1=pod 2 3=head1 NAME 4 5BIO_should_retry, BIO_should_read, BIO_should_write, 6BIO_should_io_special, BIO_retry_type, BIO_should_retry, 7BIO_get_retry_BIO, BIO_get_retry_reason - BIO retry functions 8 9=head1 SYNOPSIS 10 11 #include <openssl/bio.h> 12 13 #define BIO_should_read(a) ((a)->flags & BIO_FLAGS_READ) 14 #define BIO_should_write(a) ((a)->flags & BIO_FLAGS_WRITE) 15 #define BIO_should_io_special(a) ((a)->flags & BIO_FLAGS_IO_SPECIAL) 16 #define BIO_retry_type(a) ((a)->flags & BIO_FLAGS_RWS) 17 #define BIO_should_retry(a) ((a)->flags & BIO_FLAGS_SHOULD_RETRY) 18 19 #define BIO_FLAGS_READ 0x01 20 #define BIO_FLAGS_WRITE 0x02 21 #define BIO_FLAGS_IO_SPECIAL 0x04 22 #define BIO_FLAGS_RWS (BIO_FLAGS_READ|BIO_FLAGS_WRITE|BIO_FLAGS_IO_SPECIAL) 23 #define BIO_FLAGS_SHOULD_RETRY 0x08 24 25 BIO * BIO_get_retry_BIO(BIO *bio, int *reason); 26 int BIO_get_retry_reason(BIO *bio); 27 28=head1 DESCRIPTION 29 30These functions determine why a BIO is not able to read or write data. 31They will typically be called after a failed BIO_read() or BIO_write() 32call. 33 34BIO_should_retry() is true if the call that produced this condition 35should then be retried at a later time. 36 37If BIO_should_retry() is false then the cause is an error condition. 38 39BIO_should_read() is true if the cause of the condition is that a BIO 40needs to read data. 41 42BIO_should_write() is true if the cause of the condition is that a BIO 43needs to read data. 44 45BIO_should_io_special() is true if some "special" condition, that is a 46reason other than reading or writing is the cause of the condition. 47 48BIO_get_retry_reason() returns a mask of the cause of a retry condition 49consisting of the values B<BIO_FLAGS_READ>, B<BIO_FLAGS_WRITE>, 50B<BIO_FLAGS_IO_SPECIAL> though current BIO types will only set one of 51these. 52 53BIO_get_retry_BIO() determines the precise reason for the special 54condition, it returns the BIO that caused this condition and if 55B<reason> is not NULL it contains the reason code. The meaning of 56the reason code and the action that should be taken depends on 57the type of BIO that resulted in this condition. 58 59BIO_get_retry_reason() returns the reason for a special condition if 60passed the relevant BIO, for example as returned by BIO_get_retry_BIO(). 61 62=head1 NOTES 63 64If BIO_should_retry() returns false then the precise "error condition" 65depends on the BIO type that caused it and the return code of the BIO 66operation. For example if a call to BIO_read() on a socket BIO returns 670 and BIO_should_retry() is false then the cause will be that the 68connection closed. A similar condition on a file BIO will mean that it 69has reached EOF. Some BIO types may place additional information on 70the error queue. For more details see the individual BIO type manual 71pages. 72 73If the underlying I/O structure is in a blocking mode almost all current 74BIO types will not request a retry, because the underlying I/O 75calls will not. If the application knows that the BIO type will never 76signal a retry then it need not call BIO_should_retry() after a failed 77BIO I/O call. This is typically done with file BIOs. 78 79SSL BIOs are the only current exception to this rule: they can request a 80retry even if the underlying I/O structure is blocking, if a handshake 81occurs during a call to BIO_read(). An application can retry the failed 82call immediately or avoid this situation by setting SSL_MODE_AUTO_RETRY 83on the underlying SSL structure. 84 85While an application may retry a failed non blocking call immediately 86this is likely to be very inefficient because the call will fail 87repeatedly until data can be processed or is available. An application 88will normally wait until the necessary condition is satisfied. How 89this is done depends on the underlying I/O structure. 90 91For example if the cause is ultimately a socket and BIO_should_read() 92is true then a call to select() may be made to wait until data is 93available and then retry the BIO operation. By combining the retry 94conditions of several non blocking BIOs in a single select() call 95it is possible to service several BIOs in a single thread, though 96the performance may be poor if SSL BIOs are present because long delays 97can occur during the initial handshake process. 98 99It is possible for a BIO to block indefinitely if the underlying I/O 100structure cannot process or return any data. This depends on the behaviour of 101the platforms I/O functions. This is often not desirable: one solution 102is to use non blocking I/O and use a timeout on the select() (or 103equivalent) call. 104 105=head1 BUGS 106 107The OpenSSL ASN1 functions cannot gracefully deal with non blocking I/O: 108that is they cannot retry after a partial read or write. This is usually 109worked around by only passing the relevant data to ASN1 functions when 110the entire structure can be read or written. 111 112=head1 SEE ALSO 113 114TBA 115