[dns_filter] A bit more refactoring to increase coverage (#13334)

Signed-off-by: Alvin Baptiste <alvinsb@gmail.com>

Mirrored from https://github.com/envoyproxy/envoy @ 9d4a6fdec51de2e66efe8abfe1f28c6bb96e93c7

envoy/data/dns/v3/dns_table.proto

@@ -86,7 +86,8 @@ message DnsTable {
   // This message defines a service selection record returned for a service query in a domain
   message DnsService {
     // The name of the service without the protocol or domain name
-    string service_name = 1;
+    string service_name = 1
+        [(validate.rules).string = {min_len: 1 well_known_regex: HTTP_HEADER_NAME}];
 
     // The service protocol. This can be specified as a string or the numeric value of the protocol
     DnsServiceProtocol protocol = 2;

envoy/data/dns/v4alpha/dns_table.proto

@@ -95,7 +95,8 @@ message DnsTable {
         "envoy.data.dns.v3.DnsTable.DnsService";
 
     // The name of the service without the protocol or domain name
-    string service_name = 1;
+    string service_name = 1
+        [(validate.rules).string = {min_len: 1 well_known_regex: HTTP_HEADER_NAME}];
 
     // The service protocol. This can be specified as a string or the numeric value of the protocol
     DnsServiceProtocol protocol = 2;