Merge branch 'hashid_generation' into 'dev'

Hashid generation

Use Hashids to generate shortUrls.

Right now we will hit collisions at a 50% rate at 10k urls assuming perfect randomness. Using hashids reduces the chance of collisions as the number of urls increase.

Hashids are guarenteed unique. The downside being that as the number of urls get larger, the hashids will get longer as well. The rate is exponential though with roughly number of characters as log base alphabet length of (id + seed).

See merge request !10

go/go/models.py

@@ -4,6 +4,9 @@ from django.utils import timezone
 from django.conf import settings
 import random, string
 
+from hashids import Hashids
+hashids = Hashids(salt="srct.gmu.edu", alphabet=(string.ascii_lowercase + string.digits))
+hashids_counter = None
 
 class URL( models.Model ):
     """
@@ -20,6 +23,8 @@ class URL( models.Model ):
     clicks = models.IntegerField( default = 0 )
     expires = models.DateTimeField( blank = True, null = True )
 
+
+
     def __unicode__(self):
         return '<%s : %s>' % (self.owner.username, self.target)
 
@@ -28,17 +33,21 @@ class URL( models.Model ):
 
     @staticmethod
     def generate_valid_short():
-        selection = string.ascii_lowercase + string.digits
-        tries = 0
-        while True:
-            short = ''.join(random.choice(selection) for i in range(5))
+        global hashids_counter
+        hashids_counter += 1
+        short = hashids.encrypt(hashids_counter)
+        tries = 1
+        while tries < 100:
             try:
                 urls = URL.objects.get( short__iexact = short )
                 tries += 1
+                hashids_counter += 1
             except URL.DoesNotExist:
                 return short
-            if tries > 100:
-                return None
+        return None
+
+# this needs to be here instead of at the top because the model's manager must be available before this line
+hashids_counter = URL.objects.count()
 
 
 class RegisteredUser( models.Model ):

requirements.txt

@@ -5,6 +5,7 @@ django-auth-ldap==1.2.1
 django-piwik==0.1
 django-qrcode==0.3
 django-simple-captcha==0.4.2
+hashids==1.0.1
 gunicorn==18.0
 piwikapi==0.3
 python-ldap==2.4.15