django-brake 1.3.0

Cache-based rate-limiting for Django.

Django Brake provides a decorator to rate-limit views. Limiting can be based on IP address or a field in the request–either a GET or POST variable.

If the rate limit is exceded, either a 403 Forbidden can be sent, or the request can be annotated with a limited attribute, allowing you to take another action like adding a captcha to a form.

This is a fork of Django Ratelimit, to support:

• Django 1.3 and above

• Multiple buckets (e.g. separate endpoints)

• Allow for multiple time thresholds (periods) per bucket

• Analyze which functions were limited, and what their counts were.

The intention is to remain API compliant with Django Ratelimit.

Using Django Brake

from brake.decorators import ratelimit is the biggest thing you need to do. The @ratelimit decorator provides several optional arguments with sensible defaults (in italics).

ip:

Whether to rate-limit based on the IP. True

block:

Whether to block the request instead of annotating. False

method:

Which HTTP method(s) to rate-limit. May be a string or a list. all

field:

Which HTTP field(s) to use to rate-limit. May be a string or a list. None

rate:

The number of requests per unit time allowed. 5/m

increment:

A callable that will accept the request and response as arguments and, when called, will return True or False. If it returns False, the current request is not counted against the limit. Useful for only counting invalid login attempts against the limit, for example, and not valid ones. None

Examples

@ratelimit()
def myview(request):
    # Will be true if the same IP makes more than 5 requests/minute.
    was_limited = getattr(request, 'limited', False)
    return HttpResponse()

@ratelimit(block=True)
def myview(request):
    # If the same IP makes >5 reqs/min, will return HttpResponseForbidden
    return HttpResponse()

@ratelimit(field='username')
def login(request):
    # If the same username OR IP is used >5 times/min, this will be True.
    # The `username` value will come from GET or POST, determined by the
    # request method.
    was_limited = getattr(request, 'limited', False)
    return HttpResponse()

@ratelimit(increment=lambda req, resp: resp.count)
def login(request):
    resp = HttpResponseRedirect()
    if login_is_correct:
        # Do not count correct logins against the limit.
        resp.count = False
    else:
        resp.count = True
    return resp

@ratelimit(method='POST')
def login(request):
    # Only apply rate-limiting to POSTs.
    return HttpResponseRedirect()

@ratelimit(field=['username', 'other_field'])
def login(request):
    # Use multiple field values.
    return HttpResponse()

@ratelimit(rate='1/m')
@ratelimit(rate='10/h')
@ratelimit(rate='100/d')
def slow(request):
    # Allow 1 reqs/min, 10 per hour, and 100 per day.
    return HttpResponse()

#
## Example Login Code to *only* block login failures
##

def login(request):
    """Just a regular django login flow."""
    from brake import utils as brake_utils
    # minute, hour, day periods.
    periods = (60, 60 * 60, 24 * 60 * 60,)
    # 'login' is whatever your func.__name__ attribute would be
    # for the function that is decorated
    limits = brake_utils.get_limits(
        request, 'login', 'username', self.PERIODS
    )

    # Check limits before we even see if the form is valid.
    # This way, even if the attacker stumbles on the
    # correct passphrase, they're locked out.

    if limits:
        request.flash['error'] = 'You have been ratelimited'
        return http.HttpResponseRedirect(urlresolvers.reverse(
            'auth_login'
        ))

    form = forms.AuthenticationForm()
    if form.method == 'POST':
        form = forms.AuthenticationForm(data=request.POST):
            # Login information was not correct.
            if form.is_valid():
                # Proceed with login process, and redirect to next page.

            # If our form is invalid, we increment counters manually
            brake_utils.inc_counts(
                request,
                'login',
                'username', # Username value.
                periods
            )
            # Return to login page
            # Optionally, you can pass in the form context
            return http.HttpResponseRedirect(urlresolvers.reverse(
                'auth_login'
            ))



# If you're interested in which endpoints failed, and what the
# counts were:

@ratelimit(field='username', method='POST', rate='1/m')
def login(request):
    # Limits is a dict that looks like this:
    # {'period': 60, 'field': 'username', 'count', 1}
    # This can give you more insight into how to deal with
    # the ratelimiting issue.
    limits =  getattr(request, 'limits', {})

    if limits:
        return http.HttpResponseRedirect(urlresolvers.reverse(
            'auth_login'
        ))

Implementation Details:

Some Required Customization

By default we only track the IP that we get form request.META[‘HOST_ADDR’]. Unless your webservers are sitting directly on routable IPs and have no loadbalancers or upstream proxies, this is probably not what you want!

Since this is a deployment detail, we leave this up to those who choose to implement Django Brake. You do so with a simple bit of Inheritence and override.

# In its own module, or in your view module; however you like:

from brake.backends import cachebe

class MyBrake(cachebe.CacheBackend):
    def get_ip(self, request):
        return request.META.get(
            'HTTP_TRUE_CLIENT_IP',
            request.META.get('REMOTE_ADDR')
    )

# Now in your settings.py:

RATELIMIT_CACHE_BACKEND = 'path.to.module.MyBrake'

Note

RATELIMIT_CACHE_BACKEND is now a string of the path to a class. The class itself should be the last in the chain.

Note

RATELIMIT_STATUS_CODE is another setting you might set if you’d like the decorator to return something other than 403 if block=True.

Internals

These are variables which you do not need to modify directly, but are essential to the functioning of Brake

function_name:

This is the name of the function decorated with Brake; this allows us to separate into different “buckets” for each view. This is automatically added and doesn’t need to be specified.

period:

This is derrived from the rate information passed in as a string. It’s the number of seconds for which the increment on a bucket + period will be valid. It sets the TTL in memcache.

The cache key structure from one bad login attempt from our example above would look something like this:

# The form value derived counters:
rl:func:<function_name>:period:<60>:field:<username>:<sha1 of username>
rl:func:<function_name>:period:<3600>:field:<username>:<sha1 of username>
rl:func:<function_name>:period:<86400>:field:<username>:<sha1 of username>
# The IP derived counters:
rl:func:<function_name>:period:<60>:ip:<ip_address>
rl:func:<function_name>:period:<3600>:ip:<ip_address>
rl:func:<function_name>:period:<86500>:ip:<ip_address>

All period numbers are equivilent to the TTL for that key.

If any of these thresholds are passed, then the view will 403. This is a huge improvement in terms of usablity and security of many existing ratelimiting applications.

Testing

To run the test you need to simply run:

virtualenv django-brake
cd django-brake
. bin/activate
python setup.py develop
./test.sh

There’s no slick test runner since we’re trying not to fully integrate with Django. See brake/tests/tests.py for more code examples.

Acknowledgements

Thanks to James Socol (jsocol) on Github. A vast majority of the work on this project is his (django-ratelimit).

Also thanks to Simon Willison’s ratelimitcache, on which Jsocol’s version of this library is largly based.