logic for client ip

internal/server/middleware.go

@@ -1,6 +1,7 @@
 package server
 
 import (
+	"bytes"
 	"errors"
 	"fmt"
 	"net"
@@ -100,22 +101,88 @@ func getClientIPFromRequest(proxyCount int, r *http.Request) string {
 		}
 	}
 
-	remoteIP, _, err := net.SplitHostPort(readUserIP(r))
+	remoteIP, _, err := net.SplitHostPort(getIPAdress(r))
 	if err != nil {
 		remoteIP = r.RemoteAddr
 	}
 	return remoteIP
 }
 
-func readUserIP(r *http.Request) string {
-    IPAddress := r.Header.Get("X-Real-Ip")
-    if IPAddress == "" {
-        IPAddress = r.Header.Get("X-Forwarded-For")
+//ipRange - a structure that holds the start and end of a range of ip addresses
+type ipRange struct {
+    start net.IP
+    end net.IP
+}
+
+// inRange - check to see if a given ip address is within a range given
+func inRange(r ipRange, ipAddress net.IP) bool {
+    // strcmp type byte comparison
+    if bytes.Compare(ipAddress, r.start) >= 0 && bytes.Compare(ipAddress, r.end) < 0 {
+        return true
+    }
+    return false
+}
+
+var privateRanges = []ipRange{
+    ipRange{
+        start: net.ParseIP("10.0.0.0"),
+        end:   net.ParseIP("10.255.255.255"),
+    },
+    ipRange{
+        start: net.ParseIP("100.64.0.0"),
+        end:   net.ParseIP("100.127.255.255"),
+    },
+    ipRange{
+        start: net.ParseIP("172.16.0.0"),
+        end:   net.ParseIP("172.31.255.255"),
+    },
+    ipRange{
+        start: net.ParseIP("192.0.0.0"),
+        end:   net.ParseIP("192.0.0.255"),
+    },
+    ipRange{
+        start: net.ParseIP("192.168.0.0"),
+        end:   net.ParseIP("192.168.255.255"),
+    },
+    ipRange{
+        start: net.ParseIP("198.18.0.0"),
+        end:   net.ParseIP("198.19.255.255"),
+    },
+}
+
+
+// isPrivateSubnet - check to see if this ip is in a private subnet
+func isPrivateSubnet(ipAddress net.IP) bool {
+    // my use case is only concerned with ipv4 atm
+    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 inRange(r, ipAddress){
+                return true
+            }
+        }
     }
-    if IPAddress == "" {
-        IPAddress = r.RemoteAddr
+    return false
+}
+
+func getIPAdress(r *http.Request) string {
+    for _, h := range []string{"X-Forwarded-For", "X-Real-Ip"} {
+        addresses := strings.Split(r.Header.Get(h), ",")
+        // march from right to left until we get a public address
+        // that will be the address right before our proxy.
+        for i := len(addresses) -1 ; i >= 0; i-- {
+            ip := strings.TrimSpace(addresses[i])
+            // header can contain spaces too, strip those out.
+            realIP := net.ParseIP(ip)
+            if !realIP.IsGlobalUnicast() || isPrivateSubnet(realIP) {
+                // bad address, go to next
+                continue
+            }
+            return ip
+        }
     }
-    return IPAddress
+    return ""
 }
 
 type Captcha struct {