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
#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);
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.
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.
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.
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.
bio(7)
The
BIO_get_retry_reason() and
BIO_set_retry_reason() functions
were added in OpenSSL 1.1.0.
Copyright 2000-2018 The OpenSSL Project Authors. All Rights Reserved.
Licensed under the Apache License 2.0 (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>.