ftpanon.go

package main

import (
	"bufio"
	"flag"
	"fmt"
	"net"
	"os"
	"regexp"
	"strconv"
	"strings"
	"time"
)

var (
	reIP     = regexp.MustCompile("\\d+\\.\\d+\\.\\d+\\.\\d+")
	_workers uint
	_timeout uint
)

func readFTP(c net.Conn, buf []byte, timeout time.Duration) (int, string, error) {
	c.SetReadDeadline(time.Now().Add(time.Second * timeout))
	n, err := c.Read(buf)
	if err != nil || n < 5 {
		return 0, "", err
	}
	resp := string(buf[:n-2])
	code, err := strconv.Atoi(resp[:3])
	if err != nil {
		return 0, "", err
	}
	msg := strings.TrimSpace(resp[3:])
	return code, msg, nil
}

func tryFTPLogin(target string, timeout time.Duration) bool {
	buf := make([]byte, 8*1024)

	c, err := net.DialTimeout("tcp", target, timeout)
	if err != nil {
		return false
	}
	defer c.Close()
	if code, _, err := readFTP(c, buf, timeout); err != nil || code != 220 {
		return false
	}

	c.Write([]byte("USER anonymous\r\n"))
	if code, _, err := readFTP(c, buf, timeout); err != nil || code != 331 {
		return false
	}

	c.Write([]byte("PASS anonymous\r\n"))
	if code, _, err := readFTP(c, buf, timeout); err != nil || code != 230 {
		return false
	}

	c.Write([]byte("QUIT\r\n"))
	return true
}

func check(hosts <-chan string, results chan<- string) {
	timeout := time.Second * time.Duration(_timeout)
	for host := range hosts {
		if tryFTPLogin(fmt.Sprintf("%s:%d", host, 21), timeout) {
			results <- host
		} else {
			results <- ""
		}
	}
}

func init() {
	flag.UintVar(&_workers, "w", 100, "number of concurrent workers")
	flag.UintVar(&_timeout, "t", 2, "timeout in seconds")
	flag.Parse()
}

func main() {
	hosts := make(chan string, 100)
	results := make(chan string, 100)

	var i uint
	for i = 0; i < _workers; i++ {
		go check(hosts, results)
	}

	var nhosts uint
	go func() {
		bin := bufio.NewScanner(os.Stdin)
		for bin.Scan() {
			line := bin.Text()
			m := reIP.FindAllString(line, -1)
			if m == nil {
				continue
			}
			nhosts++
			hosts <- m[0]
		}
		close(hosts)
	}()

	for {
		host := <-results
		nhosts--
		if host != "" {
			fmt.Println(host)
		}
		if nhosts == 0 {
			break
		}
	}
}