From 21b245cd717873022b1e662b2b68c49b005cc6f4 Mon Sep 17 00:00:00 2001
From: Albert Vaca Cintora <albertvaka@gmail.com>
Date: Fri, 4 Aug 2023 08:25:45 +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-android/-/merge_requests/382
---
 core/backends/lan/lanlinkprovider.cpp | 14 +++++++++++++-
 core/backends/lan/lanlinkprovider.h   |  1 +
 2 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/core/backends/lan/lanlinkprovider.cpp b/core/backends/lan/lanlinkprovider.cpp
index d7c64465d..13c73af99 100644
--- a/core/backends/lan/lanlinkprovider.cpp
+++ b/core/backends/lan/lanlinkprovider.cpp
@@ -39,6 +39,8 @@
 static const int MAX_UNPAIRED_CONNECTIONS = 42;
 static const int MAX_REMEMBERED_IDENTITY_PACKETS = 42;
 
+static const long MILLIS_DELAY_BETWEEN_CONNECTIONS_TO_SAME_DEVICE = 500;
+
 LanLinkProvider::LanLinkProvider(bool testMode, quint16 udpBroadcastPort, quint16 udpListenPort)
     : m_server(new Server(this))
     , m_udpSocket(this)
@@ -277,12 +279,22 @@ void LanLinkProvider::udpBroadcastReceived()
             continue;
         }
 
-        if (receivedPacket->get<QString>(QStringLiteral("deviceId")) == KdeConnectConfig::instance().deviceId()) {
+        QString deviceId = receivedPacket->get<QString>(QStringLiteral("deviceId"));
+
+        if (deviceId == KdeConnectConfig::instance().deviceId()) {
             // qCDebug(KDECONNECT_CORE) << "Ignoring my own broadcast";
             delete receivedPacket;
             continue;
         }
 
+        qint64 now = QDateTime::currentMSecsSinceEpoch();
+        if (m_lastConnectionTime[deviceId] + MILLIS_DELAY_BETWEEN_CONNECTIONS_TO_SAME_DEVICE > now) {
+            qCDebug(KDECONNECT_CORE) << "Discarding second UPD packet from the same device" << deviceId << "received too quickly";
+            delete receivedPacket;
+            return;
+        }
+        m_lastConnectionTime[deviceId] = now;
+
         int tcpPort = receivedPacket->get<int>(QStringLiteral("tcpPort"));
         if (tcpPort < MIN_TCP_PORT || tcpPort > MAX_TCP_PORT) {
             qCDebug(KDECONNECT_CORE) << "TCP port outside of kdeconnect's range";
diff --git a/core/backends/lan/lanlinkprovider.h b/core/backends/lan/lanlinkprovider.h
index d60a14420..d984a0883 100644
--- a/core/backends/lan/lanlinkprovider.h
+++ b/core/backends/lan/lanlinkprovider.h
@@ -93,6 +93,7 @@ private:
         QHostAddress sender;
     };
     QMap<QSslSocket *, PendingConnect> m_receivedIdentityPackets;
+    QMap<QString, qint64> m_lastConnectionTime;
     const bool m_testMode;
     QTimer m_combineBroadcastsTimer;