add DNSName::isPartOf() + tests

tdns/dns-storage.cc

@@ -21,6 +21,27 @@ bool DNSName::makeRelative(const DNSName& root)
   return true;
 }
 
+//! Checks is this DNSName is part of root
+bool DNSName::isPartOf(const DNSName& root) const
+{
+  auto them = root.d_name.crbegin(), us = d_name.crbegin();
+  for(;;) {
+    if(them == root.d_name.crend())
+      return true;
+    if(us == d_name.crend())
+      return false;
+    
+    if(*them == *us) {
+      ++them;
+      ++us;
+    }
+    else
+      break;
+  }
+  return false;
+}
+
+
 //! Append two DNSNames
 DNSName operator+(const DNSName& a, const DNSName& b)
 {

tdns/dns-storage.hh

@@ -146,6 +146,7 @@ struct DNSName
   auto size() { return d_name.size(); }
   void clear() { d_name.clear(); }
   bool makeRelative(const DNSName& root);
+  bool isPartOf(const DNSName& root) const;
   std::string toString() const;
   bool operator==(const DNSName& rhs) const
   {

tdns/tests.cc

@@ -39,6 +39,18 @@ TEST_CASE("DNSName operations", "[dnsname]") {
 
   REQUIRE(test2.makeRelative({"org"}));
   REQUIRE(test2 == DNSName({"www", "powerdns"}));
+
+  DNSName parent({"powerdns", "com"}), root({}), child({"www", "powerdns", "com"});
+  DNSName unrelated({"www", "isc", "org"});
+  DNSName Org({"Org"});
+  REQUIRE(parent.isPartOf(root));
+  REQUIRE(child.isPartOf(parent));
+  REQUIRE(child.isPartOf(root));
+  REQUIRE(!root.isPartOf(parent));
+  REQUIRE(!parent.isPartOf(child));
+  REQUIRE(!unrelated.isPartOf(child));
+  REQUIRE(!child.isPartOf(unrelated));
+  REQUIRE(unrelated.isPartOf(Org));
 }
 
 TEST_CASE("DNS Messages", "[dnsmessage]") {