@deftypefun {int} {gnutls_session_ext_register} (gnutls_session_t @var{session}, const char * @var{name}, int @var{id}, gnutls_ext_parse_type_t @var{parse_point}, gnutls_ext_recv_func @var{recv_func}, gnutls_ext_send_func @var{send_func}, gnutls_ext_deinit_data_func @var{deinit_func}, gnutls_ext_pack_func @var{pack_func}, gnutls_ext_unpack_func @var{unpack_func}, unsigned @var{flags})
@var{session}: the session for which this extension will be set

@var{name}: the name of the extension to register

@var{id}: the numeric id of the extension

@var{parse_point}: the parse type of the extension (see gnutls_ext_parse_type_t)

@var{recv_func}: a function to receive the data

@var{send_func}: a function to send the data

@var{deinit_func}: a function deinitialize any private data

@var{pack_func}: a function which serializes the extension's private data (used on session packing for resumption)

@var{unpack_func}: a function which will deserialize the extension's private data

@var{flags}: must be zero or flags from @code{gnutls_ext_flags_t} 

This function will register a new extension type. The extension will be
only usable within the registered session. If the extension type
is already registered then @code{GNUTLS_E_ALREADY_REGISTERED}  will be returned,
unless the flag @code{GNUTLS_EXT_FLAG_OVERRIDE_INTERNAL}  is specified. The latter
flag when specified can be used to override certain extensions introduced
after 3.6.0. It is expected to be used by applications which handle
custom extensions that are not currently supported in GnuTLS, but direct
support for them may be added in the future.

Each registered extension can store temporary data into the gnutls_session_t
structure using @code{gnutls_ext_set_data()} , and they can be retrieved using
@code{gnutls_ext_get_data()} .

The validity of the extension registered can be given by the appropriate flags
of @code{gnutls_ext_flags_t} . If no validity is given, then the registered extension
will be valid for client and TLS1.2 server hello (or encrypted extensions for TLS1.3).

@strong{Returns:} @code{GNUTLS_E_SUCCESS}  on success, otherwise a negative error code.

@strong{Since:} 3.5.5
@end deftypefun