From 4efe081084f37c92a5c9d9ad53f70241c5450596 Mon Sep 17 00:00:00 2001
From: Stanislas Michalak <stanislas.michalak@gmail.com>
Date: Sun, 19 Apr 2020 23:51:33 +0200
Subject: [PATCH] Allow client to bind on a random port

---
 src/socket.cpp | 38 +++++++++++++++++++++++++-------------
 1 file changed, 25 insertions(+), 13 deletions(-)

diff --git a/src/socket.cpp b/src/socket.cpp
index f2a60c02..c33d47a3 100755
--- a/src/socket.cpp
+++ b/src/socket.cpp
@@ -54,23 +54,35 @@ void CSocket::Init ( const quint16 iPortNumber )
 
     if ( bIsClient )
     {
-        // Per definition use the port number plus ten for the client to make
-        // it possible to run server and client on the same computer. If the
-        // port is not available, try "NUM_SOCKET_PORTS_TO_TRY" times with
-        // incremented port numbers
-        quint16 iClientPortIncrement = 10; // start value: port nubmer plus ten
-        bSuccess                     = false; // initialization for while loop
-
-        while ( !bSuccess &&
-                ( iClientPortIncrement <= NUM_SOCKET_PORTS_TO_TRY ) )
+        if (iPortNumber == 0)
         {
-            UdpSocketInAddr.sin_port = htons ( iPortNumber + iClientPortIncrement );
+            // If port number is 0, bind the client to a random available port.
+            UdpSocketInAddr.sin_port = htons ( iPortNumber );
 
             bSuccess = ( ::bind ( UdpSocket ,
-                                  (sockaddr*) &UdpSocketInAddr,
-                                  sizeof ( sockaddr_in ) ) == 0 );
+                                (sockaddr*) &UdpSocketInAddr,
+                                sizeof ( sockaddr_in ) ) == 0 );
+        }
+        else
+        {
+            // Per definition use the port number plus ten for the client to make
+            // it possible to run server and client on the same computer. If the
+            // port is not available, try "NUM_SOCKET_PORTS_TO_TRY" times with
+            // incremented port numbers
+            quint16 iClientPortIncrement = 10; // start value: port nubmer plus ten
+            bSuccess                     = false; // initialization for while loop
 
-            iClientPortIncrement++;
+            while ( !bSuccess &&
+                    ( iClientPortIncrement <= NUM_SOCKET_PORTS_TO_TRY ) )
+            {
+                UdpSocketInAddr.sin_port = htons ( iPortNumber + iClientPortIncrement );
+
+                bSuccess = ( ::bind ( UdpSocket ,
+                                    (sockaddr*) &UdpSocketInAddr,
+                                    sizeof ( sockaddr_in ) ) == 0 );
+
+                iClientPortIncrement++;
+            }
         }
     }
     else