How to manage error reporting

サイトを公開している場合、DEBUG 設定は常にオフにしておかなければなりません。これにより、サーバー動作は高速になり、エラーページによって明らかになるアプリケーションの詳細が悪意あるユーザーに漏れるのを防ぎます。

However, running with DEBUG set to False means you'll never see errors generated by your site -- everyone will instead see your public error pages. You need to keep track of errors that occur in deployed sites, so Django can be configured to create reports with details about those errors.

E メールのレポート

サーバーエラー

DEBUG が False であるとき、コードがハンドリングされない例外を起こして内部サーバーエラーが起きると (厳密には、500 以上の HTTP ステータスコードを持つ全てのレスポンスが返ってくると)、Django は ADMINS 設定のリストに含まれるユーザーにメールを送信します。これにより、管理者はすぐにエラーの通知を受け取ることができます。メールには、ADMINS はエラーの説明、Python のトレースバック全体、エラーを引き起こした HTTP リクエストの詳細について書かれています。

注釈

In order to send email, Django requires a few settings telling it how to connect to your mail server. At the very least, you'll need to specify EMAIL_HOST and possibly EMAIL_HOST_USER and EMAIL_HOST_PASSWORD, though other settings may be also required depending on your mail server's configuration. Consult the Django settings documentation for a full list of email-related settings.

By default, Django will send email from root@localhost. However, some mail providers reject all email from this address. To use a different sender address, modify the SERVER_EMAIL setting.

To activate this behavior, put the email addresses of the recipients in the ADMINS setting.

参考

Server error emails are sent using the logging framework, so you can customize this behavior by customizing your logging configuration.

404 エラー

Django can also be configured to email errors about broken links (404 "page not found" errors). Django sends emails about 404 errors when:

If those conditions are met, Django will email the users listed in the MANAGERS setting whenever your code raises a 404 and the request has a referer. It doesn't bother to email for 404s that don't have a referer -- those are usually people typing in broken URLs or broken web bots. It also ignores 404s when the referer is equal to the requested URL, since this behavior is from broken web bots too.

注釈

BrokenLinkEmailsMiddleware must appear before other middleware that intercepts 404 errors, such as LocaleMiddleware or FlatpageFallbackMiddleware. Put it toward the top of your MIDDLEWARE setting.

You can tell Django to stop reporting particular 404s by tweaking the IGNORABLE_404_URLS setting. It should be a list of compiled regular expression objects. For example:

import re
IGNORABLE_404_URLS = [
    re.compile(r'\.(php|cgi)$'),
    re.compile(r'^/phpmyadmin/'),
]

In this example, a 404 to any URL ending with .php or .cgi will not be reported. Neither will any URL starting with /phpmyadmin/.

The following example shows how to exclude some conventional URLs that browsers and crawlers often request:

import re
IGNORABLE_404_URLS = [
    re.compile(r'^/apple-touch-icon.*\.png$'),
    re.compile(r'^/favicon\.ico$'),
    re.compile(r'^/robots\.txt$'),
]

(Note that these are regular expressions, so we put a backslash in front of periods to escape them.)

If you'd like to customize the behavior of django.middleware.common.BrokenLinkEmailsMiddleware further (for example to ignore requests coming from web crawlers), you should subclass it and override its methods.

参考

404 errors are logged using the logging framework. By default, these log records are ignored, but you can use them for error reporting by writing a handler and configuring logging appropriately.

Filtering error reports

警告

Filtering sensitive data is a hard problem, and it's nearly impossible to guarantee that sensitive data won't leak into an error report. Therefore, error reports should only be available to trusted team members and you should avoid transmitting error reports unencrypted over the internet (such as through email).

Filtering sensitive information

Error reports are really helpful for debugging errors, so it is generally useful to record as much relevant information about those errors as possible. For example, by default Django records the full traceback for the exception raised, each traceback frame’s local variables, and the HttpRequest’s attributes.

However, sometimes certain types of information may be too sensitive and thus may not be appropriate to be kept track of, for example a user's password or credit card number. So in addition to filtering out settings that appear to be sensitive as described in the DEBUG documentation, Django offers a set of function decorators to help you control which information should be filtered out of error reports in a production environment (that is, where DEBUG is set to False): sensitive_variables() and sensitive_post_parameters().

sensitive_variables(*variables)

If a function (either a view or any regular callback) in your code uses local variables susceptible to contain sensitive information, you may prevent the values of those variables from being included in error reports using the sensitive_variables decorator:

from django.views.decorators.debug import sensitive_variables

@sensitive_variables('user', 'pw', 'cc')
def process_info(user):
    pw = user.pass_word
    cc = user.credit_card_number
    name = user.name
    ...

In the above example, the values for the user, pw and cc variables will be hidden and replaced with stars (**********) in the error reports, whereas the value of the name variable will be disclosed.

To systematically hide all local variables of a function from error logs, do not provide any argument to the sensitive_variables decorator:

@sensitive_variables()
def my_function():
    ...

When using multiple decorators

If the variable you want to hide is also a function argument (e.g. 'user’ in the following example), and if the decorated function has multiple decorators, then make sure to place @sensitive_variables at the top of the decorator chain. This way it will also hide the function argument as it gets passed through the other decorators:

@sensitive_variables('user', 'pw', 'cc')
@some_decorator
@another_decorator
def process_info(user):
    ...
sensitive_post_parameters(*parameters)

If one of your views receives an HttpRequest object with POST parameters susceptible to contain sensitive information, you may prevent the values of those parameters from being included in the error reports using the sensitive_post_parameters decorator:

from django.views.decorators.debug import sensitive_post_parameters

@sensitive_post_parameters('pass_word', 'credit_card_number')
def record_user_profile(request):
    UserProfile.create(
        user=request.user,
        password=request.POST['pass_word'],
        credit_card=request.POST['credit_card_number'],
        name=request.POST['name'],
    )
    ...

In the above example, the values for the pass_word and credit_card_number POST parameters will be hidden and replaced with stars (**********) in the request's representation inside the error reports, whereas the value of the name parameter will be disclosed.

To systematically hide all POST parameters of a request in error reports, do not provide any argument to the sensitive_post_parameters decorator:

@sensitive_post_parameters()
def my_view(request):
    ...

All POST parameters are systematically filtered out of error reports for certain django.contrib.auth.views views (login, password_reset_confirm, password_change, and add_view and user_change_password in the auth admin) to prevent the leaking of sensitive information such as user passwords.

Custom error reports

All sensitive_variables() and sensitive_post_parameters() do is, respectively, annotate the decorated function with the names of sensitive variables and annotate the HttpRequest object with the names of sensitive POST parameters, so that this sensitive information can later be filtered out of reports when an error occurs. The actual filtering is done by Django's default error reporter filter: django.views.debug.SafeExceptionReporterFilter. This filter uses the decorators' annotations to replace the corresponding values with stars (**********) when the error reports are produced. If you wish to override or customize this default behavior for your entire site, you need to define your own filter class and tell Django to use it via the DEFAULT_EXCEPTION_REPORTER_FILTER setting:

DEFAULT_EXCEPTION_REPORTER_FILTER = 'path.to.your.CustomExceptionReporterFilter'

You may also control in a more granular way which filter to use within any given view by setting the HttpRequest’s exception_reporter_filter attribute:

def my_view(request):
    if request.user.is_authenticated:
        request.exception_reporter_filter = CustomExceptionReporterFilter()
    ...

Your custom filter class needs to inherit from django.views.debug.SafeExceptionReporterFilter and may override the following attributes and methods:

class SafeExceptionReporterFilter
cleansed_substitute

The string value to replace sensitive value with. By default it replaces the values of sensitive variables with stars (**********).

hidden_settings

A compiled regular expression object used to match settings and request.META values considered as sensitive. By default equivalent to:

import re

re.compile(r'API|TOKEN|KEY|SECRET|PASS|SIGNATURE', flags=re.IGNORECASE)
is_active(request)

Returns True to activate the filtering in get_post_parameters() and get_traceback_frame_variables(). By default the filter is active if DEBUG is False. Note that sensitive request.META values are always filtered along with sensitive setting values, as described in the DEBUG documentation.

get_post_parameters(request)

Returns the filtered dictionary of POST parameters. Sensitive values are replaced with cleansed_substitute.

get_traceback_frame_variables(request, tb_frame)

Returns the filtered dictionary of local variables for the given traceback frame. Sensitive values are replaced with cleansed_substitute.

If you need to customize error reports beyond filtering you may specify a custom error reporter class by defining the DEFAULT_EXCEPTION_REPORTER setting:

DEFAULT_EXCEPTION_REPORTER = 'path.to.your.CustomExceptionReporter'

The exception reporter is responsible for compiling the exception report data, and formatting it as text or HTML appropriately. (The exception reporter uses DEFAULT_EXCEPTION_REPORTER_FILTER when preparing the exception report data.)

Your custom reporter class needs to inherit from django.views.debug.ExceptionReporter.

class ExceptionReporter
html_template_path
New in Django 3.2.

Property that returns a pathlib.Path representing the absolute filesystem path to a template for rendering the HTML representation of the exception. Defaults to the Django provided template.

text_template_path
New in Django 3.2.

Property that returns a pathlib.Path representing the absolute filesystem path to a template for rendering the plain-text representation of the exception. Defaults to the Django provided template.

get_traceback_data()

Return a dictionary containing traceback information.

This is the main extension point for customizing exception reports, for example:

from django.views.debug import ExceptionReporter


class CustomExceptionReporter(ExceptionReporter):
    def get_traceback_data(self):
        data = super().get_traceback_data()
        # ... remove/add something here ...
        return data
get_traceback_html()

Return HTML version of exception report.

Used for HTML version of debug 500 HTTP error page.

get_traceback_text()

Return plain text version of exception report.

Used for plain text version of debug 500 HTTP error page and email reports.

As with the filter class, you may control which exception reporter class to use within any given view by setting the HttpRequest’s exception_reporter_class attribute:

def my_view(request):
    if request.user.is_authenticated:
        request.exception_reporter_class = CustomExceptionReporter()
    ...

参考

You can also set up custom error reporting by writing a custom piece of exception middleware. If you do write custom error handling, it's a good idea to emulate Django's built-in error handling and only report/log errors if DEBUG is False.

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