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1 | .\" $OpenBSD: BIO_should_retry.3,v 1.11 2023/04/30 14:03:47 schwarze Exp $ | ||
2 | .\" full merge up to: OpenSSL 99d63d46 Oct 26 13:56:48 2016 -0400 | ||
3 | .\" selective merge up to: OpenSSL 57fd5170 May 13 11:24:11 2018 +0200 | ||
4 | .\" | ||
5 | .\" This file is a derived work. | ||
6 | .\" The changes are covered by the following Copyright and license: | ||
7 | .\" | ||
8 | .\" Copyright (c) 2023 Ingo Schwarze <schwarze@openbsd.org> | ||
9 | .\" | ||
10 | .\" Permission to use, copy, modify, and distribute this software for any | ||
11 | .\" purpose with or without fee is hereby granted, provided that the above | ||
12 | .\" copyright notice and this permission notice appear in all copies. | ||
13 | .\" | ||
14 | .\" THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES | ||
15 | .\" WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF | ||
16 | .\" MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR | ||
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21 | .\" | ||
22 | .\" The original file was written by Dr. Stephen Henson <steve@openssl.org>. | ||
23 | .\" Copyright (c) 2000, 2010, 2016 The OpenSSL Project. All rights reserved. | ||
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25 | .\" Redistribution and use in source and binary forms, with or without | ||
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29 | .\" 1. Redistributions of source code must retain the above copyright | ||
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32 | .\" 2. Redistributions in binary form must reproduce the above copyright | ||
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69 | .Dd $Mdocdate: April 30 2023 $ | ||
70 | .Dt BIO_SHOULD_RETRY 3 | ||
71 | .Os | ||
72 | .Sh NAME | ||
73 | .Nm BIO_should_read , | ||
74 | .Nm BIO_should_write , | ||
75 | .Nm BIO_should_io_special , | ||
76 | .Nm BIO_retry_type , | ||
77 | .Nm BIO_should_retry , | ||
78 | .Nm BIO_get_retry_BIO , | ||
79 | .Nm BIO_get_retry_reason , | ||
80 | .Nm BIO_set_retry_reason | ||
81 | .Nd BIO retry functions | ||
82 | .Sh SYNOPSIS | ||
83 | .In openssl/bio.h | ||
84 | .Ft int | ||
85 | .Fo BIO_should_read | ||
86 | .Fa "BIO *b" | ||
87 | .Fc | ||
88 | .Ft int | ||
89 | .Fo BIO_should_write | ||
90 | .Fa "BIO *b" | ||
91 | .Fc | ||
92 | .Ft int | ||
93 | .Fo BIO_should_io_special | ||
94 | .Fa "BIO *b" | ||
95 | .Fc | ||
96 | .Ft int | ||
97 | .Fo BIO_retry_type | ||
98 | .Fa "BIO *b" | ||
99 | .Fc | ||
100 | .Ft int | ||
101 | .Fo BIO_should_retry | ||
102 | .Fa "BIO *b" | ||
103 | .Fc | ||
104 | .Fd #define BIO_FLAGS_READ 0x01 | ||
105 | .Fd #define BIO_FLAGS_WRITE 0x02 | ||
106 | .Fd #define BIO_FLAGS_IO_SPECIAL 0x04 | ||
107 | .Fd #define BIO_FLAGS_RWS \e | ||
108 | .Fd \& (BIO_FLAGS_READ|BIO_FLAGS_WRITE|BIO_FLAGS_IO_SPECIAL) | ||
109 | .Fd #define BIO_FLAGS_SHOULD_RETRY 0x08 | ||
110 | .Ft BIO * | ||
111 | .Fo BIO_get_retry_BIO | ||
112 | .Fa "BIO *bio" | ||
113 | .Fa "int *reason" | ||
114 | .Fc | ||
115 | .Ft int | ||
116 | .Fo BIO_get_retry_reason | ||
117 | .Fa "BIO *bio" | ||
118 | .Fc | ||
119 | .Ft void | ||
120 | .Fo BIO_set_retry_reason | ||
121 | .Fa "BIO *bio" | ||
122 | .Fa "int reason" | ||
123 | .Fc | ||
124 | .Sh DESCRIPTION | ||
125 | These functions determine why a BIO is not able to read or write data. | ||
126 | They will typically be called after a failed | ||
127 | .Xr BIO_read 3 | ||
128 | or | ||
129 | .Xr BIO_write 3 | ||
130 | call. | ||
131 | .Pp | ||
132 | .Fn BIO_should_retry | ||
133 | returns 1 if the call that produced this condition should be retried | ||
134 | at a later time, or 0 if an error occurred. | ||
135 | .Pp | ||
136 | .Fn BIO_should_read | ||
137 | returns 1 if the cause of the retry condition is that a BIO needs | ||
138 | to read data, or 0 otherwise. | ||
139 | .Pp | ||
140 | .Fn BIO_should_write | ||
141 | returns 1 if the cause of the retry condition is that a BIO needs | ||
142 | to write data, or 0 otherwise. | ||
143 | .Pp | ||
144 | .Fn BIO_should_io_special | ||
145 | returns 1 if some special condition (i.e. a reason other than reading | ||
146 | or writing) is the cause of the retry condition, or 0 otherwise. | ||
147 | .Pp | ||
148 | .Fn BIO_retry_type | ||
149 | returns the bitwise OR of one or more of the flags | ||
150 | .Dv BIO_FLAGS_READ , | ||
151 | .Dv BIO_FLAGS_WRITE , | ||
152 | and | ||
153 | .Dv BIO_FLAGS_IO_SPECIAL | ||
154 | representing the cause of the current retry condition, | ||
155 | or 0 if there is no retry condition. | ||
156 | Current BIO types only set one of the flags at a time. | ||
157 | .Pp | ||
158 | .Fn BIO_get_retry_BIO | ||
159 | determines the precise reason for the special condition. | ||
160 | It walks the BIO chain starting at | ||
161 | .Fa bio | ||
162 | and returns the BIO that caused this condition. | ||
163 | If there is no special condition, | ||
164 | .Fa bio | ||
165 | itself is returned. | ||
166 | If | ||
167 | .Fa reason | ||
168 | is not a | ||
169 | .Dv NULL | ||
170 | pointer, | ||
171 | .Pf * Fa reason | ||
172 | is set to one of the following reason codes: | ||
173 | .Bl -tag -width 1n -offset 3n | ||
174 | .It 0 | ||
175 | There is no special condition. | ||
176 | .It Dv BIO_RR_ACCEPT | ||
177 | .Xr accept 2 | ||
178 | would have blocked. | ||
179 | This can occur for BIOs created from | ||
180 | .Xr BIO_s_accept 3 | ||
181 | or | ||
182 | .Xr BIO_f_ssl 3 . | ||
183 | .It Dv BIO_RR_CONNECT | ||
184 | .Xr connect 2 | ||
185 | would have blocked. | ||
186 | This can occur for BIOs created from | ||
187 | .Xr BIO_s_connect 3 | ||
188 | or | ||
189 | .Xr BIO_f_ssl 3 . | ||
190 | .It Dv BIO_RR_SSL_X509_LOOKUP | ||
191 | An application callback set by | ||
192 | .Xr SSL_CTX_set_client_cert_cb 3 | ||
193 | has asked to be called again. | ||
194 | This can occur for BIOs created from | ||
195 | .Xr BIO_f_ssl 3 . | ||
196 | .El | ||
197 | .Pp | ||
198 | .Fn BIO_get_retry_reason | ||
199 | returns one of the above reason codes for a special condition that occurred in | ||
200 | .Fa bio . | ||
201 | It does not walk the chain and returns 0 if no special condition occurred in | ||
202 | .Fa bio | ||
203 | itself. | ||
204 | .Pp | ||
205 | .Fn BIO_set_retry_reason | ||
206 | sets the retry reason for a special condition for the given | ||
207 | .Fa bio . | ||
208 | It is intended to be called by functions implementing a BIO type | ||
209 | rather than by functions merely using BIOs. | ||
210 | .Pp | ||
211 | .Fn BIO_should_retry , | ||
212 | .Fn BIO_should_read , | ||
213 | .Fn BIO_should_write , | ||
214 | .Fn BIO_should_io_special , | ||
215 | and | ||
216 | .Fn BIO_retry_type | ||
217 | are implemented as macros. | ||
218 | .Pp | ||
219 | If | ||
220 | .Fn BIO_should_retry | ||
221 | returns false, then the precise "error condition" depends on | ||
222 | the BIO type that caused it and the return code of the BIO operation. | ||
223 | For example if a call to | ||
224 | .Xr BIO_read 3 | ||
225 | on a socket BIO returns 0 and | ||
226 | .Fn BIO_should_retry | ||
227 | is false, then the cause will be that the connection closed. | ||
228 | A similar condition on a file BIO will mean that it has reached EOF. | ||
229 | Some BIO types may place additional information on the error queue. | ||
230 | For more details see the individual BIO type manual pages. | ||
231 | .Pp | ||
232 | If the underlying I/O structure is in a blocking mode, | ||
233 | almost all current BIO types will not request a retry, | ||
234 | because the underlying I/O calls will not. | ||
235 | If the application knows that the BIO type will never | ||
236 | signal a retry then it need not call | ||
237 | .Fn BIO_should_retry | ||
238 | after a failed BIO I/O call. | ||
239 | This is typically done with file BIOs. | ||
240 | .Pp | ||
241 | SSL BIOs are the only current exception to this rule: | ||
242 | they can request a retry even if the underlying I/O structure | ||
243 | is blocking, if a handshake occurs during a call to | ||
244 | .Xr BIO_read 3 . | ||
245 | An application can retry the failed call immediately | ||
246 | or avoid this situation by setting | ||
247 | .Dv SSL_MODE_AUTO_RETRY | ||
248 | on the underlying SSL structure. | ||
249 | .Pp | ||
250 | While an application may retry a failed non-blocking call immediately, | ||
251 | this is likely to be very inefficient because the call will fail | ||
252 | repeatedly until data can be processed or is available. | ||
253 | An application will normally wait until the necessary condition | ||
254 | is satisfied. | ||
255 | How this is done depends on the underlying I/O structure. | ||
256 | .Pp | ||
257 | For example if the cause is ultimately a socket and | ||
258 | .Fn BIO_should_read | ||
259 | is true then a call to | ||
260 | .Xr select 2 | ||
261 | may be made to wait until data is available | ||
262 | and then retry the BIO operation. | ||
263 | By combining the retry conditions of several non-blocking BIOs in a single | ||
264 | .Xr select 2 | ||
265 | call it is possible to service several BIOs in a single thread, | ||
266 | though the performance may be poor if SSL BIOs are present because | ||
267 | long delays can occur during the initial handshake process. | ||
268 | .Pp | ||
269 | It is possible for a BIO to block indefinitely if the underlying I/O | ||
270 | structure cannot process or return any data. | ||
271 | This depends on the behaviour of the platforms I/O functions. | ||
272 | This is often not desirable: one solution is to use non-blocking I/O | ||
273 | and use a timeout on the | ||
274 | .Xr select 2 | ||
275 | (or equivalent) call. | ||
276 | .Sh SEE ALSO | ||
277 | .Xr BIO_new 3 , | ||
278 | .Xr BIO_read 3 | ||
279 | .Sh HISTORY | ||
280 | .Fn BIO_should_read , | ||
281 | .Fn BIO_should_write , | ||
282 | .Fn BIO_retry_type , | ||
283 | and | ||
284 | .Fn BIO_should_retry | ||
285 | first appeared in SSLeay 0.6.0. | ||
286 | .Fn BIO_should_io_special , | ||
287 | .Fn BIO_get_retry_BIO , | ||
288 | and | ||
289 | .Fn BIO_get_retry_reason | ||
290 | first appeared in SSLeay 0.8.0. | ||
291 | All these functions have been available since | ||
292 | .Ox 2.4 . | ||
293 | .Pp | ||
294 | .Fn BIO_set_retry_reason | ||
295 | first appeared in OpenSSL 1.1.0 and has been available since | ||
296 | .Ox 7.1 . | ||
297 | .Sh BUGS | ||
298 | The OpenSSL ASN.1 functions cannot gracefully deal with non-blocking I/O: | ||
299 | they cannot retry after a partial read or write. | ||
300 | This is usually worked around by only passing the relevant data to ASN.1 | ||
301 | functions when the entire structure can be read or written. | ||