gnutls_transport_set_fastopen(3)     gnutls     gnutls_transport_set_fastopen(3)

       gnutls_transport_set_fastopen - API function

       #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

       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

       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.

       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 called.

       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.


       Report bugs to <>.
       Home page:

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       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.

       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

gnutls                               3.6.13     gnutls_transport_set_fastopen(3)