Question

How to check whether a page has been updated without downloading the entire webpage in Php? Whether I need to look in at the header?

Answer 1

One possibility is to check the LastModified header. You can download just the headers by issuing a HEAD request. The server responds back with the HTTP headers only and you can inspect the last modified header and/or the content length header to detect changes.

Last-modified "Mon, 03 Jan 2011 13:02:54 GMT"

One thing to note is that the HTTP server does not need to send this header so this would not work in all cases. The PHP function get_headers will fetch these for you.

// By default get_headers uses a GET request to fetch the headers. If you
// want to send a HEAD request instead, you can do so using a stream context:
stream_context_set_default(
    array(
        'http' => array(
            'method' => 'HEAD'
        )
    )
);
$headers = get_headers('http://example.com');