Collapse Cookie headers in HTTP/2

Fixes #2291

bin/varnishd/cache/cache_req_fsm.c

 /*-
  * Copyright (c) 2006 Verdens Gang AS
- * Copyright (c) 2006-2015 Varnish Software AS
+ * Copyright (c) 2006-2017 Varnish Software AS
  * All rights reserved.
  *
  * Author: Poul-Henning Kamp <phk@phk.freebsd.dk>
@@ -799,6 +799,9 @@ cnt_recv(struct worker *wrk, struct req *req)
 
 	http_CollectHdr(req->http, H_Cache_Control);
 
+	if (req->http->protover == 20) // rfc7540,l,3114,3120
+		http_CollectHdrSep(req->http, H_Cookie, "; ");
+
 	if (req->req_body_status == REQ_BODY_FAIL) {
 		req->doclose = SC_OVERLOAD;
 		return (REQ_FSM_DONE);

bin/varnishtest/tests/r02291.vtc

+varnishtest "Collect cookie headers in HTTP/2"
+
+server s1 -repeat 2 {
+	rxreq
+	txresp
+} -start
+
+varnish v1 -vcl+backend { } -start
+varnish v1 -cliok "param.set feature +http2"
+
+logexpect l1 -v v1 {
+	expect * * BereqProtocol	HTTP/1.1
+	expect * = BereqHeader		"Cookie: user=alice"
+	expect * = BereqHeader		"Cookie: peer=bob"
+	expect * * BereqProtocol	HTTP/2.0
+	expect * = BereqHeader		"cookie: user=alice;  peer=bob"
+} -start
+
+client c1 {
+	txreq -hdr "Cookie: user=alice" -hdr "Cookie: peer=bob"
+	rxresp
+	expect resp.status == 200
+} -run
+
+client c2 {
+	stream 1 {
+		txreq -hdr cookie user=alice -hdr cookie peer=bob
+		rxresp
+		expect resp.status == 200
+	} -run
+} -run
+
+logexpect l1 -wait