added client Makefile

client/golang/Makefile

@@ -0,0 +1,2 @@
+build:
+	go build -ldflags="-s -w" -o saprus client.go

client/golang/client.go

@@ -0,0 +1,109 @@
+package main
+
+import (
+	"encoding/base64"
+	"encoding/binary"
+	"errors"
+	"fmt"
+	"net"
+	"strings"
+	"time"
+
+	"github.com/google/gopacket"
+	"github.com/google/gopacket/pcap"
+)
+
+func errCheck(err error) {
+	if err != nil {
+		panic(err)
+	}
+	return
+}
+
+func listenDiscoverResponse(addrChan chan string, readyFlag chan int) {
+	handle, err := pcap.OpenLive("any", int32(1600), true, pcap.BlockForever)
+	errCheck(err)
+
+	err = handle.SetBPFFilter("udp and port 8850")
+	errCheck(err)
+
+	packets := gopacket.NewPacketSource(handle, handle.LinkType()).Packets()
+
+	readyFlag <- 1
+
+	for pkt := range packets {
+		msg, err := base64.StdEncoding.DecodeString(string(pkt.ApplicationLayer().Payload()))
+		if err == nil {
+			if strings.Contains(string(msg), "clientapi") {
+				addrChan <- string(msg)
+				return
+			}
+		}
+	}
+
+	return
+}
+
+func toMaxHost(n *net.IPNet) (net.IP, error) {
+	if n.IP.To4() == nil {
+		return net.IP{}, errors.New("IP address is not IPv4")
+	}
+
+	ip := make(net.IP, len(n.IP.To4()))
+	binary.BigEndian.PutUint32(ip,
+		binary.BigEndian.Uint32(n.IP.To4())|^binary.BigEndian.Uint32(net.IP(n.Mask).To4()))
+
+	return ip, nil
+}
+
+func bcastAddresses() []string {
+	var addrs []string = nil
+	interfaceInfo, _ := net.Interfaces()
+	for i := 0; i < len(interfaceInfo); i++ {
+		addr, err := interfaceInfo[i].Addrs()
+		errCheck(err)
+		for j := 0; j < len(addr); j++ {
+			_, ipNet, _ := net.ParseCIDR(addr[j].String())
+			bcast, err := toMaxHost(ipNet)
+
+			if err != nil {
+			} else {
+				addrs = append(addrs, bcast.String())
+			}
+		}
+	}
+
+	return addrs
+}
+
+func main() {
+	sendAddrs := bcastAddresses()
+
+	addrChan := make(chan string)
+	readyFlag := make(chan int)
+
+	go listenDiscoverResponse(addrChan, readyFlag)
+
+	// Wait for device to listen
+	<- readyFlag
+
+	for i := 0; i < len(sendAddrs); i++ {
+		remoteAddr := sendAddrs[i] + ":8888"
+		remote, err := net.ResolveUDPAddr("udp4", remoteAddr)
+		errCheck(err)
+		conn, err := net.DialUDP("udp4", nil, remote)
+		errCheck(err)
+		defer conn.Close()
+
+		_, err = conn.Write([]byte(conn.LocalAddr().String() + "here"))
+		errCheck(err)
+	}
+
+	// Listen timeout
+	select {
+		case returnMSG := <- addrChan:
+			fmt.Printf("%s\n", strings.Fields(returnMSG)[1])
+		case <- time.After(5 * time.Second):
+			fmt.Printf("error\n")
+	}
+}

client/golang/go.mod

@@ -0,0 +1,7 @@
+module client
+
+go 1.18
+
+require github.com/google/gopacket v1.1.19
+
+require golang.org/x/sys v0.0.0-20190412213103-97732733099d // indirect