add IPv4 link-local address to private ranges detector, update list

169.254.0.0/16 is this new range is the same as fe80::/10 for IPv6.

Also, add comments to each entry according to provided link and replace
192.0.0.0/24 with more specific prefixes according to standard.

realip/real.go

@@ -14,17 +14,27 @@ type ipRange struct {
 	end   net.IP
 }
 
+// privateRanges contains the list of private and special-use IP ranges.
+// reference: https://www.iana.org/assignments/iana-ipv4-special-registry/iana-ipv4-special-registry.xhtml
 var privateRanges = []ipRange{
+	// IPv4 Private Ranges
 	{start: net.ParseIP("10.0.0.0"), end: net.ParseIP("10.255.255.255")},
-	{start: net.ParseIP("100.64.0.0"), end: net.ParseIP("100.127.255.255")},
 	{start: net.ParseIP("172.16.0.0"), end: net.ParseIP("172.31.255.255")},
-	{start: net.ParseIP("192.0.0.0"), end: net.ParseIP("192.0.0.255")},
 	{start: net.ParseIP("192.168.0.0"), end: net.ParseIP("192.168.255.255")},
+	// IPv4 Link-Local
+	{start: net.ParseIP("169.254.0.0"), end: net.ParseIP("169.254.255.255")},
+	// IPv4 Loopback
+	{start: net.ParseIP("127.0.0.0"), end: net.ParseIP("127.255.255.255")},
+	// IPv4 Shared Address Space (RFC 6598)
+	{start: net.ParseIP("100.64.0.0"), end: net.ParseIP("100.127.255.255")},
+	// IPv4 Benchmarking (RFC 2544)
 	{start: net.ParseIP("198.18.0.0"), end: net.ParseIP("198.19.255.255")},
-	{start: net.ParseIP("::1"), end: net.ParseIP("::1")},
+	// IPv6 Unique Local Addresses (ULA)
 	{start: net.ParseIP("fc00::"), end: net.ParseIP("fdff:ffff:ffff:ffff:ffff:ffff:ffff:ffff")},
+	// IPv6 Link-local Addresses
 	{start: net.ParseIP("fe80::"), end: net.ParseIP("febf:ffff:ffff:ffff:ffff:ffff:ffff:ffff")},
-}
+	// IPv6 Loopback Address
+	{start: net.ParseIP("::1"), end: net.ParseIP("::1")}}
 
 // Get returns real ip from the given request
 // Prioritize public IPs over private IPs