281 lines
7.6 KiB
Groff
281 lines
7.6 KiB
Groff
.\" $OpenBSD: BIO_read.3,v 1.11 2022/12/18 17:40:55 schwarze Exp $
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.\" full merge up to: OpenSSL 99d63d46 Oct 26 13:56:48 2016 -0400
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.\"
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.\" This file is a derived work.
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.\" The changes are covered by the following Copyright and license:
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.\"
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.\" Copyright (c) 2021, 2022 Ingo Schwarze <schwarze@openbsd.org>
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.\"
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.\" Permission to use, copy, modify, and distribute this software for any
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.\" purpose with or without fee is hereby granted, provided that the above
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.\" copyright notice and this permission notice appear in all copies.
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.\"
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.\" THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
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.\" WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
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.\" MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
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.\" ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
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.\" WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
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.\" ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
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.\" OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
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.\"
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.\" The original file was written by Dr. Stephen Henson <steve@openssl.org>.
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.\" Copyright (c) 2000, 2016 The OpenSSL Project. All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\"
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\"
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in
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.\" the documentation and/or other materials provided with the
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.\" distribution.
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.\"
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.\" 3. All advertising materials mentioning features or use of this
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.\" software must display the following acknowledgment:
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.\" "This product includes software developed by the OpenSSL Project
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.\" for use in the OpenSSL Toolkit. (http://www.openssl.org/)"
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.\"
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.\" 4. The names "OpenSSL Toolkit" and "OpenSSL Project" must not be used to
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.\" endorse or promote products derived from this software without
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.\" prior written permission. For written permission, please contact
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.\" openssl-core@openssl.org.
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.\"
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.\" 5. Products derived from this software may not be called "OpenSSL"
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.\" nor may "OpenSSL" appear in their names without prior written
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.\" permission of the OpenSSL Project.
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.\"
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.\" 6. Redistributions of any form whatsoever must retain the following
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.\" acknowledgment:
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.\" "This product includes software developed by the OpenSSL Project
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.\" for use in the OpenSSL Toolkit (http://www.openssl.org/)"
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE OpenSSL PROJECT ``AS IS'' AND ANY
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.\" EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE OpenSSL PROJECT OR
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.\" ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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.\" SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
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.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
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.\" LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
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.\" STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
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.\" OF THE POSSIBILITY OF SUCH DAMAGE.
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.\"
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.Dd $Mdocdate: December 18 2022 $
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.Dt BIO_READ 3
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.Os
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.Sh NAME
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.Nm BIO_read ,
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.Nm BIO_number_read ,
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.Nm BIO_gets ,
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.Nm BIO_write ,
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.Nm BIO_puts ,
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.Nm BIO_indent ,
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.Nm BIO_number_written
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.Nd BIO I/O functions
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.Sh SYNOPSIS
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.In openssl/bio.h
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.Ft int
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.Fo BIO_read
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.Fa "BIO *b"
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.Fa "void *buf"
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.Fa "int len"
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.Fc
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.Ft unsigned long
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.Fo BIO_number_read
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.Fa "BIO *b"
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.Fc
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.Ft int
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.Fo BIO_gets
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.Fa "BIO *b"
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.Fa "char *buf"
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.Fa "int size"
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.Fc
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.Ft int
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.Fo BIO_write
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.Fa "BIO *b"
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.Fa "const void *buf"
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.Fa "int len"
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.Fc
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.Ft int
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.Fo BIO_puts
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.Fa "BIO *b"
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.Fa "const char *string"
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.Fc
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.Ft int
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.Fo BIO_indent
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.Fa "BIO *b"
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.Fa "int indent"
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.Fa "int max"
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.Fc
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.Ft unsigned long
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.Fo BIO_number_written
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.Fa "BIO *b"
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.Fc
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.Sh DESCRIPTION
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.Fn BIO_read
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attempts to read
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.Fa len
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bytes from
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.Fa b
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and places the data in
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.Fa buf .
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.Pp
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.Fn BIO_number_read
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returns the grand total of bytes read from
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.Fa b
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using
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.Fn BIO_read
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so far.
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Bytes read with
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.Fn BIO_gets
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do
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.Sy not
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count.
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.Xr BIO_new 3
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and
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.Xr BIO_set 3
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initialize the counter to 0.
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When reading very large amounts of data,
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the counter will eventually wrap around from
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.Dv ULONG_MAX
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to 0.
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.Pp
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.Fn BIO_gets
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performs the BIOs "gets" operation and places the data in
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.Fa buf .
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Usually this operation will attempt to read a line of data
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from the BIO of maximum length
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.Fa size No \- 1 .
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There are exceptions to this however, for example
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.Fn BIO_gets
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on a digest BIO will calculate and return the digest
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and other BIOs may not support
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.Fn BIO_gets
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at all.
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The returned string is always NUL-terminated.
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.Pp
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.Fn BIO_write
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attempts to write
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.Fa len
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bytes from
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.Fa buf
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to
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.Fa b .
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.Pp
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.Fn BIO_puts
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attempts to write the NUL-terminated
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.Fa string
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to
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.Fa b .
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.Pp
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.Fn BIO_indent
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attempts to write
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.Fa indent
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space characters to
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.Fa b ,
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but not more than
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.Fa max
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characters.
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.Pp
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.Fn BIO_number_written
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returns the grand total of bytes written to
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.Fa b
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using
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.Fn BIO_write ,
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.Fn BIO_puts ,
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and
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.Fn BIO_indent
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so far.
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.Xr BIO_new 3
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and
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.Xr BIO_set 3
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initialize the counter to 0.
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When writing very large amounts of data,
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the counter will eventually wrap around from
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.Dv ULONG_MAX
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to 0.
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.Pp
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One technique sometimes used with blocking sockets
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is to use a system call (such as
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.Xr select 2 ,
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.Xr poll 2
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or equivalent) to determine when data is available and then call
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.Xr read 2
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to read the data.
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The equivalent with BIOs (that is call
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.Xr select 2
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on the underlying I/O structure and then call
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.Fn BIO_read
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to read the data) should
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.Em not
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be used because a single call to
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.Fn BIO_read
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can cause several reads (and writes in the case of SSL BIOs)
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on the underlying I/O structure and may block as a result.
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Instead
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.Xr select 2
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(or equivalent) should be combined with non-blocking I/O
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so successive reads will request a retry instead of blocking.
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.Pp
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See
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.Xr BIO_should_retry 3
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for details of how to determine the cause of a retry and other I/O issues.
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.Pp
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If the
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.Fn BIO_gets
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function is not supported by a BIO then it is possible to
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work around this by adding a buffering BIO
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.Xr BIO_f_buffer 3
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to the chain.
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.Sh RETURN VALUES
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.Fn BIO_indent
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returns 1 if successful, even if nothing was written,
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or 0 if writing fails.
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.Pp
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.Fn BIO_number_read
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and
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.Fn BIO_number_written
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return a number of bytes or 0 if
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.Fa b
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is a
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.Dv NULL
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pointer.
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.Pp
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The other functions return either the amount of data successfully
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read or written (if the return value is positive) or that no data
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was successfully read or written if the result is 0 or \-1.
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If the return value is \-2, then the operation is not implemented
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in the specific BIO type.
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The trailing NUL is not included in the length returned by
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.Fn BIO_gets .
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.Pp
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A 0 or \-1 return is not necessarily an indication of an error.
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In particular when the source/sink is non-blocking or of a certain type
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it may merely be an indication that no data is currently available and that
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the application should retry the operation later.
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.Sh SEE ALSO
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.Xr BIO_meth_new 3 ,
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.Xr BIO_new 3 ,
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.Xr BIO_should_retry 3
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.Sh HISTORY
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.Fn BIO_read ,
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.Fn BIO_gets ,
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.Fn BIO_write ,
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and
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.Fn BIO_puts
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first appeared in SSLeay 0.6.0.
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.Fn BIO_number_read
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and
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.Fn BIO_number_written
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first appeared in SSLeay 0.6.5.
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These functions have been available since
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.Ox 2.4 .
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.Pp
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.Fn BIO_indent
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first appeared in OpenSSL 0.9.7 and has been available since
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.Ox 3.4 .
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