NAME

       gnutls_transport_set_fastopen - API function

SYNOPSIS

       #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

       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

       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

       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.

SINCE

       3.5.3

REPORTING BUGS

       Report bugs to <bugs@gnutls.org>.
       Home page: https://www.gnutls.org

COPYRIGHT

       Copyright © 2001- 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

       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

       https://www.gnutls.org/manual/