BIO_CONNECT(3SSL) OpenSSL BIO_CONNECT(3SSL)
NAME
BIO_socket, BIO_bind, BIO_connect, BIO_listen, BIO_accept_ex,
BIO_closesocket - BIO socket communication setup routines
SYNOPSIS
#include <openssl/bio.h>
int BIO_socket(int domain, int socktype, int protocol, int options);
int BIO_bind(int sock, const BIO_ADDR *addr, int options);
int BIO_connect(int sock, const BIO_ADDR *addr, int options);
int BIO_listen(int sock, const BIO_ADDR *addr, int options);
int BIO_accept_ex(int accept_sock, BIO_ADDR *peer, int options);
int BIO_closesocket(int sock);
DESCRIPTION
BIO_socket() creates a socket in the domain domain, of type socktype and
protocol. Socket options are currently unused, but is present for
future use.
BIO_bind() binds the source address and service to a socket and may be
useful before calling BIO_connect(). The options may include
BIO_SOCK_REUSEADDR, which is described in "FLAGS" below.
BIO_connect() connects sock to the address and service given by addr.
Connection options may be zero or any combination of BIO_SOCK_KEEPALIVE,
BIO_SOCK_NONBLOCK and BIO_SOCK_NODELAY. The flags are described in
"FLAGS" below.
BIO_listen() has sock start listening on the address and service given
by addr. Connection options may be zero or any combination of
BIO_SOCK_KEEPALIVE, BIO_SOCK_NONBLOCK, BIO_SOCK_NODELAY,
BIO_SOCK_REUSEADDR and BIO_SOCK_V6_ONLY. The flags are described in
"FLAGS" below.
BIO_accept_ex() waits for an incoming connections on the given socket
accept_sock. When it gets a connection, the address and port of the
peer gets stored in peer if that one is non-NULL. Accept options may be
zero or BIO_SOCK_NONBLOCK, and is applied on the accepted socket. The
flags are described in "FLAGS" below.
BIO_closesocket() closes sock.
FLAGS
BIO_SOCK_KEEPALIVE
Enables regular sending of keep-alive messages.
BIO_SOCK_NONBLOCK
Sets the socket to nonblocking mode.
BIO_SOCK_NODELAY
Corresponds to TCP_NODELAY, and disables the Nagle algorithm. With
this set, any data will be sent as soon as possible instead of being
buffered until there's enough for the socket to send out in one go.
BIO_SOCK_REUSEADDR
Try to reuse the address and port combination for a recently closed
port.
BIO_SOCK_V6_ONLY
When creating an IPv6 socket, make it only listen for IPv6 addresses
and not IPv4 addresses mapped to IPv6.
BIO_SOCK_TFO
Enables TCP Fast Open on the socket. Uses appropriate APIs on
supported operating systems, including Linux, macOS and FreeBSD. Can
be used with BIO_connect(), BIO_set_conn_mode(),
BIO_set_bind_mode(), and BIO_listen(). On Linux kernels before
4.14, use BIO_set_conn_address() to specify the peer address before
starting the TLS handshake.
These flags are bit flags, so they are to be combined with the "|"
operator, for example:
BIO_connect(sock, addr, BIO_SOCK_KEEPALIVE | BIO_SOCK_NONBLOCK);
RETURN VALUES
BIO_socket() returns the socket number on success or INVALID_SOCKET (-1)
on error. When an error has occurred, the OpenSSL error stack will hold
the error data and errno has the system error.
BIO_bind(), BIO_connect() and BIO_listen() return 1 on success or 0 on
error. When an error has occurred, the OpenSSL error stack will hold
the error data and errno has the system error.
BIO_accept_ex() returns the accepted socket on success or INVALID_SOCKET
(-1) on error. When an error has occurred, the OpenSSL error stack will
hold the error data and errno has the system error.
SEE ALSO
BIO_ADDR(3)
HISTORY
BIO_gethostname(), BIO_get_port(), BIO_get_host_ip(),
BIO_get_accept_socket() and BIO_accept() were deprecated in OpenSSL
1.1.0. Use the functions described above instead.
COPYRIGHT
Copyright 2016-2022 The OpenSSL Project Authors. All Rights Reserved.
Licensed under the Apache License 2.0 (the "License"). You may not use
this file except in compliance with the License. You can obtain a copy
in the file LICENSE in the source distribution or at
<https://www.openssl.org/source/license.html>.
3.5.7 2026-06-09 BIO_CONNECT(3SSL)
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