]>
Commit | Line | Data |
---|---|---|
d7b9c76c DSH |
1 | =pod |
2 | ||
3 | =head1 NAME | |
4 | ||
8162f6f5 | 5 | BIO_should_read, BIO_should_write, |
8eec1389 | 6 | BIO_should_io_special, BIO_retry_type, BIO_should_retry, |
85556b4d MC |
7 | BIO_get_retry_BIO, BIO_get_retry_reason, BIO_set_retry_reason - BIO retry |
8 | functions | |
d7b9c76c DSH |
9 | |
10 | =head1 SYNOPSIS | |
11 | ||
12 | #include <openssl/bio.h> | |
13 | ||
91da5e77 RS |
14 | int BIO_should_read(BIO *b); |
15 | int BIO_should_write(BIO *b); | |
16 | int BIO_should_io_special(iBIO *b); | |
17 | int BIO_retry_type(BIO *b); | |
18 | int BIO_should_retry(BIO *b); | |
d7b9c76c | 19 | |
85556b4d MC |
20 | BIO *BIO_get_retry_BIO(BIO *bio, int *reason); |
21 | int BIO_get_retry_reason(BIO *bio); | |
22 | void BIO_set_retry_reason(BIO *bio, int reason); | |
d7b9c76c DSH |
23 | |
24 | =head1 DESCRIPTION | |
25 | ||
26 | These functions determine why a BIO is not able to read or write data. | |
b055fceb | 27 | They will typically be called after a failed BIO_read_ex() or BIO_write_ex() |
d7b9c76c DSH |
28 | call. |
29 | ||
30 | BIO_should_retry() is true if the call that produced this condition | |
31 | should then be retried at a later time. | |
32 | ||
33 | If BIO_should_retry() is false then the cause is an error condition. | |
34 | ||
57fd5170 KR |
35 | BIO_should_read() is true if the cause of the condition is that the BIO |
36 | has insufficient data to return. Check for readability and/or retry the | |
37 | last operation. | |
d7b9c76c | 38 | |
57fd5170 KR |
39 | BIO_should_write() is true if the cause of the condition is that the BIO |
40 | has pending data to write. Check for writability and/or retry the | |
41 | last operation. | |
d7b9c76c DSH |
42 | |
43 | BIO_should_io_special() is true if some "special" condition, that is a | |
44 | reason other than reading or writing is the cause of the condition. | |
45 | ||
60e24554 | 46 | BIO_retry_type() returns a mask of the cause of a retry condition |
d7b9c76c DSH |
47 | consisting of the values B<BIO_FLAGS_READ>, B<BIO_FLAGS_WRITE>, |
48 | B<BIO_FLAGS_IO_SPECIAL> though current BIO types will only set one of | |
40411564 | 49 | these. |
d7b9c76c DSH |
50 | |
51 | BIO_get_retry_BIO() determines the precise reason for the special | |
1bc74519 | 52 | condition, it returns the BIO that caused this condition and if |
d7b9c76c DSH |
53 | B<reason> is not NULL it contains the reason code. The meaning of |
54 | the reason code and the action that should be taken depends on | |
55 | the type of BIO that resulted in this condition. | |
56 | ||
57 | BIO_get_retry_reason() returns the reason for a special condition if | |
40411564 | 58 | passed the relevant BIO, for example as returned by BIO_get_retry_BIO(). |
d7b9c76c | 59 | |
85556b4d MC |
60 | BIO_set_retry_reason() sets the retry reason for a special condition for a given |
61 | BIO. This would usually only be called by BIO implementations. | |
62 | ||
d7b9c76c DSH |
63 | =head1 NOTES |
64 | ||
91da5e77 RS |
65 | BIO_should_read(), BIO_should_write(), BIO_should_io_special(), |
66 | BIO_retry_type(), and BIO_should_retry(), are implemented as macros. | |
67 | ||
d7b9c76c DSH |
68 | If BIO_should_retry() returns false then the precise "error condition" |
69 | depends on the BIO type that caused it and the return code of the BIO | |
b055fceb | 70 | operation. For example if a call to BIO_read_ex() on a socket BIO returns |
d7b9c76c DSH |
71 | 0 and BIO_should_retry() is false then the cause will be that the |
72 | connection closed. A similar condition on a file BIO will mean that it | |
73 | has reached EOF. Some BIO types may place additional information on | |
74 | the error queue. For more details see the individual BIO type manual | |
75 | pages. | |
76 | ||
40411564 DSH |
77 | If the underlying I/O structure is in a blocking mode almost all current |
78 | BIO types will not request a retry, because the underlying I/O | |
d7b9c76c DSH |
79 | calls will not. If the application knows that the BIO type will never |
80 | signal a retry then it need not call BIO_should_retry() after a failed | |
81 | BIO I/O call. This is typically done with file BIOs. | |
82 | ||
40411564 DSH |
83 | SSL BIOs are the only current exception to this rule: they can request a |
84 | retry even if the underlying I/O structure is blocking, if a handshake | |
85 | occurs during a call to BIO_read(). An application can retry the failed | |
86 | call immediately or avoid this situation by setting SSL_MODE_AUTO_RETRY | |
87 | on the underlying SSL structure. | |
d7b9c76c DSH |
88 | |
89 | While an application may retry a failed non blocking call immediately | |
d572cb6c DSH |
90 | this is likely to be very inefficient because the call will fail |
91 | repeatedly until data can be processed or is available. An application | |
92 | will normally wait until the necessary condition is satisfied. How | |
93 | this is done depends on the underlying I/O structure. | |
d7b9c76c DSH |
94 | |
95 | For example if the cause is ultimately a socket and BIO_should_read() | |
96 | is true then a call to select() may be made to wait until data is | |
97 | available and then retry the BIO operation. By combining the retry | |
98 | conditions of several non blocking BIOs in a single select() call | |
40411564 DSH |
99 | it is possible to service several BIOs in a single thread, though |
100 | the performance may be poor if SSL BIOs are present because long delays | |
1bc74519 | 101 | can occur during the initial handshake process. |
d7b9c76c DSH |
102 | |
103 | It is possible for a BIO to block indefinitely if the underlying I/O | |
acb5b343 | 104 | structure cannot process or return any data. This depends on the behaviour of |
d7b9c76c DSH |
105 | the platforms I/O functions. This is often not desirable: one solution |
106 | is to use non blocking I/O and use a timeout on the select() (or | |
107 | equivalent) call. | |
108 | ||
109 | =head1 BUGS | |
110 | ||
111 | The OpenSSL ASN1 functions cannot gracefully deal with non blocking I/O: | |
112 | that is they cannot retry after a partial read or write. This is usually | |
113 | worked around by only passing the relevant data to ASN1 functions when | |
114 | the entire structure can be read or written. | |
115 | ||
1f13ad31 PY |
116 | =head1 RETURN VALUES |
117 | ||
118 | BIO_should_read(), BIO_should_write(), BIO_should_io_special(), and | |
119 | BIO_should_retry() return either 1 or 0 based on the actual conditions | |
120 | of the B<BIO>. | |
121 | ||
122 | BIO_retry_type() returns a flag combination presenting the cause of a retry | |
123 | condition or false if there is no retry condition. | |
124 | ||
125 | BIO_get_retry_BIO() returns a valid B<BIO> structure. | |
126 | ||
127 | BIO_get_retry_reason() returns the reason for a special condition. | |
128 | ||
d7b9c76c DSH |
129 | =head1 SEE ALSO |
130 | ||
85556b4d MC |
131 | L<bio> |
132 | ||
133 | =head1 HISTORY | |
134 | ||
135 | The BIO_get_retry_reason() and BIO_set_retry_reason() functions were added in | |
e90fc053 | 136 | OpenSSL 1.1.0. |
85556b4d | 137 | |
e2f92610 RS |
138 | =head1 COPYRIGHT |
139 | ||
61f805c1 | 140 | Copyright 2000-2018 The OpenSSL Project Authors. All Rights Reserved. |
e2f92610 RS |
141 | |
142 | Licensed under the OpenSSL license (the "License"). You may not use | |
143 | this file except in compliance with the License. You can obtain a copy | |
144 | in the file LICENSE in the source distribution or at | |
145 | L<https://www.openssl.org/source/license.html>. | |
146 | ||
147 | =cut |