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);
DESCRIPTION¶
BIO_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