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gnutls_transport_set_fastopen - Man Page

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 flags);


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.



Reporting Bugs

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

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



3.8.6 gnutls