ssb-blobs

protocol for gossiping "blobs", in no particular order.

protocol

when two peers connect, they request the blobs the other peer "wants" they do this by sending a JSON object that is a map of {<blob_id>: -hop_count} (note, the hop count is negative) if they have a blob wanted by the peer, they respond with the size they have for that blob: {<blob_id>: size} (note, size is positive - this is how sizes and blobs are distinguished)

Peers can only request blobs they know about. In the legacy scuttlebot/plugins/blobs
peers would request blobs that where mentioned in an ssb-feed but this approach means they cannot know about (encrypted) blobs shared in private messages, or about blobs recursively linked from other blobs.

This protocol addresses that by implementing sympathetic wants, if a peer requests a blob that you do not have, you start to want it too. so that wants to not flood the entire network, you signal how much you want it with a hop count. If you want it for your self, you use a hop_count of -1, if you want it for a friend, you use a hop_count of -2 (and so on..)

This allows you to publish a secret blob, without creating a permanent cryptographic record of that blob.

However, this alone would mean that to upload a blob, someone else needs to request it from you, which requries both peers to be online at the same time.

To address this, we have a push method. "pushing" a blob, just makes a peer "pretend" that they want a blob, triggering sympathetic wants from intermediate nodes, ensuring that there are at least some peers that will have the blob. (currently, your peer will continue to pretend they want the blob until at least 3 peers report having it)

configuration

set adding the following to your .ssb/config file, you can control how generous ssb-blobs will be.

"blobs": {
  "stingy": boolean, //defaults to false
  "sympathy": integer, //defaults to 3
  "pushy": integer, //default to 3
  "legacy": boolean //defaults to true
}

stingy (default false)

enabling stingy mode will make your pub pretend it does not have blobs unless it wants to push those blobs to the network. (because you have uploaded that file)

sympathy (default 3)

When a peer asks for a blob, if you do not have it, then because of sympathy you'll ask for it from your other peers. the value for sympathy determines how many hops away from you that peer may be. (hops on the current network topology, not the follow graph: ssb-blobs is actually completely independent of the ssb logs)

Set to 0 to never request a blob that someone else has asked for, unless you want it also.

pushy (default 3)

when you publish a blob, tell everyone about it, until at least this many peers have taken it. (for this they will need a setting for sympathy > 0)

legacy (default true)

whether you support the legacy style blob replication, it's probably safe to disable this now since most pubs will have updated by now.

License

MIT