Don't merge Content-Encoding from IMS object before VCL, in order

to not confuse VCL by "backend" suddenly changing gzip status, but do
unconditionally smash it in there afterwards, no matter what VCL
does, so it will be correct relative to the existing body.

bin/varnishd/cache/cache.h

@@ -594,8 +594,9 @@ struct object {
 
 	uint8_t			*vary;
 
-	/* XXX: make bitmap */
-	uint8_t			gziped;
+	unsigned		gziped:1;
+	unsigned		changed_gzip:1;
+
 	/* Bit positions in the gzip stream */
 	ssize_t			gzip_start;
 	ssize_t			gzip_last;
@@ -998,7 +999,7 @@ void http_CopyHome(const struct http *hp);
 void http_Unset(struct http *hp, const char *hdr);
 void http_CollectHdr(struct http *hp, const char *hdr);
 void http_VSL_log(const struct http *hp);
-void http_Merge(const struct http *fm, struct http *to);
+void http_Merge(const struct http *fm, struct http *to, int not_ce);
 
 /* cache_http1_proto.c */
 

bin/varnishd/cache/cache_fetch.c

@@ -336,7 +336,8 @@ vbf_stp_startfetch(struct worker *wrk, struct busyobj *bo)
 
 	if (bo->ims_obj != NULL && bo->beresp->status == 304) {
 		bo->beresp->status = 200;
-		http_Merge(bo->ims_obj->http, bo->beresp);
+		http_Merge(bo->ims_obj->http, bo->beresp,
+		    bo->ims_obj->changed_gzip);
 		do_ims = 1;
 	} else
 		do_ims = 0;
@@ -464,6 +465,9 @@ vbf_stp_fetch(struct worker *wrk, struct busyobj *bo)
 	if (bo->do_gzip || (bo->is_gzip && !bo->do_gunzip))
 		obj->gziped = 1;
 
+	if (bo->do_gzip || bo->do_gunzip)
+		obj->changed_gzip = 1;
+
 	/*
 	 * Ready to fetch the body
 	 */
@@ -554,10 +558,22 @@ vbf_stp_condfetch(struct worker *wrk, struct busyobj *bo)
 	ssize_t sl, al, tl;
 	struct storage *st;
 	enum objiter_status ois;
+	char *p;
 
 	CHECK_OBJ_NOTNULL(wrk, WORKER_MAGIC);
 	CHECK_OBJ_NOTNULL(bo, BUSYOBJ_MAGIC);
 
+	if (bo->ims_obj->changed_gzip) {
+		/*
+		 * If we modified the gzip status of the IMS object, that
+		 * must control the C-E header, if any.
+		 */
+		http_Unset(bo->beresp, H_Content_Encoding);
+		if (http_GetHdr(bo->ims_obj->http, H_Content_Encoding, &p))
+			http_PrintfHeader(bo->beresp,
+			    "Content-Encoding: %s", p);
+	}
+
 	AZ(vbf_beresp2obj(bo));
 	obj = bo->fetch_obj;
 

bin/varnishd/cache/cache_http.c

@@ -641,13 +641,19 @@ http_FilterResp(const struct http *fm, struct http *to, unsigned how)
  */
 
 void
-http_Merge(const struct http *fm, struct http *to)
+http_Merge(const struct http *fm, struct http *to, int not_ce)
 {
 	unsigned u, v;
 	const char *p;
 
 	for (u = HTTP_HDR_FIRST; u < fm->nhd; u++)
 		fm->hdf[u] |= HDF_MARKER;
+	if (not_ce) {
+		u = http_findhdr(fm,
+		    H_Content_Encoding[0] - 1, H_Content_Encoding + 1);
+		if (u > 0)
+			fm->hdf[u] &= ~HDF_MARKER;
+	}
 	for (v = HTTP_HDR_FIRST; v < to->nhd; v++) {
 		p = strchr(to->hd[v].b, ':');
 		AN(p);

bin/varnishtest/tests/g00006.vtc

+varnishtest "IMS'ing g[un]zip'ed objects"
+
+server s1 {
+	rxreq
+	expect req.url == /1
+	txresp -hdr  "Last-Modified: Wed, 11 Sep 2013 13:36:55 GMT" -bodylen 20
+
+	rxreq
+	expect req.url == /1
+	expect req.http.if-modified-since == "Wed, 11 Sep 2013 13:36:55 GMT"
+	txresp -status 304 -nolen
+
+	rxreq
+	expect req.url == /2
+	txresp -hdr  "Last-Modified: Wed, 11 Sep 2013 13:36:55 GMT" -gzipbody "012345678901234567"
+
+	rxreq
+	expect req.url == /2
+	expect req.http.if-modified-since == "Wed, 11 Sep 2013 13:36:55 GMT"
+	txresp -status 304 -hdr "Content-Encoding: gzip,rot13" -nolen
+
+} -start
+
+varnish v1 -vcl+backend {
+	sub vcl_backend_response {
+		set beresp.http.foobar = beresp.http.content-encoding;
+		if (bereq.url == "/1") {
+			set beresp.do_gzip = true;
+		} else {
+			set beresp.do_gunzip = true;
+		}
+		set beresp.ttl = 1s;
+		set beresp.grace = 0s;
+		set beresp.keep = 60s;
+	}
+} -start
+
+client c1 {
+	txreq -url /1 -hdr "Accept-Encoding: gzip"
+	rxresp
+	expect resp.http.content-encoding == "gzip"
+	expect resp.http.foobar == ""
+	gunzip
+	expect resp.bodylen == 20
+
+	delay 1
+
+	txreq -url /1 -hdr "Accept-Encoding: gzip"
+	rxresp
+	expect resp.http.content-encoding == "gzip"
+	expect resp.http.foobar == ""
+	gunzip
+	expect resp.bodylen == 20
+
+	delay .2
+
+	txreq -url /2
+	rxresp
+	expect resp.http.content-encoding == "<undef>"
+	expect resp.http.foobar == "gzip"
+	expect resp.bodylen == 18
+
+	delay 1
+
+	txreq -url /2
+	rxresp
+	expect resp.http.content-encoding == "<undef>"
+	# Here we see the C-E of the IMS OBJ
+	expect resp.http.foobar == "gzip,rot13"
+	expect resp.bodylen == 18
+
+} -run