What are the limitations of using PHP/HTTP to determine which file is older between two files on different servers?

When comparing the modification dates of files on different servers using PHP and HTTP, the main limitation is that HTTP does not provide a way to directly access file metadata like modification dates. One solution is to use FTP or SSH to connect to the remote servers and retrieve the file modification dates. This way, you can accurately compare the modification dates of the files on different servers. 

<?php

// Connect to the remote server via FTP
$ftp_server = 'example.com';
$ftp_user = 'username';
$ftp_pass = 'password';

$conn_id = ftp_connect($ftp_server);
$login_result = ftp_login($conn_id, $ftp_user, $ftp_pass);

// Get the modification date of the remote file
$remote_file = '/path/to/remote/file.txt';
$remote_modification_time = ftp_mdtm($conn_id, $remote_file);

// Get the modification date of the local file
$local_file = '/path/to/local/file.txt';
$local_modification_time = filemtime($local_file);

// Compare the modification dates
if ($remote_modification_time > $local_modification_time) {
    echo 'The remote file is older.';
} elseif ($remote_modification_time < $local_modification_time) {
    echo 'The local file is older.';
} else {
    echo 'Both files have the same modification date.';
}

// Close the FTP connection
ftp_close($conn_id);

?>

Keywords

PHP HTTP file comparison timestamp cross-server

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