Add simple file logging

webmention.php

<?php

# Licensed under a CC0 1.0 Universal (CC0 1.0) Public Domain Dedication
# http://creativecommons.org/publicdomain/zero/1.0/
#
# Webmention Emailer
# ------------------
# 
#  An incremental evolution of Jeremy Keith's "minimum viable" webmention,
# I've added some minimal code to have webmentions emailed to an address
# of your choosing. Also logs the webmention with the sender's IP.

if (!isset($_POST['source']) || !isset($_POST['target'])) {
  header($_SERVER['SERVER_PROTOCOL'] . ' 400 Bad Request');
  exit;
}

ob_start();
$ch = curl_init($_POST['source']);
curl_setopt($ch,CURLOPT_USERAGENT,'mydomain (webmention.org)');
curl_setopt($ch,CURLOPT_HEADER,0);
$ok = curl_exec($ch);
curl_close($ch);
$source = ob_get_contents();
ob_end_clean();

header($_SERVER['SERVER_PROTOCOL'] . ' 202 Accepted');

if (stristr($source, $_POST['target'])) {

  /* Configure these variables.
   * If you're sending "from" yourself to yourself then there
   * will be a some duplication :)
   */
  $to_address = 'you@yourdomain.net';
  $from_address = 'sender@sender.com';
  $from_name = 'Sender Real Name';
  $reply_to = 'Real Name <reply@sender.com>';
  $subject = 'Webmention from '.$_POST['source'];
  $logfile = '/full/path/to/webmentions.log'; /* Make sure file is writeable */
  $charset = 'UTF-8';
  $sep = "\r\n";     /* Change to '\n' for Windows */
  
  $log  = "[".date("c")."] User: ".$_SERVER['REMOTE_ADDR']
    .' - Valid webmention on: <'.$_POST['source']
    .'> (target: <'.$_POST['target'].'>)'.PHP_EOL;
  file_put_contents($logfile, $log, FILE_APPEND);

  $headers = "From: $from_name <$from_address>".
    $sep.'Reply-To: ' . $reply_to .
	$sep.'X-Mailer: Mydomain (webmention.org)'.
	$sep.'Content-Transfer-Encoding: 8bit'.
	$sep.'Content-Type: text/plain; charset="'.$charset.'"'.
	$sep;

  $body = 'Valid webmention received!'.
    $sep.
    $sep.'- Mention found at: '.$_POST['source'].
    $sep.
    $sep.'- Page mentioned  : '.$_POST['target'];

  mail($to_address, $subject, $body, $headers, '-f'.$from_address);

}

?>