If we request more bytes to be allocated than double what we have already
written, then we grow the buffer by the wrong amount.
Reviewed-by: NEmilia Käsper <emilia@openssl.org>

If the underlying BUF_MEM gets realloc'd then the pointer returned could
become invalid. Therefore we should always ensure that the allocated
memory is filled in prior to any more WPACKET_* calls.
Reviewed-by: NRich Salz <rsalz@openssl.org>

All the other functions that take an argument for the number of bytes
use convenience macros for this purpose. We should do the same with
WPACKET_put_bytes().
Reviewed-by: NRich Salz <rsalz@openssl.org>

Don't call WPACKET_sub_memcpy(), WPACKET_sub_allocation_bytes() and
WPACKET_start_sub_packet_len() directly.
Reviewed-by: NRich Salz <rsalz@openssl.org>

Updated the construction code to use the new function. Also added some
convenience macros for WPACKET_sub_memcpy().
Reviewed-by: NRich Salz <rsalz@openssl.org>

Addressing more feedback comments.
Reviewed-by: NRich Salz <rsalz@openssl.org>

Reviewed-by: NRich Salz <rsalz@openssl.org>

Two locations had the same loop for writing out a value. Pull it out into
a function.
Reviewed-by: NRich Salz <rsalz@openssl.org>

This is an internal API. Some of the tests were for programmer erorr and
"should not happen" situations, so a soft assert is reasonable.
Reviewed-by: NRich Salz <rsalz@openssl.org>

A few style tweaks here and there. The main change is that curr and
packet_len are now offsets into the buffer to account for the fact that
the pointers can change if the buffer grows. Also dropped support for the
WPACKET_set_packet_len() function. I thought that was going to be needed
but so far it hasn't been. It doesn't really work any more due to the
offsets change.
Reviewed-by: NRich Salz <rsalz@openssl.org>

Reviewed-by: NRich Salz <rsalz@openssl.org>

The PACKET documentation is already in packet_locl.h so it makes sense to
have the WPACKET documentation there as well.
Reviewed-by: NRich Salz <rsalz@openssl.org>

Also added the WPACKET_cleanup() function to cleanup a WPACKET if we hit
an error.
Reviewed-by: NRich Salz <rsalz@openssl.org>

Reviewed-by: NRich Salz <rsalz@openssl.org>

No need to declare an explicit sub-packet. Just start one.
Reviewed-by: NRich Salz <rsalz@openssl.org>

To avoid confusion with the read PACKET structure.
Reviewed-by: NRich Salz <rsalz@openssl.org>

Reviewed-by: NRich Salz <rsalz@openssl.org>