channel neutral tag handling for FOSHttpCache

TagHandler.php

<?php

/**
 * Handle tagging. Both request and response are passed, 
 * so that tags can either be added to the response, or 
 * recorded with the request information.
 */
interface TagHandler
{
    /**
     * Remove/Expire cache objects based on cache tags
     */
    public function invalidateTags(array $tags);

    /**
     * Record tag information.
     *
     * Either on the response (e.g. tags header) or out of band, linked to the
     * request.
     *
     * @return ResponseInterface
     */
    public function tagPsr(RequestInterface $request, ResponseInterface $response, array $tags);

    /**
     * Record tag information.
     *
     * Either sending a plain header, or recording the tags out of band, linked to the URL.
     */
    public function tagPlain($url, array $tags);

    /**
     * Same as tagPsr but for symfony. in bundle only.
     */
    public function tagSymfony(Request, Response, array $tags);
}

// implementation detail, not part of the interface
/**
 * Get the value for the HTTP tag header.
 */
public function getTagsHeaderValue(array $tags);
/**
 * Get the HTTP header name that will hold cache tags.
 */
public function getTagsHeaderName();

the user should not have to care about the tag implementation, whether its in band or out of band. that is why i would always pass the Request and let the tag handler decide whether to store a map of tag to response id or request url or whatever, or to put the tags into the response.