make Probe a global function instead of DoHServer's

Android/app/src/go/backend/doh.go

@@ -71,10 +71,10 @@ var dohQuery = []byte{
 	0, 1, // QCLASS = IN (Internet)
 }
 
-// Probe checks if this server can handle DNS-over-HTTPS (DoH) requests.
+// Probe checks whether the [DoHServer] server can handle DNS-over-HTTPS (DoH) requests.
 //
 // If the server responds correctly, the function returns nil. Otherwise, the function returns an error.
-func (s *DoHServer) Probe() error {
+func Probe(s *DoHServer) error {
 	resp, err := s.r.Query(context.Background(), dohQuery)
 	if err != nil {
 		return fmt.Errorf("failed to send query: %w", err)

Android/app/src/go/doh/doh.go

@@ -70,7 +70,7 @@ type Summary struct {
 }
 
 // A Token is an opaque handle used to match responses to queries.
-type Token = interface{}
+type Token interface{}
 
 // Listener receives Summaries.
 type Listener interface {

Android/app/src/main/java/app/intra/net/go/GoProber.java

@@ -20,6 +20,7 @@
 import android.os.Build.VERSION_CODES;
 import app.intra.net.doh.Prober;
 import app.intra.sys.VpnController;
+import backend.Backend;
 import backend.DoHServer;
 import protect.Protector;
 
@@ -42,7 +43,7 @@ public void probe(String url, Callback callback) {
         // Protection isn't needed for Lollipop+, or if the VPN is not active.
         Protector protector = VERSION.SDK_INT >= VERSION_CODES.LOLLIPOP ? null :
             VpnController.getInstance().getIntraVpnService();
-        Probe(new DoHServer(url, dohIPs, protector, null));
+        Backend.probe(new DoHServer(url, dohIPs, protector, null));
         callback.onCompleted(true);
       } catch (Exception e) {
         callback.onCompleted(false);

Android/app/src/main/java/app/intra/net/go/GoVpnAdapter.java

@@ -88,7 +88,7 @@ String make(String template) {
   private ParcelFileDescriptor tunFd;
 
   // The Intra session object from go-tun2socks.  Initially null.
-  private Session tunnel;
+  private Session session;
   private GoIntraListener listener;
 
   public static GoVpnAdapter establish(@NonNull IntraVpnService vpnService) {
@@ -109,7 +109,7 @@ public synchronized void start() {
   }
 
   private void connectTunnel() {
-    if (tunnel != null) {
+    if (session != null) {
       return;
     }
     // VPN parameters
@@ -123,7 +123,7 @@ private void connectTunnel() {
       LogWrapper.log(Log.INFO, LOG_TAG, "Starting go-tun2socks");
       DoHServer server = makeDoHServer(dohURL);
       // connectIntraTunnel makes a copy of the file descriptor.
-      tunnel = Backend.connectSession(tunFd.getFd(), fakeDns,
+      session = Backend.connectSession(tunFd.getFd(), fakeDns,
           server, getProtector(), listener);
     } catch (Exception e) {
       LogWrapper.logException(e);
@@ -150,7 +150,7 @@ private void enableChoir() {
     }
     String file = vpnService.getFilesDir() + File.separator + CHOIR_FILENAME;
     try {
-      tunnel.enableSNIReporter(file, "intra.metrics.gstatic.com", country);
+      session.enableSNIReporter(file, "intra.metrics.gstatic.com", country);
     } catch (Exception e) {
       // Choir setup failure is logged but otherwise ignored, because it does not prevent Intra
       // from functioning correctly.
@@ -189,8 +189,8 @@ private static ParcelFileDescriptor establishVpn(IntraVpnService vpnService) {
   }
 
   public synchronized void close() {
-    if (tunnel != null) {
-      tunnel.disconnect();
+    if (session != null) {
+      session.disconnect();
     }
     if (tunFd != null) {
       try {
@@ -229,7 +229,7 @@ public synchronized void updateDohUrl() {
       // Adapter is closed.
       return;
     }
-    if (tunnel == null) {
+    if (session == null) {
       // Attempt to re-create the tunnel.  Creation may have failed originally because the DoH
       // server could not be reached.  This will update the DoH URL as well.
       connectTunnel();
@@ -241,11 +241,11 @@ public synchronized void updateDohUrl() {
     // out.
     String url = PersistentState.getServerUrl(vpnService);
     try {
-      tunnel.setDoHServer(makeDoHServer(url));
+      session.setDoHServer(makeDoHServer(url));
     } catch (Exception e) {
       LogWrapper.logException(e);
-      tunnel.disconnect();
-      tunnel = null;
+      session.disconnect();
+      session = null;
       VpnController.getInstance().onConnectionStateChanged(vpnService, IntraVpnService.State.FAILING);
     }
   }