How to get started with finding peers without opening ports?

[ChocolateLoverRaj]

I am making a small app and I'm trying to use libp2p to synchronize data between devices. I want to see other devices which are also running my app so that I can share the data with them. I can run a server for discovering peers but I also want it to work with just the public servers. The app is an iced app and I am looking for a solution that will work on the web and on the desktop.

All of the examples seem to be either for the local network or when you already know the peer id you are looking for. How can I discover which other peers are online?

[drHuangMHT]

Technically, you will need to open a port to transfer any data, including information about other active peers. So no port, no data exchange, no knowledge about other peers.

To know any information about other peers, you will need at least one connection to a peer that supports libp2p-kad. It can be your server for discovering peers, but you need at least one. But for local network, you can use libp2p-mdns that does not require an active connection, but the peer you are looking for need to be actively advertise itself on the local network also via libp2p-mdns.

[ChocolateLoverRaj]

How does https://github.com/libp2p/universal-connectivity find peers in the browser?

[drHuangMHT]

How does https://github.com/libp2p/universal-connectivity find peers in the browser?

I'm not familiar with WebRTC and browser related things, but the rust peer has these features enabled: ["identify", "ping", "tokio", "gossipsub", "macros", "relay", "kad", "rsa", "ed25519", "quic", "request-response", "dns", "memory-connection-limits", "tcp", "noise", "yamux", "autonat", "tls", "dcutr"], which basically means a full-fledged peer that uses libp2p-kad and libp2p-relay for connectivity.

[dariusc93]

The browser connects to a node that uses WebRTC-Direct (or web transport?) and sends messages to the topic which peers and the node are subscribed to. Since the webrtc transport doesnt support browser-to-browser, peers would not be able to establish a connection directly via webrtc. With web sockets, it's possible via relay but can be flakey at times.

[ChocolateLoverRaj]

In the browser how does it discover other peers and then establish a direct connection? Can I do a similar thing in Rust on native platforms?

[dariusc93]

In the browser how does it discover other peers and then establish a direct connection? Can I do a similar thing in Rust on native platforms?

There are: browser-to-node via webrtc-direct, browser-to-browser with webrtc, browser-to-node for web socket, and browser-to-node via webtransport. Commonly, in js-libp2p and go-libp2p, there is webrtc transport, which would support browser-to-browser though this connection is established over a relay. For webrtc-direct, this only establishes a connection directly to the node, but you cannot open a relay through this method (see #5453 for my attempt and the issue I came across) but still good for using DHT, Pubsub, etc., which would allow you to share info and discover peers. Same with web socket and web transport. While I am unsure about web transport and if using a relay would work, but if the node supports relay, then web socket transport could be used and the browser node can connect to that relay to establish a reservation and then from there connect to a peer, either via relay or direct. On rust-libp2p, you can do all except browser-to-browser via webrtc. You would need to use js-libp2p or and possibly go-libp2p for that. Additionally, there is no native webtransport in rust-libp2p yet (see #5564)