Update files for OpenSSL-1.0.0f import.
[dragonfly.git] / secure / lib / libcrypto / man / BIO_s_bio.3
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124.\" ========================================================================
125.\"
126.IX Title "BIO_s_bio 3"
e3261593 127.TH BIO_s_bio 3 "2012-01-04" "1.0.0f" "OpenSSL"
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128.\" For nroff, turn off justification. Always turn off hyphenation; it makes
129.\" way too many mistakes in technical documents.
130.if n .ad l
131.nh
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132.SH "NAME"
133BIO_s_bio, BIO_make_bio_pair, BIO_destroy_bio_pair, BIO_shutdown_wr,
134BIO_set_write_buf_size, BIO_get_write_buf_size, BIO_new_bio_pair,
135BIO_get_write_guarantee, BIO_ctrl_get_write_guarantee, BIO_get_read_request,
74dab6c2 136BIO_ctrl_get_read_request, BIO_ctrl_reset_read_request \- BIO pair BIO
984263bc 137.SH "SYNOPSIS"
8b0cefbb 138.IX Header "SYNOPSIS"
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139.Vb 1
140\& #include <openssl/bio.h>
e257b235 141\&
984263bc 142\& BIO_METHOD *BIO_s_bio(void);
e257b235 143\&
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144\& #define BIO_make_bio_pair(b1,b2) (int)BIO_ctrl(b1,BIO_C_MAKE_BIO_PAIR,0,b2)
145\& #define BIO_destroy_bio_pair(b) (int)BIO_ctrl(b,BIO_C_DESTROY_BIO_PAIR,0,NULL)
e257b235 146\&
984263bc 147\& #define BIO_shutdown_wr(b) (int)BIO_ctrl(b, BIO_C_SHUTDOWN_WR, 0, NULL)
e257b235 148\&
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149\& #define BIO_set_write_buf_size(b,size) (int)BIO_ctrl(b,BIO_C_SET_WRITE_BUF_SIZE,size,NULL)
150\& #define BIO_get_write_buf_size(b,size) (size_t)BIO_ctrl(b,BIO_C_GET_WRITE_BUF_SIZE,size,NULL)
e257b235 151\&
984263bc 152\& int BIO_new_bio_pair(BIO **bio1, size_t writebuf1, BIO **bio2, size_t writebuf2);
e257b235 153\&
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154\& #define BIO_get_write_guarantee(b) (int)BIO_ctrl(b,BIO_C_GET_WRITE_GUARANTEE,0,NULL)
155\& size_t BIO_ctrl_get_write_guarantee(BIO *b);
e257b235 156\&
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157\& #define BIO_get_read_request(b) (int)BIO_ctrl(b,BIO_C_GET_READ_REQUEST,0,NULL)
158\& size_t BIO_ctrl_get_read_request(BIO *b);
e257b235 159\&
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160\& int BIO_ctrl_reset_read_request(BIO *b);
161.Ve
162.SH "DESCRIPTION"
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163.IX Header "DESCRIPTION"
164\&\fIBIO_s_bio()\fR returns the method for a \s-1BIO\s0 pair. A \s-1BIO\s0 pair is a pair of source/sink
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165BIOs where data written to either half of the pair is buffered and can be read from
166the other half. Both halves must usually by handled by the same application thread
167since no locking is done on the internal data structures.
168.PP
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169Since \s-1BIO\s0 chains typically end in a source/sink \s-1BIO\s0 it is possible to make this
170one half of a \s-1BIO\s0 pair and have all the data processed by the chain under application
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171control.
172.PP
8b0cefbb 173One typical use of \s-1BIO\s0 pairs is to place \s-1TLS/SSL\s0 I/O under application control, this
984263bc 174can be used when the application wishes to use a non standard transport for
8b0cefbb 175\&\s-1TLS/SSL\s0 or the normal socket routines are inappropriate.
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176.PP
177Calls to \fIBIO_read()\fR will read data from the buffer or request a retry if no
178data is available.
179.PP
180Calls to \fIBIO_write()\fR will place data in the buffer or request a retry if the
181buffer is full.
182.PP
183The standard calls \fIBIO_ctrl_pending()\fR and \fIBIO_ctrl_wpending()\fR can be used to
184determine the amount of pending data in the read or write buffer.
185.PP
8b0cefbb 186\&\fIBIO_reset()\fR clears any data in the write buffer.
984263bc 187.PP
8b0cefbb 188\&\fIBIO_make_bio_pair()\fR joins two separate BIOs into a connected pair.
984263bc 189.PP
8b0cefbb 190\&\fIBIO_destroy_pair()\fR destroys the association between two connected BIOs. Freeing
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191up any half of the pair will automatically destroy the association.
192.PP
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193\&\fIBIO_shutdown_wr()\fR is used to close down a \s-1BIO\s0 \fBb\fR. After this call no further
194writes on \s-1BIO\s0 \fBb\fR are allowed (they will return an error). Reads on the other
195half of the pair will return any pending data or \s-1EOF\s0 when all pending data has
e257b235 196been read.
984263bc 197.PP
8b0cefbb 198\&\fIBIO_set_write_buf_size()\fR sets the write buffer size of \s-1BIO\s0 \fBb\fR to \fBsize\fR.
984263bc 199If the size is not initialized a default value is used. This is currently
8b0cefbb 20017K, sufficient for a maximum size \s-1TLS\s0 record.
984263bc 201.PP
8b0cefbb 202\&\fIBIO_get_write_buf_size()\fR returns the size of the write buffer.
984263bc 203.PP
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204\&\fIBIO_new_bio_pair()\fR combines the calls to \fIBIO_new()\fR, \fIBIO_make_bio_pair()\fR and
205\&\fIBIO_set_write_buf_size()\fR to create a connected pair of BIOs \fBbio1\fR, \fBbio2\fR
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206with write buffer sizes \fBwritebuf1\fR and \fBwritebuf2\fR. If either size is
207zero then the default size is used. \fIBIO_new_bio_pair()\fR does not check whether
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208\&\fBbio1\fR or \fBbio2\fR do point to some other \s-1BIO\s0, the values are overwritten,
209\&\fIBIO_free()\fR is not called.
984263bc 210.PP
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211\&\fIBIO_get_write_guarantee()\fR and \fIBIO_ctrl_get_write_guarantee()\fR return the maximum
212length of data that can be currently written to the \s-1BIO\s0. Writes larger than this
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213value will return a value from \fIBIO_write()\fR less than the amount requested or if the
214buffer is full request a retry. \fIBIO_ctrl_get_write_guarantee()\fR is a function
215whereas \fIBIO_get_write_guarantee()\fR is a macro.
216.PP
8b0cefbb 217\&\fIBIO_get_read_request()\fR and \fIBIO_ctrl_get_read_request()\fR return the
984263bc 218amount of data requested, or the buffer size if it is less, if the
8b0cefbb 219last read attempt at the other half of the \s-1BIO\s0 pair failed due to an
984263bc 220empty buffer. This can be used to determine how much data should be
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221written to the \s-1BIO\s0 so the next read will succeed: this is most useful
222in \s-1TLS/SSL\s0 applications where the amount of data read is usually
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223meaningful rather than just a buffer size. After a successful read
224this call will return zero. It also will return zero once new data
225has been written satisfying the read request or part of it.
226Note that \fIBIO_get_read_request()\fR never returns an amount larger
227than that returned by \fIBIO_get_write_guarantee()\fR.
228.PP
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229\&\fIBIO_ctrl_reset_read_request()\fR can also be used to reset the value returned by
230\&\fIBIO_get_read_request()\fR to zero.
984263bc 231.SH "NOTES"
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232.IX Header "NOTES"
233Both halves of a \s-1BIO\s0 pair should be freed. That is even if one half is implicit
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234freed due to a \fIBIO_free_all()\fR or \fISSL_free()\fR call the other half needs to be freed.
235.PP
8b0cefbb 236When used in bidirectional applications (such as \s-1TLS/SSL\s0) care should be taken to
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237flush any data in the write buffer. This can be done by calling \fIBIO_pending()\fR
238on the other half of the pair and, if any data is pending, reading it and sending
239it to the underlying transport. This must be done before any normal processing
240(such as calling \fIselect()\fR ) due to a request and \fIBIO_should_read()\fR being true.
241.PP
242To see why this is important consider a case where a request is sent using
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243\&\fIBIO_write()\fR and a response read with \fIBIO_read()\fR, this can occur during an
244\&\s-1TLS/SSL\s0 handshake for example. \fIBIO_write()\fR will succeed and place data in the write
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245buffer. \fIBIO_read()\fR will initially fail and \fIBIO_should_read()\fR will be true. If
246the application then waits for data to be available on the underlying transport
247before flushing the write buffer it will never succeed because the request was
248never sent!
249.SH "RETURN VALUES"
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250.IX Header "RETURN VALUES"
251\&\fIBIO_new_bio_pair()\fR returns 1 on success, with the new BIOs available in
252\&\fBbio1\fR and \fBbio2\fR, or 0 on failure, with \s-1NULL\s0 pointers stored into the
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253locations for \fBbio1\fR and \fBbio2\fR. Check the error stack for more information.
254.PP
8b0cefbb 255[\s-1XXXXX:\s0 More return values need to be added here]
984263bc 256.SH "EXAMPLE"
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257.IX Header "EXAMPLE"
258The \s-1BIO\s0 pair can be used to have full control over the network access of an
984263bc 259application. The application can call \fIselect()\fR on the socket as required
e257b235 260without having to go through the SSL-interface.
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261.PP
262.Vb 6
263\& BIO *internal_bio, *network_bio;
264\& ...
265\& BIO_new_bio_pair(internal_bio, 0, network_bio, 0);
266\& SSL_set_bio(ssl, internal_bio, internal_bio);
267\& SSL_operations();
268\& ...
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269\&
270\& application | TLS\-engine
984263bc 271\& | |
e257b235 272\& +\-\-\-\-\-\-\-\-\-\-> SSL_operations()
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273\& | /\e ||
274\& | || \e/
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275\& | BIO\-pair (internal_bio)
276\& +\-\-\-\-\-\-\-\-\-\-< BIO\-pair (network_bio)
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277\& | |
278\& socket |
e257b235 279\&
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280\& ...
281\& SSL_free(ssl); /* implicitly frees internal_bio */
282\& BIO_free(network_bio);
283\& ...
284.Ve
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285.PP
286As the \s-1BIO\s0 pair will only buffer the data and never directly access the
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287connection, it behaves non-blocking and will return as soon as the write
288buffer is full or the read buffer is drained. Then the application has to
289flush the write buffer and/or fill the read buffer.
290.PP
8b0cefbb 291Use the \fIBIO_ctrl_pending()\fR, to find out whether data is buffered in the \s-1BIO\s0
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292and must be transfered to the network. Use \fIBIO_ctrl_get_read_request()\fR to
293find out, how many bytes must be written into the buffer before the
8b0cefbb 294\&\fISSL_operation()\fR can successfully be continued.
984263bc 295.SH "WARNING"
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296.IX Header "WARNING"
297As the data is buffered, \fISSL_operation()\fR may return with a \s-1ERROR_SSL_WANT_READ\s0
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298condition, but there is still data in the write buffer. An application must
299not rely on the error value of \fISSL_operation()\fR but must assure that the
300write buffer is always flushed first. Otherwise a deadlock may occur as
301the peer might be waiting for the data before being able to continue.
302.SH "SEE ALSO"
74dab6c2 303.IX Header "SEE ALSO"
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304\&\fISSL_set_bio\fR\|(3), \fIssl\fR\|(3), \fIbio\fR\|(3),
305\&\fIBIO_should_retry\fR\|(3), \fIBIO_read\fR\|(3)