Rewrite RealIP() to avoid returning an empty string

http/request/request.go

@@ -6,8 +6,10 @@ package request
 
 import (
 	"fmt"
+	"net"
 	"net/http"
 	"strconv"
+	"strings"
 
 	"github.com/gorilla/mux"
 )
@@ -88,3 +90,30 @@ func HasQueryParam(r *http.Request, param string) bool {
 	_, ok := values[param]
 	return ok
 }
+
+// RealIP returns client's real IP address.
+func RealIP(r *http.Request) string {
+	headers := []string{"X-Forwarded-For", "X-Real-Ip"}
+	for _, header := range headers {
+		value := r.Header.Get(header)
+
+		if value != "" {
+			addresses := strings.Split(value, ",")
+			address := strings.TrimSpace(addresses[0])
+
+			if net.ParseIP(address) != nil {
+				return address
+			}
+		}
+	}
+
+	// Fallback to TCP/IP source IP address.
+	var remoteIP string
+	if strings.ContainsRune(r.RemoteAddr, ':') {
+		remoteIP, _, _ = net.SplitHostPort(r.RemoteAddr)
+	} else {
+		remoteIP = r.RemoteAddr
+	}
+
+	return remoteIP
+}