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Chapter 8. Web Basics > Program: Abusive User Checker
Recipe 8.28. Program: Abusive User Checker
Shared memory's speed makes it an ideal way to store data different web server processes need to access frequently when a file or database would be too slow. Example 8-7 shows the pc_Web_Abuse_Check class, which uses shared memory to track accesses to web pages in order to cut off users that abuse a site by bombarding it with requests.
Example 8-7. pc_Web_Abuse_Check class
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Show All class pc_Web_Abuse_Check {
var $sem_key;
var $shm_key;
var $shm_size;
var $recalc_seconds;
var $pageview_threshold;
var $sem;
var $shm;
var $data;
var $exclude;
var $block_message;
function pc_Web_Abuse_Check() {
$this->sem_key = 5000;
$this->shm_key = 5001;
$this->shm_size = 16000;
$this->recalc_seconds = 60;
$this->pageview_threshold = 30;
$this->exclude['/ok-to-bombard.html'] = 1;
$this->block_message =<<<END
<html>
<head><title>403 Forbidden</title></head>
<body>
<h1>Forbidden</h1>
You have been blocked from retrieving pages from this site due to
abusive repetitive activity from your account. If you believe this
is an error, please contact
<a href="mailto:webmaster@example.com?subject=Site+Abuse">webmaster@example.com</a>.
</body>
</html>
END;
}
function get_lock() {
$this->sem = sem_get($this->sem_key,1,0600);
if (sem_acquire($this->sem)) {
$this->shm = shm_attach($this->shm_key,$this->shm_size,0600);
$this->data = shm_get_var($this->shm,'data');
} else {
error_log("Can't acquire semaphore $this->sem_key");
}
}
function release_lock() {
if (isset($this->data)) {
shm_put_var($this->shm,'data',$this->data);
}
shm_detach($this->shm);
sem_release($this->sem);
}
function check_abuse($user) {
$this->get_lock();
if ($this->data['abusive_users'][$user]) {
// if user is on the list release the semaphore & memory
$this->release_lock();
// serve the "you are blocked" page
header('HTTP/1.0 403 Forbidden');
print $this->block_message;
return true;
} else {
// mark this user looking at a page at this time
$now = time();
if (! $this->exclude[$_SERVER['PHP_SELF']]) {
$this->data['user_traffic'][$user]++;
}
// (sometimes) tote up the list and add bad people
if (! $this->data['traffic_start']) {
$this->data['traffic_start'] = $now;
} else {
if (($now - $this->data['traffic_start']) > $this->recalc_seconds) {
while (list($k,$v) = each($this->data['user_traffic'])) {
if ($v > $this->pageview_threshold) {
$this->data['abusive_users'][$k] = $v;
// log the user's addition to the abusive user list
error_log("Abuse: [$k] (from ".$_SERVER['REMOTE_ADDR'].')');
}
}
$this->data['traffic_start'] = $now;
$this->data['user_traffic'] = array();
}
}
$this->release_lock();
}
return false;
}
}
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