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.\" ========================================================================
.\"
.IX Title "CMS_COMPRESS 3SSL"
.TH CMS_COMPRESS 3SSL "2023-10-23" "3.0.11" "OpenSSL"
.\" For nroff, turn off justification. Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
.if n .ad l
.nh
.SH "NAME"
CMS_compress \- create a CMS CompressedData structure
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 1
\& #include <openssl/cms.h>
\&
\& CMS_ContentInfo *CMS_compress(BIO *in, int comp_nid, unsigned int flags);
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
\&\fBCMS_compress()\fR creates and returns a \s-1CMS\s0 CompressedData structure. \fBcomp_nid\fR
is the compression algorithm to use or \fBNID_undef\fR to use the default
algorithm (zlib compression). \fBin\fR is the content to be compressed.
\&\fBflags\fR is an optional set of flags.
.PP
The only currently supported compression algorithm is zlib using the \s-1NID\s0
NID_zlib_compression.
.PP
If zlib support is not compiled into OpenSSL then \fBCMS_compress()\fR will return
an error.
.PP
If the \fB\s-1CMS_TEXT\s0\fR flag is set \s-1MIME\s0 headers for type \fBtext/plain\fR are
prepended to the data.
.PP
Normally the supplied content is translated into \s-1MIME\s0 canonical format (as
required by the S/MIME specifications) if \fB\s-1CMS_BINARY\s0\fR 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 \fB\s-1CMS_BINARY\s0\fR is set then
\&\fB\s-1CMS_TEXT\s0\fR is ignored.
.PP
If the \fB\s-1CMS_STREAM\s0\fR flag is set a partial \fBCMS_ContentInfo\fR structure is
returned suitable for streaming I/O: no data is read from the \s-1BIO\s0 \fBin\fR.
.PP
The compressed data is included in the CMS_ContentInfo structure, unless
\&\fB\s-1CMS_DETACHED\s0\fR is set in which case it is omitted. This is rarely used in
practice and is not supported by \fBSMIME_write_CMS()\fR.
.PP
If the flag \fB\s-1CMS_STREAM\s0\fR is set the returned \fBCMS_ContentInfo\fR structure is
\&\fBnot\fR complete and outputting its contents via a function that does not
properly finalize the \fBCMS_ContentInfo\fR structure will give unpredictable
results.
.PP
Several functions including \fBSMIME_write_CMS()\fR, \fBi2d_CMS_bio_stream()\fR,
\&\fBPEM_write_bio_CMS_stream()\fR finalize the structure. Alternatively finalization
can be performed by obtaining the streaming \s-1ASN1\s0 \fB\s-1BIO\s0\fR directly using
\&\fBBIO_new_CMS()\fR.
.PP
Additional compression parameters such as the zlib compression level cannot
currently be set.
.SH "RETURN VALUES"
.IX Header "RETURN VALUES"
\&\fBCMS_compress()\fR returns either a CMS_ContentInfo structure or \s-1NULL\s0 if an error
occurred. The error can be obtained from \fBERR_get_error\fR\|(3).
.SH "SEE ALSO"
.IX Header "SEE ALSO"
\&\fBERR_get_error\fR\|(3), \fBCMS_uncompress\fR\|(3)
.SH "HISTORY"
.IX Header "HISTORY"
The \fB\s-1CMS_STREAM\s0\fR flag was added in OpenSSL 1.0.0.
.SH "COPYRIGHT"
.IX Header "COPYRIGHT"
Copyright 2008\-2016 The OpenSSL Project Authors. All Rights Reserved.
.PP
Licensed under the Apache License 2.0 (the \*(L"License\*(R"). You may not use
this file except in compliance with the License. You can obtain a copy
in the file \s-1LICENSE\s0 in the source distribution or at
<https://www.openssl.org/source/license.html>.
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