Simple Short URLs

by Nikolai SharangovichMarch 6, 2013

With code samples, this blog post exemplifies how to easily make short URLs without employing third-party solutions.

Table of Contents

Creating short URLs

I want to share with you an idea, or how to reinvent the wheel, if you need a short URL, but can’t use side solutions, such as goo.gl, and have a short domain. You can make a URL shorter on your own. First, we need to create a model with a destination path, parameter fields, and an appropriate controller. After that, we can route.

<span class="n">get</span> <span class="s1">'/:id'</span> <span class="o">=&gt;</span> <span class="s1">'short_url#show'</span>

1	<span class="n">get</span> <span class="s1">'/:id'</span> <span class="o">=></span> <span class="s1">'short_url#show'</span>

Then, we can make a redirect to a required path with saved parameters. If you need to create a very short URL for a tweet, for example, a digital :id can eat too many symbols in the result URL. To make it shorter, we can convert an :id number to a string (what, actually, URL shorters do). I have resolved this issue with the help of the Base64 standart. In our case, it’s just an array with characters and their IDs (codes). To convert an :id number to a short string, first, we convert it into a URL with Base64. This is the example of the ShortUrl model.

<span class="k">class</span> <span class="nc">ShortUrl</span> <span class="o">&lt;</span> <span class="no">ActiveRecord</span><span class="o">::</span><span class="no">Base</span>

  <span class="no">SYMBOLS</span> <span class="o">=</span> <span class="s2">"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_"</span>
  <span class="no">DEFAULT_URL</span> <span class="o">=</span> <span class="p">[</span><span class="s2">"http://"</span><span class="p">,</span> <span class="no">APP_CONFIG</span><span class="p">[</span><span class="s1">'host'</span><span class="p">],</span> <span class="p">(</span><span class="no">APP_CONFIG</span><span class="p">[</span><span class="s1">'port'</span><span class="p">].</span><span class="nf">present?</span> <span class="p">?</span> <span class="s2">":</span><span class="si">#{</span><span class="no">APP_CONFIG</span><span class="p">[</span><span class="s1">'port'</span><span class="p">]</span><span class="si">}</span><span class="s2">"</span> <span class="p">:</span> <span class="s1">''</span><span class="p">)].</span><span class="nf">join</span>

  <span class="n">serialize</span> <span class="ss">:params</span>

  <span class="k">def</span> <span class="nc">self</span><span class="o">.</span><span class="nf">find_by_code</span> <span class="n">string</span>
    <span class="n">find</span> <span class="n">decode</span><span class="p">(</span><span class="n">string</span><span class="p">)</span>
  <span class="k">end</span>

  <span class="k">def</span> <span class="nc">self</span><span class="o">.</span><span class="nf">generate</span> <span class="n">path</span><span class="p">,</span> <span class="n">params</span>
    <span class="n">short_url_record</span> <span class="o">=</span> <span class="n">create</span> <span class="k">do</span> <span class="o">|</span><span class="n">t</span><span class="o">|</span>
      <span class="n">t</span><span class="p">.</span><span class="nf">path</span> <span class="o">=</span> <span class="n">path</span>
      <span class="n">t</span><span class="p">.</span><span class="nf">params</span> <span class="o">=</span> <span class="n">params</span>
      <span class="n">t</span><span class="p">.</span><span class="nf">save</span>
    <span class="k">end</span>
    <span class="k">if</span> <span class="n">short_url_record</span><span class="p">.</span><span class="nf">id</span>
      <span class="p">[</span><span class="no">DEFAULT_URL</span><span class="p">,</span> <span class="s1">'/'</span><span class="p">,</span> <span class="n">encode</span><span class="p">(</span><span class="n">short_url_record</span><span class="p">.</span><span class="nf">id</span><span class="p">)].</span><span class="nf">join</span>
    <span class="k">else</span>
      <span class="kp">nil</span>
    <span class="k">end</span>
  <span class="k">end</span>

  <span class="k">def</span> <span class="nf">full_path</span>
    <span class="p">[</span><span class="no">DEFAULT_URL</span><span class="p">,</span> <span class="n">path</span><span class="p">].</span><span class="nf">join</span>
  <span class="k">end</span>

  <span class="kp">private</span>

  <span class="k">def</span> <span class="nc">self</span><span class="o">.</span><span class="nf">encode</span> <span class="n">number</span>
    <span class="n">base</span> <span class="o">=</span> <span class="no">SYMBOLS</span><span class="p">.</span><span class="nf">length</span>
    <span class="n">res</span> <span class="o">=</span> <span class="p">[]</span>
    <span class="k">begin</span>
      <span class="n">code</span> <span class="o">=</span> <span class="n">number</span> <span class="o">%</span> <span class="n">base</span>
      <span class="n">number</span> <span class="o">/=</span> <span class="n">base</span>
      <span class="n">res</span> <span class="o">&lt;&lt;</span> <span class="no">SYMBOLS</span><span class="p">[</span><span class="n">code</span><span class="p">]</span>
    <span class="k">end</span> <span class="k">until</span> <span class="n">number</span> <span class="o">==</span> <span class="mi">0</span>
    <span class="n">res</span> <span class="o">&lt;&lt;</span> <span class="s1">'s'</span>
    <span class="n">res</span><span class="p">.</span><span class="nf">reverse</span><span class="p">.</span><span class="nf">join</span>
  <span class="k">end</span>

  <span class="k">def</span> <span class="nc">self</span><span class="o">.</span><span class="nf">decode</span> <span class="n">string</span>
    <span class="k">begin</span>
      <span class="n">string</span> <span class="o">=</span> <span class="n">string</span><span class="p">.</span><span class="nf">match</span><span class="p">(</span><span class="sr">/\A[s](.{1,5})\z/</span><span class="p">)[</span><span class="mi">1</span><span class="p">]</span>
      <span class="n">i</span> <span class="o">=</span> <span class="n">string</span><span class="p">.</span><span class="nf">length</span> <span class="o">-</span> <span class="mi">1</span>
      <span class="n">res</span> <span class="o">=</span> <span class="mi">0</span>
      <span class="n">string</span><span class="p">.</span><span class="nf">each_char</span> <span class="k">do</span> <span class="o">|</span><span class="n">c</span><span class="o">|</span>
        <span class="n">res</span> <span class="o">+=</span> <span class="p">(</span><span class="no">SYMBOLS</span><span class="p">.</span><span class="nf">index</span><span class="p">(</span><span class="n">c</span><span class="p">)</span> <span class="o">*</span> <span class="p">(</span><span class="no">SYMBOLS</span><span class="p">.</span><span class="nf">length</span> <span class="o">**</span> <span class="n">i</span><span class="p">))</span>
        <span class="n">i</span> <span class="o">-=</span> <span class="mi">1</span>
      <span class="k">end</span>
      <span class="n">res</span>
    <span class="k">rescue</span>
      <span class="kp">nil</span>
    <span class="k">end</span>
  <span class="k">end</span>

<span class="k">end</span>

class ShortUrl < ActiveRecord::Base

SYMBOLS = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_"

DEFAULT_URL = ["http://", APP_CONFIG['host'], (APP_CONFIG['port'].present? ? ":#{APP_CONFIG['port']}" : '')].join

serialize :params

def self.find_by_code string

find decode(string)

end

def self.generate path, params

short_url_record = create do |t|

t.path = path

t.params = params

t.save

end

if short_url_record.id

[DEFAULT_URL, '/', encode(short_url_record.id)].join

else

nil

end

def full_path

[DEFAULT_URL, path].join

end

private

def self.encode number

base = SYMBOLS.length

res = []

begin

code = number % base

number /= base

res << SYMBOLS[code]

end until number == 0

res << 's'

res.reverse.join

end

def self.decode string

begin

string = string.match(/\A[s](.{1,5})\z/)[1]

i = string.length - 1

res = 0

string.each_char do |c|

res += (SYMBOLS.index(c) * (SYMBOLS.length ** i))

i -= 1

end

res

rescue

nil

end

If you want to leave both route variants (a digital ID and a string ID), you can put a prefix before an encoded string (in this case, it’s the s character) and use regular expression constraints in the route.

<span class="n">get</span> <span class="s1">'/:id'</span> <span class="o">=&gt;</span> <span class="s1">'short_url#show'</span><span class="p">,</span> <span class="ss">constraints: </span><span class="p">{</span> <span class="ss">id: </span><span class="sr">/[s].{1,5}/</span> <span class="p">}</span>

1	<span class="n">get</span> <span class="s1">'/:id'</span> <span class="o">=></span> <span class="s1">'short_url#show'</span><span class="p">,</span> <span class="ss">constraints: </span><span class="p">{</span> <span class="ss">id: </span><span class="sr">/[s].{1,5}/</span> <span class="p">}</span>

The number of characters is limited to five, because you can encode a really big number (1073741823) with five characters that can never be used. These are some examples of encoding.

<span class="n">pry</span><span class="p">(</span><span class="n">main</span><span class="p">)</span><span class="o">&gt;</span> <span class="no">ShortUrl</span><span class="p">.</span><span class="nf">encode</span> <span class="mi">12345</span>
<span class="o">=&gt;</span> <span class="s2">"sDA5"</span>
<span class="n">pry</span><span class="p">(</span><span class="n">main</span><span class="p">)</span><span class="o">&gt;</span> <span class="no">ShortUrl</span><span class="p">.</span><span class="nf">encode</span> <span class="mi">1000000</span>
<span class="o">=&gt;</span> <span class="s2">"sD0JA"</span>

<span class="n">pry</span><span class="p">(</span><span class="n">main</span><span class="p">)</span><span class="o">&gt;</span> <span class="no">ShortUrl</span><span class="p">.</span><span class="nf">encode</span> <span class="mi">1056698302</span>
<span class="o">=&gt;</span> <span class="s2">"s-----"</span>

<span class="n">pry</span><span class="p">(</span><span class="n">main</span><span class="p">)</span><span class="o">&gt;</span> <span class="no">ShortUrl</span><span class="p">.</span><span class="nf">encode</span> <span class="mi">1827200481836</span>
<span class="o">=&gt;</span> <span class="s2">"altoros"</span>

pry(main)> ShortUrl.encode 12345

=> "sDA5"

=> "sD0JA"

=> "s-----"

=> "altoros"

Then, you should decode.

<span class="n">pry</span><span class="p">(</span><span class="n">main</span><span class="p">)</span><span class="o">&gt;</span> <span class="no">ShortUrl</span><span class="p">.</span><span class="nf">decode</span> <span class="s2">"sFFFFF"</span>
<span class="o">=&gt;</span> <span class="mi">85217605</span>

=> 85217605

So, you can generate short URLs.

<span class="no">ShortUrl</span><span class="p">.</span><span class="nf">generate</span><span class="p">(</span><span class="n">edit_user_path</span><span class="p">(</span><span class="vi">@screener</span><span class="p">),</span> <span class="ss">reply_to: </span><span class="n">reply_to</span><span class="p">)</span>

ShortUrl.generate(edit_user_path(@screener), reply_to: reply_to)

The result should look like this.

<span class="o">=&gt;</span> <span class="s2">"http://ru.by/sKa"</span>

1	<span class="o">=></span> <span class="s2">"http://ru.by/sKa"</span>

About the author

Nikolai Sharangovich is an experienced Ruby on Rails developer with a deep understanding of the object-oriented design and modern software principles. He likes to collaborate with product people to achieve a maximum impact. Find him on GitHub.

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