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| title | description | author | ms.author | monikerRange | ms.date | ms.topic | uid |
|---|---|---|---|---|---|---|---|
| Incremental migration of IHttpModules | Describes how to use the System.Web adapters to incrementally migrate HTTP modules. | twsouthwick | tasou | >= aspnetcore-6.0 | 3/11/2024 | article | migration/inc/http-modules |
ASP.NET to ASP.NET Core incremental IHttpModule migration
Modules are types that implement xref:System.Web.IHttpModule and are used in ASP.NET Framework to hook into the request pipeline at various events. In an ASP.NET Core application, these should ideally be migrated to middleware. However, there are times when this cannot be done. In order to support migration scenarios in which modules are required and cannot be moved to middleware, System.Web adapters support adding them to ASP.NET Core.
IHttpModule Example
In order to support modules, an instance of xref:System.Web.HttpApplication must be available. If no custom xref:System.Web.HttpApplication is used, a default one will be used to add the modules to. Events declared in a custom application (including Application_Start) will be registered and run accordingly.
:::code language="csharp" source="~/migration/http-modules/sample8/Program.cs" :::
Global.asax migration
This infrastructure can be used to migrate usage of Global.asax if needed. The source from Global.asax is a custom xref:System.Web.HttpApplication and the file can be included in an ASP.NET Core application. Since it is named Global, the following code can be used to register it:
:::code language="csharp" source="~/migration/http-modules/sample8/Snippets/GlobalSnippet.cs" id="snippet_AddGlobal" :::
As long as the logic within it is available in ASP.NET Core, this approach can be used to incrementally migrate reliance on Global.asax to ASP.NET Core.
Authentication/Authorization events
In order for the authentication and authorization events to run at the desired time, the following pattern should be used:
:::code language="csharp" source="~/migration/http-modules/sample8/Snippets/UseAuthenticationAndAuthorizationSnippet.cs" id="snippet_UseAuthenticationAndAuthorization" :::
If this is not done, the events will still run. However, it will be during the call of .UseSystemWebAdapters().
HTTP Module pooling
Because modules and applications in ASP.NET Framework were assigned to a request, a new instance is needed for each request. However, since they can be expensive to create, they are pooled using xref:Microsoft.Extensions.ObjectPool.ObjectPool`1. In order to customize the actual lifetime of the xref:System.Web.HttpApplication instances, a custom pool can be used:
:::code language="csharp" source="~/migration/http-modules/sample8/Snippets/HttpModulePoolingSnippet.cs" id="snippet_ObjectPool" :::