examples: example using swarm and raw tcp (no muxing)

examples/justtcp/README.md

+# libp2p 'just tcp' example
+
+## What this does
+This example starts up a libp2p swarm that listens for tcp connections behind a
+multistream muxer protocol of `/plaintext/1.0.0`. All connections made to it
+will be echoed back.
+
+## Building
+```
+$ go build
+```
+
+## Usage
+```
+$ ./justtcp
+```

examples/justtcp/main.go

+package main
+
+import (
+	"context"
+	"fmt"
+	"net"
+	"os"
+
+	transport "github.com/ipfs/go-libp2p-transport"
+	ma "github.com/jbenet/go-multiaddr"
+	smux "github.com/jbenet/go-stream-muxer"
+	"github.com/libp2p/go-libp2p/p2p/net/swarm"
+)
+
+func fatal(i interface{}) {
+	fmt.Println(i)
+	os.Exit(1)
+}
+
+type NullMux struct{}
+
+type NullMuxConn struct {
+	net.Conn
+}
+
+func (c *NullMuxConn) AcceptStream() (smux.Stream, error) {
+	panic("We don't do this")
+}
+
+func (c *NullMuxConn) IsClosed() bool {
+	return false
+}
+
+func (c *NullMuxConn) OpenStream() (smux.Stream, error) {
+	panic("if only you could see how disappointed i am in you right now")
+}
+
+func (c *NullMuxConn) Serve(_ smux.StreamHandler) {
+}
+
+func (nm NullMux) NewConn(c net.Conn, server bool) (smux.Conn, error) {
+	return &NullMuxConn{c}, nil
+}
+
+var _ smux.Transport = (*NullMux)(nil)
+
+func main() {
+	laddr, err := ma.NewMultiaddr("/ip4/0.0.0.0/tcp/5555")
+	if err != nil {
+		fatal(err)
+	}
+
+	swarm.PSTransport = new(NullMux)
+
+	s := swarm.NewBlankSwarm(context.Background(), "bob", nil)
+
+	s.AddTransport(transport.NewTCPTransport())
+
+	err = s.AddListenAddr(laddr)
+	if err != nil {
+		fatal(err)
+	}
+
+	s.SetConnHandler(func(c *swarm.Conn) {
+		fmt.Println("CALLED OUR CONN HANDLER!")
+		defer c.Close()
+		buf := make([]byte, 1024)
+		for {
+			n, err := c.RawConn().Read(buf)
+			if err != nil {
+				fmt.Println(err)
+				return
+			}
+			fmt.Printf("read: %q\n", string(buf[:n]))
+
+			_, err = c.RawConn().Write(buf[:n])
+			if err != nil {
+				fmt.Println(err)
+				return
+			}
+		}
+	})
+
+	<-make(chan bool)
+}