How can you handle errors or exceptions using an HttpModule?

When it comes to handling errors or exceptions using an HTTP module, you can utilize the 'Error' event in the ASP.NET pipeline. This event is raised when an unhandled exception occurs during the request processing. Here's an example of how you can handle errors or exceptions using an HTTP module:

public class ErrorHandlingModule : IHttpModule
{
    public void Init(HttpApplication context)
    {
        // Subscribe to the Error event
        context.Error += OnError;
    }

    public void Dispose()
    {
        // Cleanup resources, if needed
    }

    private void OnError(object sender, EventArgs e)
    {
        // Get the current exception
        Exception exception = HttpContext.Current.Server.GetLastError();

        // Log the exception
        LogException(exception);

        // Clear the error to prevent ASP.NET's default error handling
        HttpContext.Current.Server.ClearError();

        // Perform custom error handling and response generation
        HttpContext.Current.Response.StatusCode = 500; // Internal Server Error
        HttpContext.Current.Response.Write("An error occurred. Please try again later.");
        HttpContext.Current.Response.End();
    }

    private void LogException(Exception exception)
    {
        // Perform logging of the exception
        // Replace this with your actual logging implementation
        Console.WriteLine($"Exception: {exception.Message}");
        Console.WriteLine($"Stack Trace: {exception.StackTrace}");
        // ... Perform additional logging logic
    }
}

In this example, we create an 'ErrorHandlingModule' class that implements the 'IHttpModule' interface. The 'Init' method is used to subscribe to the 'Error' event of the 'HttpApplication' class.

In the 'OnError' event handler, we retrieve the current exception using 'HttpContext.Current.Server.GetLastError()'. You can then perform any custom error logging or handling logic, such as writing the exception details to a log file, sending an email notification, or storing the exception in a database.

Next, we clear the error using 'HttpContext.Current.Server.ClearError()' to prevent ASP.NET's default error handling behavior.

Finally, we customize the error response by setting the response status code, writing a user-friendly error message, and ending the response to prevent any further processing.

To use this module in an ASP.NET application, register it in the web.config file:

<system.webServer>
    <modules>
        <add name="ErrorHandlingModule" type="Namespace.ErrorHandlingModule" />
    </modules>
</system.webServer>

With this configuration, any unhandled exceptions that occur during request processing will be intercepted by the 'ErrorHandlingModule'. The module will perform custom error handling, such as logging the exception and returning a customized error response.