mod_cache.c

Apache HTTP Server 是一个功能强大的灵活的与HTTP/1.1相兼容的web服务器.这里给出的是Apache HTTP服务器的源码。

    /* read expiry date; if a bad date, then leave it so the client can
     * read it 
     */
    exps = apr_table_get(r->err_headers_out, "Expires");
    if (exps == NULL) {
        exps = apr_table_get(r->headers_out, "Expires");
    }
    if (exps != NULL) {
        if (APR_DATE_BAD == (exp = apr_date_parse_http(exps))) {
            exps = NULL;
        }
    }
    else {
        exp = APR_DATE_BAD;
    }

    /* read the last-modified date; if the date is bad, then delete it */
    lastmods = apr_table_get(r->err_headers_out, "Last-Modified");
    if (lastmods == NULL) {
        lastmods = apr_table_get(r->headers_out, "Last-Modified");
    }
    if (lastmods != NULL) {
        if (APR_DATE_BAD == (lastmod = apr_date_parse_http(lastmods))) {
            lastmods = NULL;
        }
    }
    else {
        lastmod = APR_DATE_BAD;
    }

    conf = (cache_server_conf *) ap_get_module_config(r->server->module_config, &cache_module);
    /* read the etag and cache-control from the entity */
    etag = apr_table_get(r->err_headers_out, "Etag");
    if (etag == NULL) {
        etag = apr_table_get(r->headers_out, "Etag");
    }
    cc_out = apr_table_get(r->err_headers_out, "Cache-Control");
    if (cc_out == NULL) {
        cc_out = apr_table_get(r->headers_out, "Cache-Control");
    }

    /*
     * 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. 
     */
    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) {
        /* 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.
         */
        reason = apr_psprintf(p, "Response status %d", r->status);
    } 
    else if (exps != NULL && exp == APR_DATE_BAD) {
        /* if a broken Expires header is present, don't cache it */
        reason = apr_pstrcat(p, "Broken expires header: ", exps, NULL);
    }
    else if (r->args && exps == NULL) {
        /* if query string present but no expiration time, don't cache it
         * (RFC 2616/13.9)
         */
        reason = "Query string present but no expires header";
    }
    else if (r->status == HTTP_NOT_MODIFIED &&
             !cache->handle && !cache->stale_handle) {
        /* 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.
         */
        reason = "HTTP Status 304 Not Modified";
    }
    else if (r->status == HTTP_OK && lastmods == NULL && etag == NULL 
             && (exps == NULL) && (conf->no_last_mod_ignore ==0)) {
        /* 200 OK response from HTTP/1.0 and up without Last-Modified,
         * Etag, or Expires headers.
         */
        /* Note: mod-include clears last_modified/expires/etags - this
         * is why we have an optional function for a key-gen ;-) 
         */
        reason = "No Last-Modified, Etag, or Expires headers";
    }
    else if (r->header_only) {
        /* HEAD requests */
        reason = "HTTP HEAD request";
    }
    else if (ap_cache_liststr(NULL, cc_out, "no-store", NULL)) {
        /* RFC2616 14.9.2 Cache-Control: no-store response
         * indicating do not cache, or stop now if you are
         * trying to cache it */
        reason = "Cache-Control: no-store present";
    }
    else if (ap_cache_liststr(NULL, cc_out, "private", NULL)) {
        /* RFC2616 14.9.1 Cache-Control: private
         * this object is marked for this user's eyes only. Behave
         * as a tunnel.
         */
        reason = "Cache-Control: private present";
    }
    else if (apr_table_get(r->headers_in, "Authorization") != NULL
             && !(ap_cache_liststr(NULL, cc_out, "s-maxage", NULL)
                  || ap_cache_liststr(NULL, cc_out, "must-revalidate", NULL)
                  || ap_cache_liststr(NULL, cc_out, "public", 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
         */
        reason = "Authorization required";
    }
    else if (r->no_cache) {
        /* or we've been asked not to cache it above */
        reason = "no_cache present";
    }

    if (reason) {
        ap_log_error(APLOG_MARK, APLOG_DEBUG, 0, r->server,
                     "cache: %s not cached. Reason: %s", url, reason);
        /* remove this object from the cache 
         * BillS Asks.. Why do we need to make this call to remove_url?
         * leave it in for now..
         */
        cache_remove_url(r, url);

        /* remove this filter from the chain */
        ap_remove_output_filter(f);

        /* ship the data up the stack */
        return ap_pass_brigade(f->next, in);
    }

    /* Make it so that we don't execute this path again. */
    cache->in_checked = 1;

    /* Set the content length if known. 
     */
    cl = apr_table_get(r->err_headers_out, "Content-Length");
    if (cl == NULL) {
        cl = apr_table_get(r->headers_out, "Content-Length");
    }
    if (cl) {
#if 0
        char *errp;
        if (apr_strtoff(&size, cl, &errp, 10) || *errp || size < 0) {
            cl = NULL; /* parse error, see next 'if' block */
        }
#else
        size = apr_atoi64(cl);
        if (size < 0) {
            cl = NULL;
        }
#endif
    }

    if (!cl) {
        /* if we don't get the content-length, see if we have all the 
         * buckets and use their length to calculate the size 
         */
        apr_bucket *e;
        int all_buckets_here=0;
        int unresolved_length = 0;
        size=0;
        for (e = APR_BRIGADE_FIRST(in);
             e != APR_BRIGADE_SENTINEL(in);
             e = APR_BUCKET_NEXT(e))
        {
            if (APR_BUCKET_IS_EOS(e)) {
                all_buckets_here=1;
                break;
            }
            if (APR_BUCKET_IS_FLUSH(e)) {
                unresolved_length = 1;
                continue;
            }
            if (e->length == (apr_size_t)-1) {
                break;
            }
            size += e->length;
        }
        if (!all_buckets_here) {
            size = -1;
        }
    }

    /* It's safe to cache the response.
     *
     * There are two possiblities at this point:
     * - cache->handle == NULL. In this case there is no previously
     * cached entity anywhere on the system. We must create a brand
     * new entity and store the response in it.
     * - cache->stale_handle != NULL. In this case there is a stale
     * entity in the system which needs to be replaced by new
     * content (unless the result was 304 Not Modified, which means
     * the cached entity is actually fresh, and we should update
     * the headers).
     */

    /* Did we have a stale cache entry that really is stale? */
    if (cache->stale_handle) {
        if (r->status == HTTP_NOT_MODIFIED) {
            /* Oh, hey.  It isn't that stale!  Yay! */
            cache->handle = cache->stale_handle;
            info = &cache->handle->cache_obj->info;
        }
        else {
            /* Oh, well.  Toss it. */
            cache->provider->remove_entity(cache->stale_handle);
            /* Treat the request as if it wasn't conditional. */
            cache->stale_handle = NULL;
        }
    }

    /* no cache handle, create a new entity */
    if (!cache->handle) {
        rv = cache_create_entity(r, url, size);
        info = apr_pcalloc(r->pool, sizeof(cache_info));
        /* We only set info->status upon the initial creation. */
        info->status = r->status;
    }

    if (rv != OK) {
        /* Caching layer declined the opportunity to cache the response */
        ap_remove_output_filter(f);
        return ap_pass_brigade(f->next, in);
    }

    ap_log_error(APLOG_MARK, APLOG_DEBUG, 0, r->server,
                 "cache: Caching url: %s", url);

    /*
     * 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 */
    dates = apr_table_get(r->err_headers_out, "Date");
    if (dates != NULL) {
        date_in_errhdr = 1;
    }
    else {
        dates = apr_table_get(r->headers_out, "Date");
    }
    if (dates != NULL) {
        info->date = apr_date_parse_http(dates);
    }
    else {
        info->date = APR_DATE_BAD;
    }

    now = apr_time_now();
    if (info->date == APR_DATE_BAD) {  /* No, or bad date */
        char *dates;
        /* no date header (or bad header)! */
        /* add one; N.B. use the time _now_ rather than when we were checking
         * the cache 
         */
        if (date_in_errhdr == 1) {
            apr_table_unset(r->err_headers_out, "Date");
        }
        date = now;
        dates = apr_pcalloc(r->pool, MAX_STRING_LEN);
        apr_rfc822_date(dates, now);
        apr_table_set(r->headers_out, "Date", dates);
        ap_log_error(APLOG_MARK, APLOG_DEBUG, 0, r->server,
                     "cache: Added date header");
        info->date = date;
    }
    else {
        date = info->date;
    }

    /* set response_time for HTTP/1.1 age calculations */
    info->response_time = now;

    /* get the request time */
    info->request_time = r->request_time;

    /* check last-modified date */
    if (lastmod != APR_DATE_BAD && lastmod > date) {
        /* if it's in the future, then replace by date */
        lastmod = date;
        lastmods = dates;
        ap_log_error(APLOG_MARK, APLOG_DEBUG, 0, 
                     r->server,
                     "cache: Last modified is in the future, "
                     "replacing with now");
    }
    info->lastmod = lastmod;

    /* if no expiry date then
     *   if lastmod
     *      expiry date = date + min((date - lastmod) * factor, maxexpire)
     *   else
     *      expire date = date + defaultexpire
     */
    if (exp == APR_DATE_BAD) {
        /* if lastmod == date then you get 0*conf->factor which results in
         *   an expiration time of now. This causes some problems with
         *   freshness calculations, so we choose the else path...
         */
        if ((lastmod != APR_DATE_BAD) && (lastmod < date)) {
            apr_time_t x = (apr_time_t) ((date - lastmod) * conf->factor);

            if (x > conf->maxex) {
                x = conf->maxex;
            }
            exp = date + x;
        }
        else {
            exp = date + conf->defex;