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feat(peer-store): introduce libp2p-peer-store #5724

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Description

Introduce libp2p-peer-store for a peer store implementation.

Related: #4103

Notes & open questions

Change checklist

  • I have performed a self-review of my own code
  • I have made corresponding changes to the documentation
  • I have added tests that prove my fix is effective or that my feature works
  • A changelog entry has been made in the appropriate crates

@drHuangMHT
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This is a very basic implementation, would love to hear more ideas on how to implement this!

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@elenaf9 elenaf9 left a comment

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Thanks for starting this effort @drHuangMHT!

If I understand the current implementation correctly, the purpose of this store is just to track connected peers, and explicitly added addresses. However, I think we have to keep in mind that protocols like kademlia or identify very frequently report all addresses that they learn as NewExternalAddrOfPeer. So with the current MemoryStore implementation, the store would grow unbounded with all of these addresses. I think there needs to be some GC strategy.

Also, after reading #4103 (comment), I think a peer store implementation could also do much more than just track explicitly added addresses, e.g.:

  • track how valuable a know address is, by using infos about how the address info was received, if we connected to it already, etc
  • implement a TTL for address records
  • track other meta data for a peer, e.g. public key

I don't think this needs to be implemented in this PR. But I think we could forward more of the already present info to the Store trait, so that a custom implementation can have more sophisticated logic.

Comment on lines 71 to 72
/// Peers that are currently connected.
connected_peers: HashSet<PeerId>,
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Is there a case where using a HashSet<PeerId> to track connected peers is unsuitable for a specific use case? If now, how about moving this into the Behavior, so that the Store only concerns the "address-book" part of this behavior?

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The idea of Store trait is to allow on-disk storage, now I think about it, this info will be changing in real time so it should be kept in memory anyway. Will move it into the behaviour itself.

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can we have MemoryStore<T=()> so that we are able to store data for peers (like scoring etc):

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can we have MemoryStore<T=()> so that we are able to store data for peers (like scoring etc):

MemoryStore is more of a reference implementation, I don't think it is necessary to include a generic parameter for customization since we are maintaining its internals.

misc/peer-store/src/store.rs Outdated Show resolved Hide resolved
misc/peer-store/src/lib.rs Outdated Show resolved Hide resolved
misc/peer-store/src/store.rs Outdated Show resolved Hide resolved
misc/peer-store/src/behaviour.rs Outdated Show resolved Hide resolved
misc/peer-store/src/store.rs Outdated Show resolved Hide resolved
misc/peer-store/src/store.rs Outdated Show resolved Hide resolved
_role_override: libp2p_core::Endpoint,
_port_use: libp2p_core::transport::PortUse,
) -> Result<libp2p_swarm::THandler<Self>, libp2p_swarm::ConnectionDenied> {
self.store.on_peer_connect(&peer);
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It might make more sense to remove this for FromSwarm events since a connection could be denied later on (ie connection limits, banned peer, etc.), so that way the store isnt exactly cluttered.

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That makes sense. Will favor the swarm event.

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can we instead define Store::handle_* methods that are called here and in the other NetworkBehaviour::handle_*
so that it allows us to further manage our peers?

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can we instead define Store::handle_* methods that are called here and in the other NetworkBehaviour::handle_* so that it allows us to further manage our peers?

What are those specifically? The store no longer record connected peers.

/// - contains all observed addresses of peers;
pub trait Store {
/// Called when a peer connects.
fn on_peer_connect(&mut self, peer: &PeerId);
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If we are tracking peer connections too, should we also keep tabs on the ConnectionId?

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We can, but how to store it? I think there can be multiple connections from a single peer, no?

misc/peer-store/src/store.rs Outdated Show resolved Hide resolved
misc/peer-store/src/behaviour.rs Outdated Show resolved Hide resolved
@drHuangMHT
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Oops that use<'a> syntax was stabilized in rust 1.82, the compiler on 1.80 wasn't happy with it.

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@jxs jxs left a comment

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Thanks for starting this @drHuangMHT, already looking good! left some notes to allow further customization.
cc @elenaf9

[package]
name = "libp2p-peer-store"
version = "0.1.0"
edition = "2021"
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you can add yourself as the author here :)

misc/peer-store/src/behaviour.rs Outdated Show resolved Hide resolved
misc/peer-store/src/behaviour.rs Outdated Show resolved Hide resolved
misc/peer-store/src/behaviour.rs Show resolved Hide resolved
Comment on lines 71 to 72
/// Peers that are currently connected.
connected_peers: HashSet<PeerId>,
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can we have MemoryStore<T=()> so that we are able to store data for peers (like scoring etc):

_role_override: libp2p_core::Endpoint,
_port_use: libp2p_core::transport::PortUse,
) -> Result<libp2p_swarm::THandler<Self>, libp2p_swarm::ConnectionDenied> {
self.store.on_peer_connect(&peer);
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can we instead define Store::handle_* methods that are called here and in the other NetworkBehaviour::handle_*
so that it allows us to further manage our peers?

 Store now handles FromSwarm directly; rename some on_* methods; allow removing address; update records on FromSwarm::ConnectionEstablished
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drHuangMHT commented Dec 16, 2024

  • track how valuable a know address is, by using infos about how the address info was received, if we connected to it already, etc

This can get very complicated very soon, for example how to record the activitiy on the address(there will be some overhead) and how to make it machine-readable(scoring system). The discussion will be quite lengthy.

  • implement a TTL for address records

I didn't see a good way to implement TTL(garbage collect) for records, any pointer?

  • track other meta data for a peer, e.g. public key

I don't see the remote public key being available through swarm itself, be it in the form of PeerRecord, SignedEnvelope or just PublicKey. But the pubkey is indeed a very important metadata of a peer.

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4 participants