gnutls_transport_set_fastopen(3)   gnutls   gnutls_transport_set_fastopen(3)

NAME         top

       gnutls_transport_set_fastopen - API function

SYNOPSIS         top

       #include <gnutls/socket.h>

       void gnutls_transport_set_fastopen(gnutls_session_t session, int fd,
       struct sockaddr * connect_addr, socklen_t connect_addrlen, unsigned
       int flags);

ARGUMENTS         top

       gnutls_session_t session
                   is a gnutls_session_t type.

       int fd      is the session's socket descriptor

       struct sockaddr * connect_addr
                   is the address we want to connect to

       socklen_t connect_addrlen
                   is the length of  connect_addr

       unsigned int flags
                   must be zero

DESCRIPTION         top

       Enables TCP Fast Open (TFO) for the specified TLS client session.
       That means that TCP connection establishment and the transmission of
       the first TLS client hello packet are combined. The peer's address
       must be  specified in  connect_addr and  connect_addrlen , and the
       socket specified by  fd should not be connected.

       TFO only works for TCP sockets of type AF_INET and AF_INET6.  If the
       OS doesn't support TCP fast open this function will result to gnutls
       using connect() transparently during the first write.

NOTE         top

       This function overrides all the transport callback functions.  If
       this is undesirable, TCP Fast Open must be implemented on the user
       callback functions without calling this function. When using this
       function, transport callbacks must not be set, and
       gnutls_transport_set_ptr() or gnutls_transport_set_int() must not be

       On GNU/Linux TFO has to be enabled at the system layer, that is in
       /proc/sys/net/ipv4/tcp_fastopen, bit 0 has to be set.

       This function has no effect on server sessions.

SINCE         top


REPORTING BUGS         top

       Report bugs to <>.
       Home page:

COPYRIGHT         top

       Copyright © 2001-2018 Free Software Foundation, Inc., and others.
       Copying and distribution of this file, with or without modification,
       are permitted in any medium without royalty provided the copyright
       notice and this notice are preserved.

SEE ALSO         top

       The full documentation for gnutls is maintained as a Texinfo manual.
       If the /usr/share/doc/gnutls/ directory does not contain the HTML
       form visit 

COLOPHON         top

       This page is part of the GnuTLS (GnuTLS Transport Layer Security
       Library) project.  Information about the project can be found at 
       ⟨⟩.  If you have a bug report for this manual
       page, send it to  This page was obtained from the
       tarball gnutls-3.6.2.tar.xz fetched from
       ⟨⟩ on 2018-04-30.  If you discover
       any rendering problems in this HTML version of the page, or you
       believe there is a better or more up-to-date source for the page, or
       you have corrections or improvements to the information in this
       COLOPHON (which is not part of the original manual page), send a mail

gnutls                              3.6.2   gnutls_transport_set_fastopen(3)