NAME    [Toc]    [Back]

       BIO_should_retry, BIO_should_read, BIO_should_write,
       BIO_should_io_special, BIO_retry_type, BIO_should_retry,
       BIO_get_retry_BIO, BIO_get_retry_reason - BIO retry functions

LIBRARY    [Toc]    [Back]

       libcrypto, -lcrypto

SYNOPSIS    [Toc]    [Back]

        #include <openssl/bio.h>

        #define BIO_should_read(a)             ((a)->flags & BIO_FLAGS_READ)
        #define BIO_should_write(a)            ((a)->flags & BIO_FLAGS_WRITE)
        #define BIO_should_io_special(a)       ((a)->flags & BIO_FLAGS_IO_SPECIAL)
        #define BIO_retry_type(a)              ((a)->flags & BIO_FLAGS_RWS)
        #define BIO_should_retry(a)            ((a)->flags & BIO_FLAGS_SHOULD_RETRY)

        #define BIO_FLAGS_READ         0x01
        #define BIO_FLAGS_WRITE        0x02
        #define BIO_FLAGS_IO_SPECIAL   0x04
        #define BIO_FLAGS_RWS (BIO_FLAGS_READ|BIO_FLAGS_WRITE|BIO_FLAGS_IO_SPECIAL)
        #define BIO_FLAGS_SHOULD_RETRY 0x08

        BIO *  BIO_get_retry_BIO(BIO *bio, int *reason);
        int    BIO_get_retry_reason(BIO *bio);

DESCRIPTION    [Toc]    [Back]

       These functions determine why a BIO is not able to read or
       write data.  They will typically be called after a failed
       BIO_read() or BIO_write() call.

       BIO_should_retry() is true if the call that produced this
       condition should then be retried at a later time.

       If BIO_should_retry() is false then the cause is an error
       condition.

       BIO_should_read() is true if the cause of the condition is
       that a BIO needs to read data.

       BIO_should_write() is true if the cause of the condition
       is that a BIO needs to read data.

       BIO_should_io_special() is true if some "special" condition,
 that is a reason other than reading or writing is
       the cause of the condition.

       BIO_get_retry_reason() returns a mask of the cause of a
       retry condition consisting of the values BIO_FLAGS_READ,
       BIO_FLAGS_WRITE, BIO_FLAGS_IO_SPECIAL though current BIO
       types will only set one of these.

       BIO_get_retry_BIO() determines the precise reason for the
       special condition, it returns the BIO that caused this
       condition and if reason is not NULL it contains the reason
       code. The meaning of the reason code and the action that
       should be taken depends on the type of BIO that resulted
       in this condition.

       BIO_get_retry_reason() returns the reason for a special
       condition if passed the relevant BIO, for example as
       returned by BIO_get_retry_BIO().

NOTES    [Toc]    [Back]

       If BIO_should_retry() returns false then the precise
       "error condition" depends on the BIO type that caused it
       and the return code of the BIO operation. For example if a
       call to BIO_read() on a socket BIO returns 0 and
       BIO_should_retry() is false then the cause will be that
       the connection closed. A similar condition on a file BIO
       will mean that it has reached EOF. Some BIO types may
       place additional information on the error queue. For more
       details see the individual BIO type manual pages.

       If the underlying I/O structure is in a blocking mode
       almost all current BIO types will not request a retry,
       because the underlying I/O calls will not. If the application
 knows that the BIO type will never signal a retry
       then it need not call BIO_should_retry() after a failed
       BIO I/O call. This is typically done with file BIOs.

       SSL BIOs are the only current exception to this rule: they
       can request a retry even if the underlying I/O structure
       is blocking, if a handshake occurs during a call to
       BIO_read(). An application can retry the failed call immediately
 or avoid this situation by setting
       SSL_MODE_AUTO_RETRY on the underlying SSL structure.

       While an application may retry a failed non blocking call
       immediately this is likely to be very inefficient because
       the call will fail repeatedly until data can be processed
       or is available. An application will normally wait until
       the necessary condition is satisfied. How this is done
       depends on the underlying I/O structure.

       For example if the cause is ultimately a socket and
       BIO_should_read() is true then a call to select() may be
       made to wait until data is available and then retry the
       BIO operation. By combining the retry conditions of several
 non blocking BIOs in a single select() call it is
       possible to service several BIOs in a single thread,
       though the performance may be poor if SSL BIOs are present
       because long delays can occur during the initial handshake
       process.

       It is possible for a BIO to block indefinitely if the
       underlying I/O structure cannot process or return any
       data. This depends on the behaviour of the platforms I/O
       functions. This is often not desirable: one solution is to
       use non blocking I/O and use a timeout on the select() (or
       equivalent) call.

BUGS    [Toc]    [Back]

       The OpenSSL ASN1 functions cannot gracefully deal with non
       blocking I/O: that is they cannot retry after a partial
       read or write. This is usually worked around by only passing
 the relevant data to ASN1 functions when the entire
       structure can be read or written.

SEE ALSO    [Toc]    [Back]

       TBA



2001-04-12                    0.9.6g          BIO_should_retry(3)