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import math
import random
import logging
from django.contrib.sites.models import Site
from django.core.urlresolvers import reverse
import brevisurl.settings
from brevisurl import Error
from brevisurl.backends.base import BaseBrevisUrlBackend
from brevisurl.models import ShortUrl
log = logging.getLogger(__name__)
class TokensExhaustedError(Error):
"""Exception is raised when tokens are exhausted."""
class BrevisUrlBackend(BaseBrevisUrlBackend):
def shorten_url(self, original_url):
"""
:raises: ImproperlyConfigured, django.core.exceptions.ValidationError
:raises: brevisurl.backends.local.TokensExhaustedError
"""
try:
short_url = ShortUrl.objects.get(backend=self.class_path, original_url=original_url)
log.info('Url "%s" already shortened to "%s"', original_url, short_url.shortened_url)
return short_url
except ShortUrl.DoesNotExist:
pass
try:
short_url = ShortUrl()
if self.kwargs.get('domain') is not None:
# Domain is present in keyword arguments supplied by constructor.
domain = self.kwargs.get('domain').rstrip('/')
elif brevisurl.settings.LOCAL_BACKEND_DOMAIN is not None:
# Domain is defined in settings.
domain = brevisurl.settings.LOCAL_BACKEND_DOMAIN.rstrip('/')
else:
# Domain is taken from django site framework.
domain = '{protocol:s}://{domain:s}'.format(protocol=brevisurl.settings.LOCAL_BACKEND_DOMAIN_PROTOCOL,
domain=Site.objects.get_current().domain)
# Generating url path for shortened url.
url_path = reverse('brevisurl_redirect', kwargs={'token': self.__generate_token()})
if brevisurl.settings.LOCAL_BACKEND_STRIP_TOKEN_URL_SLASH:
url_path = url_path.lstrip('/')
# Saving newly generated shortened url.
short_url.original_url = original_url
short_url.shortened_url = '{domain:s}{url_path:s}'.format(domain=domain, url_path=url_path)
short_url.backend = self.class_path
short_url.save()
log.info('Url "%s" shortened to "%s"', original_url, short_url.shortened_url)
return short_url
except Exception:
if self.fail_silently:
return None
else:
log.exception('Unknown exception raised while shortening url "%s"', original_url)
raise
def __generate_token(self):
chars = brevisurl.settings.LOCAL_BACKEND_TOKEN_CHARS
size = brevisurl.settings.LOCAL_BACKEND_TOKEN_LENGTH
if ShortUrl.objects.count() >= math.pow(len(chars), size):
raise TokensExhaustedError('Consider incrementing the token length or change the char list')
random.shuffle(chars)
while True:
token = ''.join([random.choice(chars) for x in range(size)])
if not ShortUrl.objects.filter(backend=self.class_path, shortened_url__endswith=token).count():
break
return token
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