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import math
import random
import logging
from django.contrib.sites.models import Site
from django.core.exceptions import ValidationError
from django.core.urlresolvers import reverse
from django.db import IntegrityError, transaction
import brevisurl.settings
from brevisurl import Error
from brevisurl.backends.base import BaseBrevisUrlBackend
from brevisurl.models import ShortUrl
from brevisurl.utils import absurl
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
"""
if self.kwargs.get('domain') is not None:
# Domain is present in keyword arguments supplied by constructor.
domain = self.kwargs.get('domain')
elif brevisurl.settings.LOCAL_BACKEND_DOMAIN is not None:
# Domain is defined in settings.
domain = brevisurl.settings.LOCAL_BACKEND_DOMAIN
else:
# Domain is taken from django site framework.
domain = Site.objects.get_current().domain
try:
shortened_url = self.__generate_shortened_url(domain)
try:
short_url, created = ShortUrl.objects.get_or_create(backend=self.class_path,
original_url=original_url,
defaults={'shortened_url': shortened_url})
if created:
log.info('Url "%s" shortened to "%s"', original_url, shortened_url)
else:
log.info('Url "%s" already shortened to "%s"', original_url, short_url.shortened_url)
return short_url
except (IntegrityError, ValidationError) as e:
# Check if the error is an URL validation error.
if e.message_dict.has_key('original_url'):
raise
# Generate another token.
self.__check_tokens_exhausted()
while True:
shortened_url = self.__generate_shortened_url(domain)
sid = transaction.savepoint()
try:
short_url = ShortUrl.objects.create(backend=self.class_path,
original_url=original_url,
shortened_url=shortened_url)
log.info('Url "%s" shortened to "%s"', original_url, shortened_url)
transaction.savepoint_commit()
return short_url
except (IntegrityError, ValidationError) as e:
transaction.savepoint_rollback(sid)
self.__check_tokens_exhausted()
except Exception:
if self.fail_silently:
return None
else:
log.exception('Unknown exception raised while shortening url "%s"', original_url)
raise
def __check_tokens_exhausted(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')
def __generate_shortened_url(self, domain):
chars = brevisurl.settings.LOCAL_BACKEND_TOKEN_CHARS
size = brevisurl.settings.LOCAL_BACKEND_TOKEN_LENGTH
random.shuffle(chars)
token = ''.join([random.choice(chars) for x in range(size)])
shortened_url = absurl(domain=domain,
path=reverse('brevisurl_redirect',
kwargs={'token': token}))
return shortened_url
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