=pod

=head1 NAME

BIO_set_flags, BIO_clear_flags, BIO_test_flags, BIO_get_flags,
BIO_set_retry_read, BIO_set_retry_write, BIO_set_retry_special,
BIO_clear_retry_flags, BIO_get_retry_flags
- manipulate and interpret BIO flags

=head1 SYNOPSIS

 #include <openssl/bio.h>

 void BIO_set_flags(BIO *b, int flags);
 void BIO_clear_flags(BIO *b, int flags);
 int  BIO_test_flags(const BIO *b, int flags);
 int  BIO_get_flags(const BIO *b);

 void BIO_set_retry_read(BIO *b);
 void BIO_set_retry_write(BIO *b);
 void BIO_set_retry_special(BIO *b);
 void BIO_clear_retry_flags(BIO *b);
 int  BIO_get_retry_flags(BIO *b);

=head1 DESCRIPTION

A B<BIO> has an internal set of bit flags that describe its state.  These
functions and macros are used primarily by B<BIO> implementations and by code
that builds B<BIO> chains to manipulate those flags.

BIO_set_flags() sets the bits given in I<flags> in the B<BIO> I<b>.  Any bits
already set in the B<BIO>'s flag word remain set.

BIO_clear_flags() clears the bits given in I<flags> from the B<BIO> I<b>.  Any
other bits in the flag word are left unchanged.

BIO_test_flags() tests the bits given in I<flags> in the B<BIO> I<b> and
returns a nonzero value if any of them are currently set and zero
otherwise.

BIO_get_flags() returns the current flag word from the B<BIO> I<b>.  This is
equivalent to testing for all bits and returning the result.

The following convenience macros are built on top of these primitives and are
used to maintain the retry state of a BIO:

BIO_set_retry_read() marks the B<BIO> I<b> as being in a retryable state
by setting the B<BIO_FLAGS_SHOULD_RETRY> flag. In addition, it sets the
B<BIO_FLAGS_READ> flag to indicate that the retry condition is
associated with a read operation.

BIO_set_retry_write() marks the B<BIO> I<b> as being in a retryable state
by setting the B<BIO_FLAGS_SHOULD_RETRY> flag. In addition, it sets the
B<BIO_FLAGS_WRITE> flag to indicate that the retry condition is
associated with a write operation.

BIO_set_retry_special() marks the B<BIO> I<b> as being in a retryable state
by setting the B<BIO_FLAGS_SHOULD_RETRY> flag. In addition, it sets the
B<BIO_FLAGS_IO_SPECIAL> flag to indicate that the retry condition is
associated with a read operation some "special" condition.
The precise meaning of this condition depends on the B<BIO> type.

BIO_clear_retry_flags() clears all retry-related bits from I<b>, i.e.
B<BIO_FLAGS_READ>, B<BIO_FLAGS_WRITE>, B<BIO_FLAGS_IO_SPECIAL>, and
B<BIO_FLAGS_SHOULD_RETRY>.

BIO_get_retry_flags() returns retry-related bits that are
currently set in I<b>.  The result is a subset of
B<BIO_FLAGS_RWS|BIO_FLAGS_SHOULD_RETRY>.

The retry bits are interpreted by the higher level macros
BIO_should_read(), BIO_should_write(), BIO_should_io_special(),
BIO_retry_type() and BIO_should_retry(), as documented in
L<BIO_should_retry(3)>.  Application code will typically use those macros
rather than manipulate the underlying flags directly.

The following flag bits are currently defined for use with BIO_set_flags(),
BIO_clear_flags() and BIO_test_flags():

=over 4

=item B<BIO_FLAGS_READ>

The last I/O operation should be retried when the B<BIO> becomes readable.
This flag is normally set by the B<BIO> implementation via BIO_set_retry_read()
after a failed read operation.

=item B<BIO_FLAGS_WRITE>

The last I/O operation should be retried when the B<BIO> becomes writable.
This flag is normally set by the B<BIO> implementation via BIO_set_retry_write()
after a failed write operation.

=item B<BIO_FLAGS_IO_SPECIAL>

The last I/O operation should be retried when some "special" condition
becomes true.  The precise meaning of this condition depends on the B<BIO>
type and is usually obtained via BIO_get_retry_BIO() and
BIO_get_retry_reason() as described in L<BIO_should_retry(3)>.
This flag is normally set by the B<BIO> implementation via
BIO_set_retry_special().

=item B<BIO_FLAGS_RWS>

The bitwise OR of B<BIO_FLAGS_READ>, B<BIO_FLAGS_WRITE> and
B<BIO_FLAGS_IO_SPECIAL>.  This mask is used when clearing or extracting
the retry-direction bits.

=item B<BIO_FLAGS_SHOULD_RETRY>

Set if the last I/O operation on the B<BIO> should be retried at a later time.
If this bit is not set then the condition is treated as an error.
This flag is normally set by the B<BIO> implementation.

=back

The following flag can be used only with the B<base64 encoding BIO>.
The result of using this flag with other BIOs is unpredictable.

=over 4

=item B<BIO_FLAGS_BASE64_NO_NL>

When set on a base64 filter B<BIO> this flag disables the generation of
newline characters in the encoded output and causes newlines to be ignored
in the input.  See also L<BIO_f_base64(3)>.
The flag has no effect on any other built-in B<BIO> types.

=back

The following flags can be used only with the B<memory buffer BIO> and
B<secure memory buffer BIO>. The result of using these flags with other BIOs
is unpredictable.

=over 4

=item B<BIO_FLAGS_MEM_RDONLY>

When set on a memory B<BIO> this flag indicates that the underlying buffer is
read only.  Attempts to write to such a B<BIO> will fail.
The flag has no effect on any other built-in B<BIO> types.

=item B<BIO_FLAGS_NONCLEAR_RST>

On a memory B<BIO> this flag modifies the behaviour of BIO_reset().  When it
is set, resetting the B<BIO> does not clear the underlying buffer but only
resets the current read position.
The flag has no effect on any other built-in B<BIO> types.

=item B<BIO_FLAGS_IN_EOF>

This flag is for internal use only. It should not be used outside BIO
implementations.

=back

A range of additional flag values is reserved for internal use by OpenSSL
to track kernel TLS (KTLS) state.  This range and the corresponding flag
macros are not part of the public API and must not be used by applications.

=head1 RETURN VALUES

BIO_get_flags() returns a bit mask of the flags currently set on the B<BIO>.

BIO_test_flags() returns a bit mask consisting of those flags from the
argument that are currently set in the B<BIO>. Consequently, it returns a
nonzero value if and only if at least one of the requested flags is set.

BIO_get_retry_flags() returns a bit mask consisting of those flags from
B<BIO_FLAGS_READ>, B<BIO_FLAGS_WRITE>, B<BIO_FLAGS_IO_SPECIAL>, and
B<BIO_FLAGS_SHOULD_RETRY> that are currently set in the I<BIO>.

=head1 NOTES

Ordinary application code will rarely need to call BIO_set_flags(),
BIO_clear_flags() or BIO_test_flags() directly.  They are intended for B<BIO>
implementations and for code that forwards retry state from one B<BIO> in a
chain to another.
After a failed I/O operation, applications should normally use
BIO_should_retry() and related macros as described in
L<BIO_should_retry(3)> instead of inspecting the flags directly.

These functions and macros are not thread-safe. If a single B<BIO>
is accessed from multiple threads, the caller must provide appropriate
external synchronisation.

=head1 SEE ALSO

L<BIO_should_retry(3)>, L<BIO_f_base64(3)>, L<bio(7)>

=head1 HISTORY

The functions and macros described here have been available in OpenSSL since
at least 1.1.0 (B<BIO_FLAGS_IN_EOF> since 1.1.1).

=head1 COPYRIGHT

Copyright 2025-2026 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
L<https://www.openssl.org/source/license.html>.

=cut
