Merge pull request #185 from libp2p/libp2p-examples

Libp2p examples

.gitignore

 *.swp
 examples/echo/echo
+examples/multicodecs/multicodecs

.travis.yml

@@ -11,7 +11,8 @@ install: true
 
 before_install:
   - make deps
-
+  - go get -u github.com/multiformats/go-multicodec
+  - go get -u github.com/jbenet/go-msgio
 #- go vet ./...
 script:
   - go test ./... -v

Makefile

@@ -2,6 +2,10 @@ gx:
 	go get github.com/whyrusleeping/gx
 	go get github.com/whyrusleeping/gx-go
 
+deps-examples: deps
+	go get -u github.com/multiformats/go-multicodec
+	go get -u github.com/jbenet/go-msgio
+
 deps: gx 
 	gx --verbose install --global
 	gx-go rewrite

examples/echo/README.md

@@ -25,18 +25,19 @@ From `go-libp2p` base folder:
 ## Usage
 
 ```
-> ./echo -l 1235
-2016/11/10 10:45:37 I am /ip4/127.0.0.1/tcp/1235/ipfs/QmNtX1cvrm2K6mQmMEaMxAuB4rTexhd87vpYVot4sEZzxc
-2016/11/10 10:45:37 listening for connections
+> ./echo -l 10000
+2017/03/15 14:11:32 I am /ip4/127.0.0.1/tcp/10000/ipfs/QmYo41GybvrXk8y8Xnm1P7pfA4YEXCpfnLyzgRPnNbG35e
+2017/03/15 14:11:32 Now run "./echo -l 10001 -d /ip4/127.0.0.1/tcp/10000/ipfs/QmYo41GybvrXk8y8Xnm1P7pfA4YEXCpfnLyzgRPnNbG35e -secio" on a different terminal
+2017/03/15 14:11:32 listening for connections
 ```
 
 The listener libp2p host will print its `Multiaddress`, which indicates how it
-can be reached (ip4+tcp) and its randomly generated ID (`QmNtX1cv...`)
+can be reached (ip4+tcp) and its randomly generated ID (`QmYo41Gyb...`)
 
 Now, launch another node that talks to the listener:
 
 ```
-> ./echo -d /ip4/127.0.0.1/tcp/1235/ipfs/QmNtX1cvrm2K6mQmMEaMxAuB4rTexhd87vpYVot4sEZzxc -l 1236
+> ./echo -l 10001 -d /ip4/127.0.0.1/tcp/10000/ipfs/QmYo41GybvrXk8y8Xnm1P7pfA4YEXCpfnLyzgRPnNbG35e
 ```
 
 The new node with send the message `"Hello, world!"` to the
@@ -61,9 +62,9 @@ In order to create the swarm (and a `basichost`), the example needs:
   * An
     [ipfs-procotol ID](https://godoc.org/github.com/libp2p/go-libp2p-peer#ID)
     like `QmNtX1cvrm2K6mQmMEaMxAuB4rTexhd87vpYVot4sEZzxc`. The example
-    autogenerates this on every run. An optional key-pair to secure
-    communications can be added to it. The example autogenerates them when
-    using `-secio`.
+    autogenerates a key pair on every run and uses an ID extracted from the
+    public key (the hash of the public key). When using `-secio`, it uses
+    the key pair to encrypt communications.
   * A [Multiaddress](https://godoc.org/github.com/multiformats/go-multiaddr),
     which indicates how to reach this peer. There can be several of them
     (using different protocols or locations for example). Example:

examples/echo/main.go

 package main
 
 import (
+	"bufio"
 	"context"
 	"flag"
 	"fmt"
 	"io/ioutil"
 	"log"
-	"math/rand"
-	"strings"
-	"time"
 
 	golog "github.com/ipfs/go-log"
+	crypto "github.com/libp2p/go-libp2p-crypto"
 	host "github.com/libp2p/go-libp2p-host"
 	net "github.com/libp2p/go-libp2p-net"
 	peer "github.com/libp2p/go-libp2p-peer"
 	pstore "github.com/libp2p/go-libp2p-peerstore"
 	swarm "github.com/libp2p/go-libp2p-swarm"
-	bhost "github.com/libp2p/go-libp2p/p2p/host/basic"
-	testutil "github.com/libp2p/go-testutil"
 	ma "github.com/multiformats/go-multiaddr"
 	gologging "github.com/whyrusleeping/go-logging"
+
+	peerstore "github.com/libp2p/go-libp2p-peerstore"
+	bhost "github.com/libp2p/go-libp2p/p2p/host/basic"
 )
 
-// create a 'Host' with a random peer to listen on the given address
-func makeBasicHost(listen string, secio bool) (host.Host, error) {
-	addr, err := ma.NewMultiaddr(listen)
+// makeBasicHost creates a LibP2P host with a random peer ID listening on the
+// given multiaddress. It will use secio if secio is true.
+func makeBasicHost(listenPort int, secio bool) (host.Host, error) {
+	// Generate a key pair for this host. We will use it at least
+	// to obtain a valid host ID.
+	priv, pub, err := crypto.GenerateKeyPair(crypto.RSA, 2048)
+	if err != nil {
+		return nil, err
+	}
+
+	// Obtain Peer ID from public key
+	pid, err := peer.IDFromPublicKey(pub)
 	if err != nil {
 		return nil, err
 	}
 
+	// Create a multiaddress
+	addr, err := ma.NewMultiaddr(fmt.Sprintf("/ip4/127.0.0.1/tcp/%d", listenPort))
+
+	if err != nil {
+		return nil, err
+	}
+
+	// Create a peerstore
 	ps := pstore.NewPeerstore()
-	var pid peer.ID
 
+	// If using secio, we add the keys to the peerstore
+	// for this peer ID.
 	if secio {
-		ident, err := testutil.RandIdentity()
-		if err != nil {
-			return nil, err
-		}
-
-		ident.PrivateKey()
-		ps.AddPrivKey(ident.ID(), ident.PrivateKey())
-		ps.AddPubKey(ident.ID(), ident.PublicKey())
-		pid = ident.ID()
-	} else {
-		fakepid, err := testutil.RandPeerID()
-		if err != nil {
-			return nil, err
-		}
-		pid = fakepid
+		ps.AddPrivKey(pid, priv)
+		ps.AddPubKey(pid, pub)
 	}
 
-	ctx := context.Background()
+	// Create swarm (implements libP2P Network)
+	netwrk, err := swarm.NewNetwork(
+		context.Background(),
+		[]ma.Multiaddr{addr},
+		pid,
+		ps,
+		nil)
 
-	// create a new swarm to be used by the service host
-	netw, err := swarm.NewNetwork(ctx, []ma.Multiaddr{addr}, pid, ps, nil)
-	if err != nil {
-		return nil, err
+	basicHost := bhost.New(netwrk)
+
+	// Build host multiaddress
+	hostAddr, _ := ma.NewMultiaddr(fmt.Sprintf("/ipfs/%s", basicHost.ID().Pretty()))
+
+	// Now we can build a full multiaddress to reach this host
+	// by encapsulating both addresses:
+	fullAddr := addr.Encapsulate(hostAddr)
+	log.Printf("I am %s\n", fullAddr)
+	if secio {
+		log.Printf("Now run \"./echo -l %d -d %s -secio\" on a different terminal\n", listenPort+1, fullAddr)
+	} else {
+		log.Printf("Now run \"./echo -l %d -d %s\" on a different terminal\n", listenPort+1, fullAddr)
 	}
 
-	log.Printf("I am %s/ipfs/%s\n", addr, pid.Pretty())
-	return bhost.New(netw), nil
+	return basicHost, nil
 }
 
 func main() {
-	rand.Seed(time.Now().UnixNano())
+	// LibP2P code uses golog to log messages. They log with different
+	// string IDs (i.e. "swarm"). We can control the verbosity level for
+	// all loggers with:
 	golog.SetAllLoggers(gologging.INFO) // Change to DEBUG for extra info
+
+	// Parse options from the command line
 	listenF := flag.Int("l", 0, "wait for incoming connections")
 	target := flag.String("d", "", "target peer to dial")
 	secio := flag.Bool("secio", false, "enable secio")
-
 	flag.Parse()
 
 	if *listenF == 0 {
 		log.Fatal("Please provide a port to bind on with -l")
 	}
 
-	listenaddr := fmt.Sprintf("/ip4/127.0.0.1/tcp/%d", *listenF)
-
-	ha, err := makeBasicHost(listenaddr, *secio)
+	// Make a host that listens on the given multiaddress
+	ha, err := makeBasicHost(*listenF, *secio)
 	if err != nil {
 		log.Fatal(err)
 	}
 
-	// Set a stream handler on host A
+	// Set a stream handler on host A. /echo/1.0.0 is
+	// a user-defined protocol name.
 	ha.SetStreamHandler("/echo/1.0.0", func(s net.Stream) {
 		log.Println("Got a new stream!")
 		defer s.Close()
@@ -93,8 +115,10 @@ func main() {
 		log.Println("listening for connections")
 		select {} // hang forever
 	}
-	// This is where the listener code ends
+	/**** This is where the listener code ends ****/
 
+	// The following code extracts target's the peer ID from the
+	// given multiaddress
 	ipfsaddr, err := ma.NewMultiaddr(*target)
 	if err != nil {
 		log.Fatalln(err)
@@ -110,26 +134,26 @@ func main() {
 		log.Fatalln(err)
 	}
 
-	tptaddr := strings.Split(ipfsaddr.String(), "/ipfs/")[0]
-	// This creates a MA with the "/ip4/ipaddr/tcp/port" part of the target
-	tptmaddr, err := ma.NewMultiaddr(tptaddr)
-	if err != nil {
-		log.Fatalln(err)
-	}
+	// Decapsulate the /ipfs/<peerID> part from the target
+	// /ip4/<a.b.c.d>/ipfs/<peer> becomes /ip4/<a.b.c.d>
+	targetPeerAddr, _ := ma.NewMultiaddr(
+		fmt.Sprintf("/ipfs/%s", peer.IDB58Encode(peerid)))
+	targetAddr := ipfsaddr.Decapsulate(targetPeerAddr)
 
-	// We need to add the target to our peerstore, so we know how we can
-	// contact it
-	ha.Peerstore().AddAddr(peerid, tptmaddr, pstore.PermanentAddrTTL)
+	// We have a peer ID and a targetAddr so we add it to the peerstore
+	// so LibP2P knows how to contact it
+	ha.Peerstore().AddAddr(peerid, targetAddr, peerstore.PermanentAddrTTL)
 
 	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 above
+	// it should be handled on host A by the handler we set above because
+	// we use the same /echo/1.0.0 protocol
 	s, err := ha.NewStream(context.Background(), peerid, "/echo/1.0.0")
 	if err != nil {
 		log.Fatalln(err)
 	}
 
-	_, err = s.Write([]byte("Hello, world!"))
+	_, err = s.Write([]byte("Hello, world!\n"))
 	if err != nil {
 		log.Fatalln(err)
 	}
@@ -142,18 +166,17 @@ func main() {
 	log.Printf("read reply: %q\n", out)
 }
 
-// doEcho reads some data from a stream, writes it back and closes the
-// stream.
+// doEcho reads a line of data a stream and writes it back
 func doEcho(s net.Stream) {
-	buf := make([]byte, 1024)
-	n, err := s.Read(buf)
+	buf := bufio.NewReader(s)
+	str, err := buf.ReadString('\n')
 	if err != nil {
 		log.Println(err)
 		return
 	}
 
-	log.Printf("read request: %q\n", buf[:n])
-	_, err = s.Write(buf[:n])
+	log.Printf("read: %s\n", str)
+	_, err = s.Write([]byte(str))
 	if err != nil {
 		log.Println(err)
 		return

examples/http-proxy/README.md

+# HTTP proxy service with libp2p
+
+This examples shows how to create a simple HTTP proxy service with libp2p:
+
+
+```
+                                                                                                                 XXX
+                                                                                                               XX  XXXXXX
+                                                                                                              X         XX
+                                                                                                    XXXXXXX  XX          XX XXXXXXXXXX
+                    +---------------------+                  +---------------------+              XXX      XXX            XXX        XXX
+ HTTP Request       |                     |                  |                     |             XX                                    XX
++------------------->                     |  libp2p stream   |                     |  HTTP       X                                      X
+                    |    Local peer       <------------------>   Remote peer       <------------->     HTTP SERVER - THE INTERNET      XX
+<-------------------+                     |                  |                     | Req & Resp   XX                                   X
+    HTTP Response   |   libp2p host       |                  |    libp2p host      |               XXXX XXXX XXXXXXXXXXXXXXXXXXXX   XXXX
+                    +---------------------+                  +---------------------+                                            XXXXX
+
+```
+
+In order to proxy an HTTP request, we create a local peer which listens on `localhost:9900`. HTTP requests performed to that address are tunneled via a libp2p stream to a remote peer, which then performs the HTTP requests and sends the response back to the local peer, which relays it
+to the user.
+
+Note that this is a very simple approach to a proxy, and does not perform any header management, nor supports HTTPS. The `proxy.go` code is thoroughly commeted, detailing what is happening in every step.
+
+## Build
+
+From `go-libp2p` base folder:
+
+```
+> make deps
+> go build ./examples/echo
+```
+
+## Usage
+
+First run the "remote" peer as follows. It will print a local peer address. If you would like to run this on a separate machine, please replace the IP accordingly:
+
+```sh
+$ ./http-proxy
+Proxy server is ready
+libp2p-peer addresses:
+/ip4/127.0.0.1/tcp/12000/ipfs/QmddTrQXhA9AkCpXPTkcY7e22NK73TwkUms3a44DhTKJTD
+```
+
+The run the local peer, indicating that it will need to forward http requests to the remote peer as follows:
+
+```
+$ ./http-proxy -d /ip4/127.0.0.1/tcp/12000/ipfs/QmddTrQXhA9AkCpXPTkcY7e22NK73TwkUms3a44DhTKJTD
+Proxy server is ready
+libp2p-peer addresses:
+/ip4/127.0.0.1/tcp/12001/ipfs/Qmaa2AYTha1UqcFVX97p9R1UP7vbzDLY7bqWsZw1135QvN
+proxy listening on  127.0.0.1:9900
+```
+
+As you can see, the proxy prints the listening address `127.0.0.1:9900`. You can now use this address as proxy, for example with `curl`:
+
+```
+$ curl -x "127.0.0.1:9900" "http://ipfs.io/ipfs/QmfUX75pGRBRDnjeoMkQzuQczuCup2aYbeLxz5NzeSu9G6"
+it works!
+
+```

examples/http-proxy/proxy.go

+package main
+
+import (
+	"bufio"
+	"context"
+	"flag"
+	"fmt"
+	"io"
+	"log"
+	"net/http"
+	"strings"
+
+	// We need to import libp2p's libraries that we use in this project.
+	// In order to work, these libraries need to be rewritten by gx-go.
+	crypto "github.com/libp2p/go-libp2p-crypto"
+	host "github.com/libp2p/go-libp2p-host"
+	inet "github.com/libp2p/go-libp2p-net"
+	peer "github.com/libp2p/go-libp2p-peer"
+	ps "github.com/libp2p/go-libp2p-peerstore"
+	swarm "github.com/libp2p/go-libp2p-swarm"
+	ma "github.com/multiformats/go-multiaddr"
+	manet "github.com/multiformats/go-multiaddr-net"
+
+	bhost "github.com/libp2p/go-libp2p/p2p/host/basic"
+)
+
+// Protocol defines the libp2p protocol that we will use for the libp2p proxy
+// service that we are going to provide. This will tag the streams used for
+// this service. Streams are multiplexed and their protocol tag helps
+// libp2p handle them to the right handler functions.
+const Protocol = "/proxy-example/0.0.1"
+
+// makeRandomHost creates a libp2p host with a randomly generated identity.
+// This step is described in depth in other tutorials.
+func makeRandomHost(port int) host.Host {
+	priv, pub, err := crypto.GenerateKeyPair(crypto.RSA, 2048)
+	if err != nil {
+		log.Fatalln(err)
+	}
+	pid, err := peer.IDFromPublicKey(pub)
+	if err != nil {
+		log.Fatalln(err)
+	}
+	listen, err := ma.NewMultiaddr(fmt.Sprintf("/ip4/127.0.0.1/tcp/%d", port))
+	if err != nil {
+		log.Fatalln(err)
+	}
+	ps := ps.NewPeerstore()
+	ps.AddPrivKey(pid, priv)
+	ps.AddPubKey(pid, pub)
+	n, err := swarm.NewNetwork(context.Background(),
+		[]ma.Multiaddr{listen}, pid, ps, nil)
+	if err != nil {
+		log.Fatalln(err)
+	}
+	return bhost.New(n)
+}
+
+// ProxyService provides HTTP proxying on top of libp2p by launching an
+// HTTP server which tunnels the requests to a destination peer running
+// ProxyService too.
+type ProxyService struct {
+	host      host.Host
+	dest      peer.ID
+	proxyAddr ma.Multiaddr
+}
+
+// NewProxyService attaches a proxy service to the given libp2p Host.
+// The proxyAddr parameter specifies the address on which the
+// HTTP proxy server listens. The dest parameter specifies the peer
+// ID of the remote peer in charge of performing the HTTP requests.
+//
+// ProxyAddr/dest may be nil/"" it is not necessary that this host
+// provides a listening HTTP server (and instead its only function is to
+// perform the proxied http requests it receives from a different peer.
+//
+// The addresses for the dest peer should be part of the host's peerstore.
+func NewProxyService(h host.Host, proxyAddr ma.Multiaddr, dest peer.ID) *ProxyService {
+	// We let our host know that it needs to handle streams tagged with the
+	// protocol id that we have defined, and then handle them to
+	// our own streamHandling function.
+	h.SetStreamHandler(Protocol, streamHandler)
+
+	fmt.Println("Proxy server is ready")
+	fmt.Println("libp2p-peer addresses:")
+	for _, a := range h.Addrs() {
+		fmt.Printf("%s/ipfs/%s\n", a, peer.IDB58Encode(h.ID()))
+	}
+
+	return &ProxyService{
+		host:      h,
+		dest:      dest,
+		proxyAddr: proxyAddr,
+	}
+}
+
+// streamHandler is our function to handle any libp2p-net streams that belong
+// to our protocol. The streams should contain an HTTP request which we need
+// to parse, make on behalf of the original node, and then write the response
+// on the stream, before closing it.
+func streamHandler(stream inet.Stream) {
+	// Remember to close the stream when we are done.
+	defer stream.Close()
+
+	// Create a new buffered reader, as ReadRequest needs one.
+	// The buffered reader reads from our stream, on which we
+	// have sent the HTTP request (see ServeHTTP())
+	buf := bufio.NewReader(stream)
+	// Read the HTTP request from the buffer
+	req, err := http.ReadRequest(buf)
+	if err != nil {
+		log.Println(err)
+		return
+	}
+	defer req.Body.Close()
+
+	// We need to reset these fields in the request
+	// URL as they are not maintained.
+	req.URL.Scheme = "http"
+	hp := strings.Split(req.Host, ":")
+	if len(hp) > 1 && hp[1] == "443" {
+		req.URL.Scheme = "https"
+	} else {
+		req.URL.Scheme = "http"
+	}
+	req.URL.Host = req.Host
+
+	outreq := new(http.Request)
+	*outreq = *req
+
+	// We now make the request
+	fmt.Printf("Making request to %s\n", req.URL)
+	resp, err := http.DefaultTransport.RoundTrip(outreq)
+	if err != nil {
+		log.Println(err)
+		return
+	}
+
+	// resp.Write writes whatever response we obtained for our
+	// request back to the stream.
+	resp.Write(stream)
+}
+
+// Serve listens on the ProxyService's proxy address. This effectively
+// allows to set the listening address as http proxy.
+func (p *ProxyService) Serve() {
+	_, serveArgs, _ := manet.DialArgs(p.proxyAddr)
+	fmt.Println("proxy listening on ", serveArgs)
+	if p.dest != "" {
+		http.ListenAndServe(serveArgs, p)
+	}
+}
+
+// ServeHTTP implements the http.Handler interface. WARNING: This is the
+// simplest approach to a proxy. Therefore we do not do any of the things
+// that should be done when implementing a reverse proxy (like handling
+// headers correctly). For how to do it properly, see:
+// https://golang.org/src/net/http/httputil/reverseproxy.go?s=3845:3920#L121
+//
+// ServeHTTP opens a stream to the dest peer for every HTTP request.
+// Streams are multiplexed over single connections so, unlike connections
+// themselves, they are cheap to create and dispose of.
+func (p *ProxyService) ServeHTTP(w http.ResponseWriter, r *http.Request) {
+	fmt.Printf("proxying request for %s to peer %s\n", r.URL, p.dest.Pretty())
+	// We need to send the request to the remote libp2p peer, so
+	// we open a stream to it
+	stream, err := p.host.NewStream(context.Background(), p.dest, Protocol)
+	// If an error happens, we write an error for response.
+	if err != nil {
+		log.Println(err)
+		http.Error(w, err.Error(), http.StatusInternalServerError)
+		return
+	}
+	defer stream.Close()
+
+	// r.Write() writes the HTTP request to the stream.
+	err = r.Write(stream)
+	if err != nil {
+		log.Println(err)
+		http.Error(w, err.Error(), http.StatusServiceUnavailable)
+		return
+	}
+
+	// Now we read the response that was sent from the dest
+	// peer
+	buf := bufio.NewReader(stream)
+	resp, err := http.ReadResponse(buf, r)
+	if err != nil {
+		log.Println(err)
+		http.Error(w, err.Error(), http.StatusServiceUnavailable)
+		return
+	}
+
+	// Copy any headers
+	for k, v := range resp.Header {
+		for _, s := range v {
+			w.Header().Add(k, s)
+		}
+	}
+
+	// Write response status and headers
+	w.WriteHeader(resp.StatusCode)
+
+	// Finally copy the body
+	io.Copy(w, resp.Body)
+	resp.Body.Close()
+}
+
+// addAddrToPeerstore parses a peer multiaddress and adds
+// it to the given host's peerstore, so it knows how to
+// contact it. It returns the peer ID of the remote peer.
+func addAddrToPeerstore(h host.Host, addr string) peer.ID {
+	// The following code extracts target's the peer ID from the
+	// given multiaddress
+	ipfsaddr, err := ma.NewMultiaddr(addr)
+	if err != nil {
+		log.Fatalln(err)
+	}
+	pid, err := ipfsaddr.ValueForProtocol(ma.P_IPFS)
+	if err != nil {
+		log.Fatalln(err)
+	}
+
+	peerid, err := peer.IDB58Decode(pid)
+	if err != nil {
+		log.Fatalln(err)
+	}
+
+	// Decapsulate the /ipfs/<peerID> part from the target
+	// /ip4/<a.b.c.d>/ipfs/<peer> becomes /ip4/<a.b.c.d>
+	targetPeerAddr, _ := ma.NewMultiaddr(
+		fmt.Sprintf("/ipfs/%s", peer.IDB58Encode(peerid)))
+	targetAddr := ipfsaddr.Decapsulate(targetPeerAddr)
+
+	// We have a peer ID and a targetAddr so we add
+	// it to the peerstore so LibP2P knows how to contact it
+	h.Peerstore().AddAddr(peerid, targetAddr, ps.PermanentAddrTTL)
+	return peerid
+}
+
+func main() {
+	flag.Usage = func() {
+		fmt.Println(`
+This example creates a simple HTTP Proxy using two libp2p peers. The first peer
+provides an HTTP server locally which tunnels the HTTP requests with libp2p
+to a remote peer. The remote peer performs the requests and 
+send the sends the response back.
+
+Usage: Start remote peer first with:   ./proxy
+       Then start the local peer with: ./proxy -d <remote-peer-multiaddress>
+
+Then you can do something like: curl -x "localhost:9900" "http://ipfs.io".
+This proxies sends the request through the local peer, which proxies it to
+the remote peer, which makes it and sends the response back.
+`)
+		flag.PrintDefaults()
+	}
+
+	// Parse some flags
+	destPeer := flag.String("d", "", "destination peer address")
+	port := flag.Int("p", 9900, "proxy port")
+	p2pport := flag.Int("l", 12000, "libp2p listen port")
+	flag.Parse()
+
+	// If we have a destination peer we will start a local server
+	if *destPeer != "" {
+		// We use p2pport+1 in order to not collide if the user
+		// is running the remote peer locally on that port
+		host := makeRandomHost(*p2pport + 1)
+		// Make sure our host knows how to reach destPeer
+		destPeerID := addAddrToPeerstore(host, *destPeer)
+		proxyAddr, err := ma.NewMultiaddr(fmt.Sprintf("/ip4/127.0.0.1/tcp/%d", *port))
+		if err != nil {
+			log.Fatalln(err)
+		}
+		// Create the proxy service and start the http server
+		proxy := NewProxyService(host, proxyAddr, destPeerID)
+		proxy.Serve() // serve hangs forever
+	} else {
+		host := makeRandomHost(*p2pport)
+		// In this case we only need to make sure our host
+		// knows how to handle incoming proxied requests from
+		// another peer.
+		_ = NewProxyService(host, nil, "")
+		<-make(chan struct{}) // hang forever
+	}
+
+}

examples/multicodecs/README.md

+# Using multicodecs with LibP2P
+
+This examples shows how to use multicodecs (i.e. json) to encode and transmit information between LibP2P hosts using LibP2P Streams.
+
+Multicodecs present a common interface, making it very easy to swap the codec implementation if needed.
+
+This example expects that you area already familiar with the [echo example](https://github.com/libp2p/go-libp2p/tree/master/examples/echo).
+
+## Build
+
+From `go-libp2p` base folder:
+
+```
+> make deps-examples
+> go build ./examples/multicodecs
+```
+
+## Usage
+
+```
+> ./multicodecs
+
+```
+
+## Details
+
+The example creates two LibP2P Hosts. Host1 opens a stream to Host2. Host2 has an `StreamHandler` to deal with the incoming stream. This is covered in the `echo` example.
+
+Both hosts simulate a conversation. But rather than sending raw messages on the stream, each message in the conversation is encoded under a `json` object (using the `json` multicodec). For example:
+
+```
+{
+  "Msg": "This is the message",
+  "Index": 3,
+  "HangUp": false
+}
+```
+
+The stream lasts until one of the sides closes it when the HangUp field is `true`.

examples/multicodecs/main.go

+package main
+
+import (
+	"bufio"
+	"context"
+	"fmt"
+	"log"
+	"math/rand"
+	"time"
+
+	crypto "github.com/libp2p/go-libp2p-crypto"
+	host "github.com/libp2p/go-libp2p-host"
+	inet "github.com/libp2p/go-libp2p-net"
+	peer "github.com/libp2p/go-libp2p-peer"
+	ps "github.com/libp2p/go-libp2p-peerstore"
+	swarm "github.com/libp2p/go-libp2p-swarm"
+	ma "github.com/multiformats/go-multiaddr"
+
+	bhost "github.com/libp2p/go-libp2p/p2p/host/basic"
+	multicodec "github.com/multiformats/go-multicodec"
+	json "github.com/multiformats/go-multicodec/json"
+)
+
+const proto = "/example/1.0.0"
+
+// Message is a serializable/encodable object that we will send
+// on a Stream.
+type Message struct {
+	Msg    string
+	Index  int
+	HangUp bool
+}
+
+// streamWrap wraps a libp2p stream. We encode/decode whenever we
+// write/read from a stream, so we can just carry the encoders
+// and bufios with us
+type WrappedStream struct {
+	stream inet.Stream
+	enc    multicodec.Encoder
+	dec    multicodec.Decoder
+	w      *bufio.Writer
+	r      *bufio.Reader
+}
+
+// wrapStream takes a stream and complements it with r/w bufios and
+// decoder/encoder. In order to write raw data to the stream we can use
+// wrap.w.Write(). To encode something into it we can wrap.enc.Encode().
+// Finally, we should wrap.w.Flush() to actually send the data. Handling
+// incoming data works similarly with wrap.r.Read() for raw-reading and
+// wrap.dec.Decode() to decode.
+func WrapStream(s inet.Stream) *WrappedStream {
+	reader := bufio.NewReader(s)
+	writer := bufio.NewWriter(s)
+	// This is where we pick our specific multicodec. In order to change the
+	// codec, we only need to change this place.
+	// See https://godoc.org/github.com/multiformats/go-multicodec/json
+	dec := json.Multicodec(false).Decoder(reader)
+	enc := json.Multicodec(false).Encoder(writer)
+	return &WrappedStream{
+		stream: s,
+		r:      reader,
+		w:      writer,
+		enc:    enc,
+		dec:    dec,
+	}
+}
+
+// messages that will be sent between the hosts.
+var conversationMsgs = []string{
+	"Hello!",
+	"Hey!",
+	"How are you doing?",
+	"Very good! It is great that you can send data on a stream to me!",
+	"Not only that, the data is encoded in a JSON object.",
+	"Yeah, and we are using the multicodecs interface to encode and decode.",
+	"This way we could swap it easily for, say, cbor, or msgpack!",
+	"Let's leave that as an excercise for the reader...",
+	"Agreed, our last message should activate the HangUp flag",
+	"Yes, and the example code will close streams. So sad :(. Bye!",
+}
+
+func makeRandomHost(port int) host.Host {
+	// Ignoring most errors for brevity
+	// See echo example for more details and better implementation
+	priv, pub, _ := crypto.GenerateKeyPair(crypto.RSA, 2048)
+	pid, _ := peer.IDFromPublicKey(pub)
+	listen, _ := ma.NewMultiaddr(fmt.Sprintf("/ip4/127.0.0.1/tcp/%d", port))
+	ps := ps.NewPeerstore()
+	ps.AddPrivKey(pid, priv)
+	ps.AddPubKey(pid, pub)
+	n, _ := swarm.NewNetwork(context.Background(),
+		[]ma.Multiaddr{listen}, pid, ps, nil)
+	return bhost.New(n)
+}
+
+func main() {
+	// Choose random ports between 10000-10100
+	rand.Seed(666)
+	port1 := rand.Intn(100) + 10000
+	port2 := port1 + 1
+
+	// Make 2 hosts
+	h1 := makeRandomHost(port1)
+	h2 := makeRandomHost(port2)
+	h1.Peerstore().AddAddrs(h2.ID(), h2.Addrs(), ps.PermanentAddrTTL)
+	h2.Peerstore().AddAddrs(h1.ID(), h1.Addrs(), ps.PermanentAddrTTL)
+
+	log.Printf("This is a conversation between %s and %s\n", h1.ID(), h2.ID())
+
+	// Define a stream handler for host number 2
+	h2.SetStreamHandler(proto, func(stream inet.Stream) {
+		log.Printf("%s: Received a stream", h2.ID())
+		wrappedStream := WrapStream(stream)
+		defer stream.Close()
+		handleStream(wrappedStream)
+	})
+
+	// Create new stream from h1 to h2 and start the conversation
+	stream, err := h1.NewStream(context.Background(), h2.ID(), proto)
+	if err != nil {
+		log.Fatal(err)
+	}
+	wrappedStream := WrapStream(stream)
+	// This sends the first message
+	sendMessage(0, wrappedStream)
+	// We keep the conversation on the created stream so we launch
+	// this to handle any responses
+	handleStream(wrappedStream)
+	// When we are done, close the stream on our side and exit.
+	stream.Close()
+}
+
+// receiveMessage reads and decodes a message from the stream
+func receiveMessage(ws *WrappedStream) (*Message, error) {
+	var msg Message
+	err := ws.dec.Decode(&msg)
+	if err != nil {
+		return nil, err
+	}
+	return &msg, nil
+}
+
+// sendMessage encodes and writes a message to the stream
+func sendMessage(index int, ws *WrappedStream) error {
+	msg := &Message{
+		Msg:    conversationMsgs[index],
+		Index:  index,
+		HangUp: index >= len(conversationMsgs)-1,
+	}
+
+	err := ws.enc.Encode(msg)
+	// Because output is buffered with bufio, we need to flush!
+	ws.w.Flush()
+	return err
+}
+
+// handleStream is a for loop which receives and then sends a message
+// an artificial delay of 500ms happens in-between.
+// When Message.HangUp is true, it exists. This will close the stream
+// on one of the sides. The other side's receiveMessage() will error
+// with EOF, thus also breaking out from the loop.
+func handleStream(ws *WrappedStream) {
+	for {
+		// Read
+		msg, err := receiveMessage(ws)
+		if err != nil {
+			break
+		}
+		pid := ws.stream.Conn().LocalPeer()
+		log.Printf("%s says: %s\n", pid, msg.Msg)
+		time.Sleep(500 * time.Millisecond)
+		if msg.HangUp {
+			break
+		}
+		// Send response
+		err = sendMessage(msg.Index+1, ws)
+		if err != nil {
+			break
+		}
+	}
+}