Treat RFC-illegal negative (s-)max-age values as zero.

Fixes	#887

bin/varnishd/rfc2616.c

@@ -112,7 +112,10 @@ RFC2616_Ttl(const struct sess *sp)
 		    http_GetHdrField(hp, H_Cache_Control, "max-age", &p)) &&
 		    p != NULL) {
 
-			max_age = strtoul(p, NULL, 0);
+			if (*p == '-')
+				max_age = 0;
+			else
+				max_age = strtoul(p, NULL, 0);
 			if (http_GetHdr(hp, H_Age, &p)) {
 				age = strtoul(p, NULL, 0);
 				sp->wrk->age = age;

bin/varnishtest/tests/r00887.vtc

+# $Id$
+
+test "Ticket #887"
+
+server s1 {
+	rxreq 
+	txresp -hdr "Cache-control: max-age=-1000" -body "FOO"
+	rxreq 
+	txresp -body "FOOBAR"
+} -start
+
+varnish v1 -vcl+backend {
+} -start 
+
+client c1 {
+	txreq  
+	rxresp
+	expect resp.bodylen == 3
+	txreq  
+	rxresp
+	expect resp.bodylen == 6
+} -run