CMS_COMPRESS(3)

NAME
CMS_compress - create a CMS CompressedData structure

SYNOPSIS
libcrypto
#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. Currently, the default algorithm NID_zlib_compression is the only supported algorithm. If zlib support is not compiled in, CMS_compress() always returns an error.

in provides the content to be compressed.

Any of the following flags (OR'ed together) can be passed in the flags parameter:

CMS_TEXT
    Prepend MIME headers for type text/plain to the data.

CMS_BINARY
    Do not translate the supplied content into MIME canonical format, even though that is required by the S/MIME specifications. This option should be used if the supplied data is in binary format. Otherwise, the translation will corrupt it. If CMS_BINARY is set, CMS_TEXT is ignored.

CMS_STREAM
    Return a partial CMS_ContentInfo structure suitable for streaming I/O: no data is read from in. Several functions including SMIME_write_CMS(3), i2d_CMS_bio_stream(3), or PEM_write_bio_CMS_stream(3) can be used to finalize the structure. Alternatively, finalization can be performed by obtaining the streaming ASN1 BIO directly using BIO_new_CMS(3). Outputting the contents of the CMS_ContentInfo structure via a function that does not properly finalize it will give unpredictable results.

CMS_DETACHED
    Do not include the compressed data in the CMS_ContentInfo structure. This is rarely used in practice and is not supported by SMIME_write_CMS(3).

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
CMS_ContentInfo_new(3), CMS_uncompress(3)

STANDARDS
RFC 3274: Compressed Data Content Type for Cryptographic Message Syntax (CMS)

HISTORY
CMS_compress() first appeared in OpenSSL 0.9.8h and has been available since OpenBSD 6.7.

The CMS_STREAM flag first appeared in OpenSSL 1.0.0.