=pod

=head1 NAME

BIO_new_CMS - CMS streaming filter BIO

=head1 SYNOPSIS

 #include <openssl/cms.h>

 BIO *BIO_new_CMS(BIO *out, CMS_ContentInfo *cms);

=head1 DESCRIPTION

BIO_new_CMS() returns a streaming filter BIO chain based on B<cms>. The output
of the filter is written to B<out>. Any data written to the chain is
automatically translated to a BER format CMS structure of the appropriate type.

=head1 NOTES

The chain returned by this function behaves like a standard filter 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 BIO_flush() must be called
to finalise the structure.

The B<CMS_STREAM> flag must be included in the corresponding B<flags>
parameter of the B<cms> creation function.

If an application wishes to write additional data to B<out> BIOs should be
removed from the chain using BIO_pop() and freed with BIO_free() until B<out>
is reached. If no additional data needs to be written BIO_free_all() can be
called to free up the whole chain.

Any content written through the filter is used verbatim: no canonical
translation is performed.

It is possible to chain multiple BIOs to, for example, create a triple wrapped
signed, enveloped, signed structure. In this case it is the applications
responsibility to set the inner content type of any outer CMS_ContentInfo
structures.

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 BIO_f_buffer() buffering BIO will prevent this.

=head1 BUGS

There is currently no corresponding inverse BIO: i.e. one which can decode
a CMS structure on the fly.

=head1 RETURN VALUES

BIO_new_CMS() returns a BIO chain when successful or NULL if an error
occurred. The error can be obtained from ERR_get_error(3).

=head1 SEE ALSO

L<ERR_get_error(3)>, L<CMS_sign(3)>,
L<CMS_encrypt(3)>

=head1 HISTORY

BIO_new_CMS() was added to OpenSSL 1.0.0

=head1 COPYRIGHT

Copyright 2008-2016 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
