{"id":71,"date":"2019-04-17T18:13:12","date_gmt":"2019-04-17T18:13:12","guid":{"rendered":"https:\/\/r0b3rt.com\/andr-web\/?p=71"},"modified":"2019-04-17T18:13:12","modified_gmt":"2019-04-17T18:13:12","slug":"compact-url","status":"publish","type":"post","link":"http:\/\/r0b3rt.com\/andr-web\/compact-url\/","title":{"rendered":"Compact URL"},"content":{"rendered":"

\"url-shorten\"<\/p>\n

 <\/p>\n

The heart of the project is to understand how to write a good Hashing function.<\/a><\/p>\n

Let us look at the the model.py<\/em><\/strong> inside the smallify app in the above project.<\/p>\n

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class<\/span> URL<\/span>(<\/span>models<\/span>.<\/span>Model<\/span>):<\/span>\r\n    original_url<\/span> =<\/span> models<\/span>.<\/span>CharField<\/span>(<\/span>max_length<\/span>=<\/span>300<\/span>,<\/span> unique<\/span>=<\/span> True<\/span>)<\/span>\r\n    shortened_url<\/span> =<\/span> models<\/span>.<\/span>CharField<\/span>(<\/span>max_length<\/span>=<\/span>30<\/span>,<\/span> unique<\/span> =<\/span>  True<\/span>)<\/span>\r\n    \r\n    def<\/span> shorten_url<\/span>(<\/span>self<\/span>):<\/span>\r\n        self<\/span>.<\/span>shortened_url<\/span> =<\/span> self<\/span>.<\/span>__fnv_hash<\/span>(<\/span>self<\/span>.<\/span>original_url<\/span>)<\/span>\r\n        \r\n        if<\/span>(<\/span>len<\/span>(<\/span>self<\/span>.<\/span>shortened_url<\/span>)<\/span> >=<\/span> len<\/span>(<\/span>self<\/span>.<\/span>original_url<\/span>)):<\/span>\r\n            self<\/span>.<\/span>shortened_url<\/span> =<\/span>  self<\/span>.<\/span>original_url<\/span>\r\n        \r\n        \r\n    @staticmethod<\/span>\r\n    def<\/span> __fnv_hash<\/span>(<\/span>key<\/span>):<\/span>\r\n        h<\/span> =<\/span> 2166136261<\/span>\r\n        \r\n        for<\/span> k<\/span> in<\/span> key<\/span>:<\/span>\r\n            h<\/span> =<\/span> (<\/span>h<\/span>*<\/span>16777619<\/span>)<\/span>^<\/span>ord<\/span>(<\/span>k<\/span>)<\/span>\r\n        \r\n        # Return 8 bit URL<\/span>\r\n        return<\/span> base64<\/span>.<\/span>encode<\/span>(<\/span>h<\/span>%<\/span>281474976710656<\/span>)<\/span>\r\n    \r\n    def<\/span> __str__<\/span>(<\/span>self<\/span>):<\/span>\r\n        return<\/span> models<\/span>.<\/span>Model<\/span>.<\/span>__str__<\/span>(<\/span>self<\/span>)<\/span>  \r\n<\/code><\/pre>\n<\/div>\n<\/div>\n
Why 281474976710656 ?<\/h3>\n
As we can see from the below commands, the 64th character (starts with 0 to 63) is an underscore \" _ \"<\/code>. So the value of 8 consecutive \" _ \"<\/code> is 281474976710655 and hence we do a modular division with (281474976710655 + 1)<\/p>\n
\"encoding-url-shortener\"<\/p>\n
With this, we have some basic understanding of URL Shorteners. The demo project url-shortener<\/a> in quite naive and created for this tutorial. Do check it out and let me know if you have any improvements in it. Feel free to send a pull request and looking forward to your views, opinions, and tips in the comments below.<\/p>\n","protected":false},"excerpt":{"rendered":"
  The heart of the project is to understand how to write a good Hashing function. Let us look at the the model.py inside the smallify app in the above project. class URL(models.Model): original_url = models.CharField(max_length=300, unique= True) shortened_url = models.CharField(max_length=30, unique = True) def shorten_url(self): self.shortened_url = self.__fnv_hash(self.original_url) if(len(self.shortened_url) >= len(self.original_url)): self.shortened_url = self.original_url … Continue reading “Compact URL”<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[8],"tags":[],"class_list":["post-71","post","type-post","status-publish","format-standard","hentry","category-computer-it"],"_links":{"self":[{"href":"http:\/\/r0b3rt.com\/andr-web\/wp-json\/wp\/v2\/posts\/71","targetHints":{"allow":["GET"]}}],"collection":[{"href":"http:\/\/r0b3rt.com\/andr-web\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/r0b3rt.com\/andr-web\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/r0b3rt.com\/andr-web\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"http:\/\/r0b3rt.com\/andr-web\/wp-json\/wp\/v2\/comments?post=71"}],"version-history":[{"count":1,"href":"http:\/\/r0b3rt.com\/andr-web\/wp-json\/wp\/v2\/posts\/71\/revisions"}],"predecessor-version":[{"id":72,"href":"http:\/\/r0b3rt.com\/andr-web\/wp-json\/wp\/v2\/posts\/71\/revisions\/72"}],"wp:attachment":[{"href":"http:\/\/r0b3rt.com\/andr-web\/wp-json\/wp\/v2\/media?parent=71"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/r0b3rt.com\/andr-web\/wp-json\/wp\/v2\/categories?post=71"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/r0b3rt.com\/andr-web\/wp-json\/wp\/v2\/tags?post=71"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}
It makes use of the FNV hashing algorithm<\/a>. Look at the private method __fnv_hash<\/code> in the above code snippet. It converts an arbitary length of string key<\/em> into a 8 bit URL. Here every character of the key (original url) is XORed with a random integer h<\/strong> which is also multiplied at each stage to get a good folding effect. XORing gives a good uniform distribution. After this we encode the given integer to base64<\/a>. Like a binary base has only 2 digits to represent every possible number, base64 uses 64 different characters. This gives us a more compact representation of the integer h<\/strong>. Finally, we do modular division by (281474976710655 + 1)<\/em> to get a 8 bit compact URL.<\/p>\n