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Command: BIO_s_accept | Section: 3 | Source: OpenBSD | File: BIO_s_accept.3
BIO_S_ACCEPT(3) FreeBSD Library Functions Manual BIO_S_ACCEPT(3)
NAME
BIO_s_accept, BIO_set_accept_port, BIO_get_accept_port, BIO_new_accept,
BIO_set_nbio_accept, BIO_set_accept_bios, BIO_set_bind_mode,
BIO_get_bind_mode, BIO_do_accept - accept BIO
SYNOPSIS
#include <openssl/bio.h>
const BIO_METHOD *
BIO_s_accept(void);
long
BIO_set_accept_port(BIO *b, char *name);
char *
BIO_get_accept_port(BIO *b);
BIO *
BIO_new_accept(const char *host_port);
long
BIO_set_nbio_accept(BIO *b, int n);
long
BIO_set_accept_bios(BIO *b, char *bio);
long
BIO_set_bind_mode(BIO *b, long mode);
long
BIO_get_bind_mode(BIO *b, long dummy);
#define BIO_BIND_NORMAL 0
#define BIO_BIND_REUSEADDR_IF_UNUSED 1
#define BIO_BIND_REUSEADDR 2
long
BIO_do_accept(BIO *b);
DESCRIPTION
BIO_s_accept() returns the accept BIO method. This is a wrapper round
the platform's TCP/IP socket accept(2) routines.
Using accept BIOs, TCP/IP connections can be accepted and data
transferred using only BIO routines. In this way any platform specific
operations are hidden by the BIO abstraction.
Read and write operations on an accept BIO will perform I/O on the
underlying connection. If no connection is established and the port (see
below) is set up properly then the BIO waits for an incoming connection.
Accept BIOs support BIO_puts(3) but not BIO_gets(3).
If the close flag is set on an accept BIO, then any active connection on
that chain is shut down and the socket closed when the BIO is freed.
Calling BIO_reset(3) on an accept BIO will close any active connection
and reset the BIO into a state where it awaits another incoming
connection.
BIO_get_fd(3) and BIO_set_fd(3) can be called to retrieve or set the
accept socket. See BIO_s_fd(3).
BIO_set_accept_port() uses the string name to set the accept port. The
port is represented as a string of the form host:port, where host is the
interface to use and port is the port. The host can be "*", which is
interpreted as meaning any interface; port has the same syntax as the
port specified in BIO_set_conn_port(3) for connect BIOs. It can be a
numerical port string or a string to look up using getservbyname(3) and a
string table.
BIO_new_accept() combines BIO_new(3) and BIO_set_accept_port() into a
single call. It creates a new accept BIO with port host_port.
BIO_set_nbio_accept() sets the accept socket to blocking mode (the
default) if n is 0 or non-blocking mode if n is 1.
BIO_set_accept_bios() can be used to set a chain of BIOs which will be
duplicated and prepended to the chain when an incoming connection is
received. This is useful if, for example, a buffering or SSL BIO is
required for each connection. The chain of BIOs must not be freed after
this call - they will be automatically freed when the accept BIO is
freed.
BIO_set_bind_mode() and BIO_get_bind_mode() set and retrieve the current
bind mode. If BIO_BIND_NORMAL (the default) is set, then another socket
cannot be bound to the same port. If BIO_BIND_REUSEADDR is set, then
other sockets can bind to the same port. If BIO_BIND_REUSEADDR_IF_UNUSED
is set, then an attempt is first made to use BIO_BIN_NORMAL; if this
fails and the port is not in use, then a second attempt is made using
BIO_BIND_REUSEADDR.
BIO_do_accept() serves two purposes. When it is first called, after the
accept BIO has been set up, it will attempt to create the accept socket
and bind an address to it. Second and subsequent calls to
BIO_do_accept() will await an incoming connection, or request a retry in
non-blocking mode.
NOTES
When an accept BIO is at the end of a chain, it will await an incoming
connection before processing I/O calls. When an accept BIO is not at the
end of a chain, it passes I/O calls to the next BIO in the chain.
When a connection is established, a new socket BIO is created for the
connection and appended to the chain. That is the chain is now
accept->socket. This effectively means that attempting I/O on an initial
accept socket will await an incoming connection then perform I/O on it.
If any additional BIOs have been set using BIO_set_accept_bios(), then
they are placed between the socket and the accept BIO; that is, the chain
will be accept->otherbios->socket.
If a server wishes to process multiple connections (as is normally the
case), then the accept BIO must be made available for further incoming
connections. This can be done by waiting for a connection and then
calling:
connection = BIO_pop(accept);
After this call, connection will contain a BIO for the recently
established connection and accept will now be a single BIO again which
can be used to await further incoming connections. If no further
connections will be accepted, the accept can be freed using BIO_free(3).
If only a single connection will be processed, it is possible to perform
I/O using the accept BIO itself. This is often undesirable however
because the accept BIO will still accept additional incoming connections.
This can be resolved by using BIO_pop(3) (see above) and freeing up the
accept BIO after the initial connection.
If the underlying accept socket is non-blocking and BIO_do_accept() is
called to await an incoming connection, it is possible for
BIO_should_io_special(3) with the reason BIO_RR_ACCEPT. If this happens,
then it is an indication that an accept attempt would block: the
application should take appropriate action to wait until the underlying
socket has accepted a connection and retry the call.
BIO_ctrl(3) cmd and larg arguments correspond to macros as follows:
cmd constant larg corresponding macro
BIO_C_DO_STATE_MACHINE 0 BIO_do_accept()
BIO_C_GET_ACCEPT 0 BIO_get_accept_port()
BIO_C_GET_BIND_MODE 0 BIO_get_bind_mode()
BIO_C_GET_FD 0 BIO_get_fd(3)
BIO_C_SET_ACCEPT 0 BIO_set_accept_port()
1 BIO_set_nbio_accept()
2 BIO_set_accept_bios()
BIO_C_SET_FD fd BIO_set_fd(3)
BIO_C_SET_NBIO n BIO_set_nbio(3)
BIO_C_SET_BIND_MODE mode BIO_set_bind_mode()
BIO_CTRL_GET_CLOSE 0 BIO_get_close(3)
BIO_CTRL_RESET 0 BIO_reset(3)
BIO_CTRL_SET_CLOSE flag BIO_set_close(3)
RETURN VALUES
When called on an accept BIO object, BIO_method_type(3) returns the
constant BIO_TYPE_ACCEPT and BIO_method_name(3) returns a pointer to the
static string "socket accept".
BIO_do_accept(), BIO_set_accept_port(), BIO_set_nbio_accept(),
BIO_set_accept_bios(), and BIO_set_bind_mode() return 1 for success or 0
or -1 for failure.
BIO_get_accept_port() returns the port as a string or NULL on error.
BIO_get_bind_mode() returns the set of BIO_BIND flags or -1 on failure.
BIO_new_accept() returns a BIO or NULL on error.
EXAMPLES
This example accepts two connections on port 4444, sends messages down
each and finally closes both down.
BIO *abio, *cbio, *cbio2;
ERR_load_crypto_strings();
abio = BIO_new_accept("4444");
/* First call to BIO_accept() sets up accept BIO */
if (BIO_do_accept(abio) <= 0) {
fprintf(stderr, "Error setting up accept\n");
ERR_print_errors_fp(stderr);
exit(0);
}
/* Wait for incoming connection */
if (BIO_do_accept(abio) <= 0) {
fprintf(stderr, "Error accepting connection\n");
ERR_print_errors_fp(stderr);
exit(0);
}
fprintf(stderr, "Connection 1 established\n");
/* Retrieve BIO for connection */
cbio = BIO_pop(abio);
BIO_puts(cbio, "Connection 1: Sending out Data on initial connection\n");
fprintf(stderr, "Sent out data on connection 1\n");
/* Wait for another connection */
if (BIO_do_accept(abio) <= 0) {
fprintf(stderr, "Error accepting connection\n");
ERR_print_errors_fp(stderr);
exit(0);
}
fprintf(stderr, "Connection 2 established\n");
/* Close accept BIO to refuse further connections */
cbio2 = BIO_pop(abio);
BIO_free(abio);
BIO_puts(cbio2, "Connection 2: Sending out Data on second\n");
fprintf(stderr, "Sent out data on connection 2\n");
BIO_puts(cbio, "Connection 1: Second connection established\n");
/* Close the two established connections */
BIO_free(cbio);
BIO_free(cbio2);
SEE ALSO
BIO_new(3)
HISTORY
BIO_s_accept(), BIO_set_accept_port(), BIO_new_accept(),
BIO_set_accept_bios(), and BIO_do_accept() first appeared in SSLeay
0.8.0. BIO_set_nbio_accept() and BIO_get_accept_port() first appeared in
SSLeay 0.9.0. All these functions have been available since OpenBSD 2.4.
BIO_set_bind_mode() and BIO_get_bind_mode() first appeared in SSLeay
0.9.1 and have been available since OpenBSD 2.6.
FreeBSD 14.1-RELEASE-p8 April 29, 2023 FreeBSD 14.1-RELEASE-p8