MediaRequestHandler for missing images causes errors on Content Authoring

Question

We've implemented error handling for missing images in Sitecore like so:

https://nourestani.wordpress.com/2015/05/11/error-executing-child-request-sitecore-for-404-useserversideredirect-transferrequest-vs-transfer/ which came from this post by Michael West: How do you setup a 404 and 500 error page for missing files and media items?.

This all works fine on CD servers, but we've seen an issue where on CA we get an error:

Could not find method: Process. Pipeline: /sitecore[database="SqlServer" xmlns:patch="http://www.sitecore.net/xmlconfig/"]/pipelines/httpRequestBegin/processor[type="Custom.Sitecore.Extensions.Pipelines.CustomMediaRequestHandler, Custom.Sitecore.Extensions" patch:source="Custom.Pipelines.config"

I've triple checked there are no issues with typos or anything as described here:

https://chrisperks.co/2017/03/05/error-could-not-find-method-process-pipeline-sitecoredatabasesqlserver-xmlnspatchhttpwww-sitecore-netxmlconfigpipelinesmvc-resultexecutingpatchsourcesitecore-mvc-config/

I've solved this by only deploying this patch in our CD config and not our CA config as it isn't a much of an issue on CA. However I'd like to resolve this for CA also and understand if we've missed anything or there is a better approach for this.

Further info:

Our Patch:

    <pipelines>
        <httpRequestBegin>
            <!--fix issue with missing media files throwing errors in logs-->
            <processor type="Custom.Sitecore.Extensions.Pipelines.CustomMediaRequestHandler, Custom.Sitecore.Extensions" />
        </httpRequestBegin>
    </pipelines>

The Pipline:

public class CustomMediaRequestHandler : MediaRequestHandler
    {
        protected override bool DoProcessRequest(HttpContext context)
        {
            Assert.ArgumentNotNull(context, "context");

            MediaRequest request = MediaManager.ParseMediaRequest(context.Request);

            if (request == null)
                return false;

            Media media = MediaManager.GetMedia(request.MediaUri);

            if (media != null)
                return DoProcessRequest(context, request, media);

            using (new SecurityDisabler())
                media = MediaManager.GetMedia(request.MediaUri);

            string str;

            if (media == null)
            {
                str = Settings.ItemNotFoundUrl;
            }
            else
            {
                Assert.IsNotNull(Context.Site, "site");
                str = Context.Site.LoginPage != string.Empty ? Context.Site.LoginPage : Settings.NoAccessUrl;
            }
            if (Settings.RequestErrors.UseServerSideRedirect)
                HttpContext.Current.Server.TransferRequest(str);
            else
                HttpContext.Current.Response.Redirect(str);
            return true;
        }
    }

Answer 1

I managed to resolve this thanks to John Rappel who helped out on Slack.

Whilst we had made this web config update to patch in our custom handler:

<httpHandlers>
 ...
  <add verb="*" path="sitecore_media.ashx" type="Custom.Sitecore.Extensions.CustomMediaRequestHandler , Custom.Sitecore.Extensions" />
...
</httpHandlers>

We were trying to patch it in as a pipeline as well and actually that isn't needed, it's only required as a handler. The required Pipeline is instead:

public class CustomExecuteRequest : Sitecore.Pipelines.HttpRequest.ExecuteRequest
    {
        protected override void PerformRedirect(string url)
        {
            if (Settings.RequestErrors.UseServerSideRedirect)
                HttpContext.Current.Server.TransferRequest(url);
            else
                WebUtil.Redirect(url, false);
        }
    }

Patched in like so:

<httpRequestBegin>
<processor type="Custom.Sitecore.Extensions.Pipelines.CustomExecuteRequest, Custom.Sitecore.Extensions" resolve="true" patch:instead="*[@type='Sitecore.Pipelines.HttpRequest.ExecuteRequest, Sitecore.Kernel']"/>
</httpRequestBegin>

This was due to some confusion over what was required here. This is now working in CD and CA.

John has a detailed post on this with a full solution for handling all 404s here which i'd recommend:

https://www.geekhive.com/buzz/post/2017/07/a-complete-guide-to-configuring-friendly-error-pages-in-sitecore-part-1-404-pages/