proxy_cache.c

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            char *name = vary;
            const char *h1, *h2;

            /* isolate header name */
            while (*vary && !ap_isspace(*vary) && (*vary != ','))
                ++vary;
            while (*vary && (ap_isspace(*vary) || (*vary == ','))) {
                *vary = '\0';
                ++vary;
            }

            /*
             * is this header in the request and the header in the cached
             * request identical? If not, we give up and do a straight get
             */
            h1 = ap_table_get(r->headers_in, name);
            h2 = ap_table_get(c->req_hdrs, name);
            if (h1 == h2) {
                /* both headers NULL, so a match - do nothing */
            }
            else if (h1 && h2 && !strcmp(h1, h2)) {
                /* both headers exist and are equal - do nothing */
            }
            else {

                /* headers do not match, so Vary failed */
                c->fp = cachefp;
                ap_log_error(APLOG_MARK, APLOG_DEBUG | APLOG_NOERRNO, r->server, "Vary header mismatch - object must be fetched from scratch. Declining.");
                return DECLINED;
            }
        }
    }


    /*
     * We now want to check if our cached data is still fresh. This depends
     * on a few things, in this order:
     * 
     * - RFC2616 14.9.4 End to end reload, Cache-Control: no-cache no-cache in
     * either the request or the cached response means that we must
     * revalidate the request unconditionally, overriding any expiration
     * mechanism. It's equivalent to max-age=0,must-revalidate.
     * 
     * - RFC2616 14.32 Pragma: no-cache This is treated the same as
     * Cache-Control: no-cache.
     * 
     * - RFC2616 14.9.3 Cache-Control: max-stale, must-revalidate,
     * proxy-revalidate if the max-stale request header exists, modify the
     * stale calculations below so that an object can be at most <max-stale>
     * seconds stale before we request a revalidation, _UNLESS_ a
     * must-revalidate or proxy-revalidate cached response header exists to
     * stop us doing this.
     * 
     * - RFC2616 14.9.3 Cache-Control: s-maxage the origin server specifies the
     * maximum age an object can be before it is considered stale. This
     * directive has the effect of proxy|must revalidate, which in turn means
     * simple ignore any max-stale setting.
     * 
     * - RFC2616 14.9.4 Cache-Control: max-age this header can appear in both
     * requests and responses. If both are specified, the smaller of the two
     * takes priority.
     * 
     * - RFC2616 14.21 Expires: if this request header exists in the cached
     * entity, and it's value is in the past, it has expired.
     * 
     */

    /* calculate age of object */
    age = ap_proxy_current_age(c, age_c);

    /* extract s-maxage */
    if (cc_cresp && ap_proxy_liststr(cc_cresp, "s-maxage", &val))
        smaxage = atoi(val);
    else
        smaxage = -1;

    /* extract max-age from request */
    if (cc_req && ap_proxy_liststr(cc_req, "max-age", &val))
        maxage_req = atoi(val);
    else
        maxage_req = -1;

    /* extract max-age from response */
    if (cc_cresp && ap_proxy_liststr(cc_cresp, "max-age", &val))
        maxage_cresp = atoi(val);
    else
        maxage_cresp = -1;

    /*
     * if both maxage request and response, the smaller one takes priority
     */
    if (-1 == maxage_req)
        maxage = maxage_cresp;
    else if (-1 == maxage_cresp)
        maxage = maxage_req;
    else
        maxage = MIN(maxage_req, maxage_cresp);

    /* extract max-stale */
    if (cc_req && ap_proxy_liststr(cc_req, "max-stale", &val))
        maxstale = atoi(val);
    else
        maxstale = 0;

    /* extract min-fresh */
    if (cc_req && ap_proxy_liststr(cc_req, "min-fresh", &val))
        minfresh = atoi(val);
    else
        minfresh = 0;

    /* override maxstale if must-revalidate or proxy-revalidate */
    if (maxstale && ((cc_cresp && ap_proxy_liststr(cc_cresp, "must-revalidate", NULL)) || (cc_cresp && ap_proxy_liststr(cc_cresp, "proxy-revalidate", NULL))))
        maxstale = 0;

    if (cachefp != NULL &&

    /* handle no-cache */
        !((cc_req && ap_proxy_liststr(cc_req, "no-cache", NULL)) ||
          (pragma_req && ap_proxy_liststr(pragma_req, "no-cache", NULL)) ||
          (cc_cresp && ap_proxy_liststr(cc_cresp, "no-cache", NULL)) ||
      (pragma_cresp && ap_proxy_liststr(pragma_cresp, "no-cache", NULL))) &&

    /* handle expiration */
        ((-1 < smaxage && age < (smaxage - minfresh)) ||
         (-1 < maxage && age < (maxage + maxstale - minfresh)) ||
         (c->expire != BAD_DATE && age < (c->expire - c->date + maxstale - minfresh)))
        ) {

        /* it's fresh darlings... */

        ap_log_error(APLOG_MARK, APLOG_DEBUG | APLOG_NOERRNO, r->server, "Unexpired data available");

        /* set age header on response */
        ap_table_set(c->hdrs, "Age",
                     ap_psprintf(r->pool, "%lu", (unsigned long)age));

        /* add warning if maxstale overrode freshness calculation */
        if (!((-1 < smaxage && age < smaxage) ||
              (-1 < maxage && age < maxage) ||
              (c->expire != BAD_DATE && (c->expire - c->date) > age))) {
            /* make sure we don't stomp on a previous warning */
            ap_table_merge(c->hdrs, "Warning", "110 Response is stale");
        }

        /* check conditionals (If-Modified-Since, etc) */
        c->xcache = ap_pstrcat(r->pool, "HIT from ", ap_get_server_name(r), NULL);
        return ap_proxy_cache_conditional(r, c, cachefp);


    }

    /*
     * at this point we have determined our cached data needs revalidation
     * but first - we check 1 thing:
     * 
     * RFC2616 14.9.4 - if "only-if-cached" specified, send a 504 Gateway
     * Timeout - we're not allowed to revalidate the object
     */
    if (ap_proxy_liststr(cc_req, "only-if-cached", NULL)) {
        if (cachefp)
            ap_pclosef(r->pool, ap_bfileno(cachefp, B_WR));
        return HTTP_GATEWAY_TIME_OUT;
    }


    /*
     * If we already have cached data and a last-modified date, and it is not
     * a head request, then add an If-Modified-Since.
     * 
     * If we also have an Etag, then the object must have come from an HTTP/1.1
     * server. Add an If-None-Match as well.
     * 
     * See RFC2616 13.3.4
     */

    if (cachefp != NULL && !r->header_only) {

        const char *etag = ap_table_get(c->hdrs, "Etag");

        /* If-Modified-Since */
        if (c->lmod != BAD_DATE) {
            /*
             * use the later of the one from the request and the
             * last-modified date from the cache
             */
            if (c->ims == BAD_DATE || c->ims < c->lmod) {
                const char *q;

                if ((q = ap_table_get(c->hdrs, "Last-Modified")) != NULL)
                    ap_table_set(r->headers_in, "If-Modified-Since", (char *)q);
            }
        }

        /* If-None-Match */
        if (etag) {
            ap_table_set(r->headers_in, "If-None-Match", etag);
        }

    }


    c->fp = cachefp;

    ap_log_error(APLOG_MARK, APLOG_DEBUG | APLOG_NOERRNO, r->server, "Local copy not present or expired. Declining.");

    return DECLINED;
}

/*
 * Having read the response from the client, decide what to do
 * If the response is not cachable, then delete any previously cached
 * response, and copy data from remote server to client.
 * Functions:
 *  parse dates
 *  check for an uncachable response
 *  calculate an expiry date, if one is not provided
 *  if the remote file has not been modified, then return the document
 *  from the cache, maybe updating the header line
 *  otherwise, delete the old cached file and open a new temporary file
 */
int ap_proxy_cache_update(cache_req *c, table *resp_hdrs,
                              const int is_HTTP1, int nocache)
{
#if defined(ULTRIX_BRAIN_DEATH) || defined(SINIX_D_RESOLVER_BUG)
    extern char *mktemp(char *template);
#endif
    request_rec *r = c->req;
    char *p;
    const char *expire, *lmods, *dates, *clen;
    time_t expc, date, lmod, now;
    char buff[17 * 7 + 1];
    void *sconf = r->server->module_config;
    proxy_server_conf *conf =
    (proxy_server_conf *)ap_get_module_config(sconf, &proxy_module);
    const char *cc_resp;
    table *req_hdrs;

    cc_resp = ap_table_get(resp_hdrs, "Cache-Control");

    c->tempfile = NULL;

    /* we've received the response from the origin server */

    /*
     * read expiry date; if a bad date, then leave it so the client can read
     * it
     */
    expire = ap_table_get(resp_hdrs, "Expires");
    if (expire != NULL)
        expc = ap_parseHTTPdate(expire);
    else
        expc = BAD_DATE;

    /* read the last-modified date; if the date is bad, then delete it */
    lmods = ap_table_get(resp_hdrs, "Last-Modified");
    if (lmods != NULL) {
        lmod = ap_parseHTTPdate(lmods);
        if (lmod == BAD_DATE) {
            /* kill last modified date */
            lmods = NULL;
        }
    }
    else
        lmod = BAD_DATE;


    /*
     * what responses should we not cache?
     * 
     * At this point we decide based on the response headers whether it is
     * appropriate _NOT_ to cache the data from the server. There are a whole
     * lot of conditions that prevent us from caching this data. They are
     * tested here one by one to be clear and unambiguous.
     */

    /*
     * RFC2616 13.4 we are allowed to cache 200, 203, 206, 300, 301 or 410 We
     * don't cache 206, because we don't (yet) cache partial responses. We
     * include 304 Not Modified here too as this is the origin server telling
     * us to serve the cached copy.
     */
    if ((r->status != HTTP_OK && r->status != HTTP_NON_AUTHORITATIVE && r->status != HTTP_MULTIPLE_CHOICES && r->status != HTTP_MOVED_PERMANENTLY && r->status != HTTP_NOT_MODIFIED) ||

    /* if a broken Expires header is present, don't cache it */
        (expire != NULL && expc == BAD_DATE) ||

    /*
     * if the server said 304 Not Modified but we have no cache file - pass
     * this untouched to the user agent, it's not for us.
     */
        (r->status == HTTP_NOT_MODIFIED && (c == NULL || c->fp == NULL)) ||

    /*
     * 200 OK response from HTTP/1.0 and up without a Last-Modified header
     */
        (r->status == HTTP_OK && lmods == NULL && is_HTTP1) ||

    /* HEAD requests */
        r->header_only ||

    /*
     * RFC2616 14.9.2 Cache-Control: no-store response indicating do not
     * cache, or stop now if you are trying to cache it
     */
        ap_proxy_liststr(cc_resp, "no-store", NULL) ||

    /*
     * RFC2616 14.9.1 Cache-Control: private this object is marked for this
     * user's eyes only. Behave as a tunnel.
     */
        ap_proxy_liststr(cc_resp, "private", NULL) ||

    /*
     * RFC2616 14.8 Authorisation: if authorisation is included in the
     * request, we don't cache, but we can cache if the following exceptions
     * are true: 1) If Cache-Control: s-maxage is included 2) If
     * Cache-Control: must-revalidate is included 3) If Cache-Control: public
     * is included
     */
        (ap_table_get(r->headers_in, "Authorization") != NULL

         && !(ap_proxy_liststr(cc_resp, "s-maxage", NULL) || ap_proxy_liststr(cc_resp, "must-revalidate", NULL) || ap_proxy_liststr(cc_resp, "public", NULL))
         ) ||

    /* or we've been asked not to cache it above */
        nocache) {

        ap_log_error(APLOG_MARK, APLOG_DEBUG | APLOG_NOERRNO, r->server, "Response is not cacheable, unlinking %s", c->filename);

        /* close the file */
        if (c->fp != NULL) {
            ap_pclosef(r->pool, ap_bfileno(c->fp, B_WR));
            c->fp = NULL;
        }

        /* delete the previously cached file */
        if (c->filename)
            unlink(c->filename);
        return DECLINED;        /* send data to client but not cache */
    }


    /*
     * It's safe to cache the response.
     * 
     * We now want to update the cache file header information with the new
     * date, last modified, expire and content length and write it away to
     * our cache file. First, we determine these values from the response,
     * using heuristics if appropriate.
     * 
     * In addition, we make HTTP/1.1 age calculations and write them away too.
     */

    /* Read the date. Generate one if one is not supplied */