestamp when
outputting the json log record. If string is passed, timestamp will be added
to log record using string as key. If True boolean is passed, timestamp key
will be "timestamp". Defaults to False/off.
"""
self.json_default = self._str_to_fn(kwargs.pop("json_default", None))
self.json_encoder = self._str_to_fn(kwargs.pop("json_encoder", None))
self.json_serializer = self._str_to_fn(kwargs.pop("json_serializer", json.dumps))
self.json_indent = kwargs.pop("json_indent", None)
self.json_ensure_ascii = kwargs.pop("json_ensure_ascii", True)
self.prefix = kwargs.pop("prefix", "")
self.rename_fields = kwargs.pop("rename_fields", {})
self.static_fields = kwargs.pop("static_fields", {})
reserved_attrs = kwargs.pop("reserved_attrs", RESERVED_ATTRS)
self.reserved_attrs = dict(zip(reserved_attrs, reserved_attrs))
self.timestamp = kwargs.pop("timestamp", False)
# super(JsonFormatter, self).__init__(*args, **kwargs)
logging.Formatter.__init__(self, *args, **kwargs)
if not self.json_encoder and not self.json_default:
self.json_encoder = JsonEncoder
self._required_fields = self.parse()
self._skip_fields = dict(zip(self._required_fields,
self._required_fields))
self._skip_fields.update(self.reserved_attrs)
def _str_to_fn(self, fn_as_str):
"""
If the argument is not a string, return whatever was passed in.
Parses a string such as package.module.function, imports the module
and returns the function.
:param fn_as_str: The string to parse. If not a string, return it.
"""
if not isinstance(fn_as_str, str):
return fn_as_str
path, _, function = fn_as_str.rpartition('.')
module = importlib.import_module(path)
return getattr(module, function)
def add_fields(self, log_record, record, message_dict):
"""
Override this method to implement custom logic for adding fields.
"""
for field in self._required_fields:
if field in self.rename_fields:
log_record[self.rename_fields[field]] = record.__dict__.get(field)
else:
log_record[field] = record.__dict__.get(field)
log_record.update(self.static_fields)
log_record.update(message_dict)
merge_record_extra(record, log_record, reserved=self._skip_fields)
if self.timestamp:
key = self.timestamp if type(self.timestamp) == str else 'timestamp'
log_record[key] = datetime.fromtimestamp(record.created, tz=timezone.utc)