| yuezonghe | 824eb0c | 2024-06-27 02:32:26 -0700 | [diff] [blame] | 1 | =pod |
| 2 | |
| 3 | =head1 NAME |
| 4 | |
| 5 | CMS_compress - create a CMS CompressedData structure |
| 6 | |
| 7 | =head1 SYNOPSIS |
| 8 | |
| 9 | #include <openssl/cms.h> |
| 10 | |
| 11 | CMS_ContentInfo *CMS_compress(BIO *in, int comp_nid, unsigned int flags); |
| 12 | |
| 13 | =head1 DESCRIPTION |
| 14 | |
| 15 | CMS_compress() creates and returns a CMS CompressedData structure. B<comp_nid> |
| 16 | is the compression algorithm to use or B<NID_undef> to use the default |
| 17 | algorithm (zlib compression). B<in> is the content to be compressed. |
| 18 | B<flags> is an optional set of flags. |
| 19 | |
| 20 | =head1 NOTES |
| 21 | |
| 22 | The only currently supported compression algorithm is zlib using the NID |
| 23 | NID_zlib_compression. |
| 24 | |
| 25 | If zlib support is not compiled into OpenSSL then CMS_compress() will return |
| 26 | an error. |
| 27 | |
| 28 | If the B<CMS_TEXT> flag is set MIME headers for type B<text/plain> are |
| 29 | prepended to the data. |
| 30 | |
| 31 | Normally the supplied content is translated into MIME canonical format (as |
| 32 | required by the S/MIME specifications) if B<CMS_BINARY> is set no translation |
| 33 | occurs. This option should be used if the supplied data is in binary format |
| 34 | otherwise the translation will corrupt it. If B<CMS_BINARY> is set then |
| 35 | B<CMS_TEXT> is ignored. |
| 36 | |
| 37 | If the B<CMS_STREAM> flag is set a partial B<CMS_ContentInfo> structure is |
| 38 | returned suitable for streaming I/O: no data is read from the BIO B<in>. |
| 39 | |
| 40 | The compressed data is included in the CMS_ContentInfo structure, unless |
| 41 | B<CMS_DETACHED> is set in which case it is omitted. This is rarely used in |
| 42 | practice and is not supported by SMIME_write_CMS(). |
| 43 | |
| 44 | =head1 NOTES |
| 45 | |
| 46 | If the flag B<CMS_STREAM> is set the returned B<CMS_ContentInfo> structure is |
| 47 | B<not> complete and outputting its contents via a function that does not |
| 48 | properly finalize the B<CMS_ContentInfo> structure will give unpredictable |
| 49 | results. |
| 50 | |
| 51 | Several functions including SMIME_write_CMS(), i2d_CMS_bio_stream(), |
| 52 | PEM_write_bio_CMS_stream() finalize the structure. Alternatively finalization |
| 53 | can be performed by obtaining the streaming ASN1 B<BIO> directly using |
| 54 | BIO_new_CMS(). |
| 55 | |
| 56 | Additional compression parameters such as the zlib compression level cannot |
| 57 | currently be set. |
| 58 | |
| 59 | =head1 RETURN VALUES |
| 60 | |
| 61 | CMS_compress() returns either a CMS_ContentInfo structure or NULL if an error |
| 62 | occurred. The error can be obtained from ERR_get_error(3). |
| 63 | |
| 64 | =head1 SEE ALSO |
| 65 | |
| 66 | L<ERR_get_error(3)>, L<CMS_uncompress(3)> |
| 67 | |
| 68 | =head1 HISTORY |
| 69 | |
| 70 | The B<CMS_STREAM> flag was added in OpenSSL 1.0.0. |
| 71 | |
| 72 | =head1 COPYRIGHT |
| 73 | |
| 74 | Copyright 2008-2016 The OpenSSL Project Authors. All Rights Reserved. |
| 75 | |
| 76 | Licensed under the OpenSSL license (the "License"). You may not use |
| 77 | this file except in compliance with the License. You can obtain a copy |
| 78 | in the file LICENSE in the source distribution or at |
| 79 | L<https://www.openssl.org/source/license.html>. |
| 80 | |
| 81 | =cut |