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| 124 | .\" ======================================================================== |
| 125 | .\" |
| 126 | .IX Title "BIO_should_retry 3" |
| 127 | .TH BIO_should_retry 3 "2012-01-04" "1.0.0f" "OpenSSL" |
| 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 |
| 132 | .SH "NAME" |
| 133 | BIO_should_retry, BIO_should_read, BIO_should_write, |
| 134 | BIO_should_io_special, BIO_retry_type, BIO_should_retry, |
| 135 | BIO_get_retry_BIO, BIO_get_retry_reason \- BIO retry functions |
| 136 | .SH "SYNOPSIS" |
| 137 | .IX Header "SYNOPSIS" |
| 138 | .Vb 1 |
| 139 | \& #include <openssl/bio.h> |
| 140 | \& |
| 141 | \& #define BIO_should_read(a) ((a)\->flags & BIO_FLAGS_READ) |
| 142 | \& #define BIO_should_write(a) ((a)\->flags & BIO_FLAGS_WRITE) |
| 143 | \& #define BIO_should_io_special(a) ((a)\->flags & BIO_FLAGS_IO_SPECIAL) |
| 144 | \& #define BIO_retry_type(a) ((a)\->flags & BIO_FLAGS_RWS) |
| 145 | \& #define BIO_should_retry(a) ((a)\->flags & BIO_FLAGS_SHOULD_RETRY) |
| 146 | \& |
| 147 | \& #define BIO_FLAGS_READ 0x01 |
| 148 | \& #define BIO_FLAGS_WRITE 0x02 |
| 149 | \& #define BIO_FLAGS_IO_SPECIAL 0x04 |
| 150 | \& #define BIO_FLAGS_RWS (BIO_FLAGS_READ|BIO_FLAGS_WRITE|BIO_FLAGS_IO_SPECIAL) |
| 151 | \& #define BIO_FLAGS_SHOULD_RETRY 0x08 |
| 152 | \& |
| 153 | \& BIO * BIO_get_retry_BIO(BIO *bio, int *reason); |
| 154 | \& int BIO_get_retry_reason(BIO *bio); |
| 155 | .Ve |
| 156 | .SH "DESCRIPTION" |
| 157 | .IX Header "DESCRIPTION" |
| 158 | These functions determine why a \s-1BIO\s0 is not able to read or write data. |
| 159 | They will typically be called after a failed \fIBIO_read()\fR or \fIBIO_write()\fR |
| 160 | call. |
| 161 | .PP |
| 162 | \&\fIBIO_should_retry()\fR is true if the call that produced this condition |
| 163 | should then be retried at a later time. |
| 164 | .PP |
| 165 | If \fIBIO_should_retry()\fR is false then the cause is an error condition. |
| 166 | .PP |
| 167 | \&\fIBIO_should_read()\fR is true if the cause of the condition is that a \s-1BIO\s0 |
| 168 | needs to read data. |
| 169 | .PP |
| 170 | \&\fIBIO_should_write()\fR is true if the cause of the condition is that a \s-1BIO\s0 |
| 171 | needs to read data. |
| 172 | .PP |
| 173 | \&\fIBIO_should_io_special()\fR is true if some \*(L"special\*(R" condition, that is a |
| 174 | reason other than reading or writing is the cause of the condition. |
| 175 | .PP |
| 176 | \&\fIBIO_retry_type()\fR returns a mask of the cause of a retry condition |
| 177 | consisting of the values \fB\s-1BIO_FLAGS_READ\s0\fR, \fB\s-1BIO_FLAGS_WRITE\s0\fR, |
| 178 | \&\fB\s-1BIO_FLAGS_IO_SPECIAL\s0\fR though current \s-1BIO\s0 types will only set one of |
| 179 | these. |
| 180 | .PP |
| 181 | \&\fIBIO_get_retry_BIO()\fR determines the precise reason for the special |
| 182 | condition, it returns the \s-1BIO\s0 that caused this condition and if |
| 183 | \&\fBreason\fR is not \s-1NULL\s0 it contains the reason code. The meaning of |
| 184 | the reason code and the action that should be taken depends on |
| 185 | the type of \s-1BIO\s0 that resulted in this condition. |
| 186 | .PP |
| 187 | \&\fIBIO_get_retry_reason()\fR returns the reason for a special condition if |
| 188 | passed the relevant \s-1BIO\s0, for example as returned by \fIBIO_get_retry_BIO()\fR. |
| 189 | .SH "NOTES" |
| 190 | .IX Header "NOTES" |
| 191 | If \fIBIO_should_retry()\fR returns false then the precise \*(L"error condition\*(R" |
| 192 | depends on the \s-1BIO\s0 type that caused it and the return code of the \s-1BIO\s0 |
| 193 | operation. For example if a call to \fIBIO_read()\fR on a socket \s-1BIO\s0 returns |
| 194 | 0 and \fIBIO_should_retry()\fR is false then the cause will be that the |
| 195 | connection closed. A similar condition on a file \s-1BIO\s0 will mean that it |
| 196 | has reached \s-1EOF\s0. Some \s-1BIO\s0 types may place additional information on |
| 197 | the error queue. For more details see the individual \s-1BIO\s0 type manual |
| 198 | pages. |
| 199 | .PP |
| 200 | If the underlying I/O structure is in a blocking mode almost all current |
| 201 | \&\s-1BIO\s0 types will not request a retry, because the underlying I/O |
| 202 | calls will not. If the application knows that the \s-1BIO\s0 type will never |
| 203 | signal a retry then it need not call \fIBIO_should_retry()\fR after a failed |
| 204 | \&\s-1BIO\s0 I/O call. This is typically done with file BIOs. |
| 205 | .PP |
| 206 | \&\s-1SSL\s0 BIOs are the only current exception to this rule: they can request a |
| 207 | retry even if the underlying I/O structure is blocking, if a handshake |
| 208 | occurs during a call to \fIBIO_read()\fR. An application can retry the failed |
| 209 | call immediately or avoid this situation by setting \s-1SSL_MODE_AUTO_RETRY\s0 |
| 210 | on the underlying \s-1SSL\s0 structure. |
| 211 | .PP |
| 212 | While an application may retry a failed non blocking call immediately |
| 213 | this is likely to be very inefficient because the call will fail |
| 214 | repeatedly until data can be processed or is available. An application |
| 215 | will normally wait until the necessary condition is satisfied. How |
| 216 | this is done depends on the underlying I/O structure. |
| 217 | .PP |
| 218 | For example if the cause is ultimately a socket and \fIBIO_should_read()\fR |
| 219 | is true then a call to \fIselect()\fR may be made to wait until data is |
| 220 | available and then retry the \s-1BIO\s0 operation. By combining the retry |
| 221 | conditions of several non blocking BIOs in a single \fIselect()\fR call |
| 222 | it is possible to service several BIOs in a single thread, though |
| 223 | the performance may be poor if \s-1SSL\s0 BIOs are present because long delays |
| 224 | can occur during the initial handshake process. |
| 225 | .PP |
| 226 | It is possible for a \s-1BIO\s0 to block indefinitely if the underlying I/O |
| 227 | structure cannot process or return any data. This depends on the behaviour of |
| 228 | the platforms I/O functions. This is often not desirable: one solution |
| 229 | is to use non blocking I/O and use a timeout on the \fIselect()\fR (or |
| 230 | equivalent) call. |
| 231 | .SH "BUGS" |
| 232 | .IX Header "BUGS" |
| 233 | The OpenSSL \s-1ASN1\s0 functions cannot gracefully deal with non blocking I/O: |
| 234 | that is they cannot retry after a partial read or write. This is usually |
| 235 | worked around by only passing the relevant data to \s-1ASN1\s0 functions when |
| 236 | the entire structure can be read or written. |
| 237 | .SH "SEE ALSO" |
| 238 | .IX Header "SEE ALSO" |
| 239 | \&\s-1TBA\s0 |