Converting to Base62 & URL Shortening

Generic Marketeer: Why do we need to shorten the URLs, people just click on them. It’s not like they have to memorize them; call them out to their friends

Me: Eh… no you’re right, but I do need to jam them into a SMS WAPPush along with some descriptive text, so I don’t have much room to play with

Generic Marketeer: Fine, as long as it doesn’t impact the project deadline

Cue, my good self scurying away to find a way to bang out a private URL Shortening service in as short a time as possible. The URL Storage itself was a piece of pie. But I did stumble across some nice code while I was at it. I started out with a int-to-base64 implemenation. but the + & / characters are fugly to deal with in URLs. I tried a Hex version as well but it just didn’t look bit-ly-y enough. Enter the baseAnything encoder. Just point it at any character set and it will encode/decode to that number of chars. The following extension methods convert longs to strings, and vice-versa

public static string ToBase(this long input, string baseChars)
{
    string r = string.Empty;
    int targetBase = baseChars.Length;
    do
    {
        r = string.Format("{0}{1}",
            baseChars[(int)(input % targetBase)],
            r);
        input /= targetBase;
    } while (input > 0);

    return r;
}


public static long FromBase(this string input, string baseChars)
{
    int srcBase = baseChars.Length;
    long id = 0;
    string r = input.Reverse();

    for (int i = 0; i < r.Length; i++)
    {
        int charIndex = baseChars.IndexOf(r[i]);
        id += charIndex * (long)Math.Pow(srcBase, i);
    }

    return id;
}

I’ve been using it against the first character set below, but you could easily tweak it to remove any confusing characters, or any set for that matter.

private static string ALPHANUMERIC =
    "0123456789" +
    "ABCDEFGHIJKLMNOPQRSTUVWXYZ" +
    "abcdefghijklmnopqrstuvwxyz";

//Remove 0oO1iIl - Base52
private static string ALPHANUMERIC_ALT =
    "23456789" +
    "ABCDEFGHJKLMNPRSTUVWXYZ" +
    "abcdefghjkmnpqrstuvwxyz";
}

Now all I have to do is go write a Math Engine for it ;-)

Eoin Campbell