Simplify IP rules for Wi-Fi direct mode

mobile/src/main/java/be/mygod/vpnhotspot/HotspotService.kt

@@ -169,7 +169,7 @@ class HotspotService : Service(), WifiP2pManager.ChannelListener {
                 } catch (_: Routing.InterfaceNotFoundException) {
                     startFailure(getString(R.string.exception_interface_not_found))
                     return START_NOT_STICKY
-                }.apRule().forward().dnsRedirect(dns)
+                }.rule().forward().dnsRedirect(dns)
                 if (routing.start()) {
                     this.routing = routing
                     apConfiguration = NetUtils.loadApConfiguration()
@@ -229,7 +229,8 @@ class HotspotService : Service(), WifiP2pManager.ChannelListener {
         } catch (_: Routing.InterfaceNotFoundException) {
             startFailure(getString(R.string.exception_interface_not_found), group)
             return
-        }.p2pRule().forward().dnsRedirect(dns)
+        }.ipForward()   // Wi-Fi direct doesn't enable ip_forward
+                .rule().forward().dnsRedirect(dns)
         if (routing.start()) {
             this.routing = routing
             doStart(group)

mobile/src/main/java/be/mygod/vpnhotspot/MainActivity.kt

@@ -87,7 +87,7 @@ class MainActivity : AppCompatActivity(), ServiceConnection, Toolbar.OnMenuItemC
             }
             holder.binding.device = device
             holder.binding.ipAddress = when (position) {
-                0 -> binder?.service?.routing?.hostAddress?.address?.hostAddress
+                0 -> binder?.service?.routing?.hostAddress
                 else -> arpCache[device?.deviceAddress]
             }
             holder.binding.executePendingBindings()

mobile/src/main/java/be/mygod/vpnhotspot/Routing.kt

@@ -13,43 +13,28 @@ class Routing(private val upstream: String, val downstream: String, ownerAddress
                 "while iptables -D FORWARD -j vpnhotspot_fwd; do done",
                 "iptables -F vpnhotspot_fwd",
                 "iptables -X vpnhotspot_fwd",
-                "while ip rule del lookup 62; do done",
-                "ip route flush table 62",
                 "while ip rule del priority 17999; do done")
     }
 
     class InterfaceNotFoundException : IOException()
 
-    val hostAddress = NetworkInterface.getByName(downstream)?.interfaceAddresses
+    val hostAddress: String = (ownerAddress ?: NetworkInterface.getByName(downstream)?.inetAddresses?.asSequence()
-            ?.singleOrNull { if (ownerAddress == null) it.address is Inet4Address else it.address == ownerAddress }
+            ?.singleOrNull { it is Inet4Address } ?: throw InterfaceNotFoundException()).hostAddress
-            ?: throw InterfaceNotFoundException()
     private val startScript = LinkedList<String>()
     private val stopScript = LinkedList<String>()
 
-    fun p2pRule(): Routing {
+    fun ipForward(): Routing {
-        val address = hostAddress.address.address
+        startScript.add("echo 1 >/proc/sys/net/ipv4/ip_forward")
-        val subnetPrefixLength = hostAddress.networkPrefixLength
-        // clear suffix bits
-        var done = subnetPrefixLength.toInt()
-        while (done < address.size shl 3) {
-            val index = done shr 3
-            address[index] = (address[index].toInt() and (0x7f00 shr (done and 7))).toByte()
-            done = (index + 1) shl 3
-        }
-        startScript.add("echo 1 >/proc/sys/net/ipv4/ip_forward")    // Wi-Fi direct doesn't enable ip_forward
-        startScript.add("ip route add default dev $upstream scope link table 62")
-        startScript.add("ip route add ${InetAddress.getByAddress(address).hostAddress}/$subnetPrefixLength dev $downstream scope link table 62")
-        startScript.add("ip route add broadcast 255.255.255.255 dev $downstream scope link table 62")
-        startScript.add("ip rule add iif $downstream lookup 62")
-        // removing each rule may fail if downstream is already removed
-        stopScript.addFirst("ip route flush table 62")
-        stopScript.addFirst("ip rule del iif $downstream lookup 62")
         return this
     }
 
-    /* Since Android 5.0, RULE_PRIORITY_TETHERING = 18000.
+    /**
-     * https://android.googlesource.com/platform/system/netd/+/b9baf26/server/RouteController.cpp#65 */
+     * Since Android 5.0, RULE_PRIORITY_TETHERING = 18000.
-    fun apRule(): Routing {
+     * This also works for Wi-Fi direct where there's no rule at 18000.
+     *
+     * Source: https://android.googlesource.com/platform/system/netd/+/b9baf26/server/RouteController.cpp#65
+     */
+    fun rule(): Routing {
         startScript.add("ip rule add from all iif $downstream lookup $upstream priority 17999")
         stopScript.addFirst("ip rule del from all iif $downstream lookup $upstream priority 17999")
         return this
@@ -67,7 +52,6 @@ class Routing(private val upstream: String, val downstream: String, ownerAddress
     }
 
     fun dnsRedirect(dns: String): Routing {
-        val hostAddress = hostAddress.address.hostAddress
         startScript.add("iptables -t nat -A PREROUTING -i $downstream -p tcp -d $hostAddress --dport 53 -j DNAT --to-destination $dns")
         startScript.add("iptables -t nat -A PREROUTING -i $downstream -p udp -d $hostAddress --dport 53 -j DNAT --to-destination $dns")
         stopScript.addFirst("iptables -t nat -D PREROUTING -i $downstream -p tcp -d $hostAddress --dport 53 -j DNAT --to-destination $dns")