resolved: add code to generate the wire format for a single RR

This adds dns_resource_record_to_wire_format() that generates the raw
wire-format of a single DnsResourceRecord object, and caches it in the
object, optionally in DNSSEC canonical form. This call is used later to
generate the RR serialization of RRs to verify.

This adds four new fields to DnsResourceRecord objects:

- wire_format points to the buffer with the wire-format version of the
  RR
- wire_format_size stores the size of that buffer
- wire_format_rdata_offset specifies the index into the buffer where the
  RDATA of the RR begins (i.e. the size of the key part of the RR).
- wire_format_canonical is a boolean that stores whether the cached wire
  format is in DNSSEC canonical form or not.

Note that this patch adds a mode where a DnsPacket is allocated on the
stack (instead of on the heap), so that it is cheaper to reuse the
DnsPacket object for generating this wire format. After all we reuse the
DnsPacket object for this, since it comes with all the dynamic memory
management, and serialization calls we need anyway.

1 files changed, 5 insertions, 3 deletions

diff --git a/src/resolve/resolved-dns-packet.h b/src/resolve/resolved-dns-packet.h
index b236333f61..853c94fe76 100644
--- a/src/resolve/resolved-dns-packet.h
+++ b/src/resolve/resolved-dns-packet.h
@@ -88,8 +88,10 @@ struct DnsPacket {
         uint16_t sender_port, destination_port;
         uint32_t ttl;
 
-        bool extracted;
-        bool refuse_compression;
+        bool on_stack:1;
+        bool extracted:1;
+        bool refuse_compression:1;
+        bool canonical_form:1;
 };
 
 static inline uint8_t* DNS_PACKET_DATA(DnsPacket *p) {
@@ -162,7 +164,7 @@ int dns_packet_append_raw_string(DnsPacket *p, const void *s, size_t size, size_
 int dns_packet_append_label(DnsPacket *p, const char *s, size_t l, size_t *start);
 int dns_packet_append_name(DnsPacket *p, const char *name, bool allow_compression, size_t *start);
 int dns_packet_append_key(DnsPacket *p, const DnsResourceKey *key, size_t *start);
-int dns_packet_append_rr(DnsPacket *p, const DnsResourceRecord *rr, size_t *start);
+int dns_packet_append_rr(DnsPacket *p, const DnsResourceRecord *rr, size_t *start, size_t *rdata_start);
 int dns_packet_append_opt_rr(DnsPacket *p, uint16_t max_udp_size, bool edns0_do, size_t *start);
 
 void dns_packet_truncate(DnsPacket *p, size_t sz);