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135 .\" ========================================================================
136 .\"
137 .IX Title "BIO_s_bio 3"
138 .TH BIO_s_bio 3 "2009-07-19" "1.0.1n" "OpenSSL"
139 .\" For nroff, turn off justification. Always turn off hyphenation; it makes
140 .\" way too many mistakes in technical documents.
141 .if n .ad l
142 .nh
143 .SH "NAME"
144 BIO_s_bio, BIO_make_bio_pair, BIO_destroy_bio_pair, BIO_shutdown_wr,
145 BIO_set_write_buf_size, BIO_get_write_buf_size, BIO_new_bio_pair,
146 BIO_get_write_guarantee, BIO_ctrl_get_write_guarantee, BIO_get_read_request,
147 BIO_ctrl_get_read_request, BIO_ctrl_reset_read_request \- BIO pair BIO
148 .SH "LIBRARY"
149 libcrypto, -lcrypto
150 .SH "SYNOPSIS"
151 .IX Header "SYNOPSIS"
152 .Vb 1
153 \& #include <openssl/bio.h>
154 \&
155 \& BIO_METHOD *BIO_s_bio(void);
156 \&
157 \& #define BIO_make_bio_pair(b1,b2) (int)BIO_ctrl(b1,BIO_C_MAKE_BIO_PAIR,0,b2)
158 \& #define BIO_destroy_bio_pair(b) (int)BIO_ctrl(b,BIO_C_DESTROY_BIO_PAIR,0,NULL)
159 \&
160 \& #define BIO_shutdown_wr(b) (int)BIO_ctrl(b, BIO_C_SHUTDOWN_WR, 0, NULL)
161 \&
162 \& #define BIO_set_write_buf_size(b,size) (int)BIO_ctrl(b,BIO_C_SET_WRITE_BUF_SIZE,size,NULL)
163 \& #define BIO_get_write_buf_size(b,size) (size_t)BIO_ctrl(b,BIO_C_GET_WRITE_BUF_SIZE,size,NULL)
164 \&
165 \& int BIO_new_bio_pair(BIO **bio1, size_t writebuf1, BIO **bio2, size_t writebuf2);
166 \&
167 \& #define BIO_get_write_guarantee(b) (int)BIO_ctrl(b,BIO_C_GET_WRITE_GUARANTEE,0,NULL)
168 \& size_t BIO_ctrl_get_write_guarantee(BIO *b);
169 \&
170 \& #define BIO_get_read_request(b) (int)BIO_ctrl(b,BIO_C_GET_READ_REQUEST,0,NULL)
171 \& size_t BIO_ctrl_get_read_request(BIO *b);
172 \&
173 \& int BIO_ctrl_reset_read_request(BIO *b);
174 .Ve
175 .SH "DESCRIPTION"
176 .IX Header "DESCRIPTION"
177 \&\fIBIO_s_bio()\fR returns the method for a \s-1BIO\s0 pair. A \s-1BIO\s0 pair is a pair of source/sink
178 BIOs where data written to either half of the pair is buffered and can be read from
179 the other half. Both halves must usually by handled by the same application thread
180 since no locking is done on the internal data structures.
181 .PP
182 Since \s-1BIO\s0 chains typically end in a source/sink \s-1BIO\s0 it is possible to make this
183 one half of a \s-1BIO\s0 pair and have all the data processed by the chain under application
184 control.
185 .PP
186 One typical use of \s-1BIO\s0 pairs is to place \s-1TLS/SSL I/O\s0 under application control, this
187 can be used when the application wishes to use a non standard transport for
188 \&\s-1TLS/SSL\s0 or the normal socket routines are inappropriate.
189 .PP
190 Calls to \fIBIO_read()\fR will read data from the buffer or request a retry if no
191 data is available.
192 .PP
193 Calls to \fIBIO_write()\fR will place data in the buffer or request a retry if the
194 buffer is full.
195 .PP
196 The standard calls \fIBIO_ctrl_pending()\fR and \fIBIO_ctrl_wpending()\fR can be used to
197 determine the amount of pending data in the read or write buffer.
198 .PP
199 \&\fIBIO_reset()\fR clears any data in the write buffer.
200 .PP
201 \&\fIBIO_make_bio_pair()\fR joins two separate BIOs into a connected pair.
202 .PP
203 \&\fIBIO_destroy_pair()\fR destroys the association between two connected BIOs. Freeing
204 up any half of the pair will automatically destroy the association.
205 .PP
206 \&\fIBIO_shutdown_wr()\fR is used to close down a \s-1BIO \s0\fBb\fR. After this call no further
207 writes on \s-1BIO \s0\fBb\fR are allowed (they will return an error). Reads on the other
208 half of the pair will return any pending data or \s-1EOF\s0 when all pending data has
209 been read.
210 .PP
211 \&\fIBIO_set_write_buf_size()\fR sets the write buffer size of \s-1BIO \s0\fBb\fR to \fBsize\fR.
212 If the size is not initialized a default value is used. This is currently
213 17K, sufficient for a maximum size \s-1TLS\s0 record.
214 .PP
215 \&\fIBIO_get_write_buf_size()\fR returns the size of the write buffer.
216 .PP
217 \&\fIBIO_new_bio_pair()\fR combines the calls to \fIBIO_new()\fR, \fIBIO_make_bio_pair()\fR and
218 \&\fIBIO_set_write_buf_size()\fR to create a connected pair of BIOs \fBbio1\fR, \fBbio2\fR
219 with write buffer sizes \fBwritebuf1\fR and \fBwritebuf2\fR. If either size is
220 zero then the default size is used. \fIBIO_new_bio_pair()\fR does not check whether
221 \&\fBbio1\fR or \fBbio2\fR do point to some other \s-1BIO,\s0 the values are overwritten,
222 \&\fIBIO_free()\fR is not called.
223 .PP
224 \&\fIBIO_get_write_guarantee()\fR and \fIBIO_ctrl_get_write_guarantee()\fR return the maximum
225 length of data that can be currently written to the \s-1BIO.\s0 Writes larger than this
226 value will return a value from \fIBIO_write()\fR less than the amount requested or if the
227 buffer is full request a retry. \fIBIO_ctrl_get_write_guarantee()\fR is a function
228 whereas \fIBIO_get_write_guarantee()\fR is a macro.
229 .PP
230 \&\fIBIO_get_read_request()\fR and \fIBIO_ctrl_get_read_request()\fR return the
231 amount of data requested, or the buffer size if it is less, if the
232 last read attempt at the other half of the \s-1BIO\s0 pair failed due to an
233 empty buffer. This can be used to determine how much data should be
234 written to the \s-1BIO\s0 so the next read will succeed: this is most useful
235 in \s-1TLS/SSL\s0 applications where the amount of data read is usually
236 meaningful rather than just a buffer size. After a successful read
237 this call will return zero. It also will return zero once new data
238 has been written satisfying the read request or part of it.
239 Note that \fIBIO_get_read_request()\fR never returns an amount larger
240 than that returned by \fIBIO_get_write_guarantee()\fR.
241 .PP
242 \&\fIBIO_ctrl_reset_read_request()\fR can also be used to reset the value returned by
243 \&\fIBIO_get_read_request()\fR to zero.
244 .SH "NOTES"
245 .IX Header "NOTES"
246 Both halves of a \s-1BIO\s0 pair should be freed. That is even if one half is implicit
247 freed due to a \fIBIO_free_all()\fR or \fISSL_free()\fR call the other half needs to be freed.
248 .PP
249 When used in bidirectional applications (such as \s-1TLS/SSL\s0) care should be taken to
250 flush any data in the write buffer. This can be done by calling \fIBIO_pending()\fR
251 on the other half of the pair and, if any data is pending, reading it and sending
252 it to the underlying transport. This must be done before any normal processing
253 (such as calling \fIselect()\fR ) due to a request and \fIBIO_should_read()\fR being true.
254 .PP
255 To see why this is important consider a case where a request is sent using
256 \&\fIBIO_write()\fR and a response read with \fIBIO_read()\fR, this can occur during an
257 \&\s-1TLS/SSL\s0 handshake for example. \fIBIO_write()\fR will succeed and place data in the write
258 buffer. \fIBIO_read()\fR will initially fail and \fIBIO_should_read()\fR will be true. If
259 the application then waits for data to be available on the underlying transport
260 before flushing the write buffer it will never succeed because the request was
261 never sent!
262 .SH "RETURN VALUES"
263 .IX Header "RETURN VALUES"
264 \&\fIBIO_new_bio_pair()\fR returns 1 on success, with the new BIOs available in
265 \&\fBbio1\fR and \fBbio2\fR, or 0 on failure, with \s-1NULL\s0 pointers stored into the
266 locations for \fBbio1\fR and \fBbio2\fR. Check the error stack for more information.
267 .PP
268 [\s-1XXXXX:\s0 More return values need to be added here]
269 .SH "EXAMPLE"
270 .IX Header "EXAMPLE"
271 The \s-1BIO\s0 pair can be used to have full control over the network access of an
272 application. The application can call \fIselect()\fR on the socket as required
273 without having to go through the SSL-interface.
274 .PP
275 .Vb 6
276 \& BIO *internal_bio, *network_bio;
277 \& ...
278 \& BIO_new_bio_pair(internal_bio, 0, network_bio, 0);
279 \& SSL_set_bio(ssl, internal_bio, internal_bio);
280 \& SSL_operations();
281 \& ...
282 \&
283 \& application | TLS\-engine
284 \& | |
285 \& +\-\-\-\-\-\-\-\-\-\-> SSL_operations()
286 \& | /\e ||
287 \& | || \e/
288 \& | BIO\-pair (internal_bio)
289 \& +\-\-\-\-\-\-\-\-\-\-< BIO\-pair (network_bio)
290 \& | |
291 \& socket |
292 \&
293 \& ...
294 \& SSL_free(ssl); /* implicitly frees internal_bio */
295 \& BIO_free(network_bio);
296 \& ...
297 .Ve
298 .PP
299 As the \s-1BIO\s0 pair will only buffer the data and never directly access the
300 connection, it behaves non-blocking and will return as soon as the write
301 buffer is full or the read buffer is drained. Then the application has to
302 flush the write buffer and/or fill the read buffer.
303 .PP
304 Use the \fIBIO_ctrl_pending()\fR, to find out whether data is buffered in the \s-1BIO\s0
305 and must be transfered to the network. Use \fIBIO_ctrl_get_read_request()\fR to
306 find out, how many bytes must be written into the buffer before the
307 \&\fISSL_operation()\fR can successfully be continued.
308 .SH "WARNING"
309 .IX Header "WARNING"
310 As the data is buffered, \fISSL_operation()\fR may return with a \s-1ERROR_SSL_WANT_READ\s0
311 condition, but there is still data in the write buffer. An application must
312 not rely on the error value of \fISSL_operation()\fR but must assure that the
313 write buffer is always flushed first. Otherwise a deadlock may occur as
314 the peer might be waiting for the data before being able to continue.
315 .SH "SEE ALSO"
316 .IX Header "SEE ALSO"
317 \&\fISSL_set_bio\fR\|(3), \fIssl\fR\|(3), \fIopenssl_bio\fR\|(3),
318 \&\fIBIO_should_retry\fR\|(3), \fIBIO_read\fR\|(3)