=pod

=head1 NAME

CMS_compress - create a CMS CompressedData structure

=head1 SYNOPSIS

 #include <openssl/cms.h>

 CMS_ContentInfo *CMS_compress(BIO *in, int comp_nid, unsigned int flags);

=head1 DESCRIPTION

CMS_compress() creates and returns a CMS CompressedData structure. B<comp_nid>

is the compression algorithm to use or B<NID_undef> to use the default

algorithm (zlib compression). B<in> is the content to be compressed.

B<flags> is an optional set of flags.

=head1 NOTES

The only currently supported compression algorithm is zlib using the NID

NID_zlib_compression.

If zlib support is not compiled into OpenSSL then CMS_compress() will return

an error.

If the B<CMS_TEXT> flag is set MIME headers for type B<text/plain> are

prepended to the data.

Normally the supplied content is translated into MIME canonical format (as

required by the S/MIME specifications) if B<CMS_BINARY> is set no translation

occurs. This option should be used if the supplied data is in binary format

otherwise the translation will corrupt it. If B<CMS_BINARY> is set then

B<CMS_TEXT> is ignored.

If the B<CMS_STREAM> flag is set a partial B<CMS_ContentInfo> structure is

returned suitable for streaming I/O: no data is read from the BIO B<in>.

The compressed data is included in the CMS_ContentInfo structure, unless

B<CMS_DETACHED> is set in which case it is omitted. This is rarely used in

practice and is not supported by SMIME_write_CMS().

=head1 NOTES

If the flag B<CMS_STREAM> is set the returned B<CMS_ContentInfo> structure is

B<not> complete and outputting its contents via a function that does not

properly finalize the B<CMS_ContentInfo> structure will give unpredictable

results.

Several functions including SMIME_write_CMS(), i2d_CMS_bio_stream(),

PEM_write_bio_CMS_stream() finalize the structure. Alternatively finalization

can be performed by obtaining the streaming ASN1 B<BIO> directly using

BIO_new_CMS().

Additional compression parameters such as the zlib compression level cannot

currently be set.

=head1 RETURN VALUES

CMS_compress() returns either a CMS_ContentInfo structure 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_uncompress(3)>

=head1 HISTORY

The B<CMS_STREAM> flag was added in OpenSSL 1.0.0.

=head1 COPYRIGHT

Copyright 2008-2016 The OpenSSL Project Authors. All Rights Reserved.

Licensed under the OpenSSL license (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>.

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