sd-dhcp6-client: Implement Rapid Commit

Add a Rapid Commit option to Solicit messages and expect a Reply to
be received instead of an Advertise. When receiving a DHCPv6 message
from the server in state Solicit, continue testing whether the
message is a Reply. Ease up the message type checking, it's not fatal
if the message is of a wrong type.

Add helper functions to set/get the rapid commit of a lease. See
RFC 3315, sections 17., 17.1.2., 17.1.4. and 18.1.8.

1 files changed, 3 insertions, 2 deletions

diff --git a/src/libsystemd-network/dhcp6-option.c b/src/libsystemd-network/dhcp6-option.c
index f488832cf9..e9b382c170 100644
--- a/src/libsystemd-network/dhcp6-option.c
+++ b/src/libsystemd-network/dhcp6-option.c
@@ -58,13 +58,14 @@ int dhcp6_option_append(uint8_t **buf, size_t *buflen, uint16_t code,
                         size_t optlen, const void *optval) {
         int r;
 
-        assert_return(optval, -EINVAL);
+        assert_return(optval || optlen == 0, -EINVAL);
 
         r = option_append_hdr(buf, buflen, code, optlen);
         if (r < 0)
                 return r;
 
-        memcpy(*buf, optval, optlen);
+        if (optval)
+                memcpy(*buf, optval, optlen);
 
         *buf += optlen;
         *buflen -= optlen;