django/docs/howto/error-reporting.txt

=============================
How to manage error reporting
=============================

When you're running a public site you should always turn off the
:setting:`DEBUG` setting. That will make your server run much faster, and will
also prevent malicious users from seeing details of your application that can be
revealed by the error pages.

However, running with :setting:`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.

Email reports
=============

Server errors
-------------

When :setting:`DEBUG` is ``False``, Django will email the users listed in the
:setting:`ADMINS` setting whenever your code raises an unhandled exception and
results in an internal server error (strictly speaking, for any response with
an HTTP status code of 500 or greater). This gives the administrators immediate
notification of any errors. The :setting:`ADMINS` will get a description of the
error, a complete Python traceback, and details about the HTTP request that
caused the error.

.. note::

   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 :setting:`EMAIL_HOST` and possibly
   :setting:`EMAIL_HOST_USER` and :setting:`EMAIL_HOST_PASSWORD`,
   though other settings may be also required depending on your mail
   server's configuration. Consult :doc:`the Django settings
   documentation </ref/settings>` 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 :setting:`SERVER_EMAIL` setting.

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

.. seealso::

    Server error emails are sent using the logging framework, so you can
    customize this behavior by :doc:`customizing your logging configuration
    </topics/logging>`.

404 errors
----------

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

* :setting:`DEBUG` is ``False``;

* Your :setting:`MIDDLEWARE` setting includes
  :class:`django.middleware.common.BrokenLinkEmailsMiddleware`.

If those conditions are met, Django will email the users listed in the
:setting:`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.

.. note::

    :class:`~django.middleware.common.BrokenLinkEmailsMiddleware` must appear
    before other middleware that intercepts 404 errors, such as
    :class:`~django.middleware.locale.LocaleMiddleware` or
    :class:`~django.contrib.flatpages.middleware.FlatpageFallbackMiddleware`.
    Put it toward the top of your :setting:`MIDDLEWARE` setting.

You can tell Django to stop reporting particular 404s by tweaking the
:setting:`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
:class:`django.middleware.common.BrokenLinkEmailsMiddleware` further (for
example to ignore requests coming from web crawlers), you should subclass it
and override its methods.

.. seealso::

    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 :doc:`configuring logging </topics/logging>` appropriately.

.. _filtering-error-reports:

Filtering error reports
=======================

.. warning::

    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
-------------------------------

.. currentmodule:: django.views.decorators.debug

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
:class:`~django.http.HttpRequest`’s :ref:`attributes<httprequest-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 :setting:`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
:setting:`DEBUG` is set to ``False``): :func:`sensitive_variables` and
:func:`sensitive_post_parameters`.

.. _`full traceback`: https://en.wikipedia.org/wiki/Stack_trace
.. _`traceback frame`: https://en.wikipedia.org/wiki/Stack_frame

.. function:: 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():
            ...

    .. admonition:: 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):
                ...

.. function:: sensitive_post_parameters(*parameters)

    If one of your views receives an :class:`~django.http.HttpRequest` object
    with :attr:`POST parameters<django.http.HttpRequest.POST>` 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 :mod:`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:

Custom error reports
--------------------

All :func:`sensitive_variables` and :func:`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:
:class:`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
:setting:`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()
        ...

.. currentmodule:: django.views.debug

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

.. class:: SafeExceptionReporterFilter

    .. attribute:: cleansed_substitute

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

    .. attribute:: 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)

    .. method:: is_active(request)

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

    .. method:: get_post_parameters(request)

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

    .. method:: get_traceback_frame_variables(request, tb_frame)

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

If you need to customize error reports beyond filtering you may specify a
custom error reporter class by defining the
:setting:`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
:setting:`DEFAULT_EXCEPTION_REPORTER_FILTER` when preparing the exception
report data.)

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

.. class:: ExceptionReporter

    .. attribute:: html_template_path

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

    .. attribute:: text_template_path

        Property that returns a :class:`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.

    .. method:: 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

    .. method:: get_traceback_html()

        Return HTML version of exception report.

        Used for HTML version of debug 500 HTTP error page.

    .. method:: 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()
        ...

.. seealso::

    You can also set up custom error reporting by writing a custom piece of
    :ref:`exception middleware <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 :setting:`DEBUG` is ``False``.