go-libp2p/examples/libp2p-host

The libp2p 'host'

For most applications, the host is the basic building block you'll need to get started. This guide will show how to construct and use a simple host.

The host is an abstraction that manages services on top of a swarm. It provides a clean interface to connect to a service on a given remote peer.

First, you'll need an ID, and a place to store that ID. To generate an ID, you can do the following:

import (
	"crypto/rand"

	crypto "github.com/libp2p/go-libp2p-crypto"
	peer "github.com/libp2p/go-libp2p-peer"
	pstore "github.com/libp2p/go-libp2p-peerstore"
)

// Generate an identity keypair using go's cryptographic randomness source
priv, pub, err := crypto.GenerateEd25519Key(rand.Reader)
if err != nil {
	panic(err)
}

// A peers ID is the hash of its public key
pid, err := peer.IDFromPublicKey(pub)
if err != nil {
	panic(err)
}

// We've created the identity, now we need to store it.
// A peerstore holds information about peers, including your own
ps := pstore.NewPeerstore()
ps.AddPrivKey(pid, priv)
ps.AddPubKey(pid, pub)

Next, you'll need at least one address that you want to listen on. You can go from a string to a multiaddr like this:

import ma "github.com/multiformats/go-multiaddr"

...

maddr, err := ma.NewMultiaddr("/ip4/0.0.0.0/tcp/9000")
if err != nil {
	panic(err)
}

Now you know who you are, and where you live (in a manner of speaking). The next step is setting up a 'swarm network' to handle all the peers you will connect to. The swarm handles incoming connections from other peers, and handles the negotiation of new outbound connections.

import (
	"context"
	swarm "github.com/libp2p/go-libp2p-swarm"
)

// Make a context to govern the lifespan of the swarm
ctx := context.Background()

// Put all this together
netw, err := swarm.NewNetwork(ctx, []ma.Multiaddr{maddr}, pid, ps, nil)
if err != nil {
	panic(err)
}

At this point, we have everything needed to finally construct a host. That call is the simplest one so far:

import bhost "github.com/libp2p/go-libp2p/p2p/host/basic"

myhost := bhost.New(netw)

And thats it, you have a libp2p host and you're ready to start doing some awesome p2p networking!

In future guides we will go over ways to use hosts, configure them differently (hint: there are a huge number of ways to set these up), and interesting ways to apply this technology to various applications you might want to build.

To see this code all put together, take a look at host.go.