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_name(), BIO_get_accept_name(), 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

BIO_do_accept(), BIO_set_accept_name(), BIO_set_accept_port(), BIO_set_nbio_accept(), BIO_set_accept_bios(), and BIO_set_bind_mode(), return 1 for success and 0 or -1 for failure.

BIO_get_accept_name() returns the accept name or NULL on error.

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.

EXAMPLE

This example accepts two connections on port 4444, sends messages down each and finally closes both down.

BIO *abio, *cbio, *cbio2;

/* First call to BIO_accept() sets up accept BIO */
abio = BIO_new_accept("4444");
if (BIO_do_accept(abio) <= 0) {
    fprintf(stderr, "Error setting up accept\n");
    ERR_print_errors_fp(stderr);
    exit(1);
}

/* Wait for incoming connection */
if (BIO_do_accept(abio) <= 0) {
    fprintf(stderr, "Error accepting connection\n");
    ERR_print_errors_fp(stderr);
    exit(1);
}
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(1);
}
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);

COPYRIGHT

Copyright 2000-2016 The OpenSSL Project Authors. All Rights Reserved.