httpd mod_proxy: ProxyPass negation

[Stephan A. Rickauer]

This diff backports and documents the ProxyPass negation found in
apache2, useful for excluding subdirs from being proxied, e.g.

  ProxyPass /foo/bar !
  ProxyPass /foo/ http://backend/foo/

I run this patch in production on a loaded i386 reverse proxy without
any troubles. Spacing corrections by st...@.


Index: htdocs/manual/mod/mod_proxy.html
===================================================================
RCS file: /cvs/src/usr.sbin/httpd/htdocs/manual/mod/mod_proxy.html,v
retrieving revision 1.9
diff -u -r1.9 mod_proxy.html
--- htdocs/manual/mod/mod_proxy.html    1 Aug 2006 12:53:59 -0000       1.9
+++ htdocs/manual/mod/mod_proxy.html    5 Aug 2009 12:17:58 -0000
@@ -467,7 +467,7 @@
     directive</h2>
     <a href="directive-dict.html#Syntax"
     rel="Help"><strong>Syntax:</strong></a> ProxyPass <em>path
-    url</em><br />
+    !|url</em><br />
      <a href="directive-dict.html#Default"
     rel="Help"><strong>Default:</strong></a> <em>None</em><br />
      <a href="directive-dict.html#Context"
@@ -499,6 +499,19 @@
     &lt;<samp>http://wibble.org/mirror/foo/bar</samp>&gt; to be
     internally converted into a proxy request to
     &lt;<samp>http://foo.com/bar</samp>&gt;.</p>
+
+    <p>The <code>!</code> directive is useful when you don't want
+    to reverse-proxy a subdirectory, <em>e.g.</em></p>
+<pre>
+    ProxyPass /mirror/foo/bar !
+    ProxyPass /mirror/foo http://backend.site.com
+</pre>
+    <p>will proxy all requests to <samp>/mirror/foo</samp> to
+    <samp>backend.site.com</samp> <em>except</em> requests made to
+    <samp>/mirror/foo/bar</samp>.</p>
+
+    <p><strong>Note:</strong> Order is important. You need to put the
+    exclusions <em>before</em> the general ProxyPass directive.</p>
 
     <p><strong>Warning:</strong> The <code><a
     href="#proxyrequests">ProxyRequests</a></code> directive should
Index: src/modules/proxy/mod_proxy.c
===================================================================
RCS file: /cvs/src/usr.sbin/httpd/src/modules/proxy/mod_proxy.c,v
retrieving revision 1.16
diff -u -r1.16 mod_proxy.c
--- src/modules/proxy/mod_proxy.c       9 May 2008 08:06:28 -0000       1.16
+++ src/modules/proxy/mod_proxy.c       5 Aug 2009 12:17:58 -0000
@@ -200,6 +200,10 @@
         len = alias_match(r->uri, ent[i].fake);
 
         if (len > 0) {
+            if ((ent[i].real[0] == '!') && (ent[i].real[1] == 0)) {
+                return DECLINED;
+            }
+
             r->filename = ap_pstrcat(r->pool, "proxy:", ent[i].real,
                                      r->uri + len, NULL);
             r->handler = "proxy-server";