[PHP知识库]PHP函数header_register_callback

header_register_callback 注册一个函数，在 PHP 开始发送输出时调用。

/**
 * Registers a function that will be called when PHP starts sending output.
 * The callback is executed just after PHP prepares all headers to be sent,<br>
 * and before any other output is sent, creating a window to manipulate the outgoing headers before being sent.
 * @link https://secure.php.net/manual/en/function.header-register-callback.php
 * @param callable $callback Function called just before the headers are sent.
 * @return bool true on success or false on failure.
 */
function header_register_callback ( callable $callback ) {}

?示例：

header('Content-Type: text/plain');
header('X-Powered-By: XXX');


header_register_callback(function(){
    header('X-Powered-By: YYY', true);
});

echo 'Hello world!';

//响应结果
//HTTP/1.1 200 OK
//Content-type: text/plain;charset=UTF-8
//X-Powered-By: YYY
//content-length: 12
//
//Hello world！