Make sure to validate the client's ip address

client/remote.go

@@ -0,0 +1,49 @@
+package client
+
+import (
+	"context"
+	"net/http"
+	"strings"
+)
+
+const (
+	ClientIPCtx       = "ClientIP"
+	ProxyAddressesCtx = "ProxyAddresses"
+	RemoteAddressCtx  = "RemoteAddress"
+)
+
+func EnrichContext(next http.Handler) http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		ctx := r.Context()
+
+		h := r.Header.Get("X-Forwarded-For")
+		if h != "" {
+			var proxies []string
+			ips := strings.Split(h, ",")
+			for i := range ips {
+				ips[i] = strings.TrimSpace(ips[i])
+			}
+			clientIp := ips[0]
+			if len(ips) > 1 {
+				proxies = ips[1:]
+			}
+			ctx = context.WithValue(ctx, ClientIPCtx, clientIp)
+			ctx = context.WithValue(ctx, ProxyAddressesCtx, proxies)
+		}
+
+		remote := r.Header.Get("REMOTE_ADDR")
+		ctx = context.WithValue(ctx, RemoteAddressCtx, remote)
+		if h == "" {
+			ctx = context.WithValue(ctx, ClientIPCtx, remote)
+		}
+		next.ServeHTTP(w, r.WithContext(ctx))
+	})
+}
+
+func GetClientIp(ctx context.Context) string {
+	s, ok := ctx.Value(ClientIPCtx).(string)
+	if !ok {
+		return ""
+	}
+	return s
+}