gnutls_transport_set_fastopen(3) gnutls gnutls_transport_set_fastopen(3)
gnutls gnutls
3.6.6
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
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
- 1 - Formatted: November 5, 2025
gnutls_transport_set_fastopen(3) gnutls gnutls_transport_set_fastopen(3)
gnutls gnutls
3.6.6
REPORTING BUGS
Report bugs to <bugs@gnutls.org>.
Home page: http://www.gnutls.org
COPYRIGHT
Copyright c 2001-2020 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
http://www.gnutls.org/manual/
- 2 - Formatted: November 5, 2025
