Test fixing writing bug

src/server/main.cpp

@@ -153,15 +153,28 @@ int main(int argc, char** argv) {
             }
 
             const uint8_t* ip = packet.data();
-            uint32_t srcIP = ntohl(*(uint32_t*)(ip + 12)); // IPv4 source address offset (packet comes FROM client)
+            uint32_t srcIP = ntohl(*(uint32_t*)(ip + 12)); // IPv4 source address offset
+            uint32_t dstIP = ntohl(*(uint32_t*)(ip + 16)); // IPv4 destination address offset
         
-            auto session = SessionRegistry::getInstance().getByIP(srcIP);
+            // First, check if destination IP is a registered client (e.g., server responding to client or client-to-client)
-            if (!session) {
+            auto dstSession = SessionRegistry::getInstance().getByIP(dstIP);
-                Utils::warn("TUN: No session found for source IP " + VirtualInterface::ipv4ToString(srcIP));
+            if (dstSession) {
+                // Destination is a registered client, forward to that client's session
+                udpServer->sendData(dstSession->sessionID, std::string(packet.begin(), packet.end()));
                 continue;
             }
 
-            udpServer->sendData(session->sessionID, std::string(packet.begin(), packet.end()));
+            // Destination is not a registered client, check if source is (for external routing)
+            auto srcSession = SessionRegistry::getInstance().getByIP(srcIP);
+            if (srcSession) {
+                // Source is a registered client, write to TUN interface to forward to external destination
+                tun->writePacket(packet);
+                continue;
+            }
+
+            // Neither source nor destination is registered, drop the packet
+            Utils::warn("TUN: No session found for source IP " + VirtualInterface::ipv4ToString(srcIP) + 
+                       " or destination IP " + VirtualInterface::ipv4ToString(dstIP));
         }
 
         log("Shutting down server...");