Add ExampleReader_NetworksWithin()

Author: Olaf Alders

example_test.go

@@ -155,3 +155,46 @@ func ExampleReader_Networks() {
 	// 2003::/24: Cable/DSL
 
 }
+
+// This example demonstrates how to iterate over all networks in the
+// database which are contained within an arbitrary network.
+func ExampleReader_NetworksWithin() {
+	db, err := maxminddb.Open("test-data/test-data/GeoIP2-Connection-Type-Test.mmdb")
+	if err != nil {
+		log.Fatal(err)
+	}
+	defer db.Close()
+
+	record := struct {
+		Domain string `maxminddb:"connection_type"`
+	}{}
+
+	_, network, err := net.ParseCIDR("1.0.0.0/8")
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	networks := db.NetworksWithin(network)
+	for networks.Next() {
+		subnet, err := networks.Network(&record)
+		if err != nil {
+			log.Fatal(err)
+		}
+		fmt.Printf("%s: %s\n", subnet.String(), record.Domain)
+	}
+	if networks.Err() != nil {
+		log.Fatal(networks.Err())
+	}
+
+	// Output:
+	//1.0.0.0/24: Dialup
+	//1.0.1.0/24: Cable/DSL
+	//1.0.2.0/23: Dialup
+	//1.0.4.0/22: Dialup
+	//1.0.8.0/21: Dialup
+	//1.0.16.0/20: Dialup
+	//1.0.32.0/19: Dialup
+	//1.0.64.0/18: Dialup
+	//1.0.128.0/17: Dialup
+
+}