We can not use a lenght based response when

	we transform (gzip/gunzip)
	we stream and backend didn't send c-l.

Fixes	#980

Testcase by:	Martin

bin/varnishd/cache_center.c

@@ -166,8 +166,8 @@ cnt_prepresp(struct sess *sp)
 
 	sp->wrk->res_mode = 0;
 
-	if (!sp->wrk->do_stream ||
-	    (sp->wrk->h_content_length != NULL && !sp->wrk->do_gunzip))
+	if ((sp->wrk->h_content_length != NULL || !sp->wrk->do_stream) &&
+	    !sp->wrk->do_gzip && !sp->wrk->do_gunzip)
 		sp->wrk->res_mode |= RES_LEN;
 
 	if (!sp->disable_esi && sp->obj->esidata != NULL) {

bin/varnishtest/tests/r00980.vtc

+varnishtest "r00980 test gzip on fetch with content_length and do_stream"
+
+server s1 {
+	rxreq
+	expect req.url == "/foobar"
+	expect req.http.accept-encoding == "gzip"
+	txresp -bodylen 43
+} -start
+
+varnish v1 -cliok "param.set http_gzip_support true" -vcl+backend {
+
+	sub vcl_fetch {
+		set beresp.do_gzip = true;
+		set beresp.do_stream = true;
+	}
+} -start
+
+client c1 {
+	txreq -url /foobar -hdr "Accept-Encoding: gzip"
+	rxresp
+	expect resp.http.content-encoding == "gzip"
+	gunzip
+	expect resp.bodylen == 43
+
+	txreq -url /foobar 
+	rxresp
+	expect resp.http.content-encoding == "resp.http.content-encoding"
+	expect resp.bodylen == 43
+} -run