Section: OpenSSL (3SSL)
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CMS_compress - create a CMS CompressedData structure
CMS_ContentInfo *CMS_compress(BIO *in, int comp_nid, unsigned int flags);
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.
is an optional set of flags.
The only currently supported compression algorithm is zlib using the NID
If zlib support is not compiled into OpenSSL then CMS_compress() will return
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().
If the flag CMS_STREAM
is set the returned CMS_ContentInfo
complete and outputting its contents via a function that does not
properly finalize the CMS_ContentInfo
structure will give unpredictable
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
Additional compression parameters such as the zlib compression level cannot
currently be set.
returns either a CMS_ContentInfo structure or NULL
if an error
occurred. The error can be obtained from ERR_get_error
was added to OpenSSL 0.9.8
flag was first supported in OpenSSL 1.0.0.
- RETURN VALUES
- SEE ALSO