Important note: The AssetBundle Manager is deprecated for Unity versions 2018.2 and higher. It is no longer available from the Asset Store, but you can still download it from the AssetBundleDemo Bitbucket repository. If you use Unity version 2018.2 or higher, see documentation for Addressable Assets.
Patching AssetBundles is as simple as downloading a new AssetBundle and replacing the existing one. If WWW.LoadFromCacheOrDownload or UnityWebRequest are used to manage an application’s cached AssetBundles, passing a different version parameter to the chosen API 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.
It is also possible to write a custom system for detecting changes to AssetBundles. 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 checksums, such as MD5.
Unity builds AssetBundles with data ordered in a deterministic manner. This allows applications with custom downloaders to implement differential patching.
Unity does not provide any built-in mechanism for differential patching and neither WWW.LoadFromCacheOrDownload nor UnityWebRequest perform differential patching when using the built-in caching system. If differential patching is a requirement, then a custom downloader must be written.