command-line.go

// Command line parsing using go's standard flag library.
package main

import (
	"flag"
	"fmt"
	"os"
	"strconv"
	"strings"
	"time"
)

// Command line parameter
var hostname = flag.String(
	"hostname",
	"",
	"hostname of the target system")
var timeoutSeconds = flag.Float64(
	"timeout",
	1.0,
	"Timeout in seconds. Fractional values, e.g. 0.5 are allowed")
var parallel = flag.Int(
	"parallel",
	1,
	"Maximum number of parallel connections")
var port = flag.String(
	"port",
	"",
	"a single port (80) or a single range (80-1024)")

// Set after command line parsing.
var timeout time.Duration
var portList []int

func parseCommandLine() {
	flag.Usage = func() {
		fmt.Println("A simple port scanner in go.")
		flag.PrintDefaults()
		os.Exit(1)
	}
	flag.Parse()

	// Check that mandatory arguments are defined.
	if *hostname == "" || *port == "" {
		flag.Usage()
	}
	// Special handling for ports to determine if a range is set.
	if strings.Contains(*port, "-") {
		ps := strings.Split(*port, "-")
		start, err := strconv.Atoi(ps[0])
		if err != nil {
			flag.Usage()
		}
		end, err := strconv.Atoi(ps[1])
		if err != nil {
			flag.Usage()
		}
		portList = make([]int, end-start+1)
		for i := 0; i < len(portList); i++ {
			portList[i] = start + i
		}
	} else {
		// Single port.
		sp, err := strconv.Atoi(*port)
		if err != nil {
			flag.Usage()
		}
		portList = make([]int, 1)
		portList[0] = sp
	}

	// Convert timeout from fractional seconds to time.Duration.
	var ms = int(*timeoutSeconds * 1000)
	timeout = time.Duration(ms) * time.Millisecond
}