1 files changed, 41 insertions, 0 deletions
diff --git a/control/controlknobs/controlknobs.go b/control/controlknobs/controlknobs.go
new file mode 100644
index 000000000..884c0f8dd
--- /dev/null
+++ b/control/controlknobs/controlknobs.go
@@ -0,0 +1,41 @@
+// Copyright (c) 2021 Tailscale Inc & AUTHORS All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package controlknobs contains client options configurable from control which can be turned on
+// or off. The ability to turn options on and off is for incrementally adding features in.
+package controlknobs
+
+import (
+	"os"
+	"strconv"
+	"sync/atomic"
+
+	"tailscale.com/types/opt"
+)
+
+// disableUPnP indicates whether to attempt UPnP mapping.
+var disableUPnP atomic.Value
+
+func init() {
+	v, _ := strconv.ParseBool(os.Getenv("TS_DISABLE_UPNP"))
+	var toStore opt.Bool
+	toStore.Set(v)
+	disableUPnP.Store(toStore)
+}
+
+// DisableUPnP reports the last reported value from control
+// whether UPnP portmapping should be disabled.
+func DisableUPnP() opt.Bool {
+	v, _ := disableUPnP.Load().(opt.Bool)
+	return v
+}
+
+// SetDisableUPnP will set whether UPnP connections are permitted or not,
+// intended to be set from control.
+func SetDisableUPnP(v opt.Bool) {
+	old, ok := disableUPnP.Load().(opt.Bool)
+	if !ok || old != v {
+		disableUPnP.Store(v)
+	}
+}