resolved: implement minimal EDNS0 support

This is a minimal implementation of RFC6891. Only default values
are used, so in reality this will be a noop.

EDNS0 support is dependent on the current server's feature level,
so appending the OPT pseudo RR is done when the packet is emitted,
rather than when it is assembled. To handle different feature
levels on retransmission, we strip off the OPT RR again after
sending the packet.

Similarly, to how we fall back to TCP if UDP fails, we fall back
to plain UDP if EDNS0 fails (but if EDNS0 ever succeeded we never
fall back again, and after a timeout we will retry EDNS0).

1 files changed, 1 insertions, 1 deletions

diff --git a/src/resolve/resolved-dns-scope.h b/src/resolve/resolved-dns-scope.h
index 7876410b7d..0480f702f8 100644
--- a/src/resolve/resolved-dns-scope.h
+++ b/src/resolve/resolved-dns-scope.h
@@ -80,7 +80,7 @@ DnsScope* dns_scope_free(DnsScope *s);
 void dns_scope_packet_received(DnsScope *s, usec_t rtt);
 void dns_scope_packet_lost(DnsScope *s, usec_t usec);
 
-int dns_scope_emit(DnsScope *s, int fd, DnsPacket *p);
+int dns_scope_emit(DnsScope *s, int fd, DnsServer *server, DnsPacket *p);
 int dns_scope_tcp_socket(DnsScope *s, int family, const union in_addr_union *address, uint16_t port, DnsServer **server);
 int dns_scope_udp_dns_socket(DnsScope *s, DnsServer **server);