Clarify KEEPALIVE EDNS0 option operation

diff --git a/util/data/msgparse.c b/util/data/msgparse.c
index 415973cdda833588c80b90b07a765f23379be7f5..a600a8c60151655a35de8ccca664c04132cd83f8 100644 (file)
--- a/util/data/msgparse.c
+++ b/util/data/msgparse.c
@@ -961,6 +961,10 @@ parse_edns_options_from_query(uint8_t* rdata_ptr, size_t rdata_len,
         * received one message with a TCP Keepalive EDNS option, and that
         * option must have 0 length data. Subsequent messages sent on that
         * connection will have a TCP Keepalive option.
+        *
+        * In the if-statement below, the option is added unsolicited. This
+        * means that the client has sent an KEEPALIVE option earlier. We know
+        * here this is true, because c->tcp_keepalive is set.
         */
        if (cfg && cfg->do_tcp_keepalive && c && c->type != comm_udp && c->tcp_keepalive) {
                if(!edns_opt_list_append_keepalive(&edns->opt_list_out,
@@ -999,6 +1003,14 @@ parse_edns_options_from_query(uint8_t* rdata_ptr, size_t rdata_len,
                         * Keepalive EDNS option, and that option must have 0
                         * length data. Subsequent messages sent on that
                         * connection will have a TCP Keepalive option.
+                        *
+                        * This should be the first time the client sends this
+                        * option, so c->tcp_keepalive is not set.
+                        * Besides adding the reply KEEPALIVE option, 
+                        * c->tcp_keepalive will be set so that the
+                        * option will be added unsolicited in subsequent
+                        * responses (see the comment above the if-statement
+                        * at the start of this function).
                         */
                        if (!cfg || !cfg->do_tcp_keepalive || !c ||
                                        c->type == comm_udp || c->tcp_keepalive)