1BIO_SHOULD_RETRY(3) OpenSSL BIO_SHOULD_RETRY(3)
2
6 BIO_should_read, BIO_should_write, BIO_should_io_special,
7 BIO_retry_type, BIO_should_retry, BIO_get_retry_BIO,
8 BIO_get_retry_reason, BIO_set_retry_reason - BIO retry functions
9
11 #include <openssl/bio.h>
12 int BIO_should_read(BIO *b);
14 int BIO_should_write(BIO *b);
15 int BIO_should_io_special(iBIO *b);
16 int BIO_retry_type(BIO *b);
17 int BIO_should_retry(BIO *b);
18 BIO *BIO_get_retry_BIO(BIO *bio, int *reason);
20 int BIO_get_retry_reason(BIO *bio);
21 void BIO_set_retry_reason(BIO *bio, int reason);
22
24 These functions determine why a BIO is not able to read or write data.
25 They will typically be called after a failed BIO_read_ex() or
26 BIO_write_ex() call.
27 BIO_should_retry() is true if the call that produced this condition
29 should then be retried at a later time.
30 If BIO_should_retry() is false then the cause is an error condition.
32 BIO_should_read() is true if the cause of the condition is that the BIO
34 has insufficient data to return. Check for readability and/or retry the
35 last operation.
36 BIO_should_write() is true if the cause of the condition is that the
38 BIO has pending data to write. Check for writability and/or retry the
39 last operation.
40 BIO_should_io_special() is true if some "special" condition, that is a
42 reason other than reading or writing is the cause of the condition.
43 BIO_retry_type() returns a mask of the cause of a retry condition
45 consisting of the values BIO_FLAGS_READ, BIO_FLAGS_WRITE,
46 BIO_FLAGS_IO_SPECIAL though current BIO types will only set one of
47 these.
48 BIO_get_retry_BIO() determines the precise reason for the special
50 condition, it returns the BIO that caused this condition and if reason
51 is not NULL it contains the reason code. The meaning of the reason code
52 and the action that should be taken depends on the type of BIO that
53 resulted in this condition.
54 BIO_get_retry_reason() returns the reason for a special condition if
56 passed the relevant BIO, for example as returned by
57 BIO_get_retry_BIO().
58 BIO_set_retry_reason() sets the retry reason for a special condition
60 for a given BIO. This would usually only be called by BIO
61 implementations.
62
64 BIO_should_read(), BIO_should_write(), BIO_should_io_special(),
65 BIO_retry_type(), and BIO_should_retry(), are implemented as macros.
66 If BIO_should_retry() returns false then the precise "error condition"
68 depends on the BIO type that caused it and the return code of the BIO
69 operation. For example if a call to BIO_read_ex() on a socket BIO
70 returns 0 and BIO_should_retry() is false then the cause will be that
71 the connection closed. A similar condition on a file BIO will mean that
72 it has reached EOF. Some BIO types may place additional information on
73 the error queue. For more details see the individual BIO type manual
74 pages.
75 If the underlying I/O structure is in a blocking mode almost all
77 current BIO types will not request a retry, because the underlying I/O
78 calls will not. If the application knows that the BIO type will never
79 signal a retry then it need not call BIO_should_retry() after a failed
80 BIO I/O call. This is typically done with file BIOs.
81 SSL BIOs are the only current exception to this rule: they can request
83 a retry even if the underlying I/O structure is blocking, if a
84 handshake occurs during a call to BIO_read(). An application can retry
85 the failed call immediately or avoid this situation by setting
86 SSL_MODE_AUTO_RETRY on the underlying SSL structure.
87 While an application may retry a failed non blocking call immediately
89 this is likely to be very inefficient because the call will fail
90 repeatedly until data can be processed or is available. An application
91 will normally wait until the necessary condition is satisfied. How this
92 is done depends on the underlying I/O structure.
93 For example if the cause is ultimately a socket and BIO_should_read()
95 is true then a call to select() may be made to wait until data is
96 available and then retry the BIO operation. By combining the retry
97 conditions of several non blocking BIOs in a single select() call it is
98 possible to service several BIOs in a single thread, though the
99 performance may be poor if SSL BIOs are present because long delays can
100 occur during the initial handshake process.
101 It is possible for a BIO to block indefinitely if the underlying I/O
103 structure cannot process or return any data. This depends on the
104 behaviour of the platforms I/O functions. This is often not desirable:
105 one solution is to use non blocking I/O and use a timeout on the
106 select() (or equivalent) call.
107
109 The OpenSSL ASN1 functions cannot gracefully deal with non blocking
110 I/O: that is they cannot retry after a partial read or write. This is
111 usually worked around by only passing the relevant data to ASN1
112 functions when the entire structure can be read or written.
113
115 BIO_should_read(), BIO_should_write(), BIO_should_io_special(), and
116 BIO_should_retry() return either 1 or 0 based on the actual conditions
117 of the BIO.
118 BIO_retry_type() returns a flag combination presenting the cause of a
120 retry condition or false if there is no retry condition.
121 BIO_get_retry_BIO() returns a valid BIO structure.
123 BIO_get_retry_reason() returns the reason for a special condition.
125
127 bio
128
130 The BIO_get_retry_reason() and BIO_set_retry_reason() functions were
131 added in OpenSSL 1.1.0.
132
134 Copyright 2000-2018 The OpenSSL Project Authors. All Rights Reserved.
135 Licensed under the OpenSSL license (the "License"). You may not use
137 this file except in compliance with the License. You can obtain a copy
138 in the file LICENSE in the source distribution or at
139 <https://www.openssl.org/source/license.html>.
1401.1.1i 2021-07-22 BIO_SHOULD_RETRY(3)