=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)|ERR_get_error(3)>, L<CMS_uncompress(3)|CMS_uncompress(3)> =head1 HISTORY CMS_compress() was added to OpenSSL 0.9.8 The B<CMS_STREAM> flag was first supported in OpenSSL 1.0.0. =cut