dnsparser: Add a comment explaining that the OPT RR has to be in additional

Signed-off-by: Remi Gacogne <remi.gacogne@powerdns.com>

diff --git a/pdns/dnsparser.cc b/pdns/dnsparser.cc
index 93ff63dd11d590beb32579c639cc63798f22b734..8d9e2968d7f0c81f139250436a50c90d0d080cb9 100644 (file)
--- a/pdns/dnsparser.cc
+++ b/pdns/dnsparser.cc
@@ -1162,6 +1162,7 @@ bool getEDNSUDPPayloadSizeAndZ(const char* packet, size_t length, uint16_t* payl
   {
     const dnsheader_aligned dh(packet);
     if (dh->arcount == 0) {
+      // The OPT pseudo-RR, if present, has to be in the additional section (https://datatracker.ietf.org/doc/html/rfc6891#section-6.1.1)
       return false;
     }