Add initial code

README.md

@@ -1 +1,10 @@
 # tcp-port-scanner
+
+To do a port scan on a host, provide the host's domain name or ip.
+
+```shell
+go run main.go --host 'localhost'
+```
+
+This code is based upon the examples in:
+[Black Hat Go](https://nostarch.com/blackhatgo)

main.go

@@ -0,0 +1,57 @@
+package main
+
+import (
+	"flag"
+	"fmt"
+	"net"
+	"sort"
+)
+
+var hostname string
+
+func init() {
+	flag.StringVar(&hostname, "host", "", "the host to be scanned (i.e. localhost)")
+}
+
+func worker(ports, results chan int) {
+	for p := range ports {
+		address := fmt.Sprintf("%s:%d", hostname, p)
+		conn, err := net.Dial("tcp", address)
+		if err != nil {
+			results <- 0
+			continue
+		}
+		conn.Close()
+		results <- p
+	}
+}
+
+func main() {
+	ports := make(chan int, 1000)
+	results := make(chan int)
+	var openports []int
+
+	for i := 0; i < cap(ports); i++ {
+		go worker(ports, results)
+	}
+
+	go func() {
+		for i := 1; i <= 65535; i++ {
+			ports <- i
+		}
+	}()
+
+	for i := 0; i < 65535; i++ {
+		port := <-results
+		if port != 0 {
+			openports = append(openports, port)
+		}
+	}
+
+	close(ports)
+	close(results)
+	sort.Ints(openports)
+	for _, port := range openports {
+		fmt.Printf("%d open\n", port)
+	}
+}