From 0c4ce72a0ae47f33a9a4d48c1a192f6983b1b247 Mon Sep 17 00:00:00 2001
From: Alexander Sagen <alexander@sagen.me>
Date: Mon, 22 Apr 2019 01:10:20 +0200
Subject: [PATCH] Add code

---
 main.go | 161 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 161 insertions(+)
 create mode 100644 main.go

diff --git a/main.go b/main.go
new file mode 100644
index 0000000..0887034
--- /dev/null
+++ b/main.go
@@ -0,0 +1,161 @@
+package main
+
+import (
+	"flag"
+	"fmt"
+	"math/rand"
+	"net"
+	"strconv"
+	"strings"
+	"time"
+)
+
+func main() {
+	var err error
+	var laddr, raddr net.Addr
+	var conn net.Conn
+	var ports []int
+	var sleep time.Duration
+
+	knockType := flag.String("t", "seed", "knock type (seed/seq)")
+	seed := flag.Int64("s", 0, "port generation seed, used when t=seed")
+	count := flag.Int("c", 1, "port count, used when t=seed")
+	offset := flag.Int("o", 30000, "port offset, used when t=seed")
+	seq := flag.String("q", "", "comma-separated custom port sequence, used when t=seq")
+	proto := flag.String("p", "udp", "protocol (tcp/tcp4/tcp6/udp/udp4/udp6)")
+	local := flag.String("l", "", "local address")
+	remote := flag.String("r", "", "remote address")
+	interval := flag.String("i", "", "loop interval")
+	verbose := flag.Bool("v", false, "verbose")
+	flag.Parse()
+
+	// get ports
+	switch *knockType {
+	case "seed":
+		if *count < 1 {
+			fmt.Println("port sequence empty")
+			return
+		}
+		if *offset < 0 || *offset > 65535 {
+			fmt.Println("offset should be between 0 and 65535")
+			return
+		}
+		rand.Seed(*seed)
+		ports = make([]int, *count)
+		for i := 0; i < *count; i++ {
+			ports[i] = *offset + rand.Intn(65535-*offset)
+		}
+	case "seq":
+		parts := strings.Split(*seq, ",")
+		for _, part := range parts {
+			port, err := strconv.Atoi(part)
+			if err != nil {
+				fmt.Printf("invalid port \"%s\": %v\n", part, err)
+				return
+			}
+			ports = append(ports, port)
+		}
+	default:
+		fmt.Println("invalid knock type")
+		return
+	}
+
+	if len(ports) == 0 {
+		fmt.Println("port sequence empty")
+		return
+	}
+
+	// print ports
+	if *verbose {
+		fmt.Printf("ports: ")
+		for i := 0; i < len(ports); i++ {
+			portstr := strconv.Itoa(ports[i])
+			if len(portstr) < 6 {
+				portstr += strings.Repeat(" ", 6-len(portstr))
+			}
+			fmt.Printf("%s", portstr)
+		}
+		fmt.Printf("\n")
+	}
+
+	// get protocol, resolve addresses
+	switch *proto {
+	case "tcp", "tcp4", "tcp6":
+		if laddr, err = net.ResolveTCPAddr(*proto, *local+":0"); err != nil {
+			fmt.Println(err)
+			return
+		}
+		if raddr, err = net.ResolveTCPAddr(*proto, *remote+":0"); err != nil {
+			fmt.Println(err)
+			return
+		}
+		if raddr.(*net.TCPAddr).IP == nil {
+			fmt.Println("unable to resolve remote IP")
+			return
+		}
+	case "udp", "udp4", "udp6":
+		if laddr, err = net.ResolveUDPAddr(*proto, *local+":0"); err != nil {
+			fmt.Println(err)
+			return
+		}
+		if raddr, err = net.ResolveUDPAddr(*proto, *remote+":0"); err != nil {
+			fmt.Println(err)
+			return
+		}
+		if raddr.(*net.UDPAddr).IP == nil {
+			fmt.Println("unable to resolve remote IP")
+			return
+		}
+	default:
+		fmt.Println("invalid protocol")
+	}
+
+	// get sleep interval
+	if *interval != "" {
+		if sleep, err = time.ParseDuration(*interval); err != nil {
+			fmt.Println(err)
+			return
+		}
+	}
+
+	for {
+		if *verbose {
+			fmt.Printf("knock: ")
+		}
+		for i := 0; i < len(ports); i++ {
+			switch v := raddr.(type) {
+			case *net.TCPAddr:
+				v.Port = ports[i]
+				if conn, err = net.DialTCP(*proto, laddr.(*net.TCPAddr), v); err != nil {
+					fmt.Println("dial fail")
+					return
+				}
+			case *net.UDPAddr:
+				v.Port = ports[i]
+				if conn, err = net.DialUDP(*proto, laddr.(*net.UDPAddr), v); err != nil {
+					fmt.Println("dial fail")
+					return
+				}
+			}
+			if _, err = conn.Write([]byte{}); err != nil {
+				fmt.Println("tx fail")
+				return
+			}
+			if err = conn.Close(); err != nil {
+				fmt.Println("close fail")
+				return
+			}
+			if *verbose {
+				fmt.Printf("ok    ")
+			}
+			time.Sleep(100 * time.Millisecond)
+		}
+		if *verbose {
+			fmt.Printf("\n")
+		}
+		if sleep == 0 {
+			break
+		}
+		time.Sleep(sleep)
+	}
+}