BIO_S_ACCEPT(3) BSD 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>
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(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
int
BIO_do_accept(BIO *b);
DESCRIPTIONBIO_s_accept() returns the accept BIO method. This is a wrapper round
the platform's TCP/IP socket accept routines.
Using accept BIOs, TCP/IP connections can be accepted and data trans‐
ferred using only BIO routines. In this way any platform specific opera‐
tions are hidden by the BIO abstraction.
Read and write operations on an accept BIO will perform I/O on the under‐
lying 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 shutdown and the socket closed when the BIO is freed.
Calling BIO_reset(3) on a 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. Either or both values can be "*"
which is interpreted as meaning any interface or port respectively. 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 lookup
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 setup, 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
then 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 con‐
nection 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 call‐
ing:
connection = BIO_pop(accept);
After this call, connection will contain a BIO for the recently estab‐
lished 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 applica‐
tion should take appropriate action to wait until the underlying socket
has accepted a connection and retry the call.
BIO_set_accept_port(), BIO_get_accept_port(), BIO_set_nbio_accept(),
BIO_set_accept_bios(), BIO_set_bind_mode(), BIO_get_bind_mode(), and
BIO_do_accept() are macros.
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);
BSD April 25, 2024 BSD
