From 5c99b1d32e697e842ca972c4fb7f0dabbad1e576 Mon Sep 17 00:00:00 2001
From: Albert Vaca Cintora <albertvaka@gmail.com>
Date: Fri, 4 Aug 2023 08:25:11 +0000
Subject: [PATCH] Avoid starting more than 1 connection to the same device

Since we close old connections when a new connection is received, due to
race conditions we could end up without a valid connection in this case.

Equivalent to https://invent.kde.org/network/kdeconnect-kde/-/merge_requests/580
---
 .../Backends/LanBackend/LanLinkProvider.java  | 27 ++++++++++++++-----
 1 file changed, 20 insertions(+), 7 deletions(-)

diff --git a/src/org/kde/kdeconnect/Backends/LanBackend/LanLinkProvider.java b/src/org/kde/kdeconnect/Backends/LanBackend/LanLinkProvider.java
index 7ed34001..569176f1 100644
--- a/src/org/kde/kdeconnect/Backends/LanBackend/LanLinkProvider.java
+++ b/src/org/kde/kdeconnect/Backends/LanBackend/LanLinkProvider.java
@@ -42,6 +42,7 @@ import java.security.cert.Certificate;
 import java.util.ArrayList;
 import java.util.HashMap;
 import java.util.List;
+import java.util.concurrent.ConcurrentHashMap;
 
 import javax.net.SocketFactory;
 import javax.net.ssl.SSLSocket;
@@ -64,10 +65,14 @@ public class LanLinkProvider extends BaseLinkProvider {
 
     final static int MAX_UDP_PACKET_SIZE = 1024 * 512;
 
+    final static long MILLIS_DELAY_BETWEEN_CONNECTIONS_TO_SAME_DEVICE = 500L;
+
     private final Context context;
 
     private final HashMap<String, LanLink> visibleDevices = new HashMap<>();  //Links by device id
 
+    final ConcurrentHashMap<String, Long> lastConnectionTime = new ConcurrentHashMap<>();
+
     private ServerSocket tcpServer;
     private DatagramSocket udpServer;
 
@@ -118,15 +123,21 @@ public class LanLinkProvider extends BaseLinkProvider {
         if (!identityPacket.getType().equals(NetworkPacket.PACKET_TYPE_IDENTITY)) {
             Log.e("KDE/LanLinkProvider", "Expecting an UDP identity packet");
             return;
-        } else {
-            String myId = DeviceHelper.getDeviceId(context);
-            if (deviceId.equals(myId)) {
-                //Ignore my own broadcast
-                return;
-            }
         }
 
-        Log.i("KDE/LanLinkProvider", "Broadcast identity packet received from " + identityPacket.getString("deviceName"));
+        String myId = DeviceHelper.getDeviceId(context);
+        if (deviceId.equals(myId)) {
+            //Ignore my own broadcast
+            return;
+        }
+
+        long now = System.currentTimeMillis();
+        Long last =  lastConnectionTime.get(deviceId);
+        if (last != null && (last + MILLIS_DELAY_BETWEEN_CONNECTIONS_TO_SAME_DEVICE > now)) {
+            Log.i("LanLinkProvider", "Discarding second UDP packet from the same device " + deviceId + " received too quickly");
+            return;
+        }
+        lastConnectionTime.put(deviceId, now);
 
         int tcpPort = identityPacket.getInt("tcpPort", MIN_PORT);
         if (tcpPort < MIN_PORT || tcpPort > MAX_PORT) {
@@ -134,6 +145,8 @@ public class LanLinkProvider extends BaseLinkProvider {
             return;
         }
 
+        Log.i("KDE/LanLinkProvider", "Broadcast identity packet received from " + identityPacket.getString("deviceName"));
+
         SocketFactory socketFactory = SocketFactory.getDefault();
         Socket socket = socketFactory.createSocket(address, tcpPort);
         configureSocket(socket);