legs 🦵

Legs is an interface for go-data-transfer, providing a 1:1 mechanism for maintaining a synchronized IPLD dag of data between a publisher and a subscriber's current state for that publisher.

Usage

Typically an application will be either a provider or a subscriber, but may be both.

Publisher

Create a legs publisher. Update its root to cause it to publish.

pub, err :=  NewPublisher(host, dsstore, lsys, "/legs/topic")
if err != nil {
	panic(err)
}
...
// Publish updated root.
err = publisher.UpdateRoot(ctx, lnk.(cidlink.Link).Cid)
if err != nil {
	panic(err)
}

Subscriber

The Subscriber handles subscribing to a topic, reading messages from the topic and tracking the state of each publisher.

Create a Subscriber:

sub, err := legs.NewSubscriber(dstHost, dstStore, dstLnkS, "/legs/topic", nil)
if err != nil {
	panic(err)
}

Optionally, request notification of updates:

watcher, cancelWatcher := sub.OnSyncFinished()
defer cancelWatcher()
go watch(watcher)

func watch(notifications <-chan legs.SyncFinished) {
    for {
        syncFinished := <-notifications
        // newHead is now available in the local dataStore
    }
}

To shutdown a Subscriber, call its Close() method.

A Subscriber can be created with a function that determines if the Subscriber accepts or rejects messages from a publisher. Use the AllowPeer option to specify the function.

sub, err := legs.NewSubscriber(dstHost, dstStore, dstLnkS, "/legs/topic", nil, legs.AllowPeer(allowPeer))

The Subscriber keeps track of the latest head for each publisher that it has synced. This avoids exchanging the whole DAG from scratch in every update and instead downloads only the part that has not been synced. This value is not persisted as part of the library. If you want to start a Subscriber which has already partially synced with a provider you can use the SetLatestSync method:

sub, err := legs.NewSubscriber(dstHost, dstStore, dstLnkS, "/legs/topic", nil)
if err != nil {
    panic(err)
}
// Set up partially synced publishers
if err = sub.SetLatestSync(peerID1, lastSync1) ; err != nil {
    panic(err)
}
if err = sub.SetLatestSync(peerID2, lastSync2) ; err != nil {
    panic(err)
}
if err = sub.SetLatestSync(peerID3, lastSync3) ; err != nil {
    panic(err)
}

License

Legs is dual-licensed under Apache 2.0 and MIT terms:

Apache License, Version 2.0, (LICENSE or http://www.apache.org/licenses/LICENSE-2.0)
MIT license (LICENSE-MIT or http://opensource.org/licenses/MIT)