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From Anthony Heading <heading_anth...@jpmorgan.com>
Subject mod_proxy/5834: http cacheing appears seriously broken: I suspect line c->hdrs = resp_hdrs;
Date Mon, 06 Mar 2000 17:05:49 GMT

>Number:         5834
>Category:       mod_proxy
>Synopsis:       http cacheing appears seriously broken: I suspect line c->hdrs = resp_hdrs;
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    apache
>State:          open
>Class:          sw-bug
>Submitter-Id:   apache
>Arrival-Date:   Mon Mar 06 09:10:00 PST 2000
>Originator:     heading_anthony@jpmorgan.com
>Release:        1.3.12
Solaris 2.5.1;  Linux 2.2.14
Expired cache data is *always* refetched from the server, even if 304-not-
modified was returned from the probe.   Further, many headers including
for example Content-Length are lost. 

Observable example effect is when running an http-based Debian package
update through an Apache cache, it fails with a "Size mismatch error"

What is happening is the following:

When the cache contains expired data, (ap_proxy_cache_check returns DECLINED),
I read that an "If-Modified-Since" request is sent to the server to cheeck
the data validity.   If 304 (not modified) is returned, by my experiments it
seems that the accompanying returned headers are minimal (i.e. no
application type or content length or so on).

However proxy_http.c line 452 discards the cache headers for these
minimal headers!   Much of the later code suggests that this is
wrong - the resp_headers are passed into ap_proxy_cache_update directly
anyhow so there's no need to do this, and then ap_proxy_cache_update
very clearly makes the following call sequence:

    expire = ap_table_get(resp_hdrs, "Expires");
    if (expire == NULL && c->fp != NULL) {
		/* no expiry data sent in response */
        expire = ap_table_get(c->hdrs, "Expires");

This is obviously inconsistent with a design where the caller
has set these pointers equal!

These minimal headers are then forwarded to the original client, who thus
loses any other headers info, and ap_proxy_cache_update declines to use
the (valid) cache data since it no longer knows what it is!!!!

wget -d http://www.google.com:80/images/Title_Left.gif

Note that on a clean cache machine, the first call will work fine
(full headers and Content-Length passed to the client) but
second and subsequent calls will
	1) fail to use the cache;
	2) not show a Content-Length header (or any others)
Simply removing the line mentioned above improves things for me, but
I'm not an expert on the protocol.
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