| =pod |
| |
| =head1 NAME |
| |
| CMS_compress - create a CMS CompressedData structure |
| |
| =head1 SYNOPSIS |
| |
| #include <openssl/cms.h> |
| |
| CMS_ContentInfo *CMS_compress(BIO *in, int comp_nid, unsigned int flags); |
| |
| =head1 DESCRIPTION |
| |
| CMS_compress() creates and returns a CMS CompressedData structure. B<comp_nid> |
| is the compression algorithm to use or B<NID_undef> to use the default |
| algorithm (zlib compression). B<in> is the content to be compressed. |
| B<flags> is an optional set of flags. |
| |
| =head1 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 B<CMS_TEXT> flag is set MIME headers for type B<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 B<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 B<CMS_BINARY> is set then |
| B<CMS_TEXT> is ignored. |
| |
| If the B<CMS_STREAM> flag is set a partial B<CMS_ContentInfo> structure is |
| returned suitable for streaming I/O: no data is read from the BIO B<in>. |
| |
| The compressed data is included in the CMS_ContentInfo structure, unless |
| B<CMS_DETACHED> is set in which case it is omitted. This is rarely used in |
| practice and is not supported by SMIME_write_CMS(). |
| |
| =head1 NOTES |
| |
| If the flag B<CMS_STREAM> is set the returned B<CMS_ContentInfo> structure is |
| B<not> complete and outputting its contents via a function that does not |
| properly finalize the B<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 B<BIO> directly using |
| BIO_new_CMS(). |
| |
| Additional compression parameters such as the zlib compression level cannot |
| currently be set. |
| |
| =head1 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). |
| |
| =head1 SEE ALSO |
| |
| L<ERR_get_error(3)|ERR_get_error(3)>, L<CMS_uncompress(3)|CMS_uncompress(3)> |
| |
| =head1 HISTORY |
| |
| CMS_compress() was added to OpenSSL 0.9.8 |
| The B<CMS_STREAM> flag was first supported in OpenSSL 1.0.0. |
| |
| =cut |
