examples: add classic network snake test example

Adding this example to test multiple concurrent socket connections.

examples/net/snake/init.go

@@ -0,0 +1,30 @@
+//go:build ninafw || wioterminal
+
+package main
+
+import (
+	"log"
+	"time"
+
+	"tinygo.org/x/drivers/netlink"
+	"tinygo.org/x/drivers/netlink/probe"
+)
+
+var (
+	ssid string
+	pass string
+)
+
+func init() {
+	time.Sleep(2 * time.Second)
+
+	link, _ := probe.Probe()
+
+	err := link.NetConnect(&netlink.ConnectParams{
+		Ssid:       ssid,
+		Passphrase: pass,
+	})
+	if err != nil {
+		log.Fatal(err)
+	}
+}

examples/net/snake/main.go

@@ -0,0 +1,120 @@
+// This example is the classic snake network test.  The snake is feed a steady
+// diet of pkts and the pkts work themselves thru the snake segments and exit
+// the tail.  Each snake segment is a TCP socket connection to a server.  The
+// server echos pkts received back to the snake, and serves each segment on a
+// different port.  (See server/main.go for server).
+//
+//                snake     |    server
+//                          |
+//            head ----->---|-->--+
+//             seg a        |     |
+//                    +---<-|--<--+
+//                    |     |
+//                    +-->--|-->--+
+//             seg b        |     |
+//                    +---<-|--<--+
+//                    |     |
+//                    +-->--|-->--+
+//             seg c        |     |
+//                    +---<-|--<--+
+//                    |     |
+//                    +-->--|-->--+
+//              ...         |     |
+//                    +---<-|--<--+
+//                    |     |
+//                    +-->--|-->--+
+//             seg n        |     |
+//            tail -------<-|--<--+
+//                          |
+
+// The snake segments are linked by channels and each segment is run as a go
+// func.  This forces segments to connect and run concurrently, which is a good
+// test of the underlying driver's ability to handle concurrent connections.
+
+//go:build ninafw || wioterminal
+
+package main
+
+import (
+	_ "embed"
+	"fmt"
+	"log"
+	"net"
+	"strings"
+	"time"
+)
+
+//go:embed main.go
+var code string
+
+var (
+	server string = "10.0.0.100:8080"
+)
+
+func segment(in chan []byte, out chan []byte) {
+	var buf [512]byte
+	for {
+		c, err := net.Dial("tcp", server)
+		for ; err != nil; c, err = net.Dial("tcp", server) {
+			println(err.Error())
+			time.Sleep(5 * time.Second)
+		}
+		for {
+			select {
+			case msg := <-in:
+				_, err := c.Write(msg)
+				if err != nil {
+					log.Fatal(err.Error())
+				}
+				time.Sleep(100 * time.Millisecond)
+				n, err := c.Read(buf[:])
+				if err != nil {
+					log.Fatal(err.Error())
+				}
+				out <- buf[:n]
+			}
+		}
+	}
+}
+
+func feedit(head chan []byte) {
+	for i := 0; i < 100; i++ {
+		head <- []byte(fmt.Sprintf("\n---%d---\n", i))
+		for _, line := range strings.Split(code, "\n") {
+			if len(line) == 0 {
+				line = " "
+			}
+			head <- []byte(line)
+		}
+	}
+}
+
+var head = make(chan []byte)
+var a = make(chan []byte)
+var b = make(chan []byte)
+var c = make(chan []byte)
+var d = make(chan []byte)
+var e = make(chan []byte)
+var f = make(chan []byte)
+var tail = make(chan []byte)
+
+func main() {
+
+	// The snake
+	go segment(head, a)
+	go segment(a, b)
+	go segment(b, c)
+	go segment(c, d)
+	go segment(d, e)
+	go segment(e, f)
+	go segment(f, tail)
+
+	go feedit(head)
+
+	for {
+		select {
+		case msg := <-tail:
+			println(string(msg))
+		}
+	}
+}

examples/net/snake/server/main.go

@@ -0,0 +1,34 @@
+package main
+
+import (
+	"io"
+	"log"
+	"net"
+)
+
+func main() {
+	// Listen for connections
+	l, err := net.Listen("tcp", ":8080")
+	if err != nil {
+		log.Fatal(err.Error())
+	}
+	defer l.Close()
+	println("Listening on port", ":8080")
+	for {
+		// Wait for a connection
+		conn, err := l.Accept()
+		if err != nil {
+			log.Fatal(err)
+		}
+		println("Accepted connection from", conn.RemoteAddr().String())
+		// Service the new connection in a goroutine.
+		// The loop then returns to accepting, so that
+		// multiple connections may be served concurrently
+		go func(c net.Conn) {
+			// Echo all incoming data
+			io.Copy(c, c)
+			// Shut down the connection
+			c.Close()
+		}(conn)
+	}
+}