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-.\" $OpenBSD: BIO_ctrl.3,v 1.25 2023/11/16 20:19:23 schwarze Exp $
-.\" full merge up to: OpenSSL 24a535eaf Tue Sep 22 13:14:20 2020 +0100
-.\" selective merge up to: OpenSSL 0c5bc96f Tue Mar 15 13:57:22 2022 +0000
-.\"
-.\" This file is a derived work.
-.\" The changes are covered by the following Copyright and license:
-.\"
-.\" Copyright (c) 2023 Ingo Schwarze <schwarze@openbsd.org>
-.\"
-.\" Permission to use, copy, modify, and distribute this software for any
-.\" purpose with or without fee is hereby granted, provided that the above
-.\" copyright notice and this permission notice appear in all copies.
-.\"
-.\" THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
-.\" WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
-.\" MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
-.\" ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
-.\" WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
-.\" ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
-.\" OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
-.\"
-.\" The original file was written by Dr. Stephen Henson <steve@openssl.org>.
-.\" Copyright (c) 2000, 2016 The OpenSSL Project.  All rights reserved.
-.\"
-.\" Redistribution and use in source and binary forms, with or without
-.\" modification, are permitted provided that the following conditions
-.\" are met:
-.\"
-.\" 1. Redistributions of source code must retain the above copyright
-.\"    notice, this list of conditions and the following disclaimer.
-.\"
-.\" 2. Redistributions in binary form must reproduce the above copyright
-.\"    notice, this list of conditions and the following disclaimer in
-.\"    the documentation and/or other materials provided with the
-.\"    distribution.
-.\"
-.\" 3. All advertising materials mentioning features or use of this
-.\"    software must display the following acknowledgment:
-.\"    "This product includes software developed by the OpenSSL Project
-.\"    for use in the OpenSSL Toolkit. (http://www.openssl.org/)"
-.\"
-.\" 4. The names "OpenSSL Toolkit" and "OpenSSL Project" must not be used to
-.\"    endorse or promote products derived from this software without
-.\"    prior written permission. For written permission, please contact
-.\"    openssl-core@openssl.org.
-.\"
-.\" 5. Products derived from this software may not be called "OpenSSL"
-.\"    nor may "OpenSSL" appear in their names without prior written
-.\"    permission of the OpenSSL Project.
-.\"
-.\" 6. Redistributions of any form whatsoever must retain the following
-.\"    acknowledgment:
-.\"    "This product includes software developed by the OpenSSL Project
-.\"    for use in the OpenSSL Toolkit (http://www.openssl.org/)"
-.\"
-.\" THIS SOFTWARE IS PROVIDED BY THE OpenSSL PROJECT ``AS IS'' AND ANY
-.\" EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
-.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
-.\" PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE OpenSSL PROJECT OR
-.\" ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
-.\" SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
-.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
-.\" LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
-.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
-.\" STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
-.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
-.\" OF THE POSSIBILITY OF SUCH DAMAGE.
-.\"
-.Dd $Mdocdate: November 16 2023 $
-.Dt BIO_CTRL 3
-.Os
-.Sh NAME
-.Nm BIO_ctrl ,
-.Nm BIO_callback_ctrl ,
-.Nm BIO_ptr_ctrl ,
-.Nm BIO_int_ctrl ,
-.Nm BIO_reset ,
-.Nm BIO_seek ,
-.Nm BIO_tell ,
-.Nm BIO_flush ,
-.Nm BIO_eof ,
-.Nm BIO_set_close ,
-.Nm BIO_get_close ,
-.Nm BIO_pending ,
-.Nm BIO_wpending ,
-.Nm BIO_ctrl_pending ,
-.Nm BIO_ctrl_wpending ,
-.Nm BIO_get_info_callback ,
-.Nm BIO_set_info_callback ,
-.Nm BIO_info_cb ,
-.Nm bio_info_cb
-.Nd BIO control operations
-.Sh SYNOPSIS
-.In openssl/bio.h
-.Ft long
-.Fo BIO_ctrl
-.Fa "BIO *b"
-.Fa "int cmd"
-.Fa "long larg"
-.Fa "void *parg"
-.Fc
-.Ft long
-.Fo BIO_callback_ctrl
-.Fa "BIO *b"
-.Fa "int cmd"
-.Fa "BIO_info_cb *cb"
-.Fc
-.Ft char *
-.Fo BIO_ptr_ctrl
-.Fa "BIO *b"
-.Fa "int cmd"
-.Fa "long larg"
-.Fc
-.Ft long
-.Fo BIO_int_ctrl
-.Fa "BIO *b"
-.Fa "int cmd"
-.Fa "long larg"
-.Fa "int iarg"
-.Fc
-.Ft int
-.Fo BIO_reset
-.Fa "BIO *b"
-.Fc
-.Ft int
-.Fo BIO_seek
-.Fa "BIO *b"
-.Fa "int ofs"
-.Fc
-.Ft int
-.Fo BIO_tell
-.Fa "BIO *b"
-.Fc
-.Ft int
-.Fo BIO_flush
-.Fa "BIO *b"
-.Fc
-.Ft int
-.Fo BIO_eof
-.Fa "BIO *b"
-.Fc
-.Ft int
-.Fo BIO_set_close
-.Fa "BIO *b"
-.Fa "long flag"
-.Fc
-.Ft int
-.Fo BIO_get_close
-.Fa "BIO *b"
-.Fc
-.Ft int
-.Fo BIO_pending
-.Fa "BIO *b"
-.Fc
-.Ft int
-.Fo BIO_wpending
-.Fa "BIO *b"
-.Fc
-.Ft size_t
-.Fo BIO_ctrl_pending
-.Fa "BIO *b"
-.Fc
-.Ft size_t
-.Fo BIO_ctrl_wpending
-.Fa "BIO *b"
-.Fc
-.Ft int
-.Fo BIO_get_info_callback
-.Fa "BIO *b"
-.Fa "BIO_info_cb **cbp"
-.Fc
-.Ft int
-.Fo BIO_set_info_callback
-.Fa "BIO *b"
-.Fa "BIO_info_cb *cb"
-.Fc
-.Ft typedef int
-.Fo BIO_info_cb
-.Fa "BIO *b"
-.Fa "int state"
-.Fa "int res"
-.Fc
-.Ft typedef int
-.Fo bio_info_cb
-.Fa "BIO *b"
-.Fa "int state"
-.Fa "int res"
-.Fc
-.Sh DESCRIPTION
-.Fn BIO_ctrl ,
-.Fn BIO_callback_ctrl ,
-.Fn BIO_ptr_ctrl ,
-and
-.Fn BIO_int_ctrl
-are BIO "control" operations taking arguments of various types.
-These functions are not normally called directly -
-various macros are used instead.
-The standard macros are described below.
-Macros specific to a particular type of BIO
-are described in the specific BIO's manual page
-as well as any special features of the standard calls.
-.Pp
-Depending on the
-.Fa cmd
-and on the type of
-.Fa b ,
-.Fn BIO_ctrl
-may have a read-only effect on
-.Fa b
-or change data in
-.Fa b
-or in its sub-structures.
-It may also have a side effect of changing the memory pointed to by
-.Fa parg .
-.Pp
-.Fn BIO_callback_ctrl
-does not call
-.Fn BIO_ctrl
-but instead requires that the BIO type of
-.Fa b
-provides a dedicated
-.Fa callback_ctrl
-function pointer, which is built into the library for some standard BIO
-types and can be provided with
-.Xr BIO_meth_set_callback_ctrl 3
-for application-defined BIO types.
-The only
-.Fa cmd
-supported by
-.Fn BIO_callback_ctrl
-is
-.Dv BIO_CTRL_SET_CALLBACK .
-.Pp
-.Fn BIO_ptr_ctrl
-calls
-.Fn BIO_ctrl
-with
-.Fa parg
-pointing to the location of a temporary pointer variable initialized to
-.Dv NULL .
-.Pp
-.Fn BIO_int_ctrl
-calls
-.Fn BIO_ctrl
-with
-.Fa parg
-pointing to the location of a temporary
-.Vt int
-variable initialized to
-.Fa iarg .
-If
-.Fn BIO_ctrl
-changes the value stored at
-.Pf * Fa parg ,
-the new value is ignored.
-.Pp
-.Fn BIO_reset
-typically resets a BIO to some initial state.
-In the case of file related BIOs, for example,
-it rewinds the file pointer to the start of the file.
-.Pp
-.Fn BIO_seek
-resets a file related BIO's (that is file descriptor and
-FILE BIOs) file position pointer to
-.Fa ofs
-bytes from start of file.
-.Pp
-.Fn BIO_tell
-returns the current file position of a file related BIO.
-.Pp
-.Fn BIO_flush
-normally writes out any internally buffered data.
-In some cases it is used to signal EOF and that no more data will be written.
-.Pp
-.Fn BIO_eof
-returns 1 if the BIO has read EOF.
-The precise meaning of "EOF" varies according to the BIO type.
-.Pp
-.Fn BIO_set_close
-sets the BIO
-.Fa b
-close flag to
-.Fa flag .
-.Fa flag
-can take the value
-.Dv BIO_CLOSE
-or
-.Dv BIO_NOCLOSE .
-Typically
-.Dv BIO_CLOSE
-is used in a source/sink BIO to indicate that the underlying I/O stream
-should be closed when the BIO is freed.
-.Pp
-.Fn BIO_get_close
-returns the BIO's close flag.
-.Pp
-.Fn BIO_pending ,
-.Fn BIO_ctrl_pending ,
-.Fn BIO_wpending ,
-and
-.Fn BIO_ctrl_wpending
-return the number of pending characters in the BIO's read and write buffers.
-Not all BIOs support these calls.
-.Fn BIO_ctrl_pending
-and
-.Fn BIO_ctrl_wpending
-return a
-.Vt size_t
-type and are functions.
-.Pp
-.Fn BIO_set_info_callback
-installs the function pointer
-.Fa cb
-as an info callback in
-.Fa b
-by calling
-.Fn BIO_callback_ctrl
-with a command of
-.Dv BIO_CTRL_SET_CALLBACK .
-Among the BIO types built into the library, only
-.Xr BIO_s_connect 3
-and
-.Xr BIO_f_ssl 3
-support this functionality.
-Some filter BIO types forward this control call
-to the next BIO in the chain instead of processing it themselves.
-.Pp
-.Fn BIO_get_info_callback
-places the function pointer to the info callback into
-.Pf * Fa cbp
-if any was installed using
-.Fn BIO_set_info_callback
-or
-.Fn BIO_callback_ctrl .
-If the type of
-.Fa b
-supports setting an info callback but none was installed, it stores a
-.Dv NULL
-pointer in
-.Pf * Fa cbp .
-.Pp
-The function type name
-.Vt bio_info_cb
-is a deprecated synonym for
-.Vt BIO_info_cb
-provided for backward compatibility with some existing application software.
-.Pp
-The following
-.Fa cmd
-constants correspond to macros:
-.Bl -column BIO_C_SET_SSL_RENEGOTIATE_TIMEOUT BIO_set_ssl_renegotiate_timeout(3)
-.It Fa cmd No constant                   Ta corresponding macro
-.It Dv BIO_C_DESTROY_BIO_PAIR            Ta Xr BIO_destroy_bio_pair 3
-.It Dv BIO_C_DO_STATE_MACHINE            Ta Xr BIO_do_handshake 3
-.It Dv BIO_C_FILE_SEEK                   Ta Fn BIO_seek
-.It Dv BIO_C_FILE_TELL                   Ta Fn BIO_tell
-.It Dv BIO_C_GET_ACCEPT                  Ta Xr BIO_get_accept_port 3
-.It Dv BIO_C_GET_BIND_MODE               Ta Xr BIO_get_bind_mode 3
-.It Dv BIO_C_GET_BUF_MEM_PTR             Ta Xr BIO_get_mem_ptr 3
-.It Dv BIO_C_GET_BUFF_NUM_LINES          Ta Xr BIO_get_buffer_num_lines 3
-.It Dv BIO_C_GET_CIPHER_CTX              Ta Xr BIO_get_cipher_ctx 3
-.It Dv BIO_C_GET_CIPHER_STATUS           Ta Xr BIO_get_cipher_status 3
-.It Dv BIO_C_GET_FD                      Ta Xr BIO_get_fd 3
-.It Dv BIO_C_GET_FILE_PTR                Ta Xr BIO_get_fp 3
-.It Dv BIO_C_GET_MD                      Ta Xr BIO_get_md 3
-.It Dv BIO_C_GET_MD_CTX                  Ta Xr BIO_get_md_ctx 3
-.It Dv BIO_C_GET_READ_REQUEST            Ta Xr BIO_get_read_request 3
-.It Dv BIO_C_GET_SSL                     Ta Xr BIO_get_ssl 3
-.It Dv BIO_C_GET_SSL_NUM_RENEGOTIATES    Ta Xr BIO_get_num_renegotiates 3
-.It Dv BIO_C_GET_WRITE_BUF_SIZE          Ta Xr BIO_get_write_buf_size 3
-.It Dv BIO_C_GET_WRITE_GUARANTEE         Ta Xr BIO_get_write_guarantee 3
-.It Dv BIO_C_MAKE_BIO_PAIR               Ta Xr BIO_make_bio_pair 3
-.It Dv BIO_C_RESET_READ_REQUEST          Ta Xr BIO_ctrl_reset_read_request 3
-.It Dv BIO_C_SET_BIND_MODE               Ta Xr BIO_set_bind_mode 3
-.It Dv BIO_C_SET_BUF_MEM                 Ta Xr BIO_set_mem_buf 3
-.It Dv BIO_C_SET_BUF_MEM_EOF_RETURN      Ta Xr BIO_set_mem_eof_return 3
-.It Dv BIO_C_SET_BUFF_READ_DATA          Ta Xr BIO_set_buffer_read_data 3
-.It Dv BIO_C_SET_FD                      Ta Xr BIO_set_fd 3
-.It Dv BIO_C_SET_FILE_PTR                Ta Xr BIO_set_fp 3
-.It Dv BIO_C_SET_MD                      Ta Xr BIO_set_md 3
-.It Dv BIO_C_SET_MD_CTX                  Ta Xr BIO_set_md_ctx 3
-.It Dv BIO_C_SET_NBIO                    Ta Xr BIO_set_nbio 3
-.It Dv BIO_C_SET_SSL                     Ta Xr BIO_set_ssl 3
-.It Dv BIO_C_SET_SSL_RENEGOTIATE_BYTES   Ta Xr BIO_set_ssl_renegotiate_bytes 3
-.It Dv BIO_C_SET_SSL_RENEGOTIATE_TIMEOUT Ta Xr BIO_set_ssl_renegotiate_timeout 3
-.It Dv BIO_C_SET_WRITE_BUF_SIZE          Ta Xr BIO_set_write_buf_size 3
-.It Dv BIO_C_SHUTDOWN_WR                 Ta Xr BIO_shutdown_wr 3
-.It Dv BIO_C_SSL_MODE                    Ta Xr BIO_set_ssl_mode 3
-.It Dv BIO_CTRL_DGRAM_CONNECT            Ta Xr BIO_ctrl_dgram_connect 3
-.It Dv BIO_CTRL_DGRAM_GET_PEER           Ta Xr BIO_dgram_get_peer 3
-.It Dv BIO_CTRL_DGRAM_GET_RECV_TIMER_EXP Ta Xr BIO_dgram_recv_timedout 3
-.It Dv BIO_CTRL_DGRAM_GET_SEND_TIMER_EXP Ta Xr BIO_dgram_send_timedout 3
-.It Dv BIO_CTRL_DGRAM_SET_CONNECTED      Ta Xr BIO_ctrl_set_connected 3
-.It Dv BIO_CTRL_DGRAM_SET_PEER           Ta Xr BIO_dgram_set_peer 3
-.It Dv BIO_CTRL_DUP                      Ta Xr BIO_dup_state 3
-.It Dv BIO_CTRL_EOF                      Ta Fn BIO_eof
-.It Dv BIO_CTRL_FLUSH                    Ta Fn BIO_flush
-.It Dv BIO_CTRL_GET_CALLBACK             Ta Fn BIO_get_info_callback
-.It Dv BIO_CTRL_GET_CLOSE                Ta Fn BIO_get_close
-.It Dv BIO_CTRL_INFO                     Ta Xr BIO_get_mem_data 3
-.It Dv BIO_CTRL_PENDING                  Ta Fn BIO_pending
-.It Dv BIO_CTRL_RESET                    Ta Fn BIO_reset
-.It Dv BIO_CTRL_SET_CALLBACK             Ta Fn BIO_set_info_callback
-.It Dv BIO_CTRL_SET_CLOSE                Ta Fn BIO_set_close
-.It Dv BIO_CTRL_WPENDING                 Ta Fn BIO_wpending
-.El
-.Pp
-A few
-.Fa cmd
-constants serve more than one macro each
-and are documented in the following manual pages:
-.Bl -column BIO_C_SET_BUFF_SIZE BIO_s_connect(3) -offset 3n
-.It Fa cmd No constant     Ta manual page
-.It Dv BIO_C_GET_CONNECT   Ta Xr BIO_s_connect 3
-.It Dv BIO_C_SET_ACCEPT    Ta Xr BIO_s_accept 3
-.It Dv BIO_C_SET_BUFF_SIZE Ta Xr BIO_f_buffer 3
-.It Dv BIO_C_SET_CONNECT   Ta Xr BIO_s_connect 3
-.It Dv BIO_C_SET_FILENAME  Ta Xr BIO_s_file 3
-.El
-.Pp
-Some
-.Fa cmd
-constants are not associated with any macros.
-They are documented in the following manual pages:
-.Bl -column BIO_CTRL_DGRAM_SET_RECV_TIMEOUT BIO_dgram_recv_timedout(3)\
- -offset 3n
-.It Fa cmd No constant                 Ta manual page
-.\" The following constants are intentionally undocumented because
-.\" BIO_f_asn1 has been removed from the public API.
-.\" .It Dv BIO_C_GET_EX_ARG                Ta Xr BIO_f_asn1 3
-.\" .It Dv BIO_C_SET_EX_ARG                Ta Xr BIO_f_asn1 3
-.It Dv BIO_CTRL_DGRAM_GET_FALLBACK_MTU Ta Xr BIO_dgram_set_peer 3
-.It Dv BIO_CTRL_DGRAM_GET_MTU          Ta Xr BIO_dgram_set_peer 3
-.It Dv BIO_CTRL_DGRAM_GET_RECV_TIMEOUT Ta Xr BIO_dgram_recv_timedout 3
-.It Dv BIO_CTRL_DGRAM_GET_SEND_TIMEOUT Ta Xr BIO_dgram_send_timedout 3
-.It Dv BIO_CTRL_DGRAM_SET_MTU          Ta Xr BIO_dgram_set_peer 3
-.It Dv BIO_CTRL_DGRAM_SET_NEXT_TIMEOUT Ta Xr BIO_dgram_recv_timedout 3
-.It Dv BIO_CTRL_DGRAM_SET_RECV_TIMEOUT Ta Xr BIO_dgram_recv_timedout 3
-.It Dv BIO_CTRL_DGRAM_SET_SEND_TIMEOUT Ta Xr BIO_dgram_send_timedout 3
-.It Dv BIO_CTRL_DGRAM_MTU_EXCEEDED     Ta Xr BIO_s_datagram 3
-.It Dv BIO_CTRL_POP                    Ta Xr BIO_pop 3
-.It Dv BIO_CTRL_PUSH                   Ta Xr BIO_push 3
-.El
-.Sh RETURN VALUES
-The meaning of the return values of
-.Fn BIO_ctrl ,
-.Fn BIO_callback_ctrl ,
-and
-.Fn BIO_int_ctrl
-depends on both the type of
-.Fa b
-and on the
-.Fa cmd .
-If
-.Fa b
-is a
-.Dv NULL
-pointer, no action occurs and 0 is returned.
-The return value \-2 usually indicates a fatal error.
-In particular, it is returned if the
-.Fa cmd
-is unsupported by the type of
-.Fa b .
-.Pp
-.Fn BIO_callback_ctrl
-and
-.Fn BIO_set_info_callback
-return 1 on success, 0 if
-.Fa b
-is
-.Dv NULL
-or to indicate failure of a valid
-.Fa cmd ,
-or \-2 if the
-.Fa cmd
-is not supported by
-.Fa b .
-.Pp
-.Fn BIO_ptr_ctrl
-returns
-.Dv NULL
-if the
-.Fn BIO_ctrl
-call returns a negative value or does not change
-.Pf * Fa parg ,
-or the pointer it puts into
-.Pf * Fa parg
-otherwise.
-.Pp
-.Fn BIO_int_ctrl
-returns the return value of
-.Fn BIO_ctrl .
-.Pp
-.Fn BIO_reset
-normally returns 1 for success and 0 or -1 for failure.
-File BIOs are an exception, returning 0 for success and -1 for failure.
-.Pp
-.Fn BIO_seek
-and
-.Fn BIO_tell
-both return the current file position on success
-and -1 for failure, except file BIOs which for
-.Fn BIO_seek
-always return 0 for success and -1 for failure.
-.Pp
-.Fn BIO_flush
-returns 1 for success and 0 or -1 for failure.
-.Pp
-.Fn BIO_eof
-returns 1 if EOF has been reached or 0 otherwise.
-.Pp
-.Fn BIO_set_close
-always returns 1.
-.Pp
-.Fn BIO_get_close
-returns the close flag value
-.Dv BIO_CLOSE
-or
-.Dv BIO_NOCLOSE .
-.Pp
-.Fn BIO_pending ,
-.Fn BIO_ctrl_pending ,
-.Fn BIO_wpending ,
-and
-.Fn BIO_ctrl_wpending
-return the amount of pending data.
-.Pp
-.Fn BIO_get_info_callback
-returns 1 on success, including when the type of
-.Fa b
-supports an info callback but none is installed,
-0 if
-.Fa b
-is
-.Dv NULL
-or \-2 if the type of
-.Fa b
-does not support an info callback.
-.Pp
-If a callback was installed in
-.Fa b
-using
-.Xr BIO_set_callback_ex 3
-or
-.Xr BIO_set_callback 3 ,
-it can modify the return values of all these functions.
-.Sh NOTES
-Because it can write data,
-.Fn BIO_flush
-may return 0 or -1 indicating that the call should be retried later
-in a similar manner to
-.Xr BIO_write 3 .
-The
-.Xr BIO_should_retry 3
-call should be used and appropriate action taken if the call fails.
-.Pp
-The return values of
-.Fn BIO_pending
-and
-.Fn BIO_wpending
-may not reliably determine the amount of pending data in all cases.
-For example in the case of a file BIO some data may be available in the
-.Vt FILE
-structure's internal buffers but it is not possible
-to determine this in a portable way.
-For other types of BIO they may not be supported.
-.Pp
-If they do not internally handle a particular
-.Fn BIO_ctrl
-operation, filter BIOs usually pass the operation
-to the next BIO in the chain.
-This often means there is no need to locate the required BIO for
-a particular operation: it can be called on a chain and it will
-be automatically passed to the relevant BIO.
-However, this can cause unexpected results.
-For example no current filter BIOs implement
-.Fn BIO_seek ,
-but this may still succeed if the chain ends
-in a FILE or file descriptor BIO.
-.Pp
-Source/sink BIOs return a 0 if they do not recognize the
-.Fn BIO_ctrl
-operation.
-.Sh SEE ALSO
-.Xr BIO_meth_new 3 ,
-.Xr BIO_new 3
-.Sh HISTORY
-.Fn BIO_ctrl ,
-.Fn BIO_reset ,
-.Fn BIO_flush ,
-.Fn BIO_eof ,
-.Fn BIO_set_close ,
-.Fn BIO_get_close ,
-and
-.Fn BIO_pending
-first appeared in SSLeay 0.6.0.
-.Fn BIO_wpending
-first appeared in SSLeay 0.8.1.
-.Fn BIO_ptr_ctrl ,
-.Fn BIO_int_ctrl ,
-.Fn BIO_get_info_callback
-and
-.Fn BIO_set_info_callback
-first appeared in SSLeay 0.9.0.
-All these functions have been available since
-.Ox 2.4 .
-.Pp
-.Fn BIO_seek
-and
-.Fn BIO_tell
-first appeared in SSLeay 0.9.1.
-.Fn BIO_ctrl_pending
-and
-.Fn BIO_ctrl_wpending
-first appeared in OpenSSL 0.9.4.
-These functions have been available since
-.Ox 2.6 .
-.Pp
-.Fn BIO_callback_ctrl
-first appeared in OpenSSL 0.9.5 and has been available since
-.Ox 2.7 .
-.Pp
-.Fn bio_info_cb
-first appeared with a more complicated prototype in OpenSSL 0.9.6
-and has been available since
-.Ox 2.9 .
-.Pp
-.Fn BIO_info_cb
-first appeared in OpenSSL 1.1.0h and has been available since
-.Ox 6.3 .
-.Sh BUGS
-Some of the return values are ambiguous and care should be taken.
-In particular a return value of 0 can be returned if an operation
-is not supported, if an error occurred, if EOF has not been reached
-and in the case of
-.Fn BIO_seek
-on a file BIO for a successful operation.