I was creating a project the other day that used anonymous pages for users and I wanted to make it a little less “guessable” but more human friendly than a SHA1 hash, so I decided to make a small home-brew URL shortener similar in format to Tiny URL.

The neat thing about ruby is that when you turn a Fixnum to a String with to_s you can specify the base, and when you turn a String back to a Fixnum you can also specify a base in to_i. This lends itself perfectly to turning (large) IDs into a shortened URL thats easier to remember.

In the first gist you can see how this would work with a model to make simple url shortening in rails — or, you can use randomized values to generate more user friendly “unique” tokens (as opposed to using SHA1 hashes for user confirmation/password reset pages).

# You can use the model's ID (PK/Serial) to generate a token which can be reversed:
# Example:
# Url.find(7213).shortened #=> 5kd
# Url.find_by_shortened("5kd") #=> #<Url id: 7213…>
class Url < ActiveRecord::Base
Radix = 36

# convert ID into a shortened version
def shortened
id.to_s(Radix)
end

# unconvert the shortened version back to an ID
def self.shortened_to_id(shortened)
shortened.to_i(Radix)
end

# convert and lookup
def self.find_by_shortened(shortened)
find shortened_to_id(shortened)
end
end

File: short_url_token.rb
————————

# make tinyurl-ish tokens for pages so you dont have a goofy MD5 running amuck
# Example:
# make_token #=> "32uelywr"
# NOTE: the longer the number, the longer the token
def make_token
("%d%d" % [rand(100), Time.now.to_i]).to_i.to_s(36)
end