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133 .\" ========================================================================
135 .IX Title "BIO_s_bio 3"
136 .TH BIO_s_bio 3 "2016-05-03" "1.0.2h" "OpenSSL"
137 .\" For nroff, turn off justification. Always turn off hyphenation; it makes
138 .\" way too many mistakes in technical documents.
142 BIO_s_bio, BIO_make_bio_pair, BIO_destroy_bio_pair, BIO_shutdown_wr,
143 BIO_set_write_buf_size, BIO_get_write_buf_size, BIO_new_bio_pair,
144 BIO_get_write_guarantee, BIO_ctrl_get_write_guarantee, BIO_get_read_request,
145 BIO_ctrl_get_read_request, BIO_ctrl_reset_read_request \- BIO pair BIO
147 .IX Header "SYNOPSIS"
149 \& #include <openssl/bio.h>
151 \& BIO_METHOD *BIO_s_bio(void);
153 \& #define BIO_make_bio_pair(b1,b2) (int)BIO_ctrl(b1,BIO_C_MAKE_BIO_PAIR,0,b2)
154 \& #define BIO_destroy_bio_pair(b) (int)BIO_ctrl(b,BIO_C_DESTROY_BIO_PAIR,0,NULL)
156 \& #define BIO_shutdown_wr(b) (int)BIO_ctrl(b, BIO_C_SHUTDOWN_WR, 0, NULL)
158 \& #define BIO_set_write_buf_size(b,size) (int)BIO_ctrl(b,BIO_C_SET_WRITE_BUF_SIZE,size,NULL)
159 \& #define BIO_get_write_buf_size(b,size) (size_t)BIO_ctrl(b,BIO_C_GET_WRITE_BUF_SIZE,size,NULL)
161 \& int BIO_new_bio_pair(BIO **bio1, size_t writebuf1, BIO **bio2, size_t writebuf2);
163 \& #define BIO_get_write_guarantee(b) (int)BIO_ctrl(b,BIO_C_GET_WRITE_GUARANTEE,0,NULL)
164 \& size_t BIO_ctrl_get_write_guarantee(BIO *b);
166 \& #define BIO_get_read_request(b) (int)BIO_ctrl(b,BIO_C_GET_READ_REQUEST,0,NULL)
167 \& size_t BIO_ctrl_get_read_request(BIO *b);
169 \& int BIO_ctrl_reset_read_request(BIO *b);
172 .IX Header "DESCRIPTION"
173 \&\fIBIO_s_bio()\fR returns the method for a \s-1BIO\s0 pair. A \s-1BIO\s0 pair is a pair of source/sink
174 BIOs where data written to either half of the pair is buffered and can be read from
175 the other half. Both halves must usually by handled by the same application thread
176 since no locking is done on the internal data structures.
178 Since \s-1BIO\s0 chains typically end in a source/sink \s-1BIO\s0 it is possible to make this
179 one half of a \s-1BIO\s0 pair and have all the data processed by the chain under application
182 One typical use of \s-1BIO\s0 pairs is to place \s-1TLS/SSL I/O\s0 under application control, this
183 can be used when the application wishes to use a non standard transport for
184 \&\s-1TLS/SSL\s0 or the normal socket routines are inappropriate.
186 Calls to \fIBIO_read()\fR will read data from the buffer or request a retry if no
189 Calls to \fIBIO_write()\fR will place data in the buffer or request a retry if the
192 The standard calls \fIBIO_ctrl_pending()\fR and \fIBIO_ctrl_wpending()\fR can be used to
193 determine the amount of pending data in the read or write buffer.
195 \&\fIBIO_reset()\fR clears any data in the write buffer.
197 \&\fIBIO_make_bio_pair()\fR joins two separate BIOs into a connected pair.
199 \&\fIBIO_destroy_pair()\fR destroys the association between two connected BIOs. Freeing
200 up any half of the pair will automatically destroy the association.
202 \&\fIBIO_shutdown_wr()\fR is used to close down a \s-1BIO \s0\fBb\fR. After this call no further
203 writes on \s-1BIO \s0\fBb\fR are allowed (they will return an error). Reads on the other
204 half of the pair will return any pending data or \s-1EOF\s0 when all pending data has
207 \&\fIBIO_set_write_buf_size()\fR sets the write buffer size of \s-1BIO \s0\fBb\fR to \fBsize\fR.
208 If the size is not initialized a default value is used. This is currently
209 17K, sufficient for a maximum size \s-1TLS\s0 record.
211 \&\fIBIO_get_write_buf_size()\fR returns the size of the write buffer.
213 \&\fIBIO_new_bio_pair()\fR combines the calls to \fIBIO_new()\fR, \fIBIO_make_bio_pair()\fR and
214 \&\fIBIO_set_write_buf_size()\fR to create a connected pair of BIOs \fBbio1\fR, \fBbio2\fR
215 with write buffer sizes \fBwritebuf1\fR and \fBwritebuf2\fR. If either size is
216 zero then the default size is used. \fIBIO_new_bio_pair()\fR does not check whether
217 \&\fBbio1\fR or \fBbio2\fR do point to some other \s-1BIO,\s0 the values are overwritten,
218 \&\fIBIO_free()\fR is not called.
220 \&\fIBIO_get_write_guarantee()\fR and \fIBIO_ctrl_get_write_guarantee()\fR return the maximum
221 length of data that can be currently written to the \s-1BIO.\s0 Writes larger than this
222 value will return a value from \fIBIO_write()\fR less than the amount requested or if the
223 buffer is full request a retry. \fIBIO_ctrl_get_write_guarantee()\fR is a function
224 whereas \fIBIO_get_write_guarantee()\fR is a macro.
226 \&\fIBIO_get_read_request()\fR and \fIBIO_ctrl_get_read_request()\fR return the
227 amount of data requested, or the buffer size if it is less, if the
228 last read attempt at the other half of the \s-1BIO\s0 pair failed due to an
229 empty buffer. This can be used to determine how much data should be
230 written to the \s-1BIO\s0 so the next read will succeed: this is most useful
231 in \s-1TLS/SSL\s0 applications where the amount of data read is usually
232 meaningful rather than just a buffer size. After a successful read
233 this call will return zero. It also will return zero once new data
234 has been written satisfying the read request or part of it.
235 Note that \fIBIO_get_read_request()\fR never returns an amount larger
236 than that returned by \fIBIO_get_write_guarantee()\fR.
238 \&\fIBIO_ctrl_reset_read_request()\fR can also be used to reset the value returned by
239 \&\fIBIO_get_read_request()\fR to zero.
242 Both halves of a \s-1BIO\s0 pair should be freed. That is even if one half is implicit
243 freed due to a \fIBIO_free_all()\fR or \fISSL_free()\fR call the other half needs to be freed.
245 When used in bidirectional applications (such as \s-1TLS/SSL\s0) care should be taken to
246 flush any data in the write buffer. This can be done by calling \fIBIO_pending()\fR
247 on the other half of the pair and, if any data is pending, reading it and sending
248 it to the underlying transport. This must be done before any normal processing
249 (such as calling \fIselect()\fR ) due to a request and \fIBIO_should_read()\fR being true.
251 To see why this is important consider a case where a request is sent using
252 \&\fIBIO_write()\fR and a response read with \fIBIO_read()\fR, this can occur during an
253 \&\s-1TLS/SSL\s0 handshake for example. \fIBIO_write()\fR will succeed and place data in the write
254 buffer. \fIBIO_read()\fR will initially fail and \fIBIO_should_read()\fR will be true. If
255 the application then waits for data to be available on the underlying transport
256 before flushing the write buffer it will never succeed because the request was
259 .IX Header "RETURN VALUES"
260 \&\fIBIO_new_bio_pair()\fR returns 1 on success, with the new BIOs available in
261 \&\fBbio1\fR and \fBbio2\fR, or 0 on failure, with \s-1NULL\s0 pointers stored into the
262 locations for \fBbio1\fR and \fBbio2\fR. Check the error stack for more information.
264 [\s-1XXXXX:\s0 More return values need to be added here]
267 The \s-1BIO\s0 pair can be used to have full control over the network access of an
268 application. The application can call \fIselect()\fR on the socket as required
269 without having to go through the SSL-interface.
272 \& BIO *internal_bio, *network_bio;
274 \& BIO_new_bio_pair(internal_bio, 0, network_bio, 0);
275 \& SSL_set_bio(ssl, internal_bio, internal_bio);
279 \& application | TLS\-engine
281 \& +\-\-\-\-\-\-\-\-\-\-> SSL_operations()
284 \& | BIO\-pair (internal_bio)
285 \& +\-\-\-\-\-\-\-\-\-\-< BIO\-pair (network_bio)
290 \& SSL_free(ssl); /* implicitly frees internal_bio */
291 \& BIO_free(network_bio);
295 As the \s-1BIO\s0 pair will only buffer the data and never directly access the
296 connection, it behaves non-blocking and will return as soon as the write
297 buffer is full or the read buffer is drained. Then the application has to
298 flush the write buffer and/or fill the read buffer.
300 Use the \fIBIO_ctrl_pending()\fR, to find out whether data is buffered in the \s-1BIO\s0
301 and must be transfered to the network. Use \fIBIO_ctrl_get_read_request()\fR to
302 find out, how many bytes must be written into the buffer before the
303 \&\fISSL_operation()\fR can successfully be continued.
306 As the data is buffered, \fISSL_operation()\fR may return with a \s-1ERROR_SSL_WANT_READ\s0
307 condition, but there is still data in the write buffer. An application must
308 not rely on the error value of \fISSL_operation()\fR but must assure that the
309 write buffer is always flushed first. Otherwise a deadlock may occur as
310 the peer might be waiting for the data before being able to continue.
312 .IX Header "SEE ALSO"
313 \&\fISSL_set_bio\fR\|(3), \fIssl\fR\|(3), \fIbio\fR\|(3),
314 \&\fIBIO_should_retry\fR\|(3), \fIBIO_read\fR\|(3)