@deftypefun {int} {gnutls_session_get_data2} (gnutls_session_t @var{session}, gnutls_datum_t * @var{data})

@var{session}: is a @code{gnutls_session_t}  type.

@var{data}: is a pointer to a datum that will hold the session.

Returns necessary parameters to support resumption. The client

should call this function and store the returned session data. A session

can be resumed later by calling @code{gnutls_session_set_data()}  with the returned

data. Note that under TLS 1.3, it is recommended for clients to use

session parameters only once, to prevent passive-observers from correlating

the different connections.

The returned  @code{data} are allocated and must be released using @code{gnutls_free()} .

This function will fail if called prior to handshake completion. In

case of false start TLS, the handshake completes only after data have

been successfully received from the peer.

Under TLS1.3 session resumption is possible only after a session ticket

is received by the client. To ensure that such a ticket has been received use

@code{gnutls_session_get_flags()}  and check for flag @code{GNUTLS_SFLAGS_SESSION_TICKET} ;

if this flag is not set, this function will wait for a new ticket within

an estimated rountrip, and if not received will return dummy data which

cannot lead to resumption.

To get notified when new tickets are received by the server

use @code{gnutls_handshake_set_hook_function()}  to wait for @code{GNUTLS_HANDSHAKE_NEW_SESSION_TICKET} 

messages. Each call of @code{gnutls_session_get_data2()}  after a ticket is

received, will return session resumption data corresponding to the last

received ticket.

Note that this function under TLS1.3 requires a callback to be set with

@code{gnutls_transport_set_pull_timeout_function()}  for successful operation. There

was a bug before 3.6.10 which could make this function fail if that callback

was not set. On later versions if not set, the function will return a successful

error code, but will return dummy data that cannot lead to a resumption.

@strong{Returns:} On success, @code{GNUTLS_E_SUCCESS}  (0) is returned, otherwise

an error code is returned.

@end deftypefun