http2_proto: Introduce a custom BROKE_WINDOW error

Conflicts:
	bin/varnishd/http2/cache_http2_send.c
	include/tbl/h2_error.h

bin/varnishd/http2/cache_http2_proto.c

@@ -1328,7 +1328,7 @@ h2_stream_tmo(struct h2_sess *h2, const struct h2_req *r2, vtim_real now)
 		VSLb(h2->vsl, SLT_Debug,
 		     "H2: stream %u: Hit idle_send_timeout waiting for"
 		     " WINDOW_UPDATE", r2->stream);
-		h2e = H2SE_CANCEL;
+		h2e = H2SE_BROKE_WINDOW;
 	}
 
 	if (h2e == NULL && r2->t_send != 0 &&

bin/varnishd/http2/cache_http2_send.c

@@ -412,12 +412,14 @@ H2_Send(struct worker *wrk, struct h2_req *r2, h2_frame ftyp, uint8_t flags,
     uint32_t len, const void *ptr, uint64_t *counter)
 {
 	uint64_t dummy_counter;
+	h2_error h2e;
 
 	if (counter == NULL)
 		counter = &dummy_counter;
 
 	h2_send(wrk, r2, ftyp, flags, len, ptr, counter);
 
-	if (h2_errcheck(r2, r2->h2sess) == H2SE_CANCEL)
-		H2_Send_RST(wrk, r2->h2sess, r2, r2->stream, H2SE_CANCEL);
+	h2e = h2_errcheck(r2, r2->h2sess);
+	if (h2e != NULL && h2e->val == H2SE_CANCEL->val)
+		H2_Send_RST(wrk, r2->h2sess, r2, r2->stream, h2e);
 }

include/tbl/h2_error.h

@@ -154,6 +154,13 @@ H2_ERROR(
        /* descr */     "http/2 rapid reset detected"
 )
 
+H2_ERROR(
+	/* name */	BROKE_WINDOW,
+	/* val */	8, /* CANCEL */
+	/* types */	2,
+	/* reason */	SC_NULL,
+	/* descr */	"http/2 stream out of window credits"
+)
 #  undef H2_CUSTOM_ERRORS
 #endif