Instructions on how to generate CRC checksums to use with LoadFromCacheOrDownload

Unity Engine
1

Hi there,

I’m looking for instructions on how to generate the CRC32 checksums, which are used to verify the downloaded file integrity using WWW.LoadFromCacheOrDownload.

I want to store a list of CRCs, which are pregenerated at build time and which map to the assetbundle filenames I want to download and have verified. ( Simplified I use CRC32(generated assetbundlefile) ).

Though the precreated CRCs of the assetbundle files never matches the one that the LoadFromCacheOrDownload - method is expecting.

Unfortunately, the documentation at Unity - Scripting API: WWW.LoadFromCacheOrDownload is broken at this point - look at the crc - parameter description, it suddenly stops.

The only clue I can get out of the documentation that the CRC is calculated for the “uncompressed contents”.

So, can anyone help how to accomplish generating a CRC32, which is the same LoadFromCacheOrDownload expects?

2

Hi,

In Unity 4.1 it isn’t possible to get the CRC directly. This is going to be added to the API for a future release, to make it possible to get the CRC value when building the AssetBundle.

For now the workaround is this:

  • Build your AssetBundle as usual.
  • Try to load it passing a dummy CRC value.
  • The correct CRC value will be printed in the Editor.log : Unity - Manual: Log files
  • Replaced the dummy CRC value with the one printed CRC in the log.

Answers post : Generating LoadFromCacheOrDownload CRC value - Questions & Answers - Unity Discussions