Date: Thu, 21 Aug 1997 15:32:32 +0100 (BST)
From: Paul Sutton <paul@ukweb.com>
To: new-httpd@apache.org
Subject: Re: Redirect to negotiated docs (PR#649) 
In-Reply-To: <Pine.LNX.3.95.970817170458.11205F-100000@aardvark.ukweb.com>
Message-ID: <Pine.LNX.3.95.970821152639.19539E-100000@aardvark.ukweb.com>
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On Sun, 17 Aug 1997, Paul Sutton wrote:
> On Fri, 15 Aug 1997, Roy T. Fielding wrote:
> > >Yeah, good point. The server is configured to content negotiate where
> > >there is only one variant to pick from. Kind of like an automatic
> > >permanent redirect but without the cache-ability. So presumably Apache
> > >could spot the fact that there is only one variant and then not set
> > >r->no_cache. 
> > 
> > Yes.  In fact, I thought it was doing that already.  It's crazy not to.
> > Multiviews with only a single variant is *not* negotiation.
> 
> Absolutely. Unless someone else volunteers, I'll knock up a patch for
> this. 

Ok, how about this. As a reminder, mod_negotiation marks *all* responses
to HTTP/1.0 (and earlier) requests as being uncacheable, unless explicitly
told to make them cacheable with CacheNegotiatedDocs. This is to prevent
(HTTP/1.0) browsers and proxies caching one variant which may not be the
correct one for subsequent requests. The issue is that if you are using
mod_negotiation in a trivial way to map (say) requests for index onto
index.html *with no other variants*, Apache makes your responses
non-cacheable when they probably are safely cacheable. 

This patch makes responses from mod_negotiation cacheable in the following
circumstances:

  *  Variants are found by multiviews (i.e. looking on the disk, rather
     than reading a .var file) AND
  *  there was only one matching variant found on disk AND
  *  request version is HTTP/1.0 or earlier

(responses to HTTP/1.1 clients are not forced to be uncacheable in any
cases since HTTP/1.1 requires clients to know enough to determine if a
negotiated resource is cacheable).

//pcs

Index: mod_negotiation.c
===================================================================
RCS file: /export/home/cvs/apachen/src/modules/standard/mod_negotiation.c,v
retrieving revision 1.53
diff -u -r1.53 mod_negotiation.c
--- mod_negotiation.c	1997/07/28 18:23:03	1.53
+++ mod_negotiation.c	1997/08/21 14:25:07
@@ -227,6 +227,8 @@
     array_header *accept_langs; /* accept_recs */
     array_header *avail_vars;   /* available variants */
 
+    int count_multiviews_variants; /* number of variants found on disk */
+
     int ua_can_negotiate;       /* 1 if ua can do transparent negotiate */
     int use_transparent_neg;    /* 1 if we are using transparent neg */
     int short_accept_headers;   /* 1 if ua does trans neg & sent short accpt */
@@ -649,6 +651,9 @@
     char buffer[MAX_STRING_LEN];
     enum header_state hstate;
     struct var_rec mime_info;
+
+    /* We are not using multiviews */
+    neg->count_multiviews_variants = 0;
     
     if (rr->status != HTTP_OK) {
 	return rr->status;
@@ -809,6 +814,8 @@
 	
 	new_var = push_array (neg->avail_vars);
 	memcpy (new_var, (void *)&mime_info, sizeof (var_rec));
+
+	neg->count_multiviews_variants++;
 	    
 	clean_var_rec(&mime_info);
     }
@@ -1994,7 +2001,8 @@
     
     /* Otherwise, use it. */
     
-    if (!do_cache_negotiated_docs(r->server) && (r->proto_num < 1001))
+    if ((!do_cache_negotiated_docs(r->server) && (r->proto_num < 1001))
+	&& neg->count_multiviews_variants != 1)
         r->no_cache = 1;
 
     if (na_result == na_not_applied)