Golang client.SendCall函數代碼示例

// TestTxnCoordSenderMultipleTxns verifies correct operation with
// multiple outstanding transactions.
func TestTxnCoordSenderMultipleTxns(t *testing.T) {
	defer leaktest.AfterTest(t)
	s := createTestDB(t)
	defer s.Stop()
	defer teardownHeartbeats(s.Sender)

	txn1 := newTxn(s.Clock, proto.Key("a"))
	txn2 := newTxn(s.Clock, proto.Key("b"))
	call := proto.Call{
		Args:  createPutRequest(proto.Key("a"), []byte("value"), txn1),
		Reply: &proto.PutResponse{}}
	if err := client.SendCall(s.Sender, call); err != nil {
		t.Fatal(err)
	}
	call = proto.Call{
		Args:  createPutRequest(proto.Key("b"), []byte("value"), txn2),
		Reply: &proto.PutResponse{}}
	if err := client.SendCall(s.Sender, call); err != nil {
		t.Fatal(err)
	}

	if len(s.Sender.txns) != 2 {
		t.Errorf("expected length of transactions map to be 2; got %d", len(s.Sender.txns))
	}
}

// TestTxnCoordSenderEndTxn verifies that ending a transaction
// sends resolve write intent requests and removes the transaction
// from the txns map.
func TestTxnCoordSenderEndTxn(t *testing.T) {
	defer leaktest.AfterTest(t)
	s := createTestDB(t)
	defer s.Stop()

	txn := newTxn(s.Clock, proto.Key("a"))
	pReply := &proto.PutResponse{}
	key := proto.Key("a")
	call := proto.Call{
		Args:  createPutRequest(key, []byte("value"), txn),
		Reply: pReply,
	}
	if err := client.SendCall(s.Sender, call); err != nil {
		t.Fatal(err)
	}
	if pReply.GoError() != nil {
		t.Fatal(pReply.GoError())
	}
	etReply := &proto.EndTransactionResponse{}
	if err := client.SendCall(s.Sender, proto.Call{
		Args: &proto.EndTransactionRequest{
			RequestHeader: proto.RequestHeader{
				Key:       txn.Key,
				Timestamp: txn.Timestamp,
				Txn:       pReply.Header().Txn,
			},
			Commit: true,
		},
		Reply: etReply,
	}); err != nil {
		t.Fatal(err)
	}
	verifyCleanup(key, s.Sender, s.Eng, t)
}

// TestTxnCoordIdempotentCleanup verifies that cleanupTxn is idempotent.
func TestTxnCoordIdempotentCleanup(t *testing.T) {
	defer leaktest.AfterTest(t)
	s := createTestDB(t)
	defer s.Stop()

	txn := newTxn(s.Clock, proto.Key("a"))
	pReply := &proto.PutResponse{}
	key := proto.Key("a")
	call := proto.Call{
		Args:  createPutRequest(key, []byte("value"), txn),
		Reply: pReply,
	}
	if err := client.SendCall(s.Sender, call); err != nil {
		t.Fatal(err)
	}

	if pReply.Error != nil {
		t.Fatal(pReply.GoError())
	}
	s.Sender.cleanupTxn(nil, *txn) // first call
	etReply := &proto.EndTransactionResponse{}
	if err := client.SendCall(s.Sender, proto.Call{
		Args: &proto.EndTransactionRequest{
			RequestHeader: proto.RequestHeader{
				Key:       txn.Key,
				Timestamp: txn.Timestamp,
				Txn:       txn,
			},
			Commit: true,
		},
		Reply: etReply,
	}); /* second call */ err != nil {
		t.Fatal(err)
	}
}

// TestMultiRangeScanReverseScanInconsistent verifies that a Scan/ReverseScan
// across ranges that doesn't require read consistency will set a timestamp
// using the clock local to the distributed sender.
func TestMultiRangeScanReverseScanInconsistent(t *testing.T) {
	defer leaktest.AfterTest(t)
	s, db := setupMultipleRanges(t, "b")
	defer s.Stop()

	// Write keys "a" and "b", the latter of which is the first key in the
	// second range.
	keys := []string{"a", "b"}
	ts := []time.Time{}
	b := &client.Batch{}
	for _, key := range keys {
		b.Put(key, "value")
	}
	if err := db.Run(b); err != nil {
		t.Fatal(err)
	}
	for i := range keys {
		ts = append(ts, b.Results[i].Rows[0].Timestamp())
		log.Infof("%d: %s", i, b.Results[i].Rows[0].Timestamp())
	}

	// Do an inconsistent Scan/ReverseScan from a new DistSender and verify
	// it does the read at its local clock and doesn't receive an
	// OpRequiresTxnError. We set the local clock to the timestamp of
	// the first key to verify it's used to read only key "a".
	manual := hlc.NewManualClock(ts[1].UnixNano() - 1)
	clock := hlc.NewClock(manual.UnixNano)
	ds := kv.NewDistSender(&kv.DistSenderContext{Clock: clock}, s.Gossip())

	// Scan.
	call := proto.ScanCall(proto.Key("a"), proto.Key("c"), 0)
	sr := call.Reply.(*proto.ScanResponse)
	sa := call.Args.(*proto.ScanRequest)
	sa.ReadConsistency = proto.INCONSISTENT
	if err := client.SendCall(ds, call); err != nil {
		t.Fatal(err)
	}
	if l := len(sr.Rows); l != 1 {
		t.Fatalf("expected 1 row; got %d", l)
	}
	if key := string(sr.Rows[0].Key); keys[0] != key {
		t.Errorf("expected key %q; got %q", keys[0], key)
	}

	// ReverseScan.
	call = proto.ReverseScanCall(proto.Key("a"), proto.Key("c"), 0)
	rsr := call.Reply.(*proto.ReverseScanResponse)
	rsa := call.Args.(*proto.ReverseScanRequest)
	rsa.ReadConsistency = proto.INCONSISTENT
	if err := client.SendCall(ds, call); err != nil {
		t.Fatal(err)
	}
	if l := len(rsr.Rows); l != 1 {
		t.Fatalf("expected 1 row; got %d", l)
	}
	if key := string(rsr.Rows[0].Key); keys[0] != key {
		t.Errorf("expected key %q; got %q", keys[0], key)
	}
}

// TestTxnMultipleCoord checks that a coordinator uses the Writing flag to
// enforce that only one coordinator can be used for transactional writes.
func TestTxnMultipleCoord(t *testing.T) {
	defer leaktest.AfterTest(t)
	s := createTestDB(t)
	defer s.Stop()

	for i, tc := range []struct {
		call    proto.Call
		writing bool
		ok      bool
	}{
		{proto.GetCall(proto.Key("a")), true, true},
		{proto.GetCall(proto.Key("a")), false, true},
		{proto.PutCall(proto.Key("a"), proto.Value{}), false, true},
		{proto.PutCall(proto.Key("a"), proto.Value{}), true, false},
	} {
		{
			txn := newTxn(s.Clock, proto.Key("a"))
			txn.Writing = tc.writing
			tc.call.Args.Header().Txn = txn
		}
		err := client.SendCall(s.Sender, tc.call)
		if err == nil != tc.ok {
			t.Errorf("%d: %T (writing=%t): success_expected=%t, but got: %v",
				i, tc.call.Args, tc.writing, tc.ok, err)
		}
		if err != nil {
			continue
		}

		txn := tc.call.Reply.Header().Txn
		// The transaction should come back rw if it started rw or if we just
		// wrote.
		isWrite := proto.IsTransactionWrite(tc.call.Args)
		if (tc.writing || isWrite) != txn.Writing {
			t.Errorf("%d: unexpected writing state: %s", i, txn)
		}
		if !isWrite {
			continue
		}
		// Abort for clean shutdown.
		etReply := &proto.EndTransactionResponse{}
		if err := client.SendCall(s.Sender, proto.Call{
			Args: &proto.EndTransactionRequest{
				RequestHeader: proto.RequestHeader{
					Key:       txn.Key,
					Timestamp: txn.Timestamp,
					Txn:       txn,
				},
				Commit: false,
			},
			Reply: etReply,
		}); err != nil {
			log.Warning(err)
			t.Fatal(err)
		}
	}
}

// TestMultiRangeScanWithMaxResults tests that commands which access multiple
// ranges with MaxResults parameter are carried out properly.
func TestMultiRangeScanWithMaxResults(t *testing.T) {
	defer leaktest.AfterTest(t)
	testCases := []struct {
		splitKeys []proto.Key
		keys      []proto.Key
	}{
		{[]proto.Key{proto.Key("m")},
			[]proto.Key{proto.Key("a"), proto.Key("z")}},
		{[]proto.Key{proto.Key("h"), proto.Key("q")},
			[]proto.Key{proto.Key("b"), proto.Key("f"), proto.Key("k"),
				proto.Key("r"), proto.Key("w"), proto.Key("y")}},
	}

	for i, tc := range testCases {
		s := StartTestServer(t)
		ds := kv.NewDistSender(&kv.DistSenderContext{Clock: s.Clock()}, s.Gossip())
		tds := kv.NewTxnCoordSender(ds, s.Clock(), testContext.Linearizable, nil, s.stopper)

		for _, sk := range tc.splitKeys {
			if err := s.node.ctx.DB.AdminSplit(sk); err != nil {
				t.Fatal(err)
			}
		}

		var call proto.Call
		for _, k := range tc.keys {
			call = proto.PutCall(k, proto.Value{Bytes: k})
			if err := client.SendCall(tds, call); err != nil {
				t.Fatal(err)
			}
		}

		// Try every possible ScanRequest startKey.
		for start := 0; start < len(tc.keys); start++ {
			// Try every possible maxResults, from 1 to beyond the size of key array.
			for maxResults := 1; maxResults <= len(tc.keys)-start+1; maxResults++ {
				scan := proto.ScanCall(tc.keys[start], tc.keys[len(tc.keys)-1].Next(),
					int64(maxResults))
				scan.Args.Header().Timestamp = call.Reply.Header().Timestamp
				if err := client.SendCall(tds, scan); err != nil {
					t.Fatal(err)
				}
				rows := scan.Reply.(*proto.ScanResponse).Rows
				if start+maxResults <= len(tc.keys) && len(rows) != maxResults {
					t.Errorf("%d: start=%s: expected %d rows, but got %d", i, tc.keys[start], maxResults, len(rows))
				} else if start+maxResults == len(tc.keys)+1 && len(rows) != maxResults-1 {
					t.Errorf("%d: expected %d rows, but got %d", i, maxResults-1, len(rows))
				}
			}
		}
		defer s.Stop()
	}
}

// TestTxnCoordSenderBeginTransactionMinPriority verifies that when starting
// a new transaction, a non-zero priority is treated as a minimum value.
func TestTxnCoordSenderBeginTransactionMinPriority(t *testing.T) {
	defer leaktest.AfterTest(t)
	s := createTestDB(t)
	defer s.Stop()
	defer teardownHeartbeats(s.Sender)

	reply := &proto.PutResponse{}
	if err := client.SendCall(s.Sender, proto.Call{
		Args: &proto.PutRequest{
			RequestHeader: proto.RequestHeader{
				Key:          proto.Key("key"),
				UserPriority: gogoproto.Int32(-10), // negative user priority is translated into positive priority
				Txn: &proto.Transaction{
					Name:      "test txn",
					Isolation: proto.SNAPSHOT,
					Priority:  11,
				},
			},
		},
		Reply: reply,
	}); err != nil {
		t.Fatal(err)
	}
	if reply.Txn.Priority != 11 {
		t.Errorf("expected txn priority 11; got %d", reply.Txn.Priority)
	}
}

// TestTxnCoordSenderGC verifies that the coordinator cleans up extant
// transactions after the lastUpdateNanos exceeds the timeout.
func TestTxnCoordSenderGC(t *testing.T) {
	defer leaktest.AfterTest(t)
	s := createTestDB(t)
	defer s.Stop()

	// Set heartbeat interval to 1ms for testing.
	s.Sender.heartbeatInterval = 1 * time.Millisecond

	txn := newTxn(s.Clock, proto.Key("a"))
	call := proto.Call{
		Args:  createPutRequest(proto.Key("a"), []byte("value"), txn),
		Reply: &proto.PutResponse{},
	}
	if err := client.SendCall(s.Sender, call); err != nil {
		t.Fatal(err)
	}

	// Now, advance clock past the default client timeout.
	// Locking the TxnCoordSender to prevent a data race.
	s.Sender.Lock()
	s.Manual.Set(defaultClientTimeout.Nanoseconds() + 1)
	s.Sender.Unlock()

	if err := util.IsTrueWithin(func() bool {
		// Locking the TxnCoordSender to prevent a data race.
		s.Sender.Lock()
		_, ok := s.Sender.txns[string(txn.ID)]
		s.Sender.Unlock()
		return !ok
	}, 50*time.Millisecond); err != nil {
		t.Error("expected garbage collection")
	}
}

// TestRangeLookupOptionOnReverseScan verifies that a lookup triggered by a
// ReverseScan request has the `useReverseScan` option specified.
func TestRangeLookupOptionOnReverseScan(t *testing.T) {
	defer leaktest.AfterTest(t)
	g, s := makeTestGossip(t)
	defer s()

	var testFn rpcSendFn = func(_ rpc.Options, method string, addrs []net.Addr, getArgs func(addr net.Addr) gogoproto.Message, getReply func() gogoproto.Message, _ *rpc.Context) ([]gogoproto.Message, error) {
		return []gogoproto.Message{getReply()}, nil
	}

	ctx := &DistSenderContext{
		RPCSend: testFn,
		RangeDescriptorDB: mockRangeDescriptorDB(func(k proto.Key, opts lookupOptions) ([]proto.RangeDescriptor, error) {
			if len(k) > 0 && !opts.useReverseScan {
				t.Fatalf("expected useReverseScan to be set")
			}
			return []proto.RangeDescriptor{testRangeDescriptor}, nil
		}),
	}
	ds := NewDistSender(ctx, g)
	call := proto.Call{
		Args: &proto.ReverseScanRequest{
			RequestHeader: proto.RequestHeader{Key: proto.Key("a"), EndKey: proto.Key("b")},
		},
		Reply: &proto.ReverseScanResponse{},
	}
	if err := client.SendCall(ds, call); err != nil {
		t.Fatal(err)
	}
}

// TestSendRPCRetry verifies that sendRPC failed on first address but succeed on
// second address, the second reply should be successfully returned back.
func TestSendRPCRetry(t *testing.T) {
	defer leaktest.AfterTest(t)
	g, s := makeTestGossip(t)
	defer s()
	if err := g.SetNodeDescriptor(&proto.NodeDescriptor{NodeID: 1}); err != nil {
		t.Fatal(err)
	}
	// Fill RangeDescriptor with 2 replicas
	var descriptor = proto.RangeDescriptor{
		RangeID:  1,
		StartKey: proto.Key("a"),
		EndKey:   proto.Key("z"),
	}
	for i := 1; i <= 2; i++ {
		addr := util.MakeUnresolvedAddr("tcp", fmt.Sprintf("node%d", i))
		nd := &proto.NodeDescriptor{
			NodeID:  proto.NodeID(i),
			Address: util.MakeUnresolvedAddr(addr.Network(), addr.String()),
		}
		if err := g.AddInfoProto(gossip.MakeNodeIDKey(proto.NodeID(i)), nd, time.Hour); err != nil {
			t.Fatal(err)
		}

		descriptor.Replicas = append(descriptor.Replicas, proto.Replica{
			NodeID:  proto.NodeID(i),
			StoreID: proto.StoreID(i),
		})
	}
	// Define our rpcSend stub which returns success on the second address.
	var testFn rpcSendFn = func(_ rpc.Options, method string, addrs []net.Addr, getArgs func(addr net.Addr) gogoproto.Message, getReply func() gogoproto.Message, _ *rpc.Context) ([]gogoproto.Message, error) {
		if method == "Node.Batch" {
			// reply from first address failed
			_ = getReply()
			// reply from second address succeed
			batchReply := getReply().(*proto.BatchResponse)
			reply := &proto.ScanResponse{}
			batchReply.Add(reply)
			reply.Rows = append([]proto.KeyValue{}, proto.KeyValue{Key: proto.Key("b"), Value: proto.Value{}})
			return []gogoproto.Message{batchReply}, nil
		}
		return nil, util.Errorf("unexpected method %v", method)
	}
	ctx := &DistSenderContext{
		RPCSend: testFn,
		RangeDescriptorDB: mockRangeDescriptorDB(func(_ proto.Key, _ lookupOptions) ([]proto.RangeDescriptor, error) {
			return []proto.RangeDescriptor{descriptor}, nil
		}),
	}
	ds := NewDistSender(ctx, g)
	call := proto.ScanCall(proto.Key("a"), proto.Key("d"), 1)
	sr := call.Reply.(*proto.ScanResponse)
	if err := client.SendCall(ds, call); err != nil {
		t.Fatal(err)
	}
	if l := len(sr.Rows); l != 1 {
		t.Fatalf("expected 1 row; got %d", l)
	}
}

// TestTxnCoordSenderKeyRanges verifies that multiple requests to same or
// overlapping key ranges causes the coordinator to keep track only of
// the minimum number of ranges.
func TestTxnCoordSenderKeyRanges(t *testing.T) {
	defer leaktest.AfterTest(t)
	ranges := []struct {
		start, end proto.Key
	}{
		{proto.Key("a"), proto.Key(nil)},
		{proto.Key("a"), proto.Key(nil)},
		{proto.Key("aa"), proto.Key(nil)},
		{proto.Key("b"), proto.Key(nil)},
		{proto.Key("aa"), proto.Key("c")},
		{proto.Key("b"), proto.Key("c")},
	}

	s := createTestDB(t)
	defer s.Stop()
	defer teardownHeartbeats(s.Sender)
	txn := newTxn(s.Clock, proto.Key("a"))

	for _, rng := range ranges {
		if rng.end != nil {
			delRangeReq := createDeleteRangeRequest(rng.start, rng.end, txn)
			call := proto.Call{Args: delRangeReq, Reply: &proto.DeleteRangeResponse{}}
			if err := client.SendCall(s.Sender, call); err != nil {
				t.Fatal(err)
			}
		} else {
			putReq := createPutRequest(rng.start, []byte("value"), txn)
			call := proto.Call{Args: putReq, Reply: &proto.PutResponse{}}
			if err := client.SendCall(s.Sender, call); err != nil {
				t.Fatal(err)
			}
		}
		txn.Writing = true // required for all but first req
	}

	// Verify that the transaction metadata contains only two entries
	// in its "keys" interval cache. "a" and range "aa"-"c".
	txnMeta, ok := s.Sender.txns[string(txn.ID)]
	if !ok {
		t.Fatalf("expected a transaction to be created on coordinator")
	}
	if txnMeta.keys.Len() != 2 {
		t.Errorf("expected 2 entries in keys interval cache; got %v", txnMeta.keys)
	}
}

// TestRetryOnDescriptorLookupError verifies that the DistSender retries a descriptor
// lookup on retryable errors.
func TestRetryOnDescriptorLookupError(t *testing.T) {
	defer leaktest.AfterTest(t)
	g, s := makeTestGossip(t)
	defer s()

	var testFn rpcSendFn = func(_ rpc.Options, _ string, _ []net.Addr, _ func(addr net.Addr) gogoproto.Message, getReply func() gogoproto.Message, _ *rpc.Context) ([]gogoproto.Message, error) {
		return []gogoproto.Message{getReply()}, nil
	}

	errors := []error{
		errors.New("fatal boom"),
		&proto.RangeKeyMismatchError{}, // retryable
		nil,
	}

	ctx := &DistSenderContext{
		RPCSend: testFn,
		RangeDescriptorDB: mockRangeDescriptorDB(func(k proto.Key, _ lookupOptions) ([]proto.RangeDescriptor, error) {
			// Return next error and truncate the prefix of the errors array.
			var err error
			if k != nil {
				err = errors[0]
				errors = errors[1:]
			}
			return []proto.RangeDescriptor{testRangeDescriptor}, err
		}),
	}
	ds := NewDistSender(ctx, g)
	call := proto.PutCall(proto.Key("a"), proto.Value{Bytes: []byte("value")})
	// Fatal error on descriptor lookup, propagated to reply.
	if err := client.SendCall(ds, call); err.Error() != "fatal boom" {
		t.Errorf("unexpected error: %s", err)
	}
	// Retryable error on descriptor lookup, second attempt successful.
	if err := client.SendCall(ds, call); err != nil {
		t.Errorf("unexpected error: %s", err)
	}
	if len(errors) != 0 {
		t.Fatalf("expected more descriptor lookups, leftover errors: %+v", errors)
	}
}

// TestTxnCoordSenderAddRequest verifies adding a request creates a
// transaction metadata and adding multiple requests with same
// transaction ID updates the last update timestamp.
func TestTxnCoordSenderAddRequest(t *testing.T) {
	defer leaktest.AfterTest(t)
	s := createTestDB(t)
	defer s.Stop()
	defer teardownHeartbeats(s.Sender)

	txn := newTxn(s.Clock, proto.Key("a"))
	putReq := createPutRequest(proto.Key("a"), []byte("value"), txn)

	// Put request will create a new transaction.
	call := proto.Call{Args: putReq, Reply: &proto.PutResponse{}}
	if err := client.SendCall(s.Sender, call); err != nil {
		t.Fatal(err)
	}
	txnMeta, ok := s.Sender.txns[string(txn.ID)]
	if !ok {
		t.Fatal("expected a transaction to be created on coordinator")
	}
	if !call.Reply.Header().Txn.Writing {
		t.Fatal("response Txn is not marked as writing")
	}
	ts := atomic.LoadInt64(&txnMeta.lastUpdateNanos)

	// Advance time and send another put request. Lock the coordinator
	// to prevent a data race.
	s.Sender.Lock()
	s.Manual.Set(1)
	s.Sender.Unlock()
	putReq.Txn.Writing = true
	call = proto.Call{Args: putReq, Reply: &proto.PutResponse{}}
	if err := client.SendCall(s.Sender, call); err != nil {
		t.Fatal(err)
	}
	if len(s.Sender.txns) != 1 {
		t.Errorf("expected length of transactions map to be 1; got %d", len(s.Sender.txns))
	}
	txnMeta = s.Sender.txns[string(txn.ID)]
	if lu := atomic.LoadInt64(&txnMeta.lastUpdateNanos); ts >= lu || lu != s.Manual.UnixNano() {
		t.Errorf("expected last update time to advance; got %d", lu)
	}
}

// TestRetryOnWrongReplicaError sets up a DistSender on a minimal gossip
// network and a mock of rpc.Send, and verifies that the DistSender correctly
// retries upon encountering a stale entry in its range descriptor cache.
func TestRetryOnWrongReplicaError(t *testing.T) {
	defer leaktest.AfterTest(t)
	g, s := makeTestGossip(t)
	defer s()
	// Updated below, after it has first been returned.
	badStartKey := proto.Key("m")
	newRangeDescriptor := testRangeDescriptor
	goodStartKey := newRangeDescriptor.StartKey
	newRangeDescriptor.StartKey = badStartKey
	descStale := true

	var testFn rpcSendFn = func(_ rpc.Options, method string, addrs []net.Addr, getArgs func(addr net.Addr) gogoproto.Message, getReply func() gogoproto.Message, _ *rpc.Context) ([]gogoproto.Message, error) {
		ba := getArgs(testAddress).(*proto.BatchRequest)
		if _, ok := ba.GetArg(proto.RangeLookup); ok {
			if !descStale && bytes.HasPrefix(ba.Key, keys.Meta2Prefix) {
				t.Errorf("unexpected extra lookup for non-stale replica descriptor at %s",
					ba.Key)
			}

			br := getReply().(*proto.BatchResponse)
			r := &proto.RangeLookupResponse{}
			r.Ranges = append(r.Ranges, newRangeDescriptor)
			br.Add(r)
			// If we just returned the stale descriptor, set up returning the
			// good one next time.
			if bytes.HasPrefix(ba.Key, keys.Meta2Prefix) {
				if newRangeDescriptor.StartKey.Equal(badStartKey) {
					newRangeDescriptor.StartKey = goodStartKey
				} else {
					descStale = false
				}
			}
			return []gogoproto.Message{br}, nil
		}
		// When the Scan first turns up, update the descriptor for future
		// range descriptor lookups.
		if !newRangeDescriptor.StartKey.Equal(goodStartKey) {
			return nil, &proto.RangeKeyMismatchError{RequestStartKey: ba.Key,
				RequestEndKey: ba.EndKey}
		}
		return []gogoproto.Message{getReply()}, nil
	}

	ctx := &DistSenderContext{
		RPCSend: testFn,
	}
	ds := NewDistSender(ctx, g)
	call := proto.ScanCall(proto.Key("a"), proto.Key("d"), 0)
	if err := client.SendCall(ds, call); err != nil {
		t.Errorf("scan encountered error: %s", err)
	}
}

// getTxn fetches the requested key and returns the transaction info.
func getTxn(coord *TxnCoordSender, txn *proto.Transaction) (bool, *proto.Transaction, error) {
	hr := &proto.HeartbeatTxnResponse{}
	call := proto.Call{
		Args: &proto.HeartbeatTxnRequest{
			RequestHeader: proto.RequestHeader{
				Key: txn.Key,
				Txn: txn,
			},
		},
		Reply: hr,
	}
	if err := client.SendCall(coord, call); err != nil {
		return false, nil, err
	}
	return true, hr.Txn, nil
}