Add the vfp_testgzip which verifies that gzip'ed data are

indeed gzip'ed data and extracts the magic bits should it ever
be included from ESI.

In general Varnish is not in the business of inspecting content
and with the exception of ESI we still do not do so.

What we do here is make sure that we do not serve corrupt data,
in the same sense as we bail out on chunked encoding trouble or
HTTP header trouble from the backend.

bin/varnishd/cache.h

@@ -225,6 +225,7 @@ struct vfp {
 
 extern struct vfp vfp_gunzip;
 extern struct vfp vfp_gzip;
+extern struct vfp vfp_testgzip;
 extern struct vfp vfp_esi;
 
 /*--------------------------------------------------------------------*/

bin/varnishd/cache_center.c

@@ -639,6 +639,8 @@ cnt_fetch(struct sess *sp)
 		sp->wrk->vfp = &vfp_gunzip;
 	else if (sp->wrk->do_gzip)
 		sp->wrk->vfp = &vfp_gzip;
+	else if (sp->wrk->is_gzip)
+		sp->wrk->vfp = &vfp_testgzip;
 
 	l = http_EstimateWS(sp->wrk->beresp,
 	    sp->pass ? HTTPH_R_PASS : HTTPH_A_INS, &nhttp);

bin/varnishd/cache_gzip.c

@@ -492,3 +492,78 @@ struct vfp vfp_gzip = {
         .bytes  =       vfp_gzip_bytes,
         .end    =       vfp_gzip_end,
 };
+
+/*--------------------------------------------------------------------
+ * VFP_TESTGZIP
+ *
+ * A VFP for testing that received gzip data is valid, and for
+ * collecting the magic bits while we're at it.
+ */
+
+static void __match_proto__()
+vfp_testgzip_begin(struct sess *sp, size_t estimate)
+{
+	(void)estimate;
+	sp->wrk->vgz_rx = VGZ_NewUngzip(sp, sp->ws);
+}
+
+static int __match_proto__()
+vfp_testgzip_bytes(struct sess *sp, struct http_conn *htc, ssize_t bytes)
+{
+	struct vgz *vg;
+	ssize_t l, w;
+	int i = -100;
+	uint8_t	ibuf[1024 * params->gzip_stack_buffer];
+	size_t dl;
+	const void *dp;
+	struct storage *st;
+
+	vg = sp->wrk->vgz_rx;
+	CHECK_OBJ_NOTNULL(vg, VGZ_MAGIC);
+	AZ(vg->vz.avail_in);
+	while (bytes > 0) {
+		if (FetchStorage(sp))
+			return (-1);
+		st = sp->wrk->storage;
+		l = st->space - st->len;
+		if (l > bytes)
+			l = bytes;
+		w = HTC_Read(htc, st->ptr + st->len, l);
+		if (w <= 0)
+			return (w);
+		bytes -= w;
+		VGZ_Ibuf(vg, st->ptr + st->len, w);
+		st->len += w;
+		sp->obj->len += w;
+
+		while (!VGZ_IbufEmpty(vg)) {
+			VGZ_Obuf(vg, ibuf, sizeof ibuf);
+			i = VGZ_Gunzip(vg, &dp, &dl);
+			assert(i == Z_OK || i == Z_STREAM_END);
+		}
+	}
+	if (i == Z_STREAM_END)
+		return (1);
+	return (-1);
+}
+
+static int __match_proto__()
+vfp_testgzip_end(struct sess *sp)
+{
+	struct vgz *vg;
+
+	vg = sp->wrk->vgz_rx;
+	CHECK_OBJ_NOTNULL(vg, VGZ_MAGIC);
+	VGZ_UpdateObj(vg, sp->obj);
+	VGZ_Destroy(&vg);
+	sp->obj->gziped = 1;
+	return (0);
+}
+
+struct vfp vfp_testgzip = {
+        .begin  =       vfp_testgzip_begin,
+        .bytes  =       vfp_testgzip_bytes,
+        .end    =       vfp_testgzip_end,
+};
+
+