Add support for central servers behind NAT

ChangeLog

@@ -19,6 +19,9 @@
 
 - remove ConsoleWriterFactory (#926)
 
+- add new --serverpublicip option to support central servers behind NAT,
+  coded by hoffie (#954)
+
 
 TODO fix crash if settings are changed in ASIO4All during a connection (contained in #796)
 

src/main.cpp

@@ -83,6 +83,7 @@ int main ( int argc, char** argv )
     QString      strRecordingDirName         = "";
     QString      strCentralServer            = "";
     QString      strServerInfo               = "";
+    QString      strServerPublicIP           = "";
     QString      strServerListFilter         = "";
     QString      strWelcomeMessage           = "";
     QString      strClientName               = "";
@@ -397,6 +398,20 @@ int main ( int argc, char** argv )
         }
 
 
+        // Server Public IP --------------------------------------------------
+        if ( GetStringArgument ( argc,
+                                 argv,
+                                 i,
+                                 "--serverpublicip", // no short form
+                                 "--serverpublicip",
+                                 strArgument ) )
+        {
+            strServerPublicIP = strArgument;
+            CommandLineOptions << "--serverpublicip";
+            continue;
+        }
+
+
         // Server info ---------------------------------------------------------
         if ( GetStringArgument ( argc,
                                  argv,
@@ -696,6 +711,7 @@ int main ( int argc, char** argv )
                              strHTMLStatusFileName,
                              strCentralServer,
                              strServerInfo,
+                             strServerPublicIP,
                              strServerListFilter,
                              strWelcomeMessage,
                              strRecordingDirName,
@@ -814,6 +830,9 @@ QString UsageArguments ( char **argv )
         "  -u, --numchannels     maximum number of channels\n"
         "  -w, --welcomemessage  welcome message on connect\n"
         "  -z, --startminimized  start minimizied\n"
+        "      --serverpublicip  specify your public IP address when\n"
+        "                        running a slave and your own central server\n"
+        "                        behind the same NAT\n"
         "\nClient only:\n"
         "  -M, --mutestream      starts the application in muted state\n"
         "      --mutemyown       mute me in my personal mix (headless only)\n"

src/protocol.cpp

@@ -303,6 +303,9 @@ CONNECTION LESS MESSAGES
       NOTE: In the PROTMESSID_CLM_SERVER_LIST list, this field will be empty
       as only the initial IP address should be used by the client.  Where
       necessary, that value will contain the server internal address.
+      When running a central server and a slave server behind the same NAT,
+      this field is used the other way round: It will contain the public
+      IP in this case which will be served to clients from the Internet.
 
 
 - PROTMESSID_CLM_REGISTER_SERVER_EX: Register a server, providing extended server

src/server.cpp

@@ -226,6 +226,7 @@ CServer::CServer ( const int          iNewMaxNumChan,
                    const QString&     strCentralServer,
                    const QString&     strServerInfo,
                    const QString&     strServerListFilter,
+                   const QString&     strServerPublicIP,
                    const QString&     strNewWelcomeMessage,
                    const QString&     strRecordingDirName,
                    const bool         bNDisconnectAllClientsOnQuit,
@@ -245,6 +246,7 @@ CServer::CServer ( const int          iNewMaxNumChan,
     ServerListManager           ( iPortNumber,
                                   strCentralServer,
                                   strServerInfo,
+                                  strServerPublicIP,
                                   strServerListFilter,
                                   iNewMaxNumChan,
                                   &ConnLessProtocol ),

src/server.h

@@ -176,6 +176,7 @@ class CServer :
               const QString&     strCentralServer,
               const QString&     strServerInfo,
               const QString&     strServerListFilter,
+              const QString&     strServerPublicIP,
               const QString&     strNewWelcomeMessage,
               const QString&     strRecordingDirName,
               const bool         bNDisconnectAllClientsOnQuit,

src/serverlist.cpp

@@ -29,6 +29,7 @@ CServerListManager::CServerListManager ( const quint16  iNPortNum,
                                          const QString& sNCentServAddr,
                                          const QString& strServerInfo,
                                          const QString& strServerListFilter,
+                                         const QString& strServerPublicIP,
                                          const int      iNumChannels,
                                          CProtocol*     pNConLProt )
     : eCentralServerAddressType ( AT_CUSTOM ), // must be AT_CUSTOM for the "no GUI" case
@@ -41,7 +42,18 @@ CServerListManager::CServerListManager ( const quint16  iNPortNum,
     SetCentralServerAddress ( sNCentServAddr );
 
     // set the server internal address, including internal port number
-    SlaveCurLocalHostAddress = CHostAddress( NetworkUtil::GetLocalAddress().InetAddr, iNPortNum );
+    QHostAddress qhaServerPublicIP;
+    if ( strServerPublicIP == "" )
+    {
+        // No user-supplied override via --serverpublicip -> use auto-detection
+        qhaServerPublicIP = NetworkUtil::GetLocalAddress().InetAddr;
+    }
+    else
+    {
+        // User-supplied --serverpublicip
+        qhaServerPublicIP = QHostAddress ( strServerPublicIP );
+    }
+    SlaveCurLocalHostAddress = CHostAddress ( qhaServerPublicIP, iNPortNum );
 
     // prepare the server info information
     QStringList slServInfoSeparateParams;
@@ -443,6 +455,20 @@ void CServerListManager::CentralServerQueryServerList ( const CHostAddress& Inet
                 {
                     vecServerInfo[iIdx].HostAddr = ServerList[iIdx].LHostAddr;
                 }
+                else if ( !NetworkUtil::IsPrivateNetworkIP ( InetAddr.InetAddr ) &&
+                          NetworkUtil::IsPrivateNetworkIP ( vecServerInfo[iIdx].HostAddr.InetAddr ) &&
+                          !NetworkUtil::IsPrivateNetworkIP ( ServerList[iIdx].LHostAddr.InetAddr ) )
+                {
+                    // We've got a request from a public client, the server
+                    // list's entry's primary address is a private address,
+                    // but it supplied an additional public address using
+                    // --serverpublicip.
+                    // In this case, use the latter.
+                    // This is common when running a central server with slave
+                    // servers behind a NAT and dealing with external, public
+                    // clients.
+                    vecServerInfo[iIdx].HostAddr = ServerList[iIdx].LHostAddr;
+                }
                 else
                 {
                     // create "send empty message" for all registered servers

src/serverlist.h

@@ -128,6 +128,7 @@ class CServerListManager : public QObject
                          const QString& sNCentServAddr,
                          const QString& strServerInfo,
                          const QString& strServerListFilter,
+                         const QString& strServerPublicIP,
                          const int      iNumChannels,
                          CProtocol*     pNConLProt );
 

src/util.cpp

@@ -1059,6 +1059,28 @@ QString NetworkUtil::FixAddress ( const QString& strAddress )
     return strAddress.simplified().replace ( " ", "" );
 }
 
+// Return whether the given HostAdress is within a private IP range
+// as per RFC 1918 & RFC 5735.
+bool NetworkUtil::IsPrivateNetworkIP ( const QHostAddress &qhAddr )
+{
+    // https://www.rfc-editor.org/rfc/rfc1918
+    // https://www.rfc-editor.org/rfc/rfc5735
+    static QList<QPair<QHostAddress, int>> addresses =
+    {
+        QPair<QHostAddress, int> ( QHostAddress ( "10.0.0.0" ), 8 ),
+        QPair<QHostAddress, int> ( QHostAddress ( "127.0.0.0" ), 8 ),
+        QPair<QHostAddress, int> ( QHostAddress ( "172.16.0.0" ), 12 ),
+        QPair<QHostAddress, int> ( QHostAddress ( "192.168.0.0" ), 16 ),
+    };
+
+    foreach ( auto item, addresses ) {
+        if ( qhAddr.isInSubnet ( item ) ) {
+            return true;
+        }
+    }
+    return false;
+}
+
 
 // Instrument picture data base ------------------------------------------------
 CVector<CInstPictures::CInstPictProps>& CInstPictures::GetTable ( const bool bReGenerateTable )

src/util.h

@@ -1104,6 +1104,7 @@ class NetworkUtil
     static CHostAddress GetLocalAddress();
     static QString      GetCentralServerAddress ( const ECSAddType eCentralServerAddressType,
                                                   const QString&   strCentralServerAddress );
+    static bool         IsPrivateNetworkIP ( const QHostAddress& qhAddr );
 };