More than one way to register an ASP.NET Http Handler in web.config?

Question

What is the difference of adding and removing handlers in as oppose to ?

In a new web project I made with VS2008, the handlers are defined as this:

<system.web>
        ...

      <httpHandlers>
        <remove verb="*" path="*.asmx"/>
        <add verb="*" path="*.asmx" validate="false" type="System.Web.Script.Services.ScriptHandlerFactory, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35"/>
        <add verb="*" path="*_AppService.axd" validate="false" type="System.Web.Script.Services.ScriptHandlerFactory, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35"/>
        <add verb="GET,HEAD" path="ScriptResource.axd" type="System.Web.Handlers.ScriptResourceHandler, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" validate="false"/>
        <add verb="*" path="/hello/helloworld.xml" type="HandlerTest.HelloWorldHandler, HandlerTest"/>
      </httpHandlers>
      <httpModules>
        <add name="ScriptModule" type="System.Web.Handlers.ScriptModule, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35"/>
      </httpModules>

    </system.web>

But in a pre-existing project, (ie: Community server), the http handlers are added/removed in as follows:

<system.webServer>
     <validation validateIntegratedModeConfiguration="false"/>
     <security>
      <requestFiltering allowDoubleEscaping="true"/>
     </security>
     <modules runAllManagedModulesForAllRequests="true">
      <remove name="CommunityServer"/>
      <remove name="ScriptModule"/>
      <remove name="UrlRoutingModule"/>
      <add name="CommunityServer" type="CommunityServer.CSHttpModule, CommunityServer.Components"/>
      <add name="ScriptModule" preCondition="managedHandler" type="System.Web.Handlers.ScriptModule, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35"/>
      <add name="UrlRoutingModule" type="System.Web.Routing.UrlRoutingModule, System.Web.Routing, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35"/>
     </modules>
     <handlers accessPolicy="Read, Write, Script, Execute">
      <remove name="WebServiceHandlerFactory-Integrated"/>
      <remove name="ScriptHandlerFactory"/>
      <remove name="ScriptHandlerFactoryAppServices"/>
      <remove name="ScriptResource"/>


      <add verb="GET" name="redirect" path="Utility/redirect.aspx" type="CommunityServer.Components.Redirect, CommunityServer.Components"/>
      <add verb="GET" name="aggbug" path="aggbug.aspx" type="CommunityServer.Components.HttpHandler.AggBugHandler, CommunityServer.Components"/>
      <add verb="GET" name="avatar" path="avatar.aspx" type="CommunityServer.Components.HttpHandler.AvatarHttpHandler, CommunityServer.Components"/>
      <add verb="GET" name="vcard" path="vcard.aspx" type="CommunityServer.Components.HttpHandler.VCardHttpHandler, CommunityServer.Components"/>
      <add verb="GET" name="tinyurl" path="r.ashx" type="CommunityServer.Components.HttpHandler.TinyUrlHttpHandler, CommunityServer.Components"/>
      <add verb="GET" name="weblogsubscription-confirmation" path="weblogsubscription-confirmation.ashx" type="CommunityServer.Blogs.Components.WeblogSubscriptionConfirmation, CommunityServer.Blogs"/>
      <add verb="GET" name="threadsubscription-confirmation" path="threadsubscription-confirmation.ashx" type="CommunityServer.Blogs.Components.ThreadSubscriptionConfirmation, CommunityServer.Blogs"/>
      <add verb="GET" name="cfs-file" path="cfs-file.ashx" type="CommunityServer.Components.FileHttpHandler, CommunityServer.Components"/>
      <add verb="GET" name="cfs-filesystemfile" path="cfs-filesystemfile.ashx" type="CommunityServer.Components.FileSystemFileStorageHttpHandler, CommunityServer.Components"/>
      <add verb="GET" name="resized-image" path="resized-image.ashx" type="CommunityServer.Components.ImageFileResizerHttpHandler, CommunityServer.Components"/>
      <add verb="GET,POST" name="multipleupload" path="multipleupload.ashx" type="Telligent.Glow.MultipleUploadFileHandler, Telligent.Glow"/>
      <add name="ScriptHandlerFactory" verb="*" path="*.asmx" preCondition="integratedMode" type="System.Web.Script.Services.ScriptHandlerFactory, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35"/>
      <add name="ScriptHandlerFactoryAppServices" verb="*" path="*_AppService.axd" preCondition="integratedMode" type="System.Web.Script.Services.ScriptHandlerFactory, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35"/>
      <add name="ScriptResource" verb="GET,HEAD" path="ScriptResource.axd" preCondition="integratedMode" type="System.Web.Handlers.ScriptResourceHandler, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35"/>
      <add name="UrlRoutingHandler" preCondition="integratedMode" verb="*" path="UrlRouting.axd" type="System.Web.HttpForbiddenHandler, System.Web, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a"/>
      <add name="TinyMCE" verb="GET,HEAD,POST" path="TinyMCE.ashx" type="Moxiecode.TinyMCE.Web.HttpHandler,Moxiecode.TinyMCE"/>
      <add name="Schedule" verb="*" path="schedule.ashx" type="CommunityServer.Scheduler.ScheduleHandler, CommunityServer.Scheduler" />
    </handlers>
    </system.webServer>

Why are there more than one way of registering an http handler?

Answer 1

The <system.web> section applies to IIS6 and below whereas <system.webServer> applies to IIS7 and above. The layout of web.config was re-engineered for IIS7 to make it more powerful / friendly, but at the cost of backwards compatibility.

Answer 2

The second example that you posted where they are in the '' node is the way to configure for IIS 7 allowing you to configure the server directly. The other method is "legacy" and works on all supported IIS versions.