Idea: In Suppo project we want to replace URLs in chat conversations by HTML links. Yes the first thing was to use google to find some recommendations or regular expressions BUT: On stackoverflow in article http://stackoverflow.com/questions/37684/how-to-replace-plain-urls-with-links is written:

“First off, rolling your own regexp to parse URLs is a terrible idea. You must imagine this is a common enough problem that someone has written, debugged and tested a library for it, according to the RFCs. URIs are complex”  … and there is multiple recommended libraries in Javascript (expect similar libraries in C#) like linkifyjs, anchorme.js, autolinker.js … OK so where is the problem?

The problem for me is that all of this libraries are huge … >30KB minified.

Why?

Because we are developing livechat window (Suppo) which is attached to every page of our clients and +30KB of javascript code is not acceptable when our solution has 63KB at all (included the core of jQuery library)

So what next?

Back to beginning and compose simple regular expression (is not so important to work on every URLs … suffice many of them)

C#:

public static string Linkify(this string text)
{
    // www|http|https|ftp|news|file
    text = Regex.Replace(
        text,
        @"((www\.|(http|https|ftp|news|file)+\:\/\/)[&#95;.a-z0-9-]+\.[a-z0-9\/&#95;:@=.+?,##%&~-]*[^.|\'|\# |!|\(|?|,| |>|<|;|\)])",
        "<a href=\"$1\" target=\"_blank\">$1</a>",
        RegexOptions.IgnoreCase)
        .Replace("href=\"www", "href=\"http://www");

    // mailto
    text = Regex.Replace(
        text,
        @"(([a-zA-Z0-9_\-\.])+@[a-zA-Z\ ]+?(\.[a-zA-Z]{2,6})+)",
        "<a href=\"mailto:$1\">$1</a>",
        RegexOptions.IgnoreCase);

    return text;
}

Javascript:

// www|http|https|ftp|news|file
text = text.replace(
    /((www\.|(http|https|ftp|news|file)+\:\/\/)[&#95;.a-z0-9-]+\.[a-z0-9\/&#95;:@=.+?,##%&~-]*[^.|\'|\# |!|\(|?|,| |>|<|;|\)])/gim,
    '<a href="$1" target="_blank">$1</a>');

// mailto
text = text.replace(
    /(([a-zA-Z0-9\-\_\.])+@[a-zA-Z\_]+?(\.[a-zA-Z]{2,6})+)/gim,
    '<a href="mailto:$1">$1</a>');

It’s simple: first part of code find www|http|https|ftp|news|file and replace it by <a href=”http(s):// and second part find email address and replace it by <a href=”mailto::.
That is all and it's less than 1KB of code.

Be careful when you are using your own constructor in partial classes on entities generated for LINQ to SQL (Data context entities). When you create your own constructor is really important to call the default constructor in it. Example :

Why? Because is important to execute the default generated constructor while execution of your program. This constructor contains some Initialization under your entity:

Otherwise you will getting following error:

[NullReferenceException: Object reference not set to an instance of an object.]
   System.Data.Linq.Mapping.EntitySetDefSourceAccessor`2.GetValue(T instance) +18
   System.Data.Linq.Mapping.MetaAccessor`2.GetBoxedValue(Object instance) +56
   System.Data.Linq.StandardTrackedObject.HasDeferredLoader(MetaDataMember deferredMember) +128
   System.Data.Linq.StandardTrackedObject.get_HasDeferredLoaders() +130
   System.Data.Linq.StandardChangeTracker.Track(MetaType mt, Object obj, Dictionary`2 visited, Boolean recurse, Int32 level) +269
   System.Data.Linq.StandardChangeTracker.Track(Object obj, Boolean recurse) +113
   System.Data.Linq.Table`1.InsertOnSubmit(TEntity entity) +383