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|
# -*- test-case-name: twisted.logger.test.test_flatten -*-
# Copyright (c) Twisted Matrix Laboratories.
# See LICENSE for details.
"""
Code related to "flattening" events; that is, extracting a description of all
relevant fields from the format string and persisting them for later
examination.
"""
from collections import defaultdict
from string import Formatter
from typing import Any, Dict, Optional
from ._interfaces import LogEvent
aFormatter = Formatter()
class KeyFlattener:
"""
A L{KeyFlattener} computes keys for the things within curly braces in
PEP-3101-style format strings as parsed by L{string.Formatter.parse}.
"""
def __init__(self) -> None:
"""
Initialize a L{KeyFlattener}.
"""
self.keys: Dict[str, int] = defaultdict(lambda: 0)
def flatKey(
self, fieldName: str, formatSpec: Optional[str], conversion: Optional[str]
) -> str:
"""
Compute a string key for a given field/format/conversion.
@param fieldName: A format field name.
@param formatSpec: A format spec.
@param conversion: A format field conversion type.
@return: A key specific to the given field, format and conversion, as
well as the occurrence of that combination within this
L{KeyFlattener}'s lifetime.
"""
if formatSpec is None:
formatSpec = ""
if conversion is None:
conversion = ""
result = "{fieldName}!{conversion}:{formatSpec}".format(
fieldName=fieldName,
formatSpec=formatSpec,
conversion=conversion,
)
self.keys[result] += 1
n = self.keys[result]
if n != 1:
result += "/" + str(self.keys[result])
return result
def flattenEvent(event: LogEvent) -> None:
"""
Flatten the given event by pre-associating format fields with specific
objects and callable results in a L{dict} put into the C{"log_flattened"}
key in the event.
@param event: A logging event.
"""
if event.get("log_format", None) is None:
return
if "log_flattened" in event:
fields = event["log_flattened"]
else:
fields = {}
keyFlattener = KeyFlattener()
for literalText, fieldName, formatSpec, conversion in aFormatter.parse(
event["log_format"]
):
if fieldName is None:
continue
if conversion != "r":
conversion = "s"
flattenedKey = keyFlattener.flatKey(fieldName, formatSpec, conversion)
structuredKey = keyFlattener.flatKey(fieldName, formatSpec, "")
if flattenedKey in fields:
# We've already seen and handled this key
continue
if fieldName.endswith("()"):
fieldName = fieldName[:-2]
callit = True
else:
callit = False
field = aFormatter.get_field(fieldName, (), event)
fieldValue = field[0]
if conversion == "r":
conversionFunction = repr
else: # Above: if conversion is not "r", it's "s"
conversionFunction = str
if callit:
fieldValue = fieldValue()
flattenedValue = conversionFunction(fieldValue)
fields[flattenedKey] = flattenedValue
fields[structuredKey] = fieldValue
if fields:
event["log_flattened"] = fields
def extractField(field: str, event: LogEvent) -> Any:
"""
Extract a given format field from the given event.
@param field: A string describing a format field or log key. This is the
text that would normally fall between a pair of curly braces in a
format string: for example, C{"key[2].attribute"}. If a conversion is
specified (the thing after the C{"!"} character in a format field) then
the result will always be str.
@param event: A log event.
@return: A value extracted from the field.
@raise KeyError: if the field is not found in the given event.
"""
keyFlattener = KeyFlattener()
[[literalText, fieldName, formatSpec, conversion]] = aFormatter.parse(
"{" + field + "}"
)
assert fieldName is not None
key = keyFlattener.flatKey(fieldName, formatSpec, conversion)
if "log_flattened" not in event:
flattenEvent(event)
return event["log_flattened"][key]
def flatFormat(event: LogEvent) -> str:
"""
Format an event which has been flattened with L{flattenEvent}.
@param event: A logging event.
@return: A formatted string.
"""
fieldValues = event["log_flattened"]
keyFlattener = KeyFlattener()
s = []
for literalText, fieldName, formatSpec, conversion in aFormatter.parse(
event["log_format"]
):
s.append(literalText)
if fieldName is not None:
key = keyFlattener.flatKey(fieldName, formatSpec, conversion or "s")
s.append(str(fieldValues[key]))
return "".join(s)
|
