I have a client trying to upload multiple files to FTP server in passive mode.
The client sends PASV command and the server responds with the relevant ip and port.
Is it possible to send multiple files on this one data connection? or the client need to send the PASV command and get a new port for each file?
Since the only indicator of the end of file is the close of the connection and because you cannot transfer any more data after the connection has closed, you will not be able to transfer more than one file using the same data connection.
But, maybe you tried to ask a different question, that is if is possible to have multiple data transfers (and thus multiple data connections) after a single PASV command? I can see nothing in RFC959 which directly would prevent this and reusing the same target port on the server. And because access would be done from different source ports on the client this should also not give problems with TCP connection states. But, in practice you will probably see problems because if you try to use this from the client side, because lots of servers create the listener only for a single data connection. So you better precede each data transfer with a new PASV command, like existing clients do.