Add check for null ip address

Show toast

app/src/main/java/org/kiwix/kiwixmobile/webserver/ServerStateListener.java

@@ -8,6 +8,8 @@ public interface ServerStateListener {
 
   void serverStopped();
 
+  void serverFailed();
+
   void hotspotTurnedOn(WifiConfiguration wifiConfiguration);
 
   void hotspotFailed();

app/src/main/java/org/kiwix/kiwixmobile/webserver/WebServerHelper.java

@@ -22,7 +22,7 @@ public class WebServerHelper {
   }
 
   public void startServerHelper(ServerStateListener stateListener) {
-    
+
     // 1. Get port from settings screen
     // 2. Ask user to change port in settings if port is in use.
     // OR
@@ -30,7 +30,13 @@ public class WebServerHelper {
 
     if (!isServerStarted && startAndroidWebServer()) {
       isServerStarted = true;
-      stateListener.serverStarted(getIpAddress() + ":" + port);
+      String ip = getIpAddress();
+      ip = ip.replaceAll("\n", "");
+      if (ip.length() == 0) {
+        stateListener.serverFailed();
+      } else {
+        stateListener.serverStarted("http://" + ip + ":" + port);
+      }
     }
   }
 
@@ -85,10 +91,10 @@ public class WebServerHelper {
       ip += "Something Wrong! " + e.toString() + "\n";
     }
 
-    return "http://" + ip;
+    return ip;
   }
 
   public static String getAddress() {
-    return getIpAddress() + ":" + port;
+    return "http://" + getIpAddress() + ":" + port;
   }
 }

app/src/main/java/org/kiwix/kiwixmobile/webserver/ZimHostActivity.java

@@ -18,6 +18,7 @@ import android.util.Log;
 import android.view.View;
 import android.widget.Button;
 import android.widget.TextView;
+import android.widget.Toast;
 import androidx.annotation.NonNull;
 import androidx.annotation.Nullable;
 import androidx.annotation.RequiresApi;
@@ -375,9 +376,8 @@ public class ZimHostActivity extends BaseActivity implements
   }
 
   @Override public void serverStarted(String ip) {
-    ip = ip.replaceAll("\n", "");
     this.ip = ip;
-    serverTextView.setText(getString(R.string.server_started_message) + " " + ip);
+    serverTextView.setText(getString(R.string.server_started_message) + " " + this.ip);
     startServerButton.setText(getString(R.string.stop_server_label));
     startServerButton.setBackgroundColor(getResources().getColor(R.color.stopServer));
     isServerStarted = true;
@@ -390,6 +390,11 @@ public class ZimHostActivity extends BaseActivity implements
     isServerStarted = false;
   }
 
+  @Override public void serverFailed() {
+    String message = String.format(getString(R.string.server_failed_message));
+    Toast.makeText(this, message, Toast.LENGTH_LONG).show();
+  }
+
   @Override public void hotspotTurnedOn(WifiConfiguration wifiConfiguration) {
 
     //Show an alert dialog for hotspot details

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

@@ -31,6 +31,7 @@
   <string name="hotspot_start">Starting hotspot</string>
   <string name="hotspot_running">Running Hotspot</string>
   <string name="stop_hotspot_button">STOP</string>
+  <string name="server_failed_message">Couldn’t start server. Please turn on your hotspot</string>
   <string name="hotspot_turned_on">Hotspot turned on</string>
   <string name="hotspot_details_message">Following are the details of your local hotspot.</string>
   <string name="hotspot_ssid_label">SSID : </string>