Improve captive portal handling

netenv/environment_windows.go

@@ -1,13 +1,95 @@
 package netenv
 
-import "net"
+import (
+	"bufio"
+	"bytes"
+	"context"
+	"net"
+	"os/exec"
+	"strings"
+	"sync"
+	"time"
+
+	"github.com/safing/portbase/log"
+)
+
+const (
+	nameserversRecheck = 2 * time.Second
+)
+
+var (
+	nameservers        = make([]Nameserver, 0)
+	nameserversLock    sync.Mutex
+	nameserversExpires = time.Now()
+)
 
 // Nameservers returns the currently active nameservers.
 func Nameservers() []Nameserver {
-	return nil
+	// locking
+	nameserversLock.Lock()
+	defer nameserversLock.Unlock()
+	// cache
+	if nameserversExpires.After(time.Now()) {
+		return nameservers
+	}
+	// update cache expiry when finished
+	defer func() {
+		nameserversExpires = time.Now().Add(nameserversRecheck)
+	}()
+
+	// reset
+	nameservers = make([]Nameserver, 0)
+
+	// This is a preliminary workaround until we have more time for proper interface using iphlpapi.dll
+	// TODO: make nice implementation
+
+	var output = make(chan []byte, 1)
+	module.StartWorker("get assigned nameservers", func(ctx context.Context) error {
+		cmd := exec.CommandContext(ctx, "nslookup", "localhost")
+		data, err := cmd.CombinedOutput()
+		if err != nil {
+			log.Debugf("netenv: failed to get assigned nameserves: %s", err)
+			output <- nil
+		} else {
+			output <- data
+		}
+		return nil
+	})
+
+	select {
+	case data := <-output:
+		scanner := bufio.NewScanner(bytes.NewReader(data))
+		scanner.Split(bufio.ScanLines)
+		for scanner.Scan() {
+			// check if we found the correct line
+			if !strings.HasPrefix(scanner.Text(), "Address:") {
+				continue
+			}
+			// split into fields, check if we have enough fields
+			fields := strings.Fields(scanner.Text())
+			if len(fields) < 2 {
+				continue
+			}
+			// parse nameserver, return if valid IP found
+			ns := net.ParseIP(fields[1])
+			if ns != nil {
+				nameservers = append(nameservers, Nameserver{
+					IP: ns,
+				})
+				return nameservers
+			}
+		}
+		log.Debug("netenv: could not find assigned nameserver")
+		return nameservers
+
+	case <-time.After(5 * time.Second):
+		log.Debug("netenv: timed out while getting assigned nameserves")
+	}
+
+	return nameservers
 }
 
 // Gateways returns the currently active gateways.
-func Gateways() []*net.IP {
+func Gateways() []net.IP {
 	return nil
 }