zlacker

You can treat a URL as a hash into a content-addressable store just fine. Mastodon does just that. Yet that URL also tells it where to retrieve the content if it's not available locally in a way that doesn't require tools to have any additional knowledge. If they do have additional knowledge, say of another caching layer or storage mechanism, they can use that just fine.

That is, I can just paste the URL for this article into my Mastodon instance, and if it has it, it'll fetch it from the local storage, if it doesn't it'll try to fetch it from the source, but there's nothing preventing a hierarchy of caches here, nor is there anything preventing peer to peer.

But while ActivityPub says that object id's "should" be https URL's for public objects, the basic requirement of ActivityStream is just that it's a unique URI, and there's nothing stopping an evolution of ActivityPub allowing URI's pointing to, say, IPFS or similar by content hash instead of a https URL.