Module aws_lambda_powertools.logging.formatter

Classes

class JsonFormatter (**kwargs)

AWS Lambda Logging formatter.

Formats the log message as a JSON encoded string. If the message is a dict it will be used directly. If the message can be parsed as JSON, then the parse d value is used in the output record.

Originally taken from https://gitlab.com/hadrien/aws_lambda_logging/

Return a JsonFormatter instance.

The json_default kwarg is used to specify a formatter for otherwise unserializable values. It must not throw. Defaults to a function that coerces the value to a string.

The log_record_order kwarg is used to specify the order of the keys used in the structured json logs. By default the order is: "level", "location", "message", "timestamp", "service" and "sampling_rate".

Other kwargs are used to specify log field format strings.

Expand source code

class JsonFormatter(logging.Formatter):
    """AWS Lambda Logging formatter.

    Formats the log message as a JSON encoded string.  If the message is a
    dict it will be used directly.  If the message can be parsed as JSON, then
    the parse d value is used in the output record.

    Originally taken from https://gitlab.com/hadrien/aws_lambda_logging/

    """

    def __init__(self, **kwargs):
        """Return a JsonFormatter instance.

        The `json_default` kwarg is used to specify a formatter for otherwise
        unserializable values.  It must not throw.  Defaults to a function that
        coerces the value to a string.

        The `log_record_order` kwarg is used to specify the order of the keys used in
        the structured json logs. By default the order is: "level", "location", "message", "timestamp",
        "service" and "sampling_rate".

        Other kwargs are used to specify log field format strings.
        """
        # Set the default unserializable function, by default values will be cast as str.
        self.default_json_formatter = kwargs.pop("json_default", str)
        # Set the insertion order for the log messages
        self.log_format = dict.fromkeys(kwargs.pop("log_record_order", ["level", "location", "message", "timestamp"]))
        self.reserved_keys = ["timestamp", "level", "location"]
        # Set the date format used by `asctime`
        super(JsonFormatter, self).__init__(datefmt=kwargs.pop("datefmt", None))

        self.log_format.update(self._build_root_keys(**kwargs))

    @staticmethod
    def _build_root_keys(**kwargs):
        return {
            "level": "%(levelname)s",
            "location": "%(funcName)s:%(lineno)d",
            "timestamp": "%(asctime)s",
            **kwargs,
        }

    @staticmethod
    def _get_latest_trace_id():
        xray_trace_id = os.getenv(constants.XRAY_TRACE_ID_ENV)
        return xray_trace_id.split(";")[0].replace("Root=", "") if xray_trace_id else None

    def update_formatter(self, **kwargs):
        self.log_format.update(kwargs)

    @staticmethod
    def _extract_log_message(log_record: logging.LogRecord) -> Union[Dict, str, bool, Iterable]:
        """Extract message from log record and attempt to JSON decode it

        Parameters
        ----------
        log_record : logging.LogRecord
            Log record to extract message from

        Returns
        -------
        message: Union[Dict, str, bool, Iterable]
            Extracted message
        """
        if isinstance(log_record.msg, dict):
            return log_record.msg

        message: str = log_record.getMessage()

        # Attempt to decode non-str messages e.g. msg = '{"x": "y"}'
        try:
            message = json.loads(log_record.msg)
        except (json.decoder.JSONDecodeError, TypeError, ValueError):
            pass

        return message

    def _extract_log_exception(self, log_record: logging.LogRecord) -> Optional[str]:
        """Format traceback information, if available

        Parameters
        ----------
        log_record : logging.LogRecord
            Log record to extract message from

        Returns
        -------
        log_record: Optional[str]
            Log record with constant traceback info
        """
        if log_record.exc_info:
            return self.formatException(log_record.exc_info)

        return None

    def _extract_log_exception_name(self, log_record: logging.LogRecord) -> Optional[str]:
        """Extract the exception name, if available

        Parameters
        ----------
        log_record : logging.LogRecord
            Log record to extract exception name from

        Returns
        -------
        log_record: Optional[str]
            Log record with exception name
        """
        if log_record.exc_info:
            return log_record.exc_info[0].__name__

        return None

    def _extract_log_keys(self, log_record: logging.LogRecord) -> Dict:
        """Extract and parse custom and reserved log keys

        Parameters
        ----------
        log_record : logging.LogRecord
            Log record to extract keys from

        Returns
        -------
        formatted_log: Dict
            Structured log as dictionary
        """
        record_dict = log_record.__dict__.copy()  # has extra kwargs we are after
        record_dict["asctime"] = self.formatTime(log_record, self.datefmt)

        formatted_log = {}

        # We have to iterate over a default or existing log structure
        # then replace any logging expression for reserved keys e.g. '%(level)s' to 'INFO'
        # and lastly add or replace incoming keys (those added within the constructor or .structure_logs method)
        for key, value in self.log_format.items():
            if value and key in self.reserved_keys:
                formatted_log[key] = value % record_dict
            else:
                formatted_log[key] = value

        # pick up extra keys when logging a new message e.g. log.info("my message", extra={"additional_key": "value"}
        # these messages will be added to the root of the final structure not within `message` key
        for key, value in record_dict.items():
            if key not in STD_LOGGING_KEYS:
                formatted_log[key] = value

        return formatted_log

    def format(self, record):  # noqa: A003
        formatted_log = self._extract_log_keys(log_record=record)
        formatted_log["message"] = self._extract_log_message(log_record=record)
        formatted_log["exception_name"] = self._extract_log_exception_name(log_record=record)
        formatted_log["exception"] = self._extract_log_exception(log_record=record)
        formatted_log.update({"xray_trace_id": self._get_latest_trace_id()})  # fetch latest Trace ID, if any

        # Filter out top level key with values that are None
        formatted_log = {k: v for k, v in formatted_log.items() if v is not None}

        return json.dumps(formatted_log, default=self.default_json_formatter)

Ancestors

• logging.Formatter

Methods

def format(self, record)

Format the specified record as text.

The record's attribute dictionary is used as the operand to a string formatting operation which yields the returned string. Before formatting the dictionary, a couple of preparatory steps are carried out. The message attribute of the record is computed using LogRecord.getMessage(). If the formatting string uses the time (as determined by a call to usesTime(), formatTime() is called to format the event time. If there is exception information, it is formatted using formatException() and appended to the message.

Expand source code

def format(self, record):  # noqa: A003
    formatted_log = self._extract_log_keys(log_record=record)
    formatted_log["message"] = self._extract_log_message(log_record=record)
    formatted_log["exception_name"] = self._extract_log_exception_name(log_record=record)
    formatted_log["exception"] = self._extract_log_exception(log_record=record)
    formatted_log.update({"xray_trace_id": self._get_latest_trace_id()})  # fetch latest Trace ID, if any

    # Filter out top level key with values that are None
    formatted_log = {k: v for k, v in formatted_log.items() if v is not None}

    return json.dumps(formatted_log, default=self.default_json_formatter)

def update_formatter(self, **kwargs)

Expand source code

def update_formatter(self, **kwargs):
    self.log_format.update(kwargs)