Golang Impl.Watch方法代码示例

// waitForInitialValue waits for the initial value of
// /keyspaces/test_keyspace/SrvKeyspace to appear, and match the
// provided srvKeyspace.
func waitForInitialValue(t *testing.T, ts topo.Impl, cell string, srvKeyspace *topodatapb.SrvKeyspace) (changes <-chan *topo.WatchData, cancel func()) {
	var current *topo.WatchData
	ctx := context.Background()
	start := time.Now()
	for {
		current, changes, cancel = ts.Watch(ctx, cell, "/keyspaces/test_keyspace/SrvKeyspace")
		if current.Err == topo.ErrNoNode {
			// hasn't appeared yet
			if time.Now().Sub(start) > 10*time.Second {
				t.Fatalf("time out waiting for file to appear")
			}
			time.Sleep(10 * time.Millisecond)
			continue
		}
		if current.Err != nil {
			t.Fatalf("watch failed: %v", current.Err)
		}
		// we got a valid result
		break
	}
	got := &topodatapb.SrvKeyspace{}
	if err := proto.Unmarshal(current.Contents, got); err != nil {
		t.Fatalf("cannot proto-unmarshal data: %v", err)
	}
	if !proto.Equal(got, srvKeyspace) {
		t.Fatalf("got bad data: %v expected: %v", got, srvKeyspace)
	}

	return changes, cancel
}

// checkWatch runs the tests on the Watch part of the Backend API.
// We can't just use the full API yet, so use SrvKeyspace for now.
func checkWatch(t *testing.T, ts topo.Impl) {
	ctx := context.Background()
	cell := getLocalCell(ctx, t, ts)

	// start watching something that doesn't exist -> error
	current, changes, cancel := ts.Watch(ctx, cell, "/keyspaces/test_keyspace/SrvKeyspace")
	if current.Err != topo.ErrNoNode {
		t.Errorf("watch on missing node didn't return ErrNoNode: %v %v", current, changes)
	}

	// create some data
	srvKeyspace := &topodatapb.SrvKeyspace{
		ShardingColumnName: "user_id",
	}
	if err := ts.UpdateSrvKeyspace(ctx, cell, "test_keyspace", srvKeyspace); err != nil {
		t.Fatalf("UpdateSrvKeyspace(1): %v", err)
	}

	// start watching again, it should work
	changes, cancel = waitForInitialValue(t, ts, cell, srvKeyspace)
	defer cancel()

	// change the data
	srvKeyspace.ShardingColumnName = "new_user_id"
	if err := ts.UpdateSrvKeyspace(ctx, cell, "test_keyspace", srvKeyspace); err != nil {
		t.Fatalf("UpdateSrvKeyspace(2): %v", err)
	}

	// Make sure we get the watch data, maybe not as first notice,
	// but eventually. The API specifies it is possible to get duplicate
	// notifications.
	for {
		wd, ok := <-changes
		if !ok {
			t.Fatalf("watch channel unexpectedly closed")
		}
		if wd.Err != nil {
			t.Fatalf("watch interrupted: %v", wd.Err)
		}
		got := &topodatapb.SrvKeyspace{}
		if err := proto.Unmarshal(wd.Contents, got); err != nil {
			t.Fatalf("cannot proto-unmarshal data: %v", err)
		}

		if got.ShardingColumnName == "user_id" {
			// extra first value, still good
			continue
		}
		if got.ShardingColumnName == "new_user_id" {
			// watch worked, good
			break
		}
		t.Fatalf("got unknown SrvKeyspace: %v", got)
	}

	// remove the SrvKeyspace
	if err := ts.DeleteSrvKeyspace(ctx, cell, "test_keyspace"); err != nil {
		t.Fatalf("DeleteSrvKeyspace: %v", err)
	}

	// Make sure we get the ErrNoNode notification eventually.
	// The API specifies it is possible to get duplicate
	// notifications.
	for {
		wd, ok := <-changes
		if !ok {
			t.Fatalf("watch channel unexpectedly closed")
		}
		if wd.Err == topo.ErrNoNode {
			// good
			break
		}
		if wd.Err != nil {
			t.Fatalf("bad error returned for deletion: %v", wd.Err)
		}
		// we got something, better be the right value
		got := &topodatapb.SrvKeyspace{}
		if err := proto.Unmarshal(wd.Contents, got); err != nil {
			t.Fatalf("cannot proto-unmarshal data: %v", err)
		}
		if got.ShardingColumnName == "new_user_id" {
			// good value
			continue
		}
		t.Fatalf("got unknown SrvKeyspace waiting for deletion: %v", got)
	}

	// now the channel should be closed
	if wd, ok := <-changes; ok {
		t.Fatalf("got unexpected event after error: %v", wd)
	}
}