Write to temp file before saving data (#238)

* Create temp file before saving data

On the event of full disk, we may encounter the case where the
destination file get replaced by an empty file as the
ioutil.WriteFile truncates the destination before write.

* Close the tempFile instance before moving it

* Blacklist Wireguard interfaces for ICE checks

client/internal/peer/conn.go

@@ -2,6 +2,7 @@ package peer
 
 import (
 	"context"
+	"golang.zx2c4.com/wireguard/wgctrl"
 	"net"
 	"sync"
 	"time"
@@ -87,11 +88,20 @@ func interfaceFilter(blackList []string) func(string) bool {
 		}
 	}
 	return func(iFace string) bool {
-		if len(blackListMap) == 0 {
-			return true
-		}
+
 		_, ok := blackListMap[iFace]
-		return !ok
+		if ok {
+			return false
+		}
+		// look for unlisted Wireguard interfaces
+		wg, err := wgctrl.New()
+		if err != nil {
+			log.Debugf("trying to create a wgctrl client failed with: %v", err)
+		}
+		defer wg.Close()
+
+		_, err = wg.Device(iFace)
+		return err != nil
 	}
 }