short

short.rb

require 'sinatra'
require 'redis'

$redis = Redis.new

get '/s' do
  'Enter a URL: <form method="post" action="s"><input type="text" name="url"><input type="submit" value="Shorten"></form>'
end

post '/s' do
  k = $redis.incr('short:keyspace').to_s
  $redis.set 'short:' + k, params[:url]
  "#{params[:url]} shortened to <a href='#{request.url.chomp('s') + k}'>#{request.url.chomp('s') + k}</a>"
end

get '/:key/?' do |k|
  url = $redis.get 'short:' + k
  url ? redirect(url) : 404
end

not_found { redirect '/s' }