django/docs/howto/error-reporting.txt

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 just 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 (HTTP status code 500). 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_CLASSES` 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 just people typing in broken URLs or broken Web 'bots).

.. 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 towards the top of your :setting:`MIDDLEWARE_CLASSES` setting.

You can tell Django to stop reporting particular 404s by tweaking the
:setting:`IGNORABLE_404_URLS` setting. It should be a tuple 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
-----------------------

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
: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 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`: http://en.wikipedia.org/wiki/Stack_trace
.. _`traceback frame`: http://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 mutiple 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
        mutiple 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()
        ...

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

.. class:: django.views.debug.SafeExceptionReporterFilter

.. method:: SafeExceptionReporterFilter.is_active(self, request)

    Returns ``True`` to activate the filtering operated in the other methods.
    By default the filter is active if :setting:`DEBUG` is ``False``.

.. method:: SafeExceptionReporterFilter.get_request_repr(self, request)

    Returns the representation string of the request object, that is, the
    value that would be returned by ``repr(request)``, except it uses the
    filtered dictionary of POST parameters as determined by
    :meth:`SafeExceptionReporterFilter.get_post_parameters`.

.. method:: SafeExceptionReporterFilter.get_post_parameters(self, request)

    Returns the filtered dictionary of POST parameters. By default it replaces
    the values of sensitive parameters with stars (`**********`).

.. method:: SafeExceptionReporterFilter.get_traceback_frame_variables(self, request, tb_frame)

    Returns the filtered dictionary of local variables for the given traceback
    frame. By default it replaces the values of sensitive variables with stars
    (`**********`).

.. 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``.