CMS_compress -- create a CMS CompressedData structure
Synopsis
#include <openssl/cms.h>
CMS_ContentInfo *CMS_compress(BIO *in, int comp_nid, unsigned int flags);
DESCRIPTION
CMS_compress() creates and returns a CMS CompressedData structure.
comp_nid is the compression
algorithm to use or NID_undef to use
the default algorithm (zlib compression). in is the content to be compressed. flags is an optional set of flags.
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 CMS_TEXT flag is set MIME
headers for type 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 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 CMS_BINARY is set then CMS_TEXT is ignored.
If the CMS_STREAM flag is set a
partial CMS_ContentInfo structure is
returned suitable for streaming I/O: no data is read from the BIO
in.
The compressed data is included in the CMS_ContentInfo structure,
unless CMS_DETACHED is set in which
case it is omitted. This is rarely used in practice and is not
supported by SMIME_write_CMS().
NOTES
If the flag CMS_STREAM is set the
returned CMS_ContentInfo structure
is not complete and outputting its
contents via a function that does not properly finalize the 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
BIO directly using BIO_new_CMS().
Additional compression parameters such as the zlib compression level
cannot currently be set.
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).
