first hack at a nice libp2p constructor

libp2p.go

+package libp2p
+
+import (
+	"context"
+	"crypto/rand"
+
+	crypto "github.com/libp2p/go-libp2p-crypto"
+	host "github.com/libp2p/go-libp2p-host"
+	pnet "github.com/libp2p/go-libp2p-interface-pnet"
+	metrics "github.com/libp2p/go-libp2p-metrics"
+	peer "github.com/libp2p/go-libp2p-peer"
+	pstore "github.com/libp2p/go-libp2p-peerstore"
+	swarm "github.com/libp2p/go-libp2p-swarm"
+	transport "github.com/libp2p/go-libp2p-transport"
+	bhost "github.com/libp2p/go-libp2p/p2p/host/basic"
+	mux "github.com/libp2p/go-stream-muxer"
+	ma "github.com/multiformats/go-multiaddr"
+	mplex "github.com/whyrusleeping/go-smux-multiplex"
+	msmux "github.com/whyrusleeping/go-smux-multistream"
+	yamux "github.com/whyrusleeping/go-smux-yamux"
+)
+
+type Config struct {
+	Transports  []transport.Transport
+	Muxer       mux.Transport
+	ListenAddrs []ma.Multiaddr
+	PeerKey     crypto.PrivKey
+	Peerstore   pstore.Peerstore
+	Protector   pnet.Protector
+	Reporter    metrics.Reporter
+}
+
+func Construct(ctx context.Context, cfg *Config) (host.Host, error) {
+	if cfg == nil {
+		cfg = DefaultConfig()
+	}
+
+	if cfg.PeerKey == nil {
+		priv, _, err := crypto.GenerateKeyPairWithReader(crypto.RSA, 2048, rand.Reader)
+		if err != nil {
+			return nil, err
+		}
+		cfg.PeerKey = priv
+	}
+
+	// Obtain Peer ID from public key
+	pid, err := peer.IDFromPublicKey(cfg.PeerKey.GetPublic())
+	if err != nil {
+		return nil, err
+	}
+
+	ps := cfg.Peerstore
+	if ps == nil {
+		ps = pstore.NewPeerstore()
+	}
+
+	ps.AddPrivKey(pid, cfg.PeerKey)
+	ps.AddPubKey(pid, cfg.PeerKey.GetPublic())
+
+	swrm, err := swarm.NewSwarmWithProtector(ctx, cfg.ListenAddrs, pid, ps, cfg.Protector, cfg.Muxer, cfg.Reporter)
+	if err != nil {
+		return nil, err
+	}
+
+	netw := (*swarm.Network)(swrm)
+
+	return bhost.New(netw), nil
+}
+
+func DefaultMuxer() mux.Transport {
+	// Set up stream multiplexer
+	tpt := msmux.NewBlankTransport()
+	tpt.AddTransport("/yamux/1.0.0", yamux.DefaultTransport)
+	tpt.AddTransport("/mplex/6.3.0", mplex.DefaultTransport)
+	return tpt
+}
+
+func DefaultConfig() *Config {
+	// Create a multiaddress
+	addr, err := ma.NewMultiaddr("/ip4/127.0.0.1/tcp/0")
+	if err != nil {
+		panic(err)
+	}
+
+	return &Config{
+		ListenAddrs: []ma.Multiaddr{addr},
+		Peerstore:   pstore.NewPeerstore(),
+		Muxer:       DefaultMuxer(),
+	}
+}