/
scan.go
173 lines (147 loc) · 3.24 KB
/
scan.go
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package lan
import (
"context"
"encoding/binary"
"fmt"
"net"
"sync"
"time"
"github.com/MarcPer/lanchat/logger"
)
type NetScanner interface {
FindHost(int) (string, bool)
}
type NullScanner struct{}
func (s *NullScanner) FindHost(port int) (string, bool) {
return "", false
}
type DefaultScanner struct {
Local bool
}
func (s *DefaultScanner) FindHost(port int) (string, bool) {
targets, err := findTargets()
if err != nil {
logger.Errorf("FindHost: %v\n", err)
return "", false
}
hosts := hostRange(targets)
return s.scanHost(hosts, port)
}
type targetRange struct {
selfIP string // IP from caller, to exclude from scan
netIP string // IPNet network in CIDR notation
}
// Returns list of target IP ranges to scan
func findTargets() ([]targetRange, error) {
out := make([]targetRange, 0, 4)
ifcs, err := net.Interfaces()
if err != nil {
return out, err
}
for _, ifc := range ifcs {
addrs, err := ifc.Addrs()
if err != nil {
return out, err
}
for _, address := range addrs {
if ipnet, ok := address.(*net.IPNet); ok && !ipnet.IP.IsLoopback() {
if ipnet.IP.To4() != nil {
t := targetRange{ipnet.IP.String(), ipnet.String()}
out = append(out, t)
return out, nil
}
}
}
}
return out, nil
}
func hostRange(targets []targetRange) []string {
var hosts []string
for _, t := range targets {
_, ipv4Net, err := net.ParseCIDR(t.netIP)
if err != nil {
logger.Errorf("hostRange: %v\n", err)
return []string{}
}
mask := binary.BigEndian.Uint32(ipv4Net.Mask)
start := binary.BigEndian.Uint32(ipv4Net.IP)
finish := (start & mask) | (mask ^ 0xffffffff)
for i := start + 1; i <= finish-1; i++ {
ip := make(net.IP, 4)
binary.BigEndian.PutUint32(ip, i)
if ip.String() == t.selfIP {
continue
}
hosts = append(hosts, ip.String())
}
}
return hosts
}
func (s *DefaultScanner) scanHost(ips []string, chatPort int) (string, bool) {
if s.Local {
url := fmt.Sprintf("%s:%d", "127.0.0.1", chatPort)
logger.Debugf("scanning %s\n", url)
conn, err := net.DialTimeout("tcp", url, 100*time.Millisecond)
if err == nil {
conn.Close()
return url, true
}
}
if len(ips) < 1 {
logger.Infof("No hosts to scan\n")
return "", false
}
hostInCh := make(chan string)
logger.Debugf("Scanning %d hosts\n", len(ips))
go func() {
for _, host := range ips {
hostInCh <- host
}
close(hostInCh)
}()
ctx, cancel := context.WithCancel(context.Background())
resCh := make(chan string)
wg.Add(numWorkers)
for i := 0; i < numWorkers; i++ {
go popScan(ctx, chatPort, hostInCh, resCh)
}
done := make(chan bool)
go func() {
wg.Wait()
done <- true
}()
select {
case url := <-resCh:
cancel()
return url, true
case <-done:
cancel()
return "", false
}
}
var wg sync.WaitGroup
const numWorkers = 10
const timeout = 100 * time.Millisecond
func popScan(ctx context.Context, chatPort int, in chan string, out chan string) {
for {
select {
case <-ctx.Done():
wg.Done()
return
case host, ok := <-in:
if !ok {
wg.Done()
return
}
url := fmt.Sprintf("%s:%d", host, chatPort)
logger.Debugf("scanning %s", url)
conn, err := net.DialTimeout("tcp", url, timeout)
if err == nil {
conn.Close()
out <- url
wg.Done()
return
}
}
}
}