=pod =head1 NAME CMS_compress - create a CMS CompressedData structure =head1 SYNOPSIS #include CMS_ContentInfo *CMS_compress(BIO *in, int comp_nid, unsigned int flags); =head1 DESCRIPTION CMS_compress() creates and returns a CMS CompressedData structure. B is the compression algorithm to use or B to use the default algorithm (zlib compression). B is the content to be compressed. B 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 flag is set MIME headers for type B are prepended to the data. Normally the supplied content is translated into MIME canonical format (as required by the S/MIME specifications) if B 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 is set then B is ignored. If the B flag is set a partial B structure is returned suitable for streaming I/O: no data is read from the BIO B. The compressed data is included in the CMS_ContentInfo structure, unless B 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 is set the returned B structure is B complete and outputting its contents via a function that does not properly finalize the B 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 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, L =head1 HISTORY The B 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. =cut