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131 .IX Title "BIO_should_retry 3"
132 .TH BIO_should_retry 3 "2009-07-23" "0.9.8k" "OpenSSL"
133 .SH "NAME"
134 BIO_should_retry, BIO_should_read, BIO_should_write,
135 BIO_should_io_special, BIO_retry_type, BIO_should_retry,
136 BIO_get_retry_BIO, BIO_get_retry_reason \- BIO retry functions
137 .SH "SYNOPSIS"
138 .IX Header "SYNOPSIS"
139 .Vb 1
140 \& #include <openssl/bio.h>
141 .Ve
142 .PP
143 .Vb 5
144 \& #define BIO_should_read(a) ((a)->flags & BIO_FLAGS_READ)
145 \& #define BIO_should_write(a) ((a)->flags & BIO_FLAGS_WRITE)
146 \& #define BIO_should_io_special(a) ((a)->flags & BIO_FLAGS_IO_SPECIAL)
147 \& #define BIO_retry_type(a) ((a)->flags & BIO_FLAGS_RWS)
148 \& #define BIO_should_retry(a) ((a)->flags & BIO_FLAGS_SHOULD_RETRY)
149 .Ve
150 .PP
151 .Vb 5
152 \& #define BIO_FLAGS_READ 0x01
153 \& #define BIO_FLAGS_WRITE 0x02
154 \& #define BIO_FLAGS_IO_SPECIAL 0x04
155 \& #define BIO_FLAGS_RWS (BIO_FLAGS_READ|BIO_FLAGS_WRITE|BIO_FLAGS_IO_SPECIAL)
156 \& #define BIO_FLAGS_SHOULD_RETRY 0x08
157 .Ve
158 .PP
159 .Vb 2
160 \& BIO * BIO_get_retry_BIO(BIO *bio, int *reason);
161 \& int BIO_get_retry_reason(BIO *bio);
162 .Ve
163 .SH "DESCRIPTION"
164 .IX Header "DESCRIPTION"
165 These functions determine why a \s-1BIO\s0 is not able to read or write data.
166 They will typically be called after a failed \fIBIO_read()\fR or \fIBIO_write()\fR
167 call.
168 .PP
169 \&\fIBIO_should_retry()\fR is true if the call that produced this condition
170 should then be retried at a later time.
171 .PP
172 If \fIBIO_should_retry()\fR is false then the cause is an error condition.
173 .PP
174 \&\fIBIO_should_read()\fR is true if the cause of the condition is that a \s-1BIO\s0
175 needs to read data.
176 .PP
177 \&\fIBIO_should_write()\fR is true if the cause of the condition is that a \s-1BIO\s0
178 needs to read data.
179 .PP
180 \&\fIBIO_should_io_special()\fR is true if some \*(L"special\*(R" condition, that is a
181 reason other than reading or writing is the cause of the condition.
182 .PP
183 \&\fIBIO_get_retry_reason()\fR returns a mask of the cause of a retry condition
184 consisting of the values \fB\s-1BIO_FLAGS_READ\s0\fR, \fB\s-1BIO_FLAGS_WRITE\s0\fR,
185 \&\fB\s-1BIO_FLAGS_IO_SPECIAL\s0\fR though current \s-1BIO\s0 types will only set one of
186 these.
187 .PP
188 \&\fIBIO_get_retry_BIO()\fR determines the precise reason for the special
189 condition, it returns the \s-1BIO\s0 that caused this condition and if
190 \&\fBreason\fR is not \s-1NULL\s0 it contains the reason code. The meaning of
191 the reason code and the action that should be taken depends on
192 the type of \s-1BIO\s0 that resulted in this condition.
193 .PP
194 \&\fIBIO_get_retry_reason()\fR returns the reason for a special condition if
195 passed the relevant \s-1BIO\s0, for example as returned by \fIBIO_get_retry_BIO()\fR.
196 .SH "NOTES"
197 .IX Header "NOTES"
198 If \fIBIO_should_retry()\fR returns false then the precise \*(L"error condition\*(R"
199 depends on the \s-1BIO\s0 type that caused it and the return code of the \s-1BIO\s0
200 operation. For example if a call to \fIBIO_read()\fR on a socket \s-1BIO\s0 returns
201 0 and \fIBIO_should_retry()\fR is false then the cause will be that the
202 connection closed. A similar condition on a file \s-1BIO\s0 will mean that it
203 has reached \s-1EOF\s0. Some \s-1BIO\s0 types may place additional information on
204 the error queue. For more details see the individual \s-1BIO\s0 type manual
205 pages.
206 .PP
207 If the underlying I/O structure is in a blocking mode almost all current
208 \&\s-1BIO\s0 types will not request a retry, because the underlying I/O
209 calls will not. If the application knows that the \s-1BIO\s0 type will never
210 signal a retry then it need not call \fIBIO_should_retry()\fR after a failed
211 \&\s-1BIO\s0 I/O call. This is typically done with file BIOs.
212 .PP
213 \&\s-1SSL\s0 BIOs are the only current exception to this rule: they can request a
214 retry even if the underlying I/O structure is blocking, if a handshake
215 occurs during a call to \fIBIO_read()\fR. An application can retry the failed
216 call immediately or avoid this situation by setting \s-1SSL_MODE_AUTO_RETRY\s0
217 on the underlying \s-1SSL\s0 structure.
218 .PP
219 While an application may retry a failed non blocking call immediately
220 this is likely to be very inefficient because the call will fail
221 repeatedly until data can be processed or is available. An application
222 will normally wait until the necessary condition is satisfied. How
223 this is done depends on the underlying I/O structure.
224 .PP
225 For example if the cause is ultimately a socket and \fIBIO_should_read()\fR
226 is true then a call to \fIselect()\fR may be made to wait until data is
227 available and then retry the \s-1BIO\s0 operation. By combining the retry
228 conditions of several non blocking BIOs in a single \fIselect()\fR call
229 it is possible to service several BIOs in a single thread, though
230 the performance may be poor if \s-1SSL\s0 BIOs are present because long delays
231 can occur during the initial handshake process.
232 .PP
233 It is possible for a \s-1BIO\s0 to block indefinitely if the underlying I/O
234 structure cannot process or return any data. This depends on the behaviour of
235 the platforms I/O functions. This is often not desirable: one solution
236 is to use non blocking I/O and use a timeout on the \fIselect()\fR (or
237 equivalent) call.
238 .SH "BUGS"
239 .IX Header "BUGS"
240 The OpenSSL \s-1ASN1\s0 functions cannot gracefully deal with non blocking I/O:
241 that is they cannot retry after a partial read or write. This is usually
242 worked around by only passing the relevant data to \s-1ASN1\s0 functions when
243 the entire structure can be read or written.
244 .SH "SEE ALSO"
245 .IX Header "SEE ALSO"
246 \&\s-1TBA\s0