Add dummy tun, helper functions

src/yggdrasil/tun_dummy.go

@@ -0,0 +1,19 @@
+// +build mobile
+
+package yggdrasil
+
+// This is to catch unsupported platforms
+// If your platform supports tun devices, you could try configuring it manually
+
+// Creates the TUN/TAP adapter, if supported by the Water library. Note that
+// no guarantees are made at this point on an unsupported platform.
+func (tun *tunAdapter) setup(ifname string, iftapmode bool, addr string, mtu int) error {
+	tun.mtu = getSupportedMTU(mtu)
+	return tun.setupAddress(addr)
+}
+
+// We don't know how to set the IPv6 address on an unknown platform, therefore
+// write about it to stdout and don't try to do anything further.
+func (tun *tunAdapter) setupAddress(addr string) error {
+	return nil
+}