headers_list - PHP code example

PHP Function Headers_List

The php function headers_list is an inbuilt function to send raw HTTP header information which is sent to the client or browser before any original output like HTML, XML, JSON and so on is send. The header is used to manipulate the output sent by the server and the browser by setting properties such as content type, redirection and more. It also sets the header location which redirects users to a particular page or even a specific URI. It also configures cache control.

This is an important function in web development as it helps in creating a dynamic webpage and enables the developers to make changes at runtime. However, it is also prone to errors which can cause the headers to be sent too early. This may be due to functions like print, echo or white space outside the PHP tags which can result in data being sent before the headers are set. This error is usually reported in the form of an alert or a warning in the web browser.

This function does not accept any parameter and returns a list of the response headers that are either sent or ready to be sent to the browser or client in the form of an array. It is very similar to the getallheaders() function but differs in that it lists only the headers sent or ready to be sent by PHP whereas the getallheaders() functions lists both headers sent and unsent from the server.

headers_list example

public function getName(): string
    {
        return 'dump';
    }

    public function __destruct()
    {
        if (0 === $this->clonesCount-- && !$this->isCollected && $this->dataCount) {
            $this->clonesCount = 0;
            $this->isCollected = true;

            $h = headers_list();
            $i = \count($h);
            array_unshift($h, 'Content-Type: '.\ini_get('default_mimetype'));
            while (0 !== stripos($h[$i], 'Content-Type:')) {
                --$i;
            }

            if (!\in_array(\PHP_SAPI, ['cli', 'phpdbg'], true) && stripos($h[$i], 'html')) {
                $dumper = new HtmlDumper('php://output', $this->charset);
                $dumper->setDisplayOptions(['fileLinkFormat' => $this->fileLinkFormat]);
            } else {
                $dumper = new CliDumper('php://output', $this->charset);

    public function _flush($data)
    {
        if ($this->_cancel) {
            return $data;
        }
        $contentType = null;
        $storedHeaders = array();
        $headersList = headers_list();
        foreach($this->_specificOptions['memorize_headers'] as $key=>$headerName) {
            foreach ($headersList as $headerSent) {
                $tmp = explode(':', $headerSent);
                $headerSentName = trim(array_shift($tmp));
                if (strtolower($headerName) == strtolower($headerSentName)) {
                    $headerSentValue = trim(implode(':', $tmp));
                    $storedHeaders[] = array($headerSentName, $headerSentValue);
                }
            }
        }
        $array = array(

    /** * Finds the session header amongst the headers that are to be sent, removes it, and returns * it so the caller can process it further. */
    public static function popSessionCookie(string $sessionName, #[\SensitiveParameter] string $sessionId): ?string     {
        $sessionCookie = null;
        $sessionCookiePrefix = sprintf(' %s=', urlencode($sessionName));
        $sessionCookieWithId = sprintf('%s%s;', $sessionCookiePrefix, urlencode($sessionId));
        $otherCookies = [];
        foreach (headers_list() as $h) {
            if (0 !== stripos($h, 'Set-Cookie:')) {
                continue;
            }
            if (11 === strpos($h, $sessionCookiePrefix, 11)) {
                $sessionCookie = $h;

                if (11 !== strpos($h, $sessionCookieWithId, 11)) {
                    $otherCookies[] = $h;
                }
            } else {
                $otherCookies[] = $h;
            }