add gvisor-mwe and add binary sizes to README

examples/_import_examples/gvisor-mwe/main.go

@@ -0,0 +1,93 @@
+package main
+
+import (
+	"context"
+	"fmt"
+	"net"
+	"net/netip"
+	"os"
+	"syscall"
+	"time"
+
+	gnet "github.com/usbarmory/go-net"
+)
+
+const pollTime = 5 * time.Millisecond
+
+var networkDevice NetworkDevice
+
+// NetworkDevice implements gnet.NetworkDevice for bridging with raw Ethernet I/O.
+type NetworkDevice struct {
+	send func([]byte) error
+	recv func([]byte) (int, error)
+}
+
+func (d *NetworkDevice) Transmit(buf []byte) error        { return d.send(buf) }
+func (d *NetworkDevice) Receive(buf []byte) (int, error)   { return d.recv(buf) }
+
+func main() {
+	ctx := context.Background()
+	if err := run(ctx); err != nil {
+		fmt.Println(err)
+		os.Exit(1)
+	}
+}
+
+func run(ctx context.Context) error {
+	// Create gVisor-based networking stack.
+	stack := gnet.NewGVisorStack(1)
+
+	// Configure stack with MAC, IP prefix, and gateway.
+	err := stack.Configure(
+		"aa:bb:cc:dd:ee:ff",
+		netip.MustParsePrefix("192.168.1.10/24"),
+		netip.MustParseAddr("192.168.1.1"),
+	)
+	if err != nil {
+		return fmt.Errorf("configuring stack: %w", err)
+	}
+
+	err = stack.EnableICMP()
+	if err != nil {
+		return fmt.Errorf("enabling ICMP: %w", err)
+	}
+
+	// Bridge the stack with a network device for packet I/O.
+	iface := &gnet.Interface{
+		Stack:         stack,
+		NetworkDevice: &networkDevice,
+		HandleStackErr: func(err error, tx bool) {
+			dir := "rx"
+			if tx {
+				dir = "tx"
+			}
+			fmt.Printf("stack %s err: %v\n", dir, err)
+		},
+	}
+	// Start the packet processing loop in a goroutine.
+	go iface.Start()
+
+	// Create a TCP listener on port 80 using the gVisor stack.
+	const sockStream = 0x1
+	laddr := net.TCPAddrFromAddrPort(netip.AddrPortFrom(netip.MustParseAddr("192.168.1.10"), 80))
+	c, err := stack.Socket(ctx, "tcp", syscall.AF_INET, sockStream, laddr, nil)
+	if err != nil {
+		return fmt.Errorf("creating AF_INET stream socket: %w", err)
+	}
+	listener := c.(net.Listener)
+	for ctx.Err() == nil {
+		time.Sleep(pollTime)
+		conn, err := listener.Accept()
+		if err != nil {
+			fmt.Println("conn failed:", err)
+			continue
+		}
+		go handleConn(conn)
+	}
+	return nil
+}
+
+func handleConn(conn net.Conn) {
+	defer conn.Close()
+	conn.Write([]byte("Hello from gVisor stack!"))
+}