# Notes on `go-libp2p-discovery`

## How does discovery work?
- libp2p has 3 types of `Routing` interface
- `ContentRouting`
- `Provide`
- `FindProviderAsync`
- `PeerRouting`
- `FindPeer`
- `ValueStore`
- `PutValue`
- `GetValue`
- See https://github.com/libp2p/go-libp2p-core/blob/master/routing/routing.go#L71
- `go-libp2p-kad-dht` implements every method in `routing.go` file
- See https://github.com/libp2p/go-libp2p-kad-dht/blob/master/routing.go
- __The filename corresponds to the interface implementaion.__
- Kademlia can be the instance of any of the routing interface
- `Discovery` is a more abstract and higher level interface
- `Advitiser`
- `Advertise`
- `Discoverer`
- `FindPeers`
- See https://github.com/libp2p/go-libp2p-core/blob/master/discovery/discovery.go#L24
- `RoutingDiscovery` struct implemets `Discovery` interface
- it is defined in the package `libp2p-dht-discovery`
- `RoutingDiscovery` struct wraps a `ContentRouting` interface
- `RoutingDiscovery` defines `Advertise` and `FindPeers`
- Inside `Advertise`, `Provide` is called
- Inside `FindPeers`, `FindPeerAsync` is called
- See https://github.com/libp2p/go-libp2p-discovery/blob/master/routing.go#L22
- How does `Provide` work in Kademlia?
- Provider abstraction for indirect stores.
- Some DHTs store values directly, while __an indirect store stores pointers to locations of the value__, similarly to Coral and Mainline DHT.
- __Provide makes this node announce that it can provide a value for the given key__
- Can providers provide the same cid?
- handler `handleAddProvider`
- See https://github.com/libp2p/go-libp2p-kad-dht/blob/master/handlers.go#L354
- Kademlia has a `ProviderManager` that manages a provider set for a given key
- How does `FindPeersAsync` work in Kademlia?
- Check local `Providers`
- Query `k` nearest peers to the advertised key for their `Providers`
- Store these peers into the local `Peerstore`
- How to use package `Discovery`?
- See https://github.com/libp2p/go-libp2p-examples/tree/master/chat-with-rendezvous
- See https://github.com/libp2p/go-libp2p-examples/tree/master/chat-with-mdns

###### tags: `note` `libp2p`