In some cases, a SEQUENCE that contains only optional fields may end
up empty. In some cases, this may be represented by dropping the
SEQUENCE entirely from the encoded DER.
To do this, we detect the case where WPACKET_FLAGS_ABANDON_ON_ZERO_LENGTH
is used, and adapt accordingly.
Reviewed-by: Shane Lontis <shane.lontis@oracle.com>
(Merged from https://github.com/openssl/openssl/pull/11710)
This library is meant to be small and quick. It's based on WPACKET,
which was extended to support DER writing. The way it's used is a
bit unusual, as it's used to write the structures backward into a
given buffer. A typical quick call looks like this:
/*
* Fill in this structure:
*
* something ::= SEQUENCE {
* id OBJECT IDENTIFIER,
* x [0] INTEGER OPTIONAL,
* y [1] BOOLEAN OPTIONAL,
* n INTEGER
* }
*/
unsigned char buf[nnnn], *p = NULL;
size_t encoded_len = 0;
WPACKET pkt;
int ok;
ok = WPACKET_init_der(&pkt, buf, sizeof(buf)
&& DER_w_start_sequence(&pkt, -1)
&& DER_w_bn(&pkt, -1, bn)
&& DER_w_boolean(&pkt, 1, bool)
&& DER_w_precompiled(&pkt, -1, OID, sizeof(OID))
&& DER_w_end_sequence(&pkt, -1)
&& WPACKET_finish(&pkt)
&& WPACKET_get_total_written(&pkt, &encoded_len)
&& (p = WPACKET_get_curr(&pkt)) != NULL;
Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/11450)
