int gnutls_session_get_id(gnutls_session_t session, void * session_id, size_t * session_id_size);
is a gnutls_session_t structure.
void * session_id
is a pointer to space to hold the session id.
size_t * session_id_size
is the session id's size, or it will be set by the function.
Returns the current session id. This can be used if you want to
check if the next session you tried to resume was actually
resumed. This is because resumed sessions have the same sessionID
with the original session.
Session id is some data set by the server, that identify the
current session. In TLS 1.0 and SSL 3.0 session id is always less
than 32 bytes.
On success, GNUTLS_E_SUCCESS (0) is returned, otherwise
an error code is returned.