=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

=cut
