Allow monitoring current upstreams

Fix #139.

mobile/src/main/java/be/mygod/vpnhotspot/client/ClientsFragment.kt

@@ -81,7 +81,7 @@ class ClientsFragment : Fragment() {
     data class StatsArg(val title: CharSequence, val stats: ClientStats) : Parcelable
     class StatsDialogFragment : AlertDialogFragment<StatsArg, Empty>() {
         override fun AlertDialog.Builder.prepare(listener: DialogInterface.OnClickListener) {
-            setTitle(SpanFormatter.format(getString(R.string.clients_stats_title), arg.title))
+            setTitle(SpanFormatter.format(getText(R.string.clients_stats_title), arg.title))
             val context = context
             val resources = resources
             val format = NumberFormat.getIntegerInstance(resources.configuration.locale)

mobile/src/main/java/be/mygod/vpnhotspot/preference/UpstreamsPreference.kt

@@ -0,0 +1,65 @@
+package be.mygod.vpnhotspot.preference
+
+import android.content.Context
+import android.graphics.Typeface
+import android.net.LinkProperties
+import android.text.SpannableStringBuilder
+import android.text.style.StyleSpan
+import android.util.AttributeSet
+import androidx.lifecycle.DefaultLifecycleObserver
+import androidx.lifecycle.LifecycleOwner
+import androidx.lifecycle.lifecycleScope
+import androidx.preference.Preference
+import be.mygod.vpnhotspot.R
+import be.mygod.vpnhotspot.net.monitor.FallbackUpstreamMonitor
+import be.mygod.vpnhotspot.net.monitor.UpstreamMonitor
+import be.mygod.vpnhotspot.util.SpanFormatter
+import be.mygod.vpnhotspot.util.parseNumericAddress
+
+class UpstreamsPreference(context: Context, attrs: AttributeSet) : Preference(context, attrs),
+        DefaultLifecycleObserver {
+    companion object {
+        private val internetAddress = parseNumericAddress("8.8.8.8")
+    }
+
+    private data class Interface(val ifname: String, val internet: Boolean)
+    private inner class Monitor : UpstreamMonitor.Callback {
+        private var currentInterface: Interface? = null
+        val charSequence get() = currentInterface?.run {
+            if (internet) SpannableStringBuilder(ifname).apply {
+                setSpan(StyleSpan(Typeface.BOLD), 0, length, 0)
+            } else ifname
+        } ?: "∅"
+
+        override fun onAvailable(ifname: String, properties: LinkProperties) {
+            currentInterface = Interface(ifname, properties.routes.any { it.matches(internetAddress) })
+            onUpdate()
+        }
+
+        override fun onLost() {
+            currentInterface = null
+            onUpdate()
+        }
+    }
+
+    private val primary = Monitor()
+    private val fallback = Monitor()
+
+    init {
+        (context as LifecycleOwner).lifecycle.addObserver(this)
+    }
+
+    override fun onStart(owner: LifecycleOwner) {
+        UpstreamMonitor.registerCallback(primary)
+        FallbackUpstreamMonitor.registerCallback(fallback)
+    }
+    override fun onStop(owner: LifecycleOwner) {
+        UpstreamMonitor.unregisterCallback(primary)
+        FallbackUpstreamMonitor.unregisterCallback(fallback)
+    }
+
+    private fun onUpdate() = (context as LifecycleOwner).lifecycleScope.launchWhenStarted {
+        summary = SpanFormatter.format(context.getText(R.string.settings_service_upstream_monitor_summary),
+                primary.charSequence, fallback.charSequence)
+    }
+}

mobile/src/main/res/values-zh-rCN/strings.xml

@@ -98,6 +98,8 @@
     <string name="settings_service_ip_monitor_monitor_root">Netlink 监听 (root)</string>
     <string name="settings_service_ip_monitor_poll">轮询</string>
     <string name="settings_service_ip_monitor_poll_root">轮询 (root)</string>
+    <string name="settings_service_upstream_monitor">当前上游接口</string>
+    <string name="settings_service_upstream_monitor_summary">%1$s；备用：%2$s</string>
     <string name="settings_service_upstream">上游网络接口</string>
     <string name="settings_service_upstream_auto">自动检测系统 VPN</string>
     <string name="settings_upstream_fallback">备用上游接口</string>

mobile/src/main/res/values/strings.xml

@@ -103,6 +103,8 @@
     <string name="settings_service_ip_monitor_monitor_root">Netlink monitor with root</string>
     <string name="settings_service_ip_monitor_poll">Poll</string>
     <string name="settings_service_ip_monitor_poll_root">Poll with root</string>
+    <string name="settings_service_upstream_monitor">Current upstreams</string>
+    <string name="settings_service_upstream_monitor_summary">%1$s; fallback: %2$s</string>
     <string name="settings_service_upstream">Upstream network interface</string>
     <string name="settings_service_upstream_auto">Auto detect system VPN</string>
     <string name="settings_upstream_fallback">Fallback upstream interface</string>

mobile/src/main/res/xml/pref_settings.xml

@@ -7,6 +7,10 @@
         app:summary="@string/settings_service_clean_summary"/>
     <PreferenceCategory
         app:title="@string/settings_upstream">
+        <be.mygod.vpnhotspot.preference.UpstreamsPreference
+            app:key="service.upstream.monitor"
+            app:icon="@drawable/ic_image_remove_red_eye"
+            app:title="@string/settings_service_upstream_monitor"/>
         <EditTextPreference
             app:key="service.upstream"
             app:icon="@drawable/ic_action_settings_ethernet"