CMS_compress
Section: OpenSSL (3)
Updated: 2017-05-25
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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.
Index
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- NOTES
-
- NOTES
-
- RETURN VALUES
-
- SEE ALSO
-
- HISTORY
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