add hosts example

examples/hosts/README.md

+# libp2p host example
+
+## What this does
+This example can be started in either listen mode, or dial mode.
+When running as a listener, it will sit and wait for incoming connections on
+the `/hello/1.0.0` protocol. Whenever it receives a stream, it will 
+write the message "hello libp2p" over the stream and close it.
+When run in dial mode, the node will start up, connect to the given
+address, open a stream to the target peer, and read a message on the
+protocol `/hello/1.0.0`
+
+## Building
+```
+$ go build
+```
+
+## Usage
+In one terminal:
+```
+$ ./hosts -l 4737
+```
+
+In another, copy the address printed by the listener and do:
+
+```
+$ ./hosts -d ADDRESS
+```
+

examples/hosts/main.go

+package main
+
+import (
+	"flag"
+	"fmt"
+	"io/ioutil"
+	"log"
+	"time"
+
+	pstore "github.com/ipfs/go-libp2p-peerstore"
+	host "github.com/ipfs/go-libp2p/p2p/host"
+	bhost "github.com/ipfs/go-libp2p/p2p/host/basic"
+	metrics "github.com/ipfs/go-libp2p/p2p/metrics"
+	net "github.com/ipfs/go-libp2p/p2p/net"
+	conn "github.com/ipfs/go-libp2p/p2p/net/conn"
+	swarm "github.com/ipfs/go-libp2p/p2p/net/swarm"
+	testutil "github.com/ipfs/go-libp2p/testutil"
+
+	ipfsaddr "github.com/ipfs/go-ipfs/thirdparty/ipfsaddr"
+	ma "github.com/jbenet/go-multiaddr"
+	context "golang.org/x/net/context"
+)
+
+// create a 'Host' with a random peer to listen on the given address
+func makeDummyHost(listen string) (host.Host, error) {
+	addr, err := ma.NewMultiaddr(listen)
+	if err != nil {
+		return nil, err
+	}
+
+	pid, err := testutil.RandPeerID()
+	if err != nil {
+		return nil, err
+	}
+
+	// bandwidth counter, should be optional in the future
+	bwc := metrics.NewBandwidthCounter()
+
+	// create a new swarm to be used by the service host
+	netw, err := swarm.NewNetwork(context.Background(), []ma.Multiaddr{addr}, pid, pstore.NewPeerstore(), bwc)
+	if err != nil {
+		return nil, err
+	}
+
+	log.Printf("I am %s/ipfs/%s\n", addr, pid.Pretty())
+	return bhost.New(netw), nil
+}
+
+func main() {
+	conn.EncryptConnections = false
+	listenF := flag.Int("l", 0, "wait for incoming connections")
+	target := flag.String("d", "", "target peer to dial")
+	flag.Parse()
+
+	listenaddr := fmt.Sprintf("/ip4/0.0.0.0/tcp/%d", *listenF)
+
+	ha, err := makeDummyHost(listenaddr)
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	message := []byte("hello libp2p!")
+	// Set a stream handler on host A
+	ha.SetStreamHandler("/hello/1.0.0", func(s net.Stream) {
+		defer s.Close()
+		log.Println("writing message")
+		s.Write(message)
+	})
+
+	if *target == "" {
+		log.Println("listening on for connections...")
+		for {
+			time.Sleep(time.Hour)
+		}
+	}
+
+	a, err := ipfsaddr.ParseString(*target)
+	if err != nil {
+		log.Fatalln(err)
+	}
+
+	pi := pstore.PeerInfo{
+		ID:    a.ID(),
+		Addrs: []ma.Multiaddr{a.Transport()},
+	}
+
+	log.Println("connecting to target")
+	err = ha.Connect(context.Background(), pi)
+	if err != nil {
+		log.Fatalln(err)
+	}
+
+	log.Println("opening stream...")
+	// make a new stream from host B to host A
+	// it should be handled on host A by the handler we set
+	s, err := ha.NewStream(context.Background(), "/hello/1.0.0", a.ID())
+	if err != nil {
+		log.Fatalln(err)
+	}
+
+	log.Println("reading message")
+	out, err := ioutil.ReadAll(s)
+	if err != nil {
+		log.Fatalln(err)
+	}
+
+	log.Println("GOT: ", string(out))
+}