Calling HttpSetServiceConfigurationAcl from managed code

Here's some sample C# code that sets up a namespace reservation by calling HttpSetServiceConfigurationAcl. Note that by switching a flag in the code, you can remove the namespace reservation, so this class would work well during installation as well as removal.

using System;
using System.Xml;
using System.Security.Principal;
using System.Runtime.InteropServices;
//
// No dependencies
//
// Package configuration:
// 
//
public class ReserveHttpNamespace {
    static void Main(string[] args) {
        if (args.Length != 2) {
            Console.WriteLine(
            "Usage: reserveHttpNamespace " +
            "prefix account");
            return;
        }
        try {
            ModifyReservation(args[0], args[1], false);
            Console.WriteLine("Success!");
        }
        catch (Exception x) {
            Console.WriteLine(x.Message);
        }
    }
    static void ModifyReservation(string urlPrefix,
                                  string accountName,
                                  bool removeReservation) {
        string sddl = createSddl(accountName);
        HTTP_SERVICE_CONFIG_URLACL_SET configInfo;
        configInfo.Key.UrlPrefix = urlPrefix;
        configInfo.Param.Sddl = sddl;
        HTTPAPI_VERSION httpApiVersion =
            new HTTPAPI_VERSION(1, 0);
        int errorCode = HttpInitialize(httpApiVersion,
            HTTP_INITIALIZE_CONFIG, IntPtr.Zero);
        if (0 != errorCode) throw getException(
            "HttpInitialize",
            errorCode);
        try {
            // do our best to delete any existing ACL
            errorCode = HttpDeleteServiceConfigurationAcl(
                IntPtr.Zero,
                HttpServiceConfigUrlAclInfo,
                ref configInfo,
                Marshal.SizeOf(
                    typeof(HTTP_SERVICE_CONFIG_URLACL_SET)),
                IntPtr.Zero);
            if (removeReservation) {
                if (0 != errorCode) throw getException(
                    "HttpDeleteServiceConfigurationAcl",
                    errorCode);
                return;
            }
            errorCode = HttpSetServiceConfigurationAcl(
                IntPtr.Zero,
                HttpServiceConfigUrlAclInfo,
                ref configInfo,
                Marshal.SizeOf(
                    typeof(HTTP_SERVICE_CONFIG_URLACL_SET)),
                IntPtr.Zero);
            if (0 != errorCode) throw getException(
                "HttpSetServiceConfigurationAcl",
                errorCode);
        }
        finally {
            errorCode = HttpTerminate(
                HTTP_INITIALIZE_CONFIG,
                IntPtr.Zero);
            if (0 != errorCode) throw getException(
                "HttpTerminate",
                errorCode);
        }
    }
    private static Exception getException(string fcn, int errorCode) {
        Exception x = new Exception(
            string.Format("{0} failed: {1}",
            fcn, getWin32ErrorMessage(errorCode)));
        return x;
    }
    static string createSddl(string account) {
        string sid = new NTAccount(account).Translate(
            typeof(SecurityIdentifier)).ToString();
        // DACL that Allows Generic eXecute for the user
        // specified by account
        // see help for HTTP_SERVICE_CONFIG_URLACL_PARAM
        // for details on what this means
        return string.Format("D:(A;;GX;;;{0})", sid);
    }
    static string getWin32ErrorMessage(int errorCode) {
        int hr = HRESULT_FROM_WIN32(errorCode);
        Exception x = Marshal.GetExceptionForHR(hr);
        return x.Message;
    }
    static int HRESULT_FROM_WIN32(int errorCode) {
        if (errorCode <= 0) return errorCode;
        return (int)((0x0000FFFFU &
            ((uint)errorCode)) | (7U << 16) |
            0x80000000U);
    }
    // P/Invoke stubs from http.h
    const int HttpServiceConfigUrlAclInfo = 2;
    const int HTTP_INITIALIZE_CONFIG = 2;
    [StructLayout(LayoutKind.Sequential)]
    struct HTTPAPI_VERSION {
        public HTTPAPI_VERSION(short maj, short min) {
            Major = maj; Minor = min;
        }
        short Major;
        short Minor;
    }
    [StructLayout(LayoutKind.Sequential)]
    struct HTTP_SERVICE_CONFIG_URLACL_KEY {
        [MarshalAs(UnmanagedType.LPWStr)]
        public string UrlPrefix;
    }
    [StructLayout(LayoutKind.Sequential)]
    struct HTTP_SERVICE_CONFIG_URLACL_PARAM {
        [MarshalAs(UnmanagedType.LPWStr)]
        public string Sddl;
    }
    [StructLayout(LayoutKind.Sequential)]
    struct HTTP_SERVICE_CONFIG_URLACL_SET {
        public HTTP_SERVICE_CONFIG_URLACL_KEY Key;
        public HTTP_SERVICE_CONFIG_URLACL_PARAM Param;
    }
    [DllImport("httpapi.dll", ExactSpelling = true,
            EntryPoint = "HttpSetServiceConfiguration")]
    static extern int HttpSetServiceConfigurationAcl(
        IntPtr mustBeZero, int configID,
        [In] ref HTTP_SERVICE_CONFIG_URLACL_SET configInfo,
        int configInfoLength, IntPtr mustBeZero2);
    [DllImport("httpapi.dll", ExactSpelling = true,
            EntryPoint = "HttpDeleteServiceConfiguration")]
    static extern int HttpDeleteServiceConfigurationAcl(
        IntPtr mustBeZero, int configID,
        [In] ref HTTP_SERVICE_CONFIG_URLACL_SET configInfo,
        int configInfoLength, IntPtr mustBeZero2);
    [DllImport("httpapi.dll")]
    static extern int HttpInitialize(
        HTTPAPI_VERSION version,
        int flags, IntPtr mustBeZero);
    [DllImport("httpapi.dll")]
    static extern int HttpTerminate(int flags,
        IntPtr mustBeZero);
}