Handles kiln:// URLs, translating them into the full http(s) form before executing them.

KilnUrlHandler.cs

using System;
using System.ComponentModel;
using System.Diagnostics;
using System.IO;
using System.Reflection;
using System.Runtime.InteropServices;
using System.Text;
using System.Text.RegularExpressions;
using System.Windows.Forms;

using Microsoft.Win32;

namespace KilnUrlHandler
{
    public class Program
    {
        public static void Main(string[] args)
        {
            try
            {
                if (args.Length < 1)
                {
                    RegisterForKilnScheme();
                    return;
                }

                var pattern = new Regex("^kiln://(?<Path>.+)$", RegexOptions.IgnoreCase);
                var match = pattern.Match(args[0]);
                if (!match.Success)
                {
                    return;
                }

                var kilnUrl = GetKilnUrl();
                if (kilnUrl == null) return;

                var path = match.Groups["Path"].Value;
                var fullUri = new Uri(kilnUrl, path);

                Process.Start(fullUri.AbsoluteUri);
            }
            catch (Exception exception)
            {
                MessageBox.Show(exception.Message, "Kiln URL Handler", MessageBoxButtons.OK, MessageBoxIcon.Exclamation);
            }
        }

        private static void RegisterForKilnScheme()
        {
            string executablePath = GetExecutablePath();

            Registry.SetValue("HKEY_CURRENT_USER\\Software\\Classes\\kiln",
                              "",
                              "URL: Kiln Scheme");

            Registry.SetValue("HKEY_CURRENT_USER\\Software\\Classes\\kiln",
                              "URL Protocol",
                              "");

            Registry.SetValue("HKEY_CURRENT_USER\\Software\\Classes\\kiln\\DefaultIcon",
                              "",
                              string.Format("\"{0}\"", executablePath));

            Registry.SetValue("HKEY_CURRENT_USER\\Software\\Classes\\kiln\\shell\\open\\command",
                              "",
                              string.Format("\"{0}\" \"%1\"", executablePath));
        }

        private static string GetExecutablePath()
        {
            return new Uri(Assembly.GetEntryAssembly().CodeBase).LocalPath;
        }

        private static Uri GetKilnUrl()
        {
            string profileDirectory = Environment.GetFolderPath(Environment.SpecialFolder.UserProfile);
            string[] mercurialIniFiles = Directory.GetFiles(profileDirectory, "mercurial*.ini");

            foreach (var mercurialIniFile in mercurialIniFiles)
            {
                var buffer = new StringBuilder(1024);
                uint result = GetPrivateProfileString("schemes", "kiln", "", buffer, (uint)buffer.Capacity, mercurialIniFile);
                if (result == 0)
                {
                    int lastError = Marshal.GetLastWin32Error();
                    if (lastError != ErrorSuccess && lastError != ErrorNoToken && lastError != ErrorFileNotFound)
                        throw new Win32Exception(lastError);
                    continue;
                }

                var url = buffer.ToString();
                if (Uri.IsWellFormedUriString(url, UriKind.Absolute))
                {
                    if (!url.EndsWith("/")) url += "/";
                    return new Uri(url, UriKind.Absolute);
                }
            }

            return null;
        }

        [DllImport("kernel32.dll", CharSet = CharSet.Auto, SetLastError = true)]
        private static extern uint GetPrivateProfileString(string lpAppName,
                                                           string lpKeyName,
                                                           string lpDefault,
                                                           StringBuilder lpReturnedString,
                                                           uint nSize,
                                                           string lpFileName);

        private const int ErrorSuccess      = 0;
        private const int ErrorFileNotFound = 2;
        private const int ErrorNoToken      = 1008;
    }
}