first BIO then traverses the chain to the end (normally a source/sink
BIO).
-
Some BIOs (such as memory BIOs) can be used immediately after calling
BIO_new(). Others (such as file BIOs) need some additional initialization,
and frequently a utility function exists to create and initialize such BIOs.
a source/sink BIO typically starts with I<BIO_s_> and
a filter BIO with I<BIO_f_>.
+=head2 TCP Fast Open
+
+TCP Fast Open (RFC7413), abbreviated "TFO", is supported by the BIO
+interface since OpenSSL 3.1. TFO is supported in the following operating systems:
+
+=over 4
+
+=item * Linux kernel 3.13 and later, where TFO is enabled by default.
+
+=item * Linux kernel 4.11 and later, using TCP_FASTOPEN_CONNECT.
+
+=item * FreeBSD 10.3 to 11.4, supports server TFO only.
+
+=item * FreeBSD 12.0 and later, supports both client and server TFO.
+
+=item * macOS 10.14 and later.
+
+=back
+
+Each operating system has a slightly different API for TFO. Please
+refer to the operating systems' API documentation when using
+sockets directly.
+
=head1 EXAMPLES
Create a memory BIO:
L<BIO_f_cipher(3)>, L<BIO_f_md(3)>,
L<BIO_f_null(3)>, L<BIO_f_ssl(3)>,
L<BIO_f_readbuffer(3)>,
-L<BIO_find_type(3)>, L<BIO_new(3)>,
+L<BIO_find_type(3)>,
+L<BIO_get_conn_mode(3)>,
+L<BIO_new(3)>,
L<BIO_new_bio_pair(3)>,
L<BIO_push(3)>, L<BIO_read_ex(3)>,
L<BIO_s_accept(3)>, L<BIO_s_bio(3)>,
L<BIO_s_file(3)>, L<BIO_s_mem(3)>,
L<BIO_s_null(3)>, L<BIO_s_socket(3)>,
L<BIO_set_callback(3)>,
+L<BIO_set_conn_mode(3)>,
+L<BIO_set_tfo(3)>,
+L<BIO_set_tfo_accept(3)>,
L<BIO_should_retry(3)>
=head1 COPYRIGHT
L<https://www.openssl.org/source/license.html>.
=cut
-