FTPES with TLS Session Reuse for FileZilla Server (need BouncyCastle …

…and a subclass).

Connecting to ftp.example.com on the command port and then to the corresponding IP x.x.x.x on the data port prevents the server from accepting the same TLS session.
Therefore, the Filezilla server needs to set peerHost before socket.connect to allow TLS session resumption.

src/main/java/org/apache/commons/net/ftp/FTPSClient.java

@@ -279,7 +279,6 @@ protected Socket _openDataConnection_(final int command, final String arg) throw
     @Override
     protected Socket _openDataConnection_(final String command, final String arg) throws IOException {
         final Socket socket = openDataSecureConnection(command, arg);
-        _prepareDataSocket_(socket);
         if (socket instanceof SSLSocket) {
             final SSLSocket sslSocket = (SSLSocket) socket;
 
@@ -313,7 +312,7 @@ protected Socket _openDataConnection_(final String command, final String arg) th
      */
     protected void _prepareDataSocket_(final Socket socket) throws IOException {
     }
-
+    
     /**
      * Check the value that can be set in PROT Command value.
      *
@@ -831,6 +830,8 @@ private Socket openDataSecureConnection(final String command, final String arg)
                 }
                 socket = server.accept();
 
+                _prepareDataSocket_(socket);
+
                 // Ensure the timeout is set before any commands are issued on the new socket
                 if (soTimeoutMillis >= 0) {
                     socket.setSoTimeout(soTimeoutMillis);
@@ -871,6 +872,8 @@ private Socket openDataSecureConnection(final String command, final String arg)
                 socket = _socketFactory_.createSocket();
             }
 
+            _prepareDataSocket_(socket);
+
             if (getReceiveDataSocketBufferSize() > 0) {
                 socket.setReceiveBufferSize(getReceiveDataSocketBufferSize());
             }