How to create short links using C# and database ID’s

I recently had a project where I wanted my web site content to utilize short URLs. Â These short URL’s would be easier to utilize on Twitter where the message is limited to 140 characters. Â At this stage link shortening is old news and I could use one of the many available linkÂ shorteningÂ services (Bit.ly, Goo.gl) to generate these links. Â However, I dislike the idea of encouraging visitors to tweet a Bit.ly link, as opposed to my own links.

Using database ID’s to create short links

To address this my original idea was to simply rely on the auto-incremented row ID’s for each item in the database. Â For the database table, this looks something like this:

ID	Title
1	Budgeting for your CMS or Web Project
2	How many web browsers support responsive design?
…	…
95131	Wanted: Video-conferencing solution for mid-sized teams

Which means it would be easy to utilize shortened URL’s that look like this:

http://mywebsite.com/1
http://mywebsite.com/2
http://mywebsite.com/95131

However, these URL’s aren’t as short as they could be. Â By only utilizing numbers (0-9) we’re not utilizing other valid characters (A-Z, a-z, -, _) that could potentially be used to create shorter URL’s.

Using Base 64 to create shorter URL’s

The numbers I’m utilizing for my database ID’s are using numbers based on 10. Â Using this type of number I’m only utilizing the 0-9 characters Â However, numbers that are based on 64 utilize other characters to represent numbers for which we do not have a character.

The way base 64 numbers are represented matches nicely with the characters that can be used in a URL. Â Therefore, by converting my base 10 database id’s into base 64 I’ll get a shorter URL. Â At the same time, I can be assured that the shortened URL’s aren’t duplicated since they are based on a unique database ID.

C# code for converting a Base-10 Integer to a Base-64 String

Ultimately, I wanted a solution that would work like this:

ShortUrl.Shrink(95131) => Returns “XOb”
ShortUrl.Expand(“XOb”) => Returns 95131

Here is the code I came up with.

using System; using System.Linq; using System.Text.RegularExpressions; namespace MvcApplication.Helpers { public static class ShortUrl { /// <summary> /// Converts a Base-10 Integer to Base-64. This will effectively shorten the number of characters used to represent a number > 10. /// </summary> public static string Shrink(int Number) { return ConvertDecToBase(Number, 64); } /// <summary> /// Converts a Base-64 Number (represented as a string) into a Base-10 Integer. This will effectively expand the numbers of characters needed to represent the number. /// </summary> /// <param name="NumberString"></param> /// <returns></returns> public static int Expand(string NumberString) { return ConvertBaseToDec(NumberString, 64); } private static string DefaultChars = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz"; private static string Base64Chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_"; private static int ConvertBaseToDec(string NumberString, int Base) { string Chars; if (Base == 64) { NumberString = Regex.Replace(NumberString, "^A+", ""); Chars = Base64Chars; } else { NumberString = Regex.Replace(NumberString, "^0+", ""); Chars = DefaultChars; } int Dec = 0; for (int i = 0; i <= NumberString.Length - 1; i++) { int CharNum = Chars.IndexOf(NumberString[i]); int Conversion = CharNum * IntPow(Base, (NumberString.Length - (i + 1))); Dec = Dec + Conversion; } return Dec; } private static string ConvertDecToBase(int OriginalNumber, int Base) { char[] Chars; if (Base == 64) { Chars = Base64Chars.ToCharArray(); } else { Chars = DefaultChars.ToCharArray(); } string encoded = ""; encoded = ConvertDecToBase(OriginalNumber, Base, encoded, Chars); return encoded; } private static string ConvertDecToBase(int Number, int Base, string EncodedString, char[] Chars) { if (Number < Base) { EncodedString = EncodedString + Chars[Number]; } else { int NewNumber = Number / Base; EncodedString = ConvertDecToBase(NewNumber, Base, EncodedString, Chars); Number = Number - (NewNumber * Base); if (Number < Base) { EncodedString = EncodedString + Chars[Number]; } } return EncodedString; } private static int IntPow(int x, int pow) { int ret = 1; while (pow != 0) { if ((pow & 1) == 1) ret *= x; x *= x; pow >>= 1; } return ret; } } }

Some notes

The reason I didn’t use C#’s built-in Base-64 encoding is because it adds padding to the string. Â As a result, the Base-64 string often becomes longer than the original decimal number. Â (Making it useless for link shortening)
There are decimal numbers that, when converted to Base-64, will turn into offensive words. Â I haven’t dealt with this yet.
Someone else created a Base-10 to Base-64 converter with C#. Â It looks like this code uses bit-shifting. Â This is probably faster (and more clever), but I had trouble understanding the code.
There is a nice website that you can use to test these conversions.
That website is based on some PHP-code that can be found here.

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thanks for nice guide. It seems that, it’s not so hard to create link by using C#
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why simply don’t use:
string sourceString = “string t short hash”; string hashCode = String.Format(“{0:X}”, sourceString.GetHashCode());

Using database ID’s to create short links

Using Base 64 to create shorter URL’s

C# code for converting a Base-10 Integer to a Base-64 String

Some notes

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