BIO_s_accept(3) OpenSSL BIO_s_accept(3)NAME
BIO_s_accept, BIO_set_accept_port, BIO_get_accept_port,
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
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() but not BIO_gets().
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() 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() and BIO_set_fd() 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() for connect BIOs, that is it can be a numerical
port string or a string to lookup using getservbyname() and a string
table.
BIO_new_accept() combines BIO_new() and BIO_set_accept_port() into a
single call: that is 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 and 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 functions. 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
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().
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() (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() 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_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.
RETURN VALUES
TBA
EXAMPLE
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
TBA
1.0.1f 2014-01-06 BIO_s_accept(3)
