How can PHP developers ensure the safe usage of URLs in file uploads and external connections without compromising security?

To ensure the safe usage of URLs in file uploads and external connections in PHP without compromising security, developers should validate and sanitize the URLs before using them. This can be done by checking the URL format, ensuring it starts with "http://" or "https://", and using functions like filter_var() with the FILTER_VALIDATE_URL filter to validate URLs. Additionally, developers should avoid using user-inputted URLs directly in functions like file_get_contents() to prevent security vulnerabilities.

// Validate and sanitize URL before using it
$url = filter_var($url, FILTER_VALIDATE_URL);
if ($url === false) {
    // Invalid URL, handle error
} else {
    // URL is valid, proceed with safe usage
}