1=pod 2 3=head1 NAME 4 5CMS_compress - create a CMS CompressedData structure 6 7=head1 SYNOPSIS 8 9 #include <openssl/cms.h> 10 11 CMS_ContentInfo *CMS_compress(BIO *in, int comp_nid, unsigned int flags); 12 13=head1 DESCRIPTION 14 15CMS_compress() creates and returns a CMS CompressedData structure. B<comp_nid> 16is the compression algorithm to use or B<NID_undef> to use the default 17algorithm (zlib compression). B<in> is the content to be compressed. 18B<flags> is an optional set of flags. 19 20=head1 NOTES 21 22The only currently supported compression algorithm is zlib using the NID 23NID_zlib_compression. 24 25If zlib support is not compiled into OpenSSL then CMS_compress() will return 26an error. 27 28If the B<CMS_TEXT> flag is set MIME headers for type B<text/plain> are 29prepended to the data. 30 31Normally the supplied content is translated into MIME canonical format (as 32required by the S/MIME specifications) if B<CMS_BINARY> is set no translation 33occurs. This option should be used if the supplied data is in binary format 34otherwise the translation will corrupt it. If B<CMS_BINARY> is set then 35B<CMS_TEXT> is ignored. 36 37If the B<CMS_STREAM> flag is set a partial B<CMS_ContentInfo> structure is 38returned suitable for streaming I/O: no data is read from the BIO B<in>. 39 40The compressed data is included in the CMS_ContentInfo structure, unless 41B<CMS_DETACHED> is set in which case it is omitted. This is rarely used in 42practice and is not supported by SMIME_write_CMS(). 43 44=head1 NOTES 45 46If the flag B<CMS_STREAM> is set the returned B<CMS_ContentInfo> structure is 47B<not> complete and outputting its contents via a function that does not 48properly finalize the B<CMS_ContentInfo> structure will give unpredictable 49results. 50 51Several functions including SMIME_write_CMS(), i2d_CMS_bio_stream(), 52PEM_write_bio_CMS_stream() finalize the structure. Alternatively finalization 53can be performed by obtaining the streaming ASN1 B<BIO> directly using 54BIO_new_CMS(). 55 56Additional compression parameters such as the zlib compression level cannot 57currently be set. 58 59=head1 RETURN VALUES 60 61CMS_compress() returns either a CMS_ContentInfo structure or NULL if an error 62occurred. The error can be obtained from ERR_get_error(3). 63 64=head1 SEE ALSO 65 66L<ERR_get_error(3)|ERR_get_error(3)>, L<CMS_uncompress(3)|CMS_uncompress(3)> 67 68=head1 HISTORY 69 70CMS_compress() was added to OpenSSL 0.9.8 71The B<CMS_STREAM> flag was first supported in OpenSSL 1.0.0. 72 73=cut 74