11.2.4 Input and Output

The underlying transport of a TLS session can be any Scheme input/output port (see Ports and File Descriptors). This has to be specified using set-session-transport-port!.

However, for better performance, a raw file descriptor can be specified, using set-session-transport-fd!. For instance, if the transport layer is a socket port over an OS-provided socket, you can use the port->fdes or fileno procedure to obtain the underlying file descriptor and pass it to set-session-transport-fd! (see port->fdes and fileno). This would work as follows:

     (let ((socket (socket PF_INET SOCK_STREAM 0))
           (session (make-session connection-end/client)))
     
       ;;
       ;; Establish a TCP connection...
       ;;
     
       ;; Use the file descriptor that underlies SOCKET.
       (set-session-transport-fd! session (fileno socket)))

Once a TLS session is established, data can be communicated through it (i.e., via the TLS record layer) using the port returned by session-record-port:

     (let ((session (make-session connection-end/client)))
     
       ;;
       ;; Initialize the various parameters of SESSION, set up
       ;; a network connection, etc...
       ;;
     
       (let ((i/o (session-record-port session)))
         (write "Hello peer!" i/o)
         (let ((greetings (read i/o)))
     
           ;; ...
     
           (bye session close-request/rdwr))))

A lower-level I/O API is provided by record-send and record-receive! which take an SRFI-4 vector to represent the data sent or received. While it might improve performance, it is much less convenient than the above and should rarely be needed.