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BIO_SHOULD_RETRY(3)		    OpenSSL		   BIO_SHOULD_RETRY(3)

NAME
       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_set_retry_reason - BIO	retry functions

SYNOPSIS
	#include <openssl/bio.h>

	int BIO_should_read(BIO	*b);
	int BIO_should_write(BIO *b);
	int BIO_should_io_special(iBIO *b);
	int BIO_retry_type(BIO *b);
	int BIO_should_retry(BIO *b);

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

DESCRIPTION
       These functions determine why a BIO is not able to read or write	data.
       They will typically be called after a failed BIO_read_ex() or
       BIO_write_ex() 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 the BIO
       has insufficient	data to	return.	Check for readability and/or retry the
       last operation.

       BIO_should_write() is true if the cause of the condition	is that	the
       BIO has pending data to write. Check for	writability and/or retry the
       last operation.

       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_retry_type()	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().

       BIO_set_retry_reason() sets the retry reason for	a special condition
       for a given BIO.	This would usually only	be called by BIO
       implementations.

NOTES
       BIO_should_read(), BIO_should_write(), BIO_should_io_special(),
       BIO_retry_type(), and BIO_should_retry(), are implemented as macros.

       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_ex() 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
       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.

RETURN VALUES
       BIO_should_read(), BIO_should_write(), BIO_should_io_special(), and
       BIO_should_retry() return either	1 or 0 based on	the actual conditions
       of the BIO.

       BIO_retry_type()	returns	a flag combination presenting the cause	of a
       retry condition or false	if there is no retry condition.

       BIO_get_retry_BIO() returns a valid BIO structure.

       BIO_get_retry_reason() returns the reason for a special condition.

SEE ALSO
       bio

HISTORY
       The BIO_get_retry_reason() and BIO_set_retry_reason() functions were
       added in	OpenSSL	1.1.0.

COPYRIGHT
       Copyright 2000-2018 The OpenSSL Project Authors.	All Rights Reserved.

       Licensed	under the OpenSSL license (the "License").  You	may not	use
       this file except	in compliance with the License.	 You can obtain	a copy
       in the file LICENSE in the source distribution or at
       <https://www.openssl.org/source/license.html>.

1.1.1a				  2018-11-20		   BIO_SHOULD_RETRY(3)

NAME | SYNOPSIS | DESCRIPTION | NOTES | BUGS | RETURN VALUES | SEE ALSO | HISTORY | COPYRIGHT

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