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129 .\" ========================================================================
131 .IX Title "BIO_s_accept 3"
132 .TH BIO_s_accept 3 "2017-12-07" "1.0.2n" "OpenSSL"
133 .\" For nroff, turn off justification. Always turn off hyphenation; it makes
134 .\" way too many mistakes in technical documents.
138 BIO_s_accept, BIO_set_accept_port, BIO_get_accept_port, BIO_new_accept,
139 BIO_set_nbio_accept, BIO_set_accept_bios, BIO_set_bind_mode,
140 BIO_get_bind_mode, BIO_do_accept \- accept BIO
142 .IX Header "SYNOPSIS"
144 \& #include <openssl/bio.h>
146 \& BIO_METHOD *BIO_s_accept(void);
148 \& long BIO_set_accept_port(BIO *b, char *name);
149 \& char *BIO_get_accept_port(BIO *b);
151 \& BIO *BIO_new_accept(char *host_port);
153 \& long BIO_set_nbio_accept(BIO *b, int n);
154 \& long BIO_set_accept_bios(BIO *b, char *bio);
156 \& long BIO_set_bind_mode(BIO *b, long mode);
157 \& long BIO_get_bind_mode(BIO *b, long dummy);
159 \& #define BIO_BIND_NORMAL 0
160 \& #define BIO_BIND_REUSEADDR_IF_UNUSED 1
161 \& #define BIO_BIND_REUSEADDR 2
163 \& int BIO_do_accept(BIO *b);
166 .IX Header "DESCRIPTION"
167 \&\fIBIO_s_accept()\fR returns the accept \s-1BIO\s0 method. This is a wrapper
168 round the platform's \s-1TCP/IP\s0 socket accept routines.
170 Using accept BIOs, \s-1TCP/IP\s0 connections can be accepted and data
171 transferred using only \s-1BIO\s0 routines. In this way any platform
172 specific operations are hidden by the \s-1BIO\s0 abstraction.
174 Read and write operations on an accept \s-1BIO\s0 will perform I/O
175 on the underlying connection. If no connection is established
176 and the port (see below) is set up properly then the \s-1BIO\s0
177 waits for an incoming connection.
179 Accept BIOs support \fIBIO_puts()\fR but not \fIBIO_gets()\fR.
181 If the close flag is set on an accept \s-1BIO\s0 then any active
182 connection on that chain is shutdown and the socket closed when
183 the \s-1BIO\s0 is freed.
185 Calling \fIBIO_reset()\fR on a accept \s-1BIO\s0 will close any active
186 connection and reset the \s-1BIO\s0 into a state where it awaits another
189 \&\fIBIO_get_fd()\fR and \fIBIO_set_fd()\fR can be called to retrieve or set
190 the accept socket. See \fIBIO_s_fd\fR\|(3)
192 \&\fIBIO_set_accept_port()\fR uses the string \fBname\fR to set the accept
193 port. The port is represented as a string of the form \*(L"host:port\*(R",
194 where \*(L"host\*(R" is the interface to use and \*(L"port\*(R" is the port.
195 The host can be can be \*(L"*\*(R" which is interpreted as meaning
196 any interface; \*(L"port\*(R" has the same syntax
197 as the port specified in \fIBIO_set_conn_port()\fR for connect BIOs,
198 that is it can be a numerical port string or a string to lookup
199 using \fIgetservbyname()\fR and a string table.
201 \&\fIBIO_new_accept()\fR combines \fIBIO_new()\fR and \fIBIO_set_accept_port()\fR into
202 a single call: that is it creates a new accept \s-1BIO\s0 with port
205 \&\fIBIO_set_nbio_accept()\fR sets the accept socket to blocking mode
206 (the default) if \fBn\fR is 0 or non blocking mode if \fBn\fR is 1.
208 \&\fIBIO_set_accept_bios()\fR can be used to set a chain of BIOs which
209 will be duplicated and prepended to the chain when an incoming
210 connection is received. This is useful if, for example, a
211 buffering or \s-1SSL BIO\s0 is required for each connection. The
212 chain of BIOs must not be freed after this call, they will
213 be automatically freed when the accept \s-1BIO\s0 is freed.
215 \&\fIBIO_set_bind_mode()\fR and \fIBIO_get_bind_mode()\fR set and retrieve
216 the current bind mode. If \s-1BIO_BIND_NORMAL \s0(the default) is set
217 then another socket cannot be bound to the same port. If
218 \&\s-1BIO_BIND_REUSEADDR\s0 is set then other sockets can bind to the
219 same port. If \s-1BIO_BIND_REUSEADDR_IF_UNUSED\s0 is set then and
220 attempt is first made to use \s-1BIO_BIN_NORMAL,\s0 if this fails
221 and the port is not in use then a second attempt is made
222 using \s-1BIO_BIND_REUSEADDR.\s0
224 \&\fIBIO_do_accept()\fR serves two functions. When it is first
225 called, after the accept \s-1BIO\s0 has been setup, it will attempt
226 to create the accept socket and bind an address to it. Second
227 and subsequent calls to \fIBIO_do_accept()\fR will await an incoming
228 connection, or request a retry in non blocking mode.
231 When an accept \s-1BIO\s0 is at the end of a chain it will await an
232 incoming connection before processing I/O calls. When an accept
233 \&\s-1BIO\s0 is not at then end of a chain it passes I/O calls to the next
234 \&\s-1BIO\s0 in the chain.
236 When a connection is established a new socket \s-1BIO\s0 is created for
237 the connection and appended to the chain. That is the chain is now
238 accept\->socket. This effectively means that attempting I/O on
239 an initial accept socket will await an incoming connection then
242 If any additional BIOs have been set using \fIBIO_set_accept_bios()\fR
243 then they are placed between the socket and the accept \s-1BIO,\s0
244 that is the chain will be accept\->otherbios\->socket.
246 If a server wishes to process multiple connections (as is normally
247 the case) then the accept \s-1BIO\s0 must be made available for further
248 incoming connections. This can be done by waiting for a connection and
252 \& connection = BIO_pop(accept);
255 After this call \fBconnection\fR will contain a \s-1BIO\s0 for the recently
256 established connection and \fBaccept\fR will now be a single \s-1BIO\s0
257 again which can be used to await further incoming connections.
258 If no further connections will be accepted the \fBaccept\fR can
259 be freed using \fIBIO_free()\fR.
261 If only a single connection will be processed it is possible to
262 perform I/O using the accept \s-1BIO\s0 itself. This is often undesirable
263 however because the accept \s-1BIO\s0 will still accept additional incoming
264 connections. This can be resolved by using \fIBIO_pop()\fR (see above)
265 and freeing up the accept \s-1BIO\s0 after the initial connection.
267 If the underlying accept socket is non-blocking and \fIBIO_do_accept()\fR is
268 called to await an incoming connection it is possible for
269 \&\fIBIO_should_io_special()\fR with the reason \s-1BIO_RR_ACCEPT.\s0 If this happens
270 then it is an indication that an accept attempt would block: the application
271 should take appropriate action to wait until the underlying socket has
272 accepted a connection and retry the call.
274 \&\fIBIO_set_accept_port()\fR, \fIBIO_get_accept_port()\fR, \fIBIO_set_nbio_accept()\fR,
275 \&\fIBIO_set_accept_bios()\fR, \fIBIO_set_bind_mode()\fR, \fIBIO_get_bind_mode()\fR and
276 \&\fIBIO_do_accept()\fR are macros.
278 .IX Header "RETURN VALUES"
282 This example accepts two connections on port 4444, sends messages
283 down each and finally closes both down.
286 \& BIO *abio, *cbio, *cbio2;
287 \& ERR_load_crypto_strings();
288 \& abio = BIO_new_accept("4444");
290 \& /* First call to BIO_accept() sets up accept BIO */
291 \& if(BIO_do_accept(abio) <= 0) {
292 \& fprintf(stderr, "Error setting up accept\en");
293 \& ERR_print_errors_fp(stderr);
297 \& /* Wait for incoming connection */
298 \& if(BIO_do_accept(abio) <= 0) {
299 \& fprintf(stderr, "Error accepting connection\en");
300 \& ERR_print_errors_fp(stderr);
303 \& fprintf(stderr, "Connection 1 established\en");
304 \& /* Retrieve BIO for connection */
305 \& cbio = BIO_pop(abio);
306 \& BIO_puts(cbio, "Connection 1: Sending out Data on initial connection\en");
307 \& fprintf(stderr, "Sent out data on connection 1\en");
308 \& /* Wait for another connection */
309 \& if(BIO_do_accept(abio) <= 0) {
310 \& fprintf(stderr, "Error accepting connection\en");
311 \& ERR_print_errors_fp(stderr);
314 \& fprintf(stderr, "Connection 2 established\en");
315 \& /* Close accept BIO to refuse further connections */
316 \& cbio2 = BIO_pop(abio);
318 \& BIO_puts(cbio2, "Connection 2: Sending out Data on second\en");
319 \& fprintf(stderr, "Sent out data on connection 2\en");
321 \& BIO_puts(cbio, "Connection 1: Second connection established\en");
322 \& /* Close the two established connections */
327 .IX Header "SEE ALSO"