Chunk downloader does not account for iostore files, it fails to mount .utoc files

Development Pipeline & Plugins
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Hi,

I am trying to build a system for live ops delivery using CDN. We created a system and pipeline which works with .pak files but since we are moving closer to production we are looking into encryptions as well as faster load times so we shifted our builds to generate iostore files. The older setup to download and mount the chunks that are only the .pak files was using chunkdownloader plugin internally. Chunkdownloader is good for downloading the files of all types including .utoc, .ucas, .pak but it fails in mounting the .utoc files. We went through the document which clearly shows .utoc files present in the Manifest files.. which kind of indicates that chunk downloader is capable of downloading and mounting any type of file. Am i missing a step that is necessary to mount these files

Sharing the errors below

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Hello,

The development of the ChunkDownloader was stopped and official support for IOStore was never added. We are aware of licensees who were able to extend the plugin to add such support. You might be able to find solutions on the forums: Epic Developer Community

Regards,

Martin

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Is this still true? I cannot load ucas file using ChunkDownloader, which as OP says, the official docs say they are supported.

Tried with very basic project in brand new 5.7.4

Keeping the asset files in the Content/Pak folder and the game runs fine
Move extra chunks to downloader:

  • downloader downloads manifest
  • downloader downloads ucas,pak,utoc
  • downloader reads pak, utoc
  • downloader fails to read ucas, “invalid pak”
    — this happens as magic != Pak_Magic during archive serialization

please advise on path forward.

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I checked on the pro forums and all the answer say pak only. I am going to attempt to rewrite the downloader to open containers with iostore and will attempt to post my solution if I find one.

@Svegn2 , please stop me if IOstore is actually supported but MOST IMPORTANTLY please update the documentation for ChunkDownloader “Implementing ChunkDownloader” as all the examples from Epic show IOStore and I’ve wasted a lot of time trying to get something working that was never going to work.

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Okay so the solution for my project was to just call FCoreDelegates::OnMountAllPacks.Execute(PersistentDownloadDir/“PakCache”);

the downloader does everything good except the mounting, and with iostore you probably just want it to mount all the pak cache.

I do mine in a PreEarlyLoadingScreen module before GameInstance is created.

I briefly investigated modifying the ChunkDownloader but even restricting it to only mounting .pak files ( which is what io store wants you to do when calling Mount individually ) it still crashes and I moved on.