HTTP 404 Error WebConfig Event Receiver for Sharepoint 2010

httpErrorEventReceiver.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Runtime.InteropServices;
using System.Security.Permissions;
using Microsoft.SharePoint;
using Microsoft.SharePoint.Administration;
using Microsoft.SharePoint.Security;

namespace Client.Project.Infrastructure.EventReceiver
{
    /// <summary>
    /// This class handles events raised during feature activation, deactivation, installation, uninstallation, and upgrade.
    /// </summary>
    /// <remarks>
    /// The GUID attached to this class may be used during packaging and should not be modified.
    /// </remarks>

    [Guid("00000000-0000-0000-0000-000000000000")]
    public class CustomErrors : SPFeatureReceiver
    {
        #region properties

        private const string WebModificationOwnerName = "Automatic Http Error Pages Deploy Owner";

        #endregion properties

        #region overrides

        public override void FeatureActivated(SPFeatureReceiverProperties properties)
        {
            var webApp = properties.Feature.Parent as SPWebApplication;
            RemoveAllModifications(webApp, WebModificationOwnerName);
            AddEntryIntoWebConfig(webApp);
        }

        public override void FeatureDeactivating(SPFeatureReceiverProperties properties)
        {
            var webApp = properties.Feature.Parent as SPWebApplication;
            RemoveAllModifications(webApp, WebModificationOwnerName);

        }

        // Uncomment the method below to handle the event raised after a feature has been installed.

        //public override void FeatureInstalled(SPFeatureReceiverProperties properties)
        //{
        //}


        // Uncomment the method below to handle the event raised before a feature is uninstalled.

        //public override void FeatureUninstalling(SPFeatureReceiverProperties properties)
        //{
        //}

        // Uncomment the method below to handle the event raised when a feature is upgrading.

        //public override void FeatureUpgrading(SPFeatureReceiverProperties properties, string upgradeActionName, System.Collections.Generic.IDictionary<string, string> parameters)
        //{
        //}

        #endregion overrides

        #region private methods
        private void AddEntryIntoWebConfig(SPWebApplication webApp)
        {
            RemoveAllModifications(webApp, WebModificationOwnerName);

            string name, value, xpath, xPthRemove, xPthStatusCode;

            xpath = "configuration/system.webServer";
            xPthRemove = "configuration/system.webServer/httpErrors[1=1]";
            xPthStatusCode = "configuration/system.webServer/httpErrors[2=2]";

            #region 404
            //<HttpErrors errorMode="Custom" existingResponse="Auto" >
            name = "httpErrors[@errorMode='Custom'][@existingResponse='Auto']";
            value = "<httpErrors errorMode='Custom' existingResponse='Auto'></httpErrors>";
            ModifyWebConfig(webApp, xpath, name, value);
            webApp.WebService.Update();

            //<remove statusCode="404" subStatusCode="-1" />
            name = "remove[@statusCode='404'][@subStatusCode='-1']";
            value = "<remove statusCode='404' subStatusCode='-1' />";
            ModifyWebConfig(webApp, xPthRemove, name, value);

            //<error statusCode="404" prefixLanguageFilePath="" path="/_layouts/project/customerrors/PageNotFound.aspx" responseMode="ExecuteURL" />
            name = @"error[@statusCode='404'][@prefixLanguageFilePath=''][@path='/_layouts/project/customerrors/PageNotFound.aspx'][@responseMode='ExecuteURL']";
            value = @"<error statusCode='404' prefixLanguageFilePath='' path='/_layouts/project/customerrors/PageNotFound.aspx' responseMode='ExecuteURL' />";
            ModifyWebConfig(webApp, xPthStatusCode, name, value);

            #endregion 404

            try
            {
                webApp.WebService.ApplyWebConfigModifications();
            }
            catch (Exception ex)
            {
                RemoveAllModifications(webApp, WebModificationOwnerName);
                webApp.Update();
                webApp.WebService.ApplyWebConfigModifications();
                throw new Exception(string.Format("An error was encounted, web config mods added in this current spfeature install have been removed. Error Details: {0}", ex.Message));
            }
        }

        private void ModifyWebConfig(SPWebApplication webApp, string path, string nameModif, string valueModif)
        {
            SPWebConfigModification modification = new SPWebConfigModification(nameModif, path);
            modification.Value = valueModif;
            modification.Sequence = 0;
            modification.Type = SPWebConfigModification.SPWebConfigModificationType.EnsureChildNode;
            modification.Owner = WebModificationOwnerName;

            webApp.WebConfigModifications.Add(modification);
            webApp.Update();
        }

        private void RemoveAllModifications(SPWebApplication webApp, string owner)
        {
            List<SPWebConfigModification> modificationsToRemove = webApp.WebConfigModifications.Where(m => m.Owner == owner).ToList();

            foreach (SPWebConfigModification modification in modificationsToRemove)
                webApp.WebConfigModifications.Remove(modification);

            webApp.Update();
            webApp.WebService.ApplyWebConfigModifications();
        }

        #endregion private methods
    }
}