@deftypefun {void} {gnutls_handshake_set_hook_function} (gnutls_session_t @var{session}, unsigned int @var{htype}, int @var{when}, gnutls_handshake_hook_func @var{func})
@var{session}: is a @code{gnutls_session_t}  type

@var{htype}: the @code{gnutls_handshake_description_t}  of the message to hook at

@var{when}: @code{GNUTLS_HOOK_} * depending on when the hook function should be called

@var{func}: is the function to be called

This function will set a callback to be called after or before the specified
handshake message has been received or generated. This is a
generalization of @code{gnutls_handshake_set_post_client_hello_function()} .

To call the hook function prior to the message being generated or processed
use @code{GNUTLS_HOOK_PRE}  as  @code{when} parameter, @code{GNUTLS_HOOK_POST}  to call
after, and @code{GNUTLS_HOOK_BOTH}  for both cases.

This callback must return 0 on success or a gnutls error code to
terminate the handshake.

To hook at all handshake messages use an  @code{htype} of @code{GNUTLS_HANDSHAKE_ANY} .

@strong{Warning:} You should not use this function to terminate the
handshake based on client input unless you know what you are
doing. Before the handshake is finished there is no way to know if
there is a man-in-the-middle attack being performed.
@end deftypefun