1=pod 2 3=head1 NAME 4 5BIO_should_read, BIO_should_write, 6BIO_should_io_special, BIO_retry_type, BIO_should_retry, 7BIO_get_retry_BIO, BIO_get_retry_reason, BIO_set_retry_reason - BIO retry 8functions 9 10=head1 SYNOPSIS 11 12 #include <openssl/bio.h> 13 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); 19 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); 23 24=head1 DESCRIPTION 25 26These functions determine why a BIO is not able to read or write data. 27They will typically be called after a failed BIO_read_ex() or BIO_write_ex() 28call. 29 30BIO_should_retry() is true if the call that produced this condition 31should then be retried at a later time. 32 33If BIO_should_retry() is false then the cause is an error condition. 34 35BIO_should_read() is true if the cause of the condition is that the BIO 36has insufficient data to return. Check for readability and/or retry the 37last operation. 38 39BIO_should_write() is true if the cause of the condition is that the BIO 40has pending data to write. Check for writability and/or retry the 41last operation. 42 43BIO_should_io_special() is true if some "special" condition, that is a 44reason other than reading or writing is the cause of the condition. 45 46BIO_retry_type() returns a mask of the cause of a retry condition 47consisting of the values B<BIO_FLAGS_READ>, B<BIO_FLAGS_WRITE>, 48B<BIO_FLAGS_IO_SPECIAL> though current BIO types will only set one of 49these. 50 51BIO_get_retry_BIO() determines the precise reason for the special 52condition, it returns the BIO that caused this condition and if 53B<reason> is not NULL it contains the reason code. The meaning of 54the reason code and the action that should be taken depends on 55the type of BIO that resulted in this condition. 56 57BIO_get_retry_reason() returns the reason for a special condition if 58passed the relevant BIO, for example as returned by BIO_get_retry_BIO(). 59 60BIO_set_retry_reason() sets the retry reason for a special condition for a given 61BIO. This would usually only be called by BIO implementations. 62 63=head1 NOTES 64 65BIO_should_read(), BIO_should_write(), BIO_should_io_special(), 66BIO_retry_type(), and BIO_should_retry(), are implemented as macros. 67 68If BIO_should_retry() returns false then the precise "error condition" 69depends on the BIO type that caused it and the return code of the BIO 70operation. For example if a call to BIO_read_ex() on a socket BIO returns 710 and BIO_should_retry() is false then the cause will be that the 72connection closed. A similar condition on a file BIO will mean that it 73has reached EOF. Some BIO types may place additional information on 74the error queue. For more details see the individual BIO type manual 75pages. 76 77If the underlying I/O structure is in a blocking mode almost all current 78BIO types will not request a retry, because the underlying I/O 79calls will not. If the application knows that the BIO type will never 80signal a retry then it need not call BIO_should_retry() after a failed 81BIO I/O call. This is typically done with file BIOs. 82 83SSL BIOs are the only current exception to this rule: they can request a 84retry even if the underlying I/O structure is blocking, if a handshake 85occurs during a call to BIO_read(). An application can retry the failed 86call immediately or avoid this situation by setting SSL_MODE_AUTO_RETRY 87on the underlying SSL structure. 88 89While an application may retry a failed non blocking call immediately 90this is likely to be very inefficient because the call will fail 91repeatedly until data can be processed or is available. An application 92will normally wait until the necessary condition is satisfied. How 93this is done depends on the underlying I/O structure. 94 95For example if the cause is ultimately a socket and BIO_should_read() 96is true then a call to select() may be made to wait until data is 97available and then retry the BIO operation. By combining the retry 98conditions of several non blocking BIOs in a single select() call 99it is possible to service several BIOs in a single thread, though 100the performance may be poor if SSL BIOs are present because long delays 101can occur during the initial handshake process. 102 103It is possible for a BIO to block indefinitely if the underlying I/O 104structure cannot process or return any data. This depends on the behaviour of 105the platforms I/O functions. This is often not desirable: one solution 106is to use non blocking I/O and use a timeout on the select() (or 107equivalent) call. 108 109=head1 BUGS 110 111The OpenSSL ASN1 functions cannot gracefully deal with non blocking I/O: 112that is they cannot retry after a partial read or write. This is usually 113worked around by only passing the relevant data to ASN1 functions when 114the entire structure can be read or written. 115 116=head1 RETURN VALUES 117 118BIO_should_read(), BIO_should_write(), BIO_should_io_special(), and 119BIO_should_retry() return either 1 or 0 based on the actual conditions 120of the B<BIO>. 121 122BIO_retry_type() returns a flag combination presenting the cause of a retry 123condition or false if there is no retry condition. 124 125BIO_get_retry_BIO() returns a valid B<BIO> structure. 126 127BIO_get_retry_reason() returns the reason for a special condition. 128 129=head1 SEE ALSO 130 131L<bio(7)> 132 133=head1 HISTORY 134 135The BIO_get_retry_reason() and BIO_set_retry_reason() functions were added in 136OpenSSL 1.1.0. 137 138=head1 COPYRIGHT 139 140Copyright 2000-2018 The OpenSSL Project Authors. All Rights Reserved. 141 142Licensed under the Apache License 2.0 (the "License"). You may not use 143this file except in compliance with the License. You can obtain a copy 144in the file LICENSE in the source distribution or at 145L<https://www.openssl.org/source/license.html>. 146 147=cut 148
