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=head1 NAME

SMIME_read_CMS_ex, SMIME_read_CMS - parse S/MIME message

=head1 SYNOPSIS

 #include <openssl/cms.h>

 CMS_ContentInfo *SMIME_read_CMS_ex(BIO *bio, int flags, BIO **bcont,
                                    CMS_ContentInfo **cms);
 CMS_ContentInfo *SMIME_read_CMS(BIO *in, BIO **bcont);

=head1 DESCRIPTION

SMIME_read_CMS() parses a message in S/MIME format.

B<in> is a BIO to read the message from.

If cleartext signing is used then the content is saved in a memory bio which is
written to B<*bcont>, otherwise B<*bcont> is set to NULL.

The parsed CMS_ContentInfo structure is returned or NULL if an
error occurred.

SMIME_read_CMS_ex() is similar to SMIME_read_CMS() but optionally a previously
created I<cms> CMS_ContentInfo object can be supplied as well as some I<flags>.
To create a I<cms> object use L<CMS_ContentInfo_new_ex(3)>.
If the I<flags> argument contains B<CMS_BINARY> then the input is assumed to be
in binary format and is not translated to canonical form.
If in addition B<SMIME_ASCIICRLF> is set then the binary input is assumed
to be followed by B<CR> and B<LF> characters, else only by an B<LF> character.
If I<flags> is 0 and I<cms> is NULL then it is identical to SMIME_read_CMS().

=head1 NOTES

If B<*bcont> is not NULL then the message is clear text signed. B<*bcont> can
then be passed to CMS_verify() with the B<CMS_DETACHED> flag set.

Otherwise the type of the returned structure can be determined
using CMS_get0_type().

To support future functionality if B<bcont> is not NULL B<*bcont> should be
initialized to NULL. For example:

 BIO *cont = NULL;
 CMS_ContentInfo *cms;

 cms = SMIME_read_CMS(in, &cont);

=head1 BUGS

The MIME parser used by SMIME_read_CMS() is somewhat primitive.  While it will
handle most S/MIME messages more complex compound formats may not work.

The parser assumes that the CMS_ContentInfo structure is always base64 encoded
and will not handle the case where it is in binary format or uses quoted
printable format.

The use of a memory BIO to hold the signed content limits the size of message
which can be processed due to memory restraints: a streaming single pass option
should be available.

=head1 RETURN VALUES

SMIME_read_CMS_ex() and SMIME_read_CMS() return a valid B<CMS_ContentInfo>
structure or B<NULL> if an error occurred. The error can be obtained from
ERR_get_error(3).

=head1 SEE ALSO

L<ERR_get_error(3)>,
L<CMS_sign(3)>,
L<CMS_verify(3)>,
L<CMS_encrypt(3)>,
L<CMS_decrypt(3)>

=head1 HISTORY

The function SMIME_read_CMS_ex() was added in OpenSSL 3.0.

=head1 COPYRIGHT

Copyright 2008-2021 The OpenSSL Project Authors. All Rights Reserved.

Licensed under the Apache License 2.0 (the "License").  You may not use
this file except in compliance with the License.  You can obtain a copy
in the file LICENSE in the source distribution or at
L<https://www.openssl.org/source/license.html>.

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