.\" $OpenBSD: BIO_new_CMS.3,v 1.8 2021/12/12 17:31:18 schwarze Exp $
.\" full merge up to: OpenSSL df75c2bfc Dec 9 01:02:36 2018 +0100
.\"
.\" This file was written by Dr. Stephen Henson <steve@openssl.org>.
.\" Copyright (c) 2008 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: December 12 2021 $
.Dt BIO_NEW_CMS 3
.Os
.Sh NAME
.Nm BIO_new_CMS
.Nd CMS streaming filter BIO
.Sh SYNOPSIS
.In openssl/cms.h
.Ft BIO *
.Fo BIO_new_CMS
.Fa "BIO *out"
.Fa "CMS_ContentInfo *cms"
.Fc
.Sh DESCRIPTION
.Fn BIO_new_CMS
returns a streaming filter
.Vt BIO
chain based on
.Fa cms .
The output of the filter is written to
.Fa out .
Any data written to the chain is automatically translated
to a BER format CMS structure of the appropriate type.
.Pp
The chain returned by this function behaves like a standard filter
.Vt BIO .
It supports non blocking I/O.
Content is processed and streamed on the fly and not all held in memory
at once: so it is possible to encode very large structures.
After all content has been written through the chain,
.Xr BIO_flush 3
must be called to finalise the structure.
.Pp
The
.Dv CMS_STREAM
flag must be included in the corresponding
.Fa flags
parameter of the
.Fa cms
creation function.
.Pp
If an application wishes to write additional data to
.Fa out ,
BIOs should be removed from the chain using
.Xr BIO_pop 3
and freed with
.Xr BIO_free 3
until
.Fa out
is reached.
If no additional data needs to be written,
.Xr BIO_free_all 3
can be called to free up the whole chain.
.Pp
Any content written through the filter is used verbatim:
no canonical translation is performed.
.Pp
It is possible to chain multiple BIOs to, for example,
create a triple wrapped signed, enveloped, signed structure.
In this case it is the application's responsibility
to set the inner content type of any outer
.Vt CMS_ContentInfo
structures.
.Pp
Large numbers of small writes through the chain should be avoided as this
will produce an output consisting of lots of OCTET STRING structures.
Prepending a
.Xr BIO_f_buffer 3
buffering BIO will prevent this.
.Sh RETURN VALUES
.Fn BIO_new_CMS
returns a
.Vt BIO
chain when successful or
.Dv NULL
if an error occurred.
The error can be obtained from
.Xr ERR_get_error 3 .
.Sh SEE ALSO
.Xr BIO_new 3 ,
.Xr BIO_new_NDEF 3 ,
.Xr CMS_ContentInfo_new 3 ,
.Xr CMS_encrypt 3 ,
.Xr CMS_sign 3
.Sh HISTORY
.Fn BIO_new_CMS
first appeared in OpenSSL 1.0.0
and has been available since
.Ox 6.7 .
.Sh BUGS
There is currently no corresponding inverse BIO
which can decode a CMS structure on the fly.