PHP获取当前请求IP

if (!empty($_SERVER["HTTP_CLIENT_IP"]) && strcasecmp($_SERVER["HTTP_CLIENT_IP"], "unknown")) {
    $ip = $_SERVER["HTTP_CLIENT_IP"];
} elseif (!empty($_SERVER["HTTP_X_FORWARDED_FOR"]) && strcasecmp($_SERVER["HTTP_X_FORWARDED_FOR"], "unknown")) {
    $ip = $_SERVER["HTTP_X_FORWARDED_FOR"];
} elseif (!empty($_SERVER["REMOTE_ADDR"]) && strcasecmp($_SERVER["REMOTE_ADDR"], "unknown")) {
    $ip = $_SERVER["REMOTE_ADDR"];
} else {
    $ip = "unknown";
}