What are the potential pitfalls of relying on client-side caching mechanisms when developing PHP applications?

Potential pitfalls of relying on client-side caching mechanisms when developing PHP applications include the risk of outdated or incorrect data being displayed to users, security vulnerabilities due to sensitive information being stored on the client-side, and limited control over cache expiration and invalidation. To mitigate these risks, developers should implement server-side caching mechanisms to control the caching behavior and ensure the accuracy and security of cached data.

// Example of implementing server-side caching in PHP using the APCu extension

$key = 'cached_data';
$ttl = 3600; // Cache expiration time in seconds

if ($data = apcu_fetch($key)) {
    // Use cached data
    echo $data;
} else {
    // Retrieve data from database or API
    $data = fetchDataFromSource();

    // Store data in cache
    apcu_store($key, $data, $ttl);

    // Display data
    echo $data;
}

function fetchDataFromSource() {
    // Code to fetch data from database or API
    return 'Data fetched from source';
}