Updated HenriFormatter from Named Formats Redux

HenriFormatter.cs

// http://haacked.com/archive/2009/01/14/named-formats-redux.aspx#70485

using System;
using System.Text;
using System.Web;
using System.Web.UI;

namespace StringLib
{
    public static class HenriFormatter
    {
        public static string HenriFormat(this string format, object source)
        {
            if (format == null)
                throw new ArgumentNullException("format");

            var result = new StringBuilder(format.Length * 2);
            var expression = new StringBuilder();
            
            var e = format.GetEnumerator();
            while (e.MoveNext())
            {
                var ch = e.Current;
                if (ch == '{')
                {
                    while (true)
                    {
                        if (!e.MoveNext())
                            throw new FormatException();

                        ch = e.Current;
                        if (ch == '}')
                        {
                            result.Append(OutExpression(source, expression.ToString()));
                            expression.Length = 0;
                            break;
                        }
                        if (ch == '{')
                        {
                            result.Append(ch);
                            break;
                        }
                        expression.Append(ch);
                    }
                }
                else if (ch == '}')
                {
                    if (!e.MoveNext() || e.Current != '}')
                        throw new FormatException();
                    result.Append('}');
                }
                else
                {
                    result.Append(ch);
                }
            }

            return result.ToString();
        }

        private static string OutExpression(object source, string expression)
        {
            string format = "{0}";

            int colonIndex = expression.IndexOf(':');
            if (colonIndex > 0)
            {
                format = "{0:" + expression.Substring(colonIndex + 1) + "}";
                expression = expression.Substring(0, colonIndex);
            }

            try
            {
                if (String.IsNullOrEmpty(format))
                {
                    if (source is RouteData)
                        source = ((RouteData) (source)).Values;

                    var dict = source as IDictionary<string, object>;
                    return dict != null ? dict[expression].ToString() : (DataBinder.Eval(source, expression) ?? "").ToString();
                }
                return DataBinder.Eval(source, expression, "{0:" + format + "}") ?? "";
            }
            catch (HttpException)
            {
                throw new FormatException();
            }
        }
    }
}

Strange, but I think too that line #82 should be return DataBinder.Eval(source, expression, format) ?? "";. Simply running "Hi {name}!".HenriFormat(new { name = "Henri" }) throws a FormatException.
Debugging to line #82 the value of the "{0:" + format + "}" expression becomes this: "{0:{0}}"
(on .net 4.5.2)

After the change both of these pass, so format parameters are respected:

"Hi {name}!".HenriFormat(new { name = "Henri" }).Should().Be("Hi Henri!");
"{data:yyyy.MM}".HenriFormat(new { data = new DateTime(2015, 2, 1) }).Should().Be("2015.02");

btw do you still use it after several years?

@AkosLukacs github notifications are pretty stupid and just flood noise instead of actual important ones. I was using this around the time you posted. I haven't used it this year as i've been doing very high performance webscale development, generally trying to avoid string manipulation entirely.