IdConverter

Introduction

Sometimes we need to hide the real id of the database to the user of a web application. The following implementation allow us to apply a completely random biyective function to a given ID to show it to the user and get it back again applying the inverse function.

How it works

The ids of an Sql database are base 10 integers, to get a shorter id we need to write that number in a higher base. To accomplish that we need to define an alphabet representing each digit of another numeric base. If we choose base 64 we need to map numbers 0 to 63 each one to a symbol in our new alphabet. The symbols in the new alphabet will be used to "create" the id in base 64. To obtain the corresponding id in base 64 we just convert the original base 10 id to base 64 using the mapped characters applying the following algorithm:

pre: numberToConver >= 0 and baseToConvert > 1 and DigitsList.length = 0

post: DigitList contains each digit of the numberToConvert in base baseToConvert

num = numberToConvert

while num > 0

remainder = modulo(num, baseToConvert)

DigitsList.add(remainder)

num = num / baseToConvert

return DigitsList.reverse

Then for each element in the DigitsList we must get the corresponding symbol in our alphabet. The inverse function is analogous.

Requirements

We must to be capable to define several alphabets to enconde our ids to be used in differents parts of our web application.
We must get shorten ids than the originals.
We must broke the current ids from MongoDB.
We must define random alphabets from the ascii table and to be able to exclude certain characters.
We need a way to identify each alphabet and the converted ids.

Analysis

We need some data structures to work with differents alphabets
We need a way to identify the encoded ids, the alphabet and the base
We need a way to broke the string of the original id
We need an algorithm to encode and decode the ids
We need a way to ask for a new alphabet when needed
We need to save and load alphabets from a database

Design