NAME¶
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).
SEE ALSO¶
ERR_get_error(3),
CMS_uncompress(3)
HISTORY¶
CMS_compress() was added to OpenSSL 0.9.8 The
CMS_STREAM flag was
first supported in OpenSSL 1.0.0.