add server pinger

src/main/java/cc.fascinated/common/IPUtils.java

@@ -0,0 +1,42 @@
+package cc.fascinated.common;
+
+import jakarta.servlet.http.HttpServletRequest;
+import lombok.experimental.UtilityClass;
+
+@UtilityClass
+public class IPUtils {
+    /**
+     * The headers that contain the IP.
+     */
+    private static final String[] IP_HEADERS = new String[] {
+            "CF-Connecting-IP",
+            "X-Forwarded-For"
+    };
+
+    /**
+     * Get the real IP from the given request.
+     *
+     * @param request the request
+     * @return the real IP
+     */
+    public static String getRealIp(HttpServletRequest request) {
+        String ip = request.getRemoteAddr();
+        for (String headerName : IP_HEADERS) {
+            String header = request.getHeader(headerName);
+            if (header == null) {
+                continue;
+            }
+            if (!header.contains(",")) { // Handle single IP
+                ip = header;
+                break;
+            }
+            // Handle multiple IPs
+            String[] ips = header.split(",");
+            for (String ipHeader : ips) {
+                ip = ipHeader;
+                break;
+            }
+        }
+        return ip;
+    }
+}