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135 .\" ========================================================================
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137 .IX Title "BIO_should_retry 3"
138 .TH BIO_should_retry 3 "2011-06-05" "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_should_retry, BIO_should_read, BIO_should_write,
145 BIO_should_io_special, BIO_retry_type, BIO_should_retry,
146 BIO_get_retry_BIO, BIO_get_retry_reason \- BIO retry functions
147 .SH "LIBRARY"
148 libcrypto, -lcrypto
149 .SH "SYNOPSIS"
150 .IX Header "SYNOPSIS"
151 .Vb 1
152 \& #include <openssl/bio.h>
153 \&
154 \& #define BIO_should_read(a) ((a)\->flags & BIO_FLAGS_READ)
155 \& #define BIO_should_write(a) ((a)\->flags & BIO_FLAGS_WRITE)
156 \& #define BIO_should_io_special(a) ((a)\->flags & BIO_FLAGS_IO_SPECIAL)
157 \& #define BIO_retry_type(a) ((a)\->flags & BIO_FLAGS_RWS)
158 \& #define BIO_should_retry(a) ((a)\->flags & BIO_FLAGS_SHOULD_RETRY)
159 \&
160 \& #define BIO_FLAGS_READ 0x01
161 \& #define BIO_FLAGS_WRITE 0x02
162 \& #define BIO_FLAGS_IO_SPECIAL 0x04
163 \& #define BIO_FLAGS_RWS (BIO_FLAGS_READ|BIO_FLAGS_WRITE|BIO_FLAGS_IO_SPECIAL)
164 \& #define BIO_FLAGS_SHOULD_RETRY 0x08
165 \&
166 \& BIO * BIO_get_retry_BIO(BIO *bio, int *reason);
167 \& int BIO_get_retry_reason(BIO *bio);
168 .Ve
169 .SH "DESCRIPTION"
170 .IX Header "DESCRIPTION"
171 These functions determine why a \s-1BIO\s0 is not able to read or write data.
172 They will typically be called after a failed \fIBIO_read()\fR or \fIBIO_write()\fR
173 call.
174 .PP
175 \&\fIBIO_should_retry()\fR is true if the call that produced this condition
176 should then be retried at a later time.
177 .PP
178 If \fIBIO_should_retry()\fR is false then the cause is an error condition.
179 .PP
180 \&\fIBIO_should_read()\fR is true if the cause of the condition is that a \s-1BIO\s0
181 needs to read data.
182 .PP
183 \&\fIBIO_should_write()\fR is true if the cause of the condition is that a \s-1BIO\s0
184 needs to read data.
185 .PP
186 \&\fIBIO_should_io_special()\fR is true if some \*(L"special\*(R" condition, that is a
187 reason other than reading or writing is the cause of the condition.
188 .PP
189 \&\fIBIO_retry_type()\fR returns a mask of the cause of a retry condition
190 consisting of the values \fB\s-1BIO_FLAGS_READ\s0\fR, \fB\s-1BIO_FLAGS_WRITE\s0\fR,
191 \&\fB\s-1BIO_FLAGS_IO_SPECIAL\s0\fR though current \s-1BIO\s0 types will only set one of
192 these.
193 .PP
194 \&\fIBIO_get_retry_BIO()\fR determines the precise reason for the special
195 condition, it returns the \s-1BIO\s0 that caused this condition and if
196 \&\fBreason\fR is not \s-1NULL\s0 it contains the reason code. The meaning of
197 the reason code and the action that should be taken depends on
198 the type of \s-1BIO\s0 that resulted in this condition.
199 .PP
200 \&\fIBIO_get_retry_reason()\fR returns the reason for a special condition if
201 passed the relevant \s-1BIO,\s0 for example as returned by \fIBIO_get_retry_BIO()\fR.
202 .SH "NOTES"
203 .IX Header "NOTES"
204 If \fIBIO_should_retry()\fR returns false then the precise \*(L"error condition\*(R"
205 depends on the \s-1BIO\s0 type that caused it and the return code of the \s-1BIO\s0
206 operation. For example if a call to \fIBIO_read()\fR on a socket \s-1BIO\s0 returns
207 0 and \fIBIO_should_retry()\fR is false then the cause will be that the
208 connection closed. A similar condition on a file \s-1BIO\s0 will mean that it
209 has reached \s-1EOF.\s0 Some \s-1BIO\s0 types may place additional information on
210 the error queue. For more details see the individual \s-1BIO\s0 type manual
211 pages.
212 .PP
213 If the underlying I/O structure is in a blocking mode almost all current
214 \&\s-1BIO\s0 types will not request a retry, because the underlying I/O
215 calls will not. If the application knows that the \s-1BIO\s0 type will never
216 signal a retry then it need not call \fIBIO_should_retry()\fR after a failed
217 \&\s-1BIO I/O\s0 call. This is typically done with file BIOs.
218 .PP
219 \&\s-1SSL\s0 BIOs are the only current exception to this rule: they can request a
220 retry even if the underlying I/O structure is blocking, if a handshake
221 occurs during a call to \fIBIO_read()\fR. An application can retry the failed
222 call immediately or avoid this situation by setting \s-1SSL_MODE_AUTO_RETRY\s0
223 on the underlying \s-1SSL\s0 structure.
224 .PP
225 While an application may retry a failed non blocking call immediately
226 this is likely to be very inefficient because the call will fail
227 repeatedly until data can be processed or is available. An application
228 will normally wait until the necessary condition is satisfied. How
229 this is done depends on the underlying I/O structure.
230 .PP
231 For example if the cause is ultimately a socket and \fIBIO_should_read()\fR
232 is true then a call to \fIselect()\fR may be made to wait until data is
233 available and then retry the \s-1BIO\s0 operation. By combining the retry
234 conditions of several non blocking BIOs in a single \fIselect()\fR call
235 it is possible to service several BIOs in a single thread, though
236 the performance may be poor if \s-1SSL\s0 BIOs are present because long delays
237 can occur during the initial handshake process.
238 .PP
239 It is possible for a \s-1BIO\s0 to block indefinitely if the underlying I/O
240 structure cannot process or return any data. This depends on the behaviour of
241 the platforms I/O functions. This is often not desirable: one solution
242 is to use non blocking I/O and use a timeout on the \fIselect()\fR (or
243 equivalent) call.
244 .SH "BUGS"
245 .IX Header "BUGS"
246 The OpenSSL \s-1ASN1\s0 functions cannot gracefully deal with non blocking I/O:
247 that is they cannot retry after a partial read or write. This is usually
248 worked around by only passing the relevant data to \s-1ASN1\s0 functions when
249 the entire structure can be read or written.
250 .SH "SEE ALSO"
251 .IX Header "SEE ALSO"
252 \&\s-1TBA\s0