A DD4T.net Implementation - Custom Binary Publisher

The default way to publish binaries in DD4T is implemented in class DD4T.Templates.Base.Utils.BinaryPublisher and uses method RenderedItem.AddBinary(Component). This produces binaries that have their TCM URI as suffix in their filename. In my recent project, we had a requirement that binary file names should be clean (without the TCM URI suffix). Therefore, it was time to modify the way DD4T was publishing binaries.

The method in charge with publishing binaries is called PublishItem and is defined in class BinaryPublisher. I therefore extended the BinaryPublisher and overrode method PublishItem.

public class CustomBinaryPublisher : BinaryPublisher
{
    private Template currentTemplate;
    private TcmUri structureGroupUri;

In its simplest form, method PublishItem just takes the item and passes it to the AddBinary. In order to accomplish the requirement, we must specify a filename while publishing. This is the file name part of the binary path of Component.BinaryContent.Filename.

In case there is a Structure Group specified, we use the AddBinary method that takes this into account.

protected override void PublishItem(Item item, TcmUri itemUri)
{
    string url;
    Stream stream = item.GetAsStream();
    RenderedItem renderedItem = engine.PublishingContext.RenderedItem;
    Component component = engine.GetObject(item.Properties["TCMURI"]) as Component;
    BinaryContent binaryContent = component.BinaryContent;
    string mimeType = binaryContent.MultimediaType.MimeType;
    string fileName = Path.GetFileName(binaryContent.Filename);

    if (string.IsNullOrEmpty(structureGroupUri))
    {
        url = renderedItem.AddBinary(stream, fileName, string.Empty, component, mimeType).Url;
    }
    else
    {
        StructureGroup structureGroup = engine.GetObject(structureGroupUri) as StructureGroup;
        url = renderedItem.AddBinary(stream, fileName, structureGroup, string.Empty, component, mimeType).Url;
    }

    item.Properties["PublishedPath"] = url;
}

A word of caution: the code above causes publishing to fail in case there are more than one Multimedia Components that contain a binary with the same name. This is because publishing the two Multimedia Components would in face result in the binaries being overwritten on disk.

The error will show up as "Phase: Deployment Prepare Commit Phase failed. Unable to prepare transaction" in the Publishing Queue. On a closer inspection, the core log on the Deployer side will show error "ProcessingException: Attempting to deploy a binary xxx to a location where a different binary is already stored Existing binary: yyy", which means exactly that -- a binary with id yyy is already published with the same name and in the same location as binary with id xxx currently being deployed.

However, this might not be an issue, if all Multimedia Components in the system have different file names (i.e. different binary file names).

The current custom binary publisher is however not used in this way. In a follow-up post, I will present a way to call the PublishItem method from a Template Building Block (TBB).