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.\" ========================================================================
.\"
.IX Title "BIO_s_accept 3"
.TH BIO_s_accept 3 "2019-12-20" "1.0.2u" "OpenSSL"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
.if n .ad l
.nh
.SH "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
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 1
\& #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);
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
\&\fBBIO_s_accept()\fR returns the accept \s-1BIO\s0 method. This is a wrapper
round the platform's \s-1TCP/IP\s0 socket accept routines.
.PP
Using accept BIOs, \s-1TCP/IP\s0 connections can be accepted and data
transferred using only \s-1BIO\s0 routines. In this way any platform
specific operations are hidden by the \s-1BIO\s0 abstraction.
.PP
Read and write operations on an accept \s-1BIO\s0 will perform I/O
on the underlying connection. If no connection is established
and the port (see below) is set up properly then the \s-1BIO\s0
waits for an incoming connection.
.PP
Accept BIOs support \fBBIO_puts()\fR but not \fBBIO_gets()\fR.
.PP
If the close flag is set on an accept \s-1BIO\s0 then any active
connection on that chain is shutdown and the socket closed when
the \s-1BIO\s0 is freed.
.PP
Calling \fBBIO_reset()\fR on a accept \s-1BIO\s0 will close any active
connection and reset the \s-1BIO\s0 into a state where it awaits another
incoming connection.
.PP
\&\fBBIO_get_fd()\fR and \fBBIO_set_fd()\fR can be called to retrieve or set
the accept socket. See \fBBIO_s_fd\fR\|(3)
.PP
\&\fBBIO_set_accept_port()\fR uses the string \fBname\fR to set the accept
port. The port is represented as a string of the form \*(L"host:port\*(R",
where \*(L"host\*(R" is the interface to use and \*(L"port\*(R" is the port.
The host can be can be \*(L"*\*(R" which is interpreted as meaning
any interface; \*(L"port\*(R" has the same syntax
as the port specified in \fBBIO_set_conn_port()\fR for connect BIOs,
that is it can be a numerical port string or a string to lookup
using \fBgetservbyname()\fR and a string table.
.PP
\&\fBBIO_new_accept()\fR combines \fBBIO_new()\fR and \fBBIO_set_accept_port()\fR into
a single call: that is it creates a new accept \s-1BIO\s0 with port
\&\fBhost_port\fR.
.PP
\&\fBBIO_set_nbio_accept()\fR sets the accept socket to blocking mode
(the default) if \fBn\fR is 0 or non blocking mode if \fBn\fR is 1.
.PP
\&\fBBIO_set_accept_bios()\fR 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 \s-1SSL BIO\s0 is required for each connection. The
chain of BIOs must not be freed after this call, they will
be automatically freed when the accept \s-1BIO\s0 is freed.
.PP
\&\fBBIO_set_bind_mode()\fR and \fBBIO_get_bind_mode()\fR set and retrieve
the current bind mode. If \s-1BIO_BIND_NORMAL\s0 (the default) is set
then another socket cannot be bound to the same port. If
\&\s-1BIO_BIND_REUSEADDR\s0 is set then other sockets can bind to the
same port. If \s-1BIO_BIND_REUSEADDR_IF_UNUSED\s0 is set then and
attempt is first made to use \s-1BIO_BIN_NORMAL,\s0 if this fails
and the port is not in use then a second attempt is made
using \s-1BIO_BIND_REUSEADDR.\s0
.PP
\&\fBBIO_do_accept()\fR serves two functions. When it is first
called, after the accept \s-1BIO\s0 has been setup, it will attempt
to create the accept socket and bind an address to it. Second
and subsequent calls to \fBBIO_do_accept()\fR will await an incoming
connection, or request a retry in non blocking mode.
.SH "NOTES"
.IX Header "NOTES"
When an accept \s-1BIO\s0 is at the end of a chain it will await an
incoming connection before processing I/O calls. When an accept
\&\s-1BIO\s0 is not at then end of a chain it passes I/O calls to the next
\&\s-1BIO\s0 in the chain.
.PP
When a connection is established a new socket \s-1BIO\s0 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.
.PP
If any additional BIOs have been set using \fBBIO_set_accept_bios()\fR
then they are placed between the socket and the accept \s-1BIO,\s0
that is the chain will be accept\->otherbios\->socket.
.PP
If a server wishes to process multiple connections (as is normally
the case) then the accept \s-1BIO\s0 must be made available for further
incoming connections. This can be done by waiting for a connection and
then calling:
.PP
.Vb 1
\& connection = BIO_pop(accept);
.Ve
.PP
After this call \fBconnection\fR will contain a \s-1BIO\s0 for the recently
established connection and \fBaccept\fR will now be a single \s-1BIO\s0
again which can be used to await further incoming connections.
If no further connections will be accepted the \fBaccept\fR can
be freed using \fBBIO_free()\fR.
.PP
If only a single connection will be processed it is possible to
perform I/O using the accept \s-1BIO\s0 itself. This is often undesirable
however because the accept \s-1BIO\s0 will still accept additional incoming
connections. This can be resolved by using \fBBIO_pop()\fR (see above)
and freeing up the accept \s-1BIO\s0 after the initial connection.
.PP
If the underlying accept socket is non-blocking and \fBBIO_do_accept()\fR is
called to await an incoming connection it is possible for
\&\fBBIO_should_io_special()\fR with the reason \s-1BIO_RR_ACCEPT.\s0 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.
.PP
\&\fBBIO_set_accept_port()\fR, \fBBIO_get_accept_port()\fR, \fBBIO_set_nbio_accept()\fR,
\&\fBBIO_set_accept_bios()\fR, \fBBIO_set_bind_mode()\fR, \fBBIO_get_bind_mode()\fR and
\&\fBBIO_do_accept()\fR are macros.
.SH "RETURN VALUES"
.IX Header "RETURN VALUES"
\&\s-1TBA\s0
.SH "EXAMPLE"
.IX Header "EXAMPLE"
This example accepts two connections on port 4444, sends messages
down each and finally closes both down.
.PP
.Vb 3
\& 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\en");
\&        ERR_print_errors_fp(stderr);
\&        exit(0);                
\& }
\&
\& /* Wait for incoming connection */
\& if(BIO_do_accept(abio) <= 0) {
\&        fprintf(stderr, "Error accepting connection\en");
\&        ERR_print_errors_fp(stderr);
\&        exit(0);                
\& }
\& fprintf(stderr, "Connection 1 established\en");
\& /* Retrieve BIO for connection */
\& cbio = BIO_pop(abio);
\& BIO_puts(cbio, "Connection 1: Sending out Data on initial connection\en");
\& fprintf(stderr, "Sent out data on connection 1\en");
\& /* Wait for another connection */
\& if(BIO_do_accept(abio) <= 0) {
\&        fprintf(stderr, "Error accepting connection\en");
\&        ERR_print_errors_fp(stderr);
\&        exit(0);                
\& }
\& fprintf(stderr, "Connection 2 established\en");
\& /* Close accept BIO to refuse further connections */
\& cbio2 = BIO_pop(abio);
\& BIO_free(abio);
\& BIO_puts(cbio2, "Connection 2: Sending out Data on second\en");
\& fprintf(stderr, "Sent out data on connection 2\en");
\&
\& BIO_puts(cbio, "Connection 1: Second connection established\en");
\& /* Close the two established connections */
\& BIO_free(cbio);
\& BIO_free(cbio2);
.Ve
.SH "SEE ALSO"
.IX Header "SEE ALSO"
\&\s-1TBA\s0

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✏️ BIO_set_nbio_accept.3ssl