Patching AssetBundles is as simple as downloading a new AssetBundle and replacing the existing one. If UnityWebRequestAssetBundle.GetAssetBundle is used to manage an application’s cached AssetBundles, passing a different version or hash parameter will trigger a download of the new AssetBundles.
The more difficult problem to solve in the patching system is detecting which AssetBundles to replace. A patching system requires two lists of information:
The patcher should download the list of server-side AssetBundles and compare the AssetBundle lists. Missing AssetBundles, or AssetBundles whose versioning information has changed, should be re-downloaded.
Unity does not provide any built-in mechanism for differential patching and UnityWebRequestAssetBundle.GetAssetBundle does not perform differential patching when using the built-in caching system. Instead it always downloads the new AssetBundle file in its entirety. If differential patching is a requirement, then a custom downloader must be written. Unity builds AssetBundles with data ordered in a deterministic manner, so a file patch for a rebuilt AssetBundle can potentially be much smaller than the full file. The uncompressed or chunk-based compressionA method of storing data that reduces the amount of storage space it requires. See Texture Compression, Animation Compression, Audio Compression, Build Compression.
See in Glossary (LZ4) will patch better than the default full file compression (LZMA). Most developers who write their own system choose to use an industry-standard data format for their AssetBundle file lists, such as JSON, and a standard C# class for computing file content hashes, such as MD5. The file content hash can serve as an AssetBundle version, or you can use more traditional version numbers if those are generated by your build systems.