jsonlogger.py

'''
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 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", {})
        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 parse(self):
        """
        Parses format string looking for substitutions

        This method is responsible for returning a list of fields (as strings)
        to include in all log messages.
        """
        standard_formatters = re.compile(r'\((.+?)\)', re.IGNORECASE)
        return standard_formatters.findall(self._fmt)

    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(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)

    def process_log_record(self, log_record):
        """
        Override this method to implement custom logic
        on the possibly ordered dictionary.
        """
        return log_record

    def jsonify_log_record(self, log_record):
        """Returns a json string of the log record."""
        return self.json_serializer(log_record,
                                    default=self.json_default,
                                    cls=self.json_encoder,
                                    indent=self.json_indent,
                                    ensure_ascii=self.json_ensure_ascii)

    def serialize_log_record(self, log_record):
        """Returns the final representation of the log record."""
        return "%s%s" % (self.prefix, self.jsonify_log_record(log_record))

    def format(self, record):
        """Formats a log record and serializes to json"""
        message_dict = {}
        if isinstance(record.msg, dict):
            message_dict = record.msg
            record.message = None
        else:
            record.message = record.getMessage()
        # only format time if needed
        if "asctime" in self._required_fields:
            record.asctime = self.formatTime(record, self.datefmt)

        # Display formatted exception, but allow overriding it in the
        # user-supplied dict.
        if record.exc_info and not message_dict.get('exc_info'):
            message_dict['exc_info'] = self.formatException(record.exc_info)
        if not message_dict.get('exc_info') and record.exc_text:
            message_dict['exc_info'] = record.exc_text
        # Display formatted record of stack frames
        # default format is a string returned from :func:`traceback.print_stack`
        try:
            if record.stack_info and not message_dict.get('stack_info'):
                message_dict['stack_info'] = self.formatStack(record.stack_info)
        except AttributeError:
            # Python2.7 doesn't have stack_info.
            pass

        try:
            log_record = OrderedDict()
        except NameError:
            log_record = {}

        self.add_fields(log_record, record, message_dict)
        log_record = self.process_log_record(log_record)

        return self.serialize_log_record(log_record)