[flask]自定义请求日志

前言

flask默认会在控制台输出非结构化的请求日志，如果要输出json格式的日志，并且要把请求日志写到单独的文件中，可以通过先禁用默认请求日志，然后在钩子函数中自行记录请求的方式来实现。

定义日志器

下面代码定义了两个JSON日志格式化器，JsonFormatter 的日志格式是给普通代码内使用的，会记录调用函数、调用文件等信息，AccessLogFormatter的日志格式用于记录请求日志，记录请求路径、响应状态码、响应时间等信息。

FlaskLogger通过继承logging.Logger来实现一些自定义功能，比如指定格式化器、创建日志目录等。

class JsonFormatter(logging.Formatter):
    def format(self, record: logging.LogRecord):
        log_record = {
            "@timestamp": self.formatTime(record, "%Y-%m-%dT%H:%M:%S%z"), # format iso 8601
            "level": record.levelname,
            "name": record.name,
            "file": record.filename,
            "lineno": record.lineno,
            "func": record.funcName,
            "message": record.getMessage(),
        }
        return json.dumps(log_record)

class AccessLogFormatter(logging.Formatter):
    def format(self, record: logging.LogRecord):
        log_record = {
            "@timestamp": self.formatTime(record, "%Y-%m-%dT%H:%M:%S%z"), # format iso 8601
            "remote_addr": getattr(record, "remote_addr", ""),
            "scheme": getattr(record, "scheme", ""),
            "method": getattr(record, "method", ""),
            "host": getattr(record, "host", ""),
            "path": getattr(record, "path", ""),
            "status": getattr(record, "status", ""),
            "response_length": getattr(record, "response_length", ""),
            "response_time": getattr(record, "response_time", 0),
        }
        return json.dumps(log_record)

class FlaskLogger(logging.Logger):
    """自定义日志类, 设置请求日志和普通日志两个不同的日志器

    Args:
        name: str, 日志器名称, 默认为 __name__
        level: int, 日志级别, 默认为 DEBUG
        logfile: str, 日志文件名, 默认为 app.log
        logdir: str, 日志文件目录, 默认为当前目录
        access_log: bool, 是否用于记录访问日志, 默认为 False
        console: bool, 是否输出到控制台, 默认为 True
        json_log: bool, 是否使用json格式的日志, 默认为 True
    """
    def __init__(
        self,
        name: str = __name__,
        level: int = logging.DEBUG,
        logfile: str = "app.log",
        logdir: str = "",
        access_log: bool = False,
        console: bool = True,
        json_log: bool = True,
    ):
        super().__init__(name, level)
        self.logfile = logfile
        self.logdir = logdir
        self.access_log = access_log
        self.console = console
        self.json_log = json_log
        self.setup_logpath()
        self.setup_handler()

    def setup_logpath(self):
        """设置日志文件路径, 如果创建日志器时未指定日志目录, 则使用当前目录"""
        if not self.logdir:
            return

        p = Path(self.logdir)
        if not p.exists():
            try:
                p.mkdir(parents=True, exist_ok=True)
            except Exception as e:
                print(f"Failed to create log directory: {e}")
                sys.exit(1)

        self.logfile = p / self.logfile

    def setup_handler(self):
        if self.json_log:
            formatter = self.set_json_formatter()
        else:
            formatter = self.set_plain_formatter()
        handler_file = self.set_handler_file(formatter)
        handler_stdout = self.set_handler_stdout(formatter)
        self.addHandler(handler_file)
        if self.console:
            self.addHandler(handler_stdout)

    def set_plain_formatter(self):
        fmt = "%(asctime)s | %(levelname)s | %(name)s | %(filename)s:%(lineno)d | %(funcName)s | %(message)s"
        datefmt = "%Y-%m-%dT%H:%M:%S%z"
        return logging.Formatter(fmt, datefmt=datefmt)

    def set_json_formatter(self):
        """设置json格式的日志"""
        if self.access_log:
            return AccessLogFormatter()
        return JsonFormatter()

    def set_handler_stdout(self, formatter: logging.Formatter):
        handler = logging.StreamHandler(sys.stdout)
        handler.setFormatter(formatter)
        return handler

    def set_handler_file(self, formatter: logging.Formatter):
        handler = TimedRotatingFileHandler(
            filename=self.logfile,
            when="midnight",
            interval=1,
            backupCount=7,
            encoding="utf-8",
        )
        handler.setFormatter(formatter)
        return handler

实例化示例

access_logger = FlaskLogger("access", logdir="logs", access_log=True, logfile="access.log")
logger = FlaskLogger(logdir="logs")

钩子函数内记录请求日志

借助flask内置的钩子函数和全局对象，可以记录到每个请求的信息。

from flask import g, request, Response
import time

@app.before_request
def start_timer():
    # 通过全局对象 g 来记录请求开始时间
    g.start_time = time.time()

@app.after_request
def log_request(response: Response):
    """记录每次请求的日志"""
    response_length = (
        response.content_length if response.content_length is not None else "-"
    )
    log_message = {
        "remote_addr": request.remote_addr,
        "method": request.method,
        "scheme": request.scheme,
        "host": request.host,
        "path": request.path,
        "status": response.status_code,
        "response_length": response_length,
        "response_time": round(time.time() - g.start_time, 4),
    }
    access_logger.info("", extra=log_message)
    return response

基本使用示例

实例化Flask对象，禁用默认日志，定义路由等

from flask import Flask
import traceback

app = Flask(__name__)

@app.errorhandler(Exception)
def handle_exception(e):
    """全局拦截异常"""
    logger.error(f"An exception occurred, {traceback.format_exc()}", exc_info=e)
    return "An error occurred", 500

@app.get("/")
def hello():
    # 普通请求
    logger.info("Hello World")
    return "hello world"

@app.get("/error")
def raise_error():
    # 模拟错误请求，观察是否全局捕获
    raise Exception("Error")

@app.get("/slow")
def slow():
    # 模拟慢请求，观察请求日志的响应时间
    time.sleep(5)
    return "slow"

if __name__ == "__main__":
    # 禁用默认的日志器
    default_logger = logging.getLogger("werkzeug")
    default_logger.disabled = True

    app.run(host="127.0.0.1", port=5000)

访问测试，logs目录会生成access.log和app.log文件，控制台输出示例

{"@timestamp": "2025-04-26T00:26:20+0800", "level": "INFO", "name": "__main__", "file": "app.py", "lineno": 162, "func": "hello", "message": "Hello World"}
{"@timestamp": "2025-04-26T00:26:20+0800", "remote_addr": "127.0.0.1", "scheme": "http", "method": "GET", "host": "127.0.0.1:5000", "path": "/", "status": 200, "response_length": 11, "response_time": 0.0003}
{"@timestamp": "2025-04-26T00:26:20+0800", "level": "INFO", "name": "__main__", "file": "app.py", "lineno": 162, "func": "hello", "message": "Hello World"}
{"@timestamp": "2025-04-26T00:26:20+0800", "remote_addr": "127.0.0.1", "scheme": "http", "method": "GET", "host": "127.0.0.1:5000", "path": "/", "status": 200, "response_length": 11, "response_time": 0.0003}
{"@timestamp": "2025-04-26T00:29:47+0800", "remote_addr": "127.0.0.1", "scheme": "http", "method": "GET", "host": "127.0.0.1:5000", "path": "/slow", "status": 200, "response_length": 4, "response_time": 5.0002}
{"@timestamp": "2025-04-26T00:31:02+0800", "level": "ERROR", "name": "__main__", "file": "app.py", "lineno": 129, "func": "handle_exception", "message": "An exception occurred, Traceback (most recent call last):\n  File \"/xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/lib/python3.11/site-packages/flask/app.py\", line 917, in full_dispatch_request\n    rv = self.dispatch_request()\n         ^^^^^^^^^^^^^^^^^^^^^^^\n  File \"/xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/lib/python3.11/site-packages/flask/app.py\", line 902, in dispatch_request\n    return self.ensure_sync(self.view_functions[rule.endpoint])(**view_args)  # type: ignore[no-any-return]\n           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^\n  File \"/xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/demo1/app.py\", line 168, in raise_error\n    raise Exception(\"Error\")\nException: Error\n"}
{"@timestamp": "2025-04-26T00:31:02+0800", "remote_addr": "127.0.0.1", "scheme": "http", "method": "GET", "host": "127.0.0.1:5000", "path": "/error", "status": 500, "response_length": 17, "response_time": 0.0011}

完整使用示例

from flask import Flask, request, g, Response
import logging
import sys
from logging.handlers import TimedRotatingFileHandler
import json
from pathlib import Path
import traceback
import time

app = Flask(__name__)

class JsonFormatter(logging.Formatter):
    def format(self, record: logging.LogRecord):
        log_record = {
            "@timestamp": self.formatTime(record, "%Y-%m-%dT%H:%M:%S%z"), # format iso 8601
            "level": record.levelname,
            "name": record.name,
            "file": record.filename,
            "lineno": record.lineno,
            "func": record.funcName,
            "message": record.getMessage(),
        }
        return json.dumps(log_record)

class AccessLogFormatter(logging.Formatter):
    def format(self, record: logging.LogRecord):
        log_record = {
            "@timestamp": self.formatTime(record, "%Y-%m-%dT%H:%M:%S%z"), # format iso 8601
            "remote_addr": getattr(record, "remote_addr", ""),
            "scheme": getattr(record, "scheme", ""),
            "method": getattr(record, "method", ""),
            "host": getattr(record, "host", ""),
            "path": getattr(record, "path", ""),
            "status": getattr(record, "status", ""),
            "response_length": getattr(record, "response_length", ""),
            "response_time": getattr(record, "response_time", 0),
        }
        return json.dumps(log_record)

class FlaskLogger(logging.Logger):
    """自定义日志类, 设置请求日志和普通日志两个不同的日志器

    Args:
        name: str, 日志器名称, 默认为 __name__
        level: int, 日志级别, 默认为 DEBUG
        logfile: str, 日志文件名, 默认为 app.log
        logdir: str, 日志文件目录, 默认为当前目录
        access_log: bool, 是否用于记录访问日志, 默认为 False
        console: bool, 是否输出到控制台, 默认为 True
        json_log: bool, 是否使用json格式的日志, 默认为 True
    """
    def __init__(
        self,
        name: str = __name__,
        level: int = logging.DEBUG,
        logfile: str = "app.log",
        logdir: str = "",
        access_log: bool = False,
        console: bool = True,
        json_log: bool = True,
    ):
        super().__init__(name, level)
        self.logfile = logfile
        self.logdir = logdir
        self.access_log = access_log
        self.console = console
        self.json_log = json_log
        self.setup_logpath()
        self.setup_handler()

    def setup_logpath(self):
        """设置日志文件路径, 如果创建日志器时未指定日志目录, 则使用当前目录"""
        if not self.logdir:
            return

        p = Path(self.logdir)
        if not p.exists():
            try:
                p.mkdir(parents=True, exist_ok=True)
            except Exception as e:
                print(f"Failed to create log directory: {e}")
                sys.exit(1)

        self.logfile = p / self.logfile

    def setup_handler(self):
        if self.json_log:
            formatter = self.set_json_formatter()
        else:
            formatter = self.set_plain_formatter()
        handler_file = self.set_handler_file(formatter)
        handler_stdout = self.set_handler_stdout(formatter)
        self.addHandler(handler_file)
        if self.console:
            self.addHandler(handler_stdout)

    def set_plain_formatter(self):
        fmt = "%(asctime)s | %(levelname)s | %(name)s | %(filename)s:%(lineno)d | %(funcName)s | %(message)s"
        datefmt = "%Y-%m-%dT%H:%M:%S%z"
        return logging.Formatter(fmt, datefmt=datefmt)

    def set_json_formatter(self):
        """设置json格式的日志"""
        if self.access_log:
            return AccessLogFormatter()
        return JsonFormatter()

    def set_handler_stdout(self, formatter: logging.Formatter):
        handler = logging.StreamHandler(sys.stdout)
        handler.setFormatter(formatter)
        return handler

    def set_handler_file(self, formatter: logging.Formatter):
        handler = TimedRotatingFileHandler(
            filename=self.logfile,
            when="midnight",
            interval=1,
            backupCount=7,
            encoding="utf-8",
        )
        handler.setFormatter(formatter)
        return handler

access_logger = FlaskLogger("access", logdir="logs", access_log=True, logfile="access.log")
logger = FlaskLogger(logdir="logs")

@app.errorhandler(Exception)
def handle_exception(e):
    """全局拦截异常"""
    logger.error(f"An exception occurred, {traceback.format_exc()}", exc_info=e)
    return "An error occurred", 500

@app.before_request
def start_timer():
    # 通过全局对象 g 来记录请求开始时间
    g.start_time = time.time()

@app.after_request
def log_request(response: Response):
    """记录每次请求的日志"""
    response_length = (
        response.content_length if response.content_length is not None else "-"
    )
    log_message = {
        "remote_addr": request.remote_addr,
        "method": request.method,
        "scheme": request.scheme,
        "host": request.host,
        "path": request.path,
        "status": response.status_code,
        "response_length": response_length,
        "response_time": round(time.time() - g.start_time, 4),
    }
    access_logger.info("", extra=log_message)
    return response

@app.get("/")
def hello():
    # 普通请求
    logger.info("Hello World")
    return "hello world"

@app.get("/error")
def raise_error():
    # 模拟错误请求，观察是否全局捕获
    raise Exception("Error")

@app.get("/slow")
def slow():
    # 模拟慢请求，观察请求日志的响应时间
    time.sleep(5)
    return "slow"

if __name__ == "__main__":
    # 禁用默认的日志器
    default_logger = logging.getLogger("werkzeug")
    default_logger.disabled = True

    app.run(host="127.0.0.1", port=5000)

参考

• Flask - logging
• Python - logging