Improve echo example:

  * Extended explanations and links to relevant godocs
  * Some renames (the host is not dummy, it's a basic)
  * Use addAddr() and let NewStream open the connection

License: MIT
Signed-off-by: Hector Sanjuan <hector@protocol.ai>

examples/echo/README.md

 # Echo client/server with libp2p
 
-This example can be started in either listen mode (server), or dial mode (client).
+This is an example that quickly shows how to use the `go-libp2p` stack,
+including Host/Basichost, Network/Swarm, Streams, Peerstores and
+Multiaddresses.
 
-In listen mode, it will sit and wait for incoming connections on
-the `/echo/1.0.0` protocol. Whenever it receives a stream, it will
-write whatever message it received, and close the stream.
+This example can be started in either listen mode, or dial mode.
 
-In dial mode, it will connect to the target peer on the given address.
-It then opens a stream, writes a short message on the same protocol,
-and print whatever reply it receives.
+In listen mode, it will sit and wait for incoming connections on the
+`/echo/1.0.0` protocol. Whenever it receives a stream, it will write the
+message "Hello, world!" over the stream and close it.
+
+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 `/echo/1.0.0`.
 
 ## Build
 
+From `go-libp2p` base folder:
+
 ```
 > make deps
 > go build ./examples/hosts
@@ -22,20 +27,68 @@ and print whatever reply it receives.
 In one terminal:
 
 ```
-> ./hosts -l 4737
-2016/11/06 04:37:00 I am /ip4/127.0.0.1/tcp/4737/ipfs/QmXzbaXtBw6mU29WoeYrCtcRLVbT8asWCcEFVuDy4w6pdq
-2016/11/06 04:37:00 listening for connections
-2016/11/06 04:37:01 got a new stream
-2016/11/06 04:37:01 read request: "Hello, world!"
+> ./hosts -l 1235
+2016/11/10 10:45:37 I am /ip4/127.0.0.1/tcp/1234/ipfs/QmNtX1cvrm2K6mQmMEaMxAuB4rTexhd87vpYVot4sEZzxc
+2016/11/10 10:45:37 listening for connections
 ```
 
-In another, copy the address printed by the listener and do:
+The listener libp2p host will print its `Multiaddress`, which indicates how it
+can be reached (ip4+tcp) and its randomly generated ID (`QmNtX1cv...`)
+
+Now, launch another node that talks to the listener:
 
 ```
-> ./hosts -d /ip4/127.0.0.1/tcp/4737/ipfs/QmXzbaXtBw6mU29WoeYrCtcRLVbT8asWCcEFVuDy4w6pdq
-2016/11/06 04:37:01 I am /ip4/127.0.0.1/tcp/0/ipfs/QmeMNYMmkgoyd8M7y925r4yVVDjKtiYtU4rNCyj7wDWzk1
-2016/11/06 04:37:01 connecting to target
-2016/11/06 04:37:01 opening stream
-2016/11/06 04:37:01 read reply: "Hello, world!"
->
+> ./hosts -d /ip4/127.0.0.1/tcp/1234/ipfs/QmNtX1cvrm2K6mQmMEaMxAuB4rTexhd87vpYVot4sEZzxc -l 1236
 ```
+
+
+The new node with send the message `Hello, world!` to the
+listener, which will in turn echo it over the stream and close it. The
+listener logs the message, and the sender logs the response.
+
+
+## Details
+
+The `makeBasicHost()` function creates a
+[go-libp2p-basichost](https://godoc.org/github.com/libp2p/go-libp2p/p2p/host/basic)
+object. `basichost` objects wrap
+[go-libp2 swarms](https://godoc.org/github.com/libp2p/go-libp2p-swarm#Swarm)
+and should be used preferentially. A
+[go-libp2p-swarm Network](https://godoc.org/github.com/libp2p/go-libp2p-swarm#Network)
+is a `swarm` which complies to the
+[go-libp2p-net Network interface](https://godoc.org/github.com/libp2p/go-libp2p-net#Network)
+and takes care of maintaining streams, connections, multiplexing different
+protocols on them, handling incoming connections etc.
+
+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`.
+  * 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:
+    `/ip4/127.0.0.1/tcp/1234`.
+  * A
+    [go-libp2p-peerstore](https://godoc.org/github.com/libp2p/go-libp2p-peerstore),
+    which is used as a address book which matches node IDs to the
+    multiaddresses through which they can be contacted. This peerstore gets
+    autopopulated when manually opening a connection (with
+    [`Connect()`](https://godoc.org/github.com/libp2p/go-libp2p/p2p/host/basic#BasicHost.Connect). Alternatively,
+    we can manually
+    [`AddAddr()`](https://godoc.org/github.com/libp2p/go-libp2p-peerstore#AddrManager.AddAddr)
+    as in the example.
+
+A `basichost` can now open streams (bi-directional channel between to peers)
+using
+[NewStream](https://godoc.org/github.com/libp2p/go-libp2p/p2p/host/basic#BasicHost.NewStream)
+and use them to send and receive data tagged with a `Protocol.ID` (a
+string). The host can also listen for incoming connections for a given
+`Protocol` with
+[`SetStreamHandle()`](https://godoc.org/github.com/libp2p/go-libp2p/p2p/host/basic#BasicHost.SetStreamHandler).
+
+The example makes use of all of this to enable communication between a
+listener and a sender using protocol `/echo/1.0.0` (which could be any other thing).

examples/echo/main.go

@@ -8,20 +8,22 @@ import (
 	"log"
 	"strings"
 
-	bhost "github.com/libp2p/go-libp2p/p2p/host/basic"
-
+	golog "github.com/ipfs/go-log"
 	host "github.com/libp2p/go-libp2p-host"
 	inet "github.com/libp2p/go-libp2p-net"
 	net "github.com/libp2p/go-libp2p-net"
 	peer "github.com/libp2p/go-libp2p-peer"
+	peerstore "github.com/libp2p/go-libp2p-peerstore"
 	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"
 )
 
 // create a 'Host' with a random peer to listen on the given address
-func makeDummyHost(listen string, secio bool) (host.Host, error) {
+func makeBasicHost(listen string, secio bool) (host.Host, error) {
 	addr, err := ma.NewMultiaddr(listen)
 	if err != nil {
 		return nil, err
@@ -61,30 +63,36 @@ func makeDummyHost(listen string, secio bool) (host.Host, error) {
 }
 
 func main() {
+	golog.SetAllLoggers(gologging.INFO) // Change to DEBUG for extra info
 	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 := makeDummyHost(listenaddr, *secio)
+	ha, err := makeBasicHost(listenaddr, *secio)
 	if err != nil {
 		log.Fatal(err)
 	}
 
 	// Set a stream handler on host A
 	ha.SetStreamHandler("/echo/1.0.0", func(s net.Stream) {
-		log.Println("got a new stream")
-		doEcho(s)
+		log.Println("Got a new stream!")
 		defer s.Close()
+		doEcho(s)
 	})
 
 	if *target == "" {
 		log.Println("listening for connections")
 		select {} // hang forever
 	}
+	// This is where the listener code ends
 
 	ipfsaddr, err := ma.NewMultiaddr(*target)
 	if err != nil {
@@ -102,25 +110,19 @@ func main() {
 	}
 
 	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)
 	}
 
-	pi := pstore.PeerInfo{
-		ID:    peerid,
-		Addrs: []ma.Multiaddr{tptmaddr},
-	}
-
-	log.Println("connecting to target")
-	err = ha.Connect(context.Background(), pi)
-	if err != nil {
-		log.Fatalln(err)
-	}
+	// We need to add the target to our peerstore, so we know how we can
+	// contact it
+	ha.Peerstore().AddAddr(peerid, tptmaddr, 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
+	// it should be handled on host A by the handler we set above
 	s, err := ha.NewStream(context.Background(), peerid, "/echo/1.0.0")
 	if err != nil {
 		log.Fatalln(err)
@@ -139,6 +141,8 @@ func main() {
 	log.Printf("read reply: %q\n", out)
 }
 
+// doEcho reads some data from a stream, writes it back and closes the
+// stream.
 func doEcho(s inet.Stream) {
 	buf := make([]byte, 1024)
 	n, err := s.Read(buf)