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.