11.2.4 Input and Output

The underlying transport of a TLS session can be any Scheme input/output port (see (guile)Ports and File Descriptors section ‘Ports and File Descriptors’ in The GNU Guile Reference Manual). 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: (guile)Ports and File Descriptors section ‘Ports and File Descriptors’ in The GNU Guile Reference Manual). 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.