improve remote addr parsing as requested at: https://github.com/kataras/iris/issues/1453

Former-commit-id: e5fde988eda9bf582b04285a1c77ba123910a699

core/netutil/ip.go

@@ -0,0 +1,59 @@
+package netutil
+
+import (
+	"bytes"
+	"net"
+	"strings"
+)
+
+/* Based on:
+https://husobee.github.io/golang/ip-address/2015/12/17/remote-ip-go.html requested at:
+https://github.com/kataras/iris/issues/1453
+*/
+
+//IPRange is a structure that holds the start and end of a range of IP Addresses.
+type IPRange struct {
+	Start net.IP `json:"start" yaml:"Start" toml"Start"`
+	End   net.IP `json:"end" yaml:"End" toml"End"`
+}
+
+// IPInRange reports whether a given IP Address is within a range given.
+func IPInRange(r IPRange, ipAddress net.IP) bool {
+	return bytes.Compare(ipAddress, r.Start) >= 0 && bytes.Compare(ipAddress, r.End) < 0
+}
+
+// IPIsPrivateSubnet reports whether this "ipAddress" is in a private subnet.
+func IPIsPrivateSubnet(ipAddress net.IP, privateRanges []IPRange) bool {
+	// IPv4 for now.
+	if ipCheck := ipAddress.To4(); ipCheck != nil {
+		// iterate over all our ranges.
+		for _, r := range privateRanges {
+			// check if this ip is in a private range.
+			if IPInRange(r, ipAddress) {
+				return true
+			}
+		}
+	}
+	return false
+}
+
+// GetIPAddress returns a valid public IP Address from a collection of IP Addresses
+// and a range of private subnets.
+//
+// Reports whether a valid IP was found.
+func GetIPAddress(ipAddresses []string, privateRanges []IPRange) (string, bool) {
+	// march from right to left until we get a public address
+	// that will be the address right before our proxy.
+	for i := len(ipAddresses) - 1; i >= 0; i-- {
+		ip := strings.TrimSpace(ipAddresses[i])
+		realIP := net.ParseIP(ip)
+		if !realIP.IsGlobalUnicast() || IPIsPrivateSubnet(realIP, privateRanges) {
+			// bad address, go to next
+			continue
+		}
+		return ip, true
+
+	}
+
+	return "", false
+}