1=pod
2
3=head1 NAME
4
5CMS_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
15CMS_compress() creates and returns a CMS CompressedData structure. B<comp_nid>
16is the compression algorithm to use or B<NID_undef> to use the default
17algorithm (zlib compression). B<in> is the content to be compressed.
18B<flags> is an optional set of flags.
19
20=head1 NOTES
21
22The only currently supported compression algorithm is zlib using the NID
23NID_zlib_compression.
24
25If zlib support is not compiled into OpenSSL then CMS_compress() will return
26an error.
27
28If the B<CMS_TEXT> flag is set MIME headers for type B<text/plain> are
29prepended to the data.
30
31Normally the supplied content is translated into MIME canonical format (as
32required by the S/MIME specifications) if B<CMS_BINARY> is set no translation
33occurs. This option should be used if the supplied data is in binary format
34otherwise the translation will corrupt it. If B<CMS_BINARY> is set then
35B<CMS_TEXT> is ignored.
36
37If the B<CMS_STREAM> flag is set a partial B<CMS_ContentInfo> structure is
38returned suitable for streaming I/O: no data is read from the BIO B<in>.
39
40The compressed data is included in the CMS_ContentInfo structure, unless
41B<CMS_DETACHED> is set in which case it is omitted. This is rarely used in
42practice and is not supported by SMIME_write_CMS().
43
44=head1 NOTES
45
46If the flag B<CMS_STREAM> is set the returned B<CMS_ContentInfo> structure is
47B<not> complete and outputting its contents via a function that does not
48properly finalize the B<CMS_ContentInfo> structure will give unpredictable
49results.
50
51Several functions including SMIME_write_CMS(), i2d_CMS_bio_stream(),
52PEM_write_bio_CMS_stream() finalize the structure. Alternatively finalization
53can be performed by obtaining the streaming ASN1 B<BIO> directly using
54BIO_new_CMS().
55
56Additional compression parameters such as the zlib compression level cannot
57currently be set.
58
59=head1 RETURN VALUES
60
61CMS_compress() returns either a CMS_ContentInfo structure or NULL if an error
62occurred. The error can be obtained from ERR_get_error(3).
63
64=head1 SEE ALSO
65
66L<ERR_get_error(3)|ERR_get_error(3)>, L<CMS_uncompress(3)|CMS_uncompress(3)>
67
68=head1 HISTORY
69
70CMS_compress() was added to OpenSSL 0.9.8
71The B<CMS_STREAM> flag was first supported in OpenSSL 1.0.0.
72
73=cut
74