Don't do automatic backend retry if we have received anything from the

backend at all.  The retry is only (pseudo-)valid when we have not received
anything at all, indicating that the backend closed before it got our request.

Also don't retry if we sent the request body (not part of test-case).

Fixes #1156

bin/varnishd/cache/cache_fetch.c

@@ -480,6 +480,8 @@ FetchHdr(struct req *req, int need_host_hdr, int sendbody)
 
 	/* Deal with any message-body the request might have */
 	i = FetchReqBody(req, sendbody);
+	if (sendbody && req->reqbodydone)
+		retry = -1;
 	if (WRW_FlushRelease(wrk) || i > 0) {
 		VSLb(req->vsl, SLT_FetchError,
 		    "backend write error: %d (%s)",
@@ -520,6 +522,7 @@ FetchHdr(struct req *req, int need_host_hdr, int sendbody)
 			return (retry);
 		}
 		if (first) {
+			retry = -1;
 			first = 0;
 			VTCP_set_read_timeout(vc->fd,
 			    vc->between_bytes_timeout);

bin/varnishtest/tests/r01156.vtc

+varnishtest "Don't retry if backend ever sent anything"
+
+server s1 {
+	rxreq
+	expect req.url == /1
+	txresp -bodylen 1
+
+	rxreq
+	expect req.url == /2
+	close
+	accept
+
+	rxreq
+	expect req.url == /2
+	txresp -bodylen 2
+
+	rxreq
+	expect req.url == /3
+	send "200 "
+	delay .1
+	close
+	accept
+
+	rxreq
+	expect req.url == /4
+	txresp -bodylen 4
+} -start
+
+varnish v1 -vcl+backend {} -start
+
+client c1 {
+	txreq -url /1
+	rxresp
+	expect resp.status == 200
+	expect resp.bodylen == 1
+
+	# This one should get retried
+	txreq -url /2
+	rxresp
+	expect resp.status == 200
+	expect resp.bodylen == 2
+
+	# This one should not get retried
+	txreq -url /3
+	rxresp
+	expect resp.status == 503
+} -run
+client c1 {
+	txreq -url /4
+	rxresp
+	expect resp.status == 200
+	expect resp.bodylen == 4
+} -run