silverstripe-framework/src/Control/Middleware/HTTPCacheControlMiddleware.php

<?php

namespace SilverStripe\Control\Middleware;

use InvalidArgumentException;
use SilverStripe\Control\HTTP;
use SilverStripe\Control\HTTPRequest;
use SilverStripe\Control\HTTPResponse;
use SilverStripe\Control\HTTPResponse_Exception;
use SilverStripe\Core\Config\Configurable;
use SilverStripe\Core\Injector\Injectable;
use SilverStripe\Core\Injector\Injector;
use SilverStripe\Core\Resettable;

class HTTPCacheControlMiddleware implements HTTPMiddleware, Resettable
{
    use Configurable;
    use Injectable;

    const STATE_ENABLED = 'enabled';

    const STATE_PUBLIC = 'public';

    const STATE_PRIVATE = 'private';

    const STATE_DISABLED = 'disabled';

    /**
     * Generate response for the given request
     *
     * @todo Refactor HTTP::add_cache_headers() (e.g. etag handling) into this middleware
     *
     * @param HTTPRequest $request
     * @param callable $delegate
     * @return HTTPResponse
     */
    public function process(HTTPRequest $request, callable $delegate)
    {
        try {
            $response = $delegate($request);
        } catch (HTTPResponse_Exception $ex) {
            $response = $ex->getResponse();
        }

		// If sessions exist we assume that the responses should not be cached by CDNs / proxies as we are
		// likely to be supplying information relevant to the current user only
		if ($request->getSession()->getAll()) {
			// Don't force in case user code chooses to opt in to public caching
			$this->privateCache();
		}

        HTTP::add_cache_headers($response);
        return $response;
    }

	/**
	 * List of states, each of which contains a key of standard directives.
     * Each directive should either be a numeric value, true to enable,
     * or (bool)false or null to disable.
     * Top level key states include `disabled`, `private`, `public`, `enabled`
     * in descending order of precedence.
     *
     * This allows directives to be set independently for individual states.
	 *
	 * @var array
	 */
	protected $stateDirectives = [
	    self::STATE_DISABLED => [
	        'no-cache' => true,
			'no-store' => true,
			'must-revalidate' => true,
        ],
        self::STATE_PRIVATE => [
            'private' => true,
            'must-revalidate' => true,
        ],
        self::STATE_PUBLIC => [
            'public' => true,
            'must-revalidate' => true,
        ],
        self::STATE_ENABLED => [
            'must-revalidate' => true,
        ],
    ];

    /**
     * Current state
     *
     * @var string
     */
	protected $state = self::STATE_ENABLED;

	/**
	 * Forcing level of previous setting; higher number wins
	 * Combination of consts belo
	 *w
	 * @var int
	 */
	protected $forcingLevel = 0;

	/**
	 * Forcing level forced, optionally combined with one of the below.
	 */
	const LEVEL_FORCED = 10;

	/**
	 * Forcing level caching disabled. Overrides public/private.
	 */
	const LEVEL_DISABLED = 3;

	/**
	 * Forcing level private-cached. Overrides public.
	 */
	const LEVEL_PRIVATE = 2;

	/**
	 * Forcing level public cached. Lowest priority.
	 */
	const LEVEL_PUBLIC = 1;

	/**
	 * Forcing level caching enabled.
	 */
	const LEVEL_ENABLED = 0;

	/**
	 * A list of allowed cache directives for HTTPResponses
	 *
	 * This doesn't include any experimental directives,
	 * use the config system to add to these if you want to enable them
	 *
	 * @config
	 * @var array
	 */
	private static $allowed_directives = array(
		'public',
		'private',
		'no-cache',
		'max-age',
		's-maxage',
		'must-revalidate',
		'proxy-revalidate',
		'no-store',
		'no-transform',
	);

    /**
     * Set current state. Should only be invoked internally after processing precedence rules.
     *
     * @param string $state
     * @return $this
     */
	protected function setState($state)
    {
        if (!array_key_exists($state, $this->stateDirectives)) {
            throw new InvalidArgumentException("Invalid state {$state}");
        }
        $this->state = $state;
        return $this;
    }

    /**
     * Get current state
     *
     * @return string
     */
    public function getState()
    {
        return $this->state;
    }

	/**
	 * Instruct the cache to apply a change with a given level, optionally
	 * modifying it with a force flag to increase priority of this action.
	 *
	 * If the apply level was successful, the change is made and the internal level
	 * threshold is incremented.
	 *
	 * @param int $level Priority of the given change
	 * @param bool $force If usercode has requested this action is forced to a higher priority.
	 * Note: Even if $force is set to true, other higher-priority forced changes can still
	 * cause a change to be rejected if it is below the required threshold.
	 * @return bool True if the given change is accepted, and that the internal
	 * level threshold is updated (if necessary) to the new minimum level.
	 */
	protected function applyChangeLevel($level, $force)
	{
		$forcingLevel = $level + ($force ? self::LEVEL_FORCED : 0);
		if ($forcingLevel < $this->forcingLevel) {
			return false;
		}
		$this->forcingLevel = $forcingLevel;
		return true;
	}

	/**
	 * Low level method for setting directives include any experimental or custom ones added via config.
     * You need to specify the state (or states) to apply this directive to.
     * Can also remove directives with false
	 *
     * @param array|string $states State(s) to apply this directive to
	 * @param string $directive
	 * @param int|string|bool $value Flag to set for this value. Set to false to remove, or true to set.
     * String or int value assign a specific value.
	 * @return $this
	 */
	public function setStateDirective($states, $directive, $value = true)
	{
	    if ($value === null) {
	        throw new InvalidArgumentException("Invalid directive value");
        }
		// make sure the directive is in the list of allowed directives
		$allowedDirectives = $this->config()->get('allowed_directives');
		$directive = strtolower($directive);
		if (!in_array($directive, $allowedDirectives)) {
            throw new InvalidArgumentException('Directive ' . $directive . ' is not allowed');
        }
        foreach ((array)$states as $state) {
		    if (!array_key_exists($state, $this->stateDirectives)) {
                throw new InvalidArgumentException("Invalid state {$state}");
            }
            // Set or unset directive
            if ($value === false) {
		        unset($this->stateDirectives[$state][$directive]);
            } else {
                $this->stateDirectives[$state][$directive] = $value;
            }
        }
		return $this;
	}

    /**
	 * Low level method to set directives from an associative array
	 *
     * @param array|string $states State(s) to apply this directive to
	 * @param array $directives
	 * @return $this
	 */
	public function setStateDirectivesFromArray($states, $directives)
    {
        foreach ($directives as $directive => $value) {
            $this->setStateDirective($states, $directive, $value);
        }
        return $this;
    }

	/**
	 * Low level method for removing directives
	 *
     * @param array|string $states State(s) to remove this directive from
	 * @param string $directive
	 * @return $this
	 */
	public function removeStateDirective($states, $directive)
    {
        $this->setStateDirective($states, $directive, false);
        return $this;
    }

	/**
	 * Low level method to check if a directive is currently set
	 *
     * @param string $state State(s) to apply this directive to
	 * @param string $directive
	 * @return bool
	 */
	public function hasStateDirective($state, $directive)
	{
        $directive = strtolower($directive);
        return isset($this->stateDirectives[$state][$directive]);
	}

    /**
     * Check if the current state has the given directive.
     *
     * @param string $directive
     * @return bool
     */
	public function hasDirective($directive)
    {
        return $this->hasStateDirective($this->getState(), $directive);
    }

	/**
	 * Low level method to get the value of a directive for a state.
     * Returns false if there is no directive.
     * True means the flag is set, otherwise the value of the directive.
	 *
     * @param string $state
	 * @param string $directive
	 * @return int|string|bool
	 */
	public function getStateDirective($state, $directive)
	{
		$directive = strtolower($directive);
        if (isset($this->stateDirectives[$state][$directive])) {
            return $this->stateDirectives[$state][$directive];
        }
        return false;
	}

    /**
     * Get the value of the given directive for the current state
     *
     * @param string $directive
     * @return bool|int|string
     */
    public function getDirective($directive)
    {
	    return $this->getStateDirective($this->getState(), $directive);
    }

    /**
     * Get directives for the given state
     *
     * @param string $state
     * @return array
     */
    public function getStateDirectives($state)
    {
        return $this->stateDirectives[$state];
    }

    /**
     * Get all directives for the currently active state
     *
     * @return array
     */
    public function getDirectives()
    {
        return $this->getStateDirectives($this->getState());
    }

	/**
	 * The cache should not store anything about the client request or server response.
	 * Affects all non-disabled states. Use setStateDirective() instead to set for a single state.
	 * Set the no-store directive (also removes max-age and s-maxage for consistency purposes)
	 *
	 * @param bool $noStore
	 *
	 * @return $this
	 */
	public function setNoStore($noStore = true)
	{
	    // Affect all non-disabled states
        $applyTo = [self::STATE_ENABLED, self::STATE_PRIVATE, self::STATE_PUBLIC];
        if ($noStore) {
			$this->setStateDirective($applyTo, 'no-store');
			$this->removeStateDirective($applyTo, 'max-age');
			$this->removeStateDirective($applyTo, 's-maxage');
		} else {
			$this->removeStateDirective($applyTo, 'no-store');
		}
		return $this;
	}

	/**
	 * Forces caches to submit the request to the origin server for validation before releasing a cached copy.
     * Affects all non-disabled states. Use setStateDirective() instead to set for a single state.
	 *
	 * @param bool $noCache
	 * @return $this
	 */
	public function setNoCache($noCache = true)
	{
	    // Affect all non-disabled states
	    $applyTo = [self::STATE_ENABLED, self::STATE_PRIVATE, self::STATE_PUBLIC];
		$this->setStateDirective($applyTo, 'no-cache', $noCache);
		return $this;
	}

	/**
	 * Specifies the maximum amount of time (seconds) a resource will be considered fresh.
	 * This directive is relative to the time of the request.
     * Affects all non-disabled states. Use setStateDirective() instead to set for a single state.
	 *
	 * @param int $age
	 * @return $this
	 */
	public function setMaxAge($age)
	{
	    // Affect all non-disabled states
	    $applyTo = [self::STATE_ENABLED, self::STATE_PRIVATE, self::STATE_PUBLIC];
		$this->setStateDirective($applyTo, 'max-age', $age);
		return $this;
	}

	/**
	 * Overrides max-age or the Expires header, but it only applies to shared caches (e.g., proxies)
	 * and is ignored by a private cache.
	 * Affects all non-disabled states. Use setStateDirective() instead to set for a single state.
     *
	 * @param int $age
	 * @return $this
	 */
	public function setSharedMaxAge($age)
	{
		// Affect all non-disabled states
	    $applyTo = [self::STATE_ENABLED, self::STATE_PRIVATE, self::STATE_PUBLIC];
		$this->setStateDirective($applyTo, 's-maxage', $age);
		return $this;
	}

	/**
	 * The cache must verify the status of the stale resources before using it and expired ones should not be used.
	 * Affects all non-disabled states. Use setStateDirective() instead to set for a single state.
     *
	 * @param bool $mustRevalidate
	 * @return $this
	 */
	public function setMustRevalidate($mustRevalidate = true)
	{
		$applyTo = [self::STATE_ENABLED, self::STATE_PRIVATE, self::STATE_PUBLIC];
		$this->setStateDirective($applyTo, 'must-revalidate', $mustRevalidate);
		return $this;
	}

	/**
	 * Simple way to set cache control header to a cacheable state.
     *
     * The resulting cache-control headers will be chosen from the 'enabled' set of directives.
	 *
	 * Does not set `public` directive. Usually, `setMaxAge()` is sufficient. Use `publicCache()` if this is explicitly required.
	 * See https://developers.google.com/web/fundamentals/performance/optimizing-content-efficiency/http-caching#public_vs_private
	 *
	 * @see https://docs.silverstripe.org/en/developer_guides/performance/http_cache_headers/
	 * @param bool $force Force the cache to public even if its unforced private or public
	 * @return $this
	 */
	public function enableCache($force = false)
	{
		// Only execute this if its forcing level is high enough
		if ($this->applyChangeLevel(self::LEVEL_ENABLED, $force)) {
            $this->setState(self::STATE_ENABLED);
        }
        return $this;
	}

	/**
     * Simple way to set cache control header to a non-cacheable state.
	 * Use this method over `privateCache()` if you are unsure about caching details.
     * Takes precendence over unforced `enableCache()`, `privateCache()` or `publicCache()` calls.
     *
     * The resulting cache-control headers will be chosen from the 'disabled' set of directives.
	 *
	 * Removes all state and replaces it with `no-cache, no-store, must-revalidate`. Although `no-store` is sufficient
	 * the others are added under recommendation from Mozilla (https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Cache-Control#Examples)
	 *
	 * Does not set `private` directive, use `privateCache()` if this is explicitly required.
	 * See https://developers.google.com/web/fundamentals/performance/optimizing-content-efficiency/http-caching#public_vs_private
	 *
	 * @see https://docs.silverstripe.org/en/developer_guides/performance/http_cache_headers/
	 * @param bool $force Force the cache to diabled even if it's forced private or public
	 * @return $this
	 */
	public function disableCache($force = false)
	{
		// Only execute this if its forcing level is high enough
		if ($this->applyChangeLevel(self::LEVEL_DISABLED, $force )) {
			$this->setState(self::STATE_DISABLED);
		}
		return $this;
	}

	/**
	 * Advanced way to set cache control header to a non-cacheable state.
	 * Indicates that the response is intended for a single user and must not be stored by a shared cache.
	 * A private cache (e.g. Web Browser) may store the response.
     *
     * The resulting cache-control headers will be chosen from the 'private' set of directives.
	 *
	 * @see https://docs.silverstripe.org/en/developer_guides/performance/http_cache_headers/
	 * @param bool $force Force the cache to private even if it's forced public
	 * @return $this
	 */
	public function privateCache($force = false)
	{
		// Only execute this if its forcing level is high enough
		if ($this->applyChangeLevel(self::LEVEL_PRIVATE, $force)) {
			$this->setState(self::STATE_PRIVATE);
		}
		return $this;
	}

	/**
 	 * Advanced way to set cache control header to a cacheable state.
	 * Indicates that the response may be cached by any cache. (eg: CDNs, Proxies, Web browsers)
     *
     * The resulting cache-control headers will be chosen from the 'private' set of directives.
	 *
	 * @see https://docs.silverstripe.org/en/developer_guides/performance/http_cache_headers/
	 * @param bool $force Force the cache to public even if it's private, unless it's been forced private
	 * @return $this
	 */
	public function publicCache($force = false)
	{
		// Only execute this if its forcing level is high enough
		if (!$this->applyChangeLevel(self::LEVEL_PUBLIC, $force)) {
			$this->setState(self::STATE_PUBLIC);
		}
		return $this;
	}

	/**
	 * Generate and add the `Cache-Control` header to a response object
	 *
	 * @param HTTPResponse $response
	 *
	 * @return $this
	 */
	public function applyToResponse($response)
	{
		$headers = $this->generateHeaders();
		foreach ($headers as $name => $value) {
			$response->addHeader($name, $value);
		}
		return $this;
	}

	/**
	 * Generate the cache header
	 *
	 * @return string
	 */
	protected function generateCacheHeader()
	{
		$cacheControl = [];
		foreach ($this->getDirectives() as $directive => $value) {
			if ($value === true) {
				$cacheControl[] = $directive;
			} else {
				$cacheControl[] = $directive . '=' . $value;
			}
		}
		return implode(', ', $cacheControl);
	}

	/**
	 * Generate all headers to output
	 *
	 * @return array
	 */
	public function generateHeaders()
	{
		return array(
			'Cache-Control' => $this->generateCacheHeader(),
		);
	}

	/**
	 * Reset registered http cache control and force a fresh instance to be built
	 */
	public static function reset()
    {
		Injector::inst()->unregisterNamedObject(__CLASS__);
	}
}