Set network number to first IP in network

when looking up a network that is more specific than the network in the
database using NetworksWithin.

Previously, the network number would be set to the network number of the
provided *net.IPNet. This changes it to the canonical form.

traverse.go

@@ -95,6 +95,10 @@ func (r *Reader) NetworksWithin(network *net.IPNet, options ...NetworksOption) *
 	}
 
 	pointer, bit := r.traverseTree(ip, 0, uint(prefixLength))
+
+	if bit < prefixLength {
+		ip = ip.Mask(net.CIDRMask(bit, len(ip)*8))
+	}
 	networks.nodes = []netNode{
 		{
 			ip:      ip,

traverse_test.go

@@ -85,6 +85,27 @@ var tests = []networkTest{
 			"1.1.1.1/32",
 		},
 	},
+	{
+		Network:  "1.1.1.2/32",
+		Database: "ipv4",
+		Expected: []string{
+			"1.1.1.2/31",
+		},
+	},
+	{
+		Network:  "1.1.1.3/32",
+		Database: "ipv4",
+		Expected: []string{
+			"1.1.1.2/31",
+		},
+	},
+	{
+		Network:  "1.1.1.19/32",
+		Database: "ipv4",
+		Expected: []string{
+			"1.1.1.16/28",
+		},
+	},
 	{
 		Network:  "255.255.255.0/24",
 		Database: "ipv4",