core/zero: add usage reporter (#5281)

* wip

* add response

* handle empty email

* use set, update log

* add test

* add coalesce, comments, test

* add test, fix bug

* use builtin cmp.Or

* remove wait ready call

* use api error

pkg/grpc/databroker/sync_test.go

@@ -0,0 +1,67 @@
+package databroker_test
+
+import (
+	"context"
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+	grpc "google.golang.org/grpc"
+
+	"github.com/pomerium/pomerium/internal/databroker"
+	"github.com/pomerium/pomerium/internal/testutil"
+	databrokerpb "github.com/pomerium/pomerium/pkg/grpc/databroker"
+	"github.com/pomerium/pomerium/pkg/grpc/session"
+	"github.com/pomerium/pomerium/pkg/grpc/user"
+	"github.com/pomerium/pomerium/pkg/protoutil"
+)
+
+func Test_SyncLatestRecords(t *testing.T) {
+	t.Parallel()
+
+	ctx, clearTimeout := context.WithTimeout(context.Background(), time.Minute)
+	defer clearTimeout()
+
+	cc := testutil.NewGRPCServer(t, func(s *grpc.Server) {
+		databrokerpb.RegisterDataBrokerServiceServer(s, databroker.New())
+	})
+
+	c := databrokerpb.NewDataBrokerServiceClient(cc)
+
+	expected := []*user.User{
+		{Id: "u1"},
+		{Id: "u2"},
+		{Id: "u3"},
+	}
+
+	for _, u := range expected {
+		_, err := c.Put(ctx, &databrokerpb.PutRequest{
+			Records: []*databrokerpb.Record{
+				databrokerpb.NewRecord(u),
+			},
+		})
+		require.NoError(t, err)
+	}
+
+	// add a non-user record to make sure it gets ignored
+	_, err := c.Put(ctx, &databrokerpb.PutRequest{
+		Records: []*databrokerpb.Record{
+			{
+				Id:   "u4",
+				Type: protoutil.GetTypeURL(new(user.User)),
+				Data: protoutil.NewAny(&session.Session{Id: "s1"}),
+			},
+		},
+	})
+	require.NoError(t, err)
+
+	var actual []*user.User
+	serverVersion, latestRecordVersion, err := databrokerpb.SyncLatestRecords(context.Background(), c, func(u *user.User) {
+		actual = append(actual, u)
+	})
+	assert.NoError(t, err)
+	assert.NotZero(t, serverVersion)
+	assert.Equal(t, uint64(4), latestRecordVersion)
+	testutil.AssertProtoEqual(t, expected, actual)
+}