fix: UpdateState() not called when service becomes unresolvable

When a service was resolved and became unreachable, cc.UpdateState() was not
called.
The clientConn continued to use the afore resolved addresses.

Author: Fabian Holler

consul/resolver.go

@@ -121,7 +121,8 @@ func (c *consulResolver) watcher() {
 			// data newer then the passed opts.WaitIndex is available.
 			// We check if the returned addrs changed to not call
 			// cc.UpdateState() unnecessary for unchanged addresses.
-			if len(addrs) == 0 || reflect.DeepEqual(addrs, lastAddrs) {
+			if (len(addrs) == 0 && len(lastAddrs) == 0) ||
+				reflect.DeepEqual(addrs, lastAddrs) {
 				// sleep a bit to prevent that query() is
 				// called in a tight-loop if the consul server
 				// returns multiple time immediately, despite

consul/resolver_test.go

@@ -313,6 +313,61 @@ func TestResolveAddrChange(t *testing.T) {
 	r.Close()
 }
 
+func TestResolveAddrChangesToUnresolvable(t *testing.T) {
+	health := &consulMockHealthClient{}
+	cleanup := replaceCreateHealthClientFn(
+		func(cfg *consul.Config) (consulHealthEndpoint, error) {
+			return health, nil
+		},
+	)
+	defer cleanup()
+
+	addrs1 := []*consul.AgentService{
+		&consul.AgentService{
+			Address: "localhost",
+			Port:    5678,
+		},
+	}
+	addrs2 := []*consul.AgentService{}
+
+	cc := testClientConn{}
+	newAddressCallCnt := cc.getNewAddressCallCnt()
+	target := resolver.Target{Endpoint: "user-service"}
+	b := NewBuilder()
+
+	health.setResolveAddrs(addrs1)
+
+	r, err := b.Build(target, &cc, resolver.BuildOptions{})
+	if err != nil {
+		t.Fatal("Build() failed:", err.Error())
+	}
+
+	r.ResolveNow(resolver.ResolveNowOptions{})
+
+	for newAddressCallCnt == cc.getNewAddressCallCnt() {
+		time.Sleep(time.Millisecond)
+	}
+
+	resolvedAddrs := cc.getAddrs()
+	if !cmpResolveResults(resolvedAddrs, addrs1) {
+		t.Errorf("resolved address '%+v', expected: '%+v'", resolvedAddrs, addrs1)
+	}
+
+	newAddressCallCnt = cc.getNewAddressCallCnt()
+	health.setResolveAddrs(addrs2)
+	r.ResolveNow(resolver.ResolveNowOptions{})
+	for newAddressCallCnt == cc.getNewAddressCallCnt() {
+		time.Sleep(time.Millisecond)
+	}
+
+	resolvedAddrs = cc.getAddrs()
+	if !cmpResolveResults(resolvedAddrs, addrs2) {
+		t.Errorf("resolved address after change '%+v', expected: '%+v'", resolvedAddrs, addrs1)
+	}
+
+	r.Close()
+}
+
 func TestErrorIsReportedOnQueryErrors(t *testing.T) {
 	queryErr := errors.New("query failed")
 	health := &consulMockHealthClient{err: queryErr}