actor: check for tx after the subscription in wsWaiter, fix #2805

Don't wait for VUB block, solve this race immediately.

pkg/rpcclient/actor/waiter.go

@@ -244,6 +244,7 @@ func (w *EventWaiter) WaitAny(ctx context.Context, vub uint32, hashes ...util.Ui
 		}()
 	}
 	if wsWaitErr == nil {
+		trig := trigger.Application
 		for _, h := range hashes {
 			txsID, err := w.ws.ReceiveExecutions(&neorpc.ExecutionFilter{Container: &h}, aerRcvr)
 			if err != nil {
@@ -260,22 +261,28 @@ func (w *EventWaiter) WaitAny(ctx context.Context, vub uint32, hashes ...util.Ui
 				}
 				unsubErrs <- nil
 			}()
+			// There is a potential race between subscription and acceptance, so
+			// do a polling check once _after_ the subscription.
+			appLog, err := w.ws.GetApplicationLog(h, &trig)
+			if err == nil {
+				res = &state.AppExecResult{
+					Container: appLog.Container,
+					Execution: appLog.Executions[0],
+				}
+				break // We have the result, no need for other subscriptions.
+			}
 		}
 	}
 
-	if wsWaitErr == nil {
+	if wsWaitErr == nil && res == nil {
 		select {
-		case b, ok := <-bRcvr:
+		case _, ok := <-bRcvr:
 			if !ok {
 				// We're toast, retry with non-ws client.
 				wsWaitErr = ErrMissedEvent
 				break
 			}
-			// We can easily end up in a situation when subscription was performed too late and
-			// the desired transaction and VUB-th block have already got accepted before the
-			// subscription happened. Thus, always retry with non-ws client, it will perform
-			// AER requests and make sure.
-			wsWaitErr = fmt.Errorf("block #%d was received by EventWaiter", b.Index)
+			waitErr = ErrTxNotAccepted
 		case aer, ok := <-aerRcvr:
 			if !ok {
 				// We're toast, retry with non-ws client.

pkg/rpcclient/actor/waiter_test.go

@@ -133,13 +133,12 @@ func TestWSWaiter_Wait(t *testing.T) {
 	require.ErrorIs(t, err, someErr)
 
 	// AER is in chain immediately.
+	aer, err := w.Wait(h, bCount-1, nil)
+	require.NoError(t, err)
+	require.Equal(t, expected, aer)
+
+	// Auxiliary things for asynchronous tests.
 	doneCh := make(chan struct{})
-	go func() {
-		aer, err := w.Wait(h, bCount-1, nil)
-		require.NoError(t, err)
-		require.Equal(t, expected, aer)
-		doneCh <- struct{}{}
-	}()
 	check := func(t *testing.T, trigger func()) {
 		timer := time.NewTimer(time.Second)
 		var triggerFired bool
@@ -159,6 +158,15 @@ func TestWSWaiter_Wait(t *testing.T) {
 		}
 		require.True(t, triggerFired)
 	}
+
+	// AER received after the subscription.
+	c.RPCClient.appLog = nil
+	go func() {
+		aer, err = w.Wait(h, bCount-1, nil)
+		require.NoError(t, err)
+		require.Equal(t, expected, aer)
+		doneCh <- struct{}{}
+	}()
 	check(t, func() {
 		c.chLock.RLock()
 		defer c.chLock.RUnlock()
@@ -166,7 +174,6 @@ func TestWSWaiter_Wait(t *testing.T) {
 	})
 
 	// Missing AER after VUB.
-	c.RPCClient.appLog = nil
 	go func() {
 		_, err = w.Wait(h, bCount-2, nil)
 		require.ErrorIs(t, err, ErrTxNotAccepted)

pkg/services/rpcsrv/client_test.go

@@ -5,6 +5,7 @@ import (
 	"context"
 	"encoding/base64"
 	"encoding/hex"
+	"encoding/json"
 	"fmt"
 	"math/big"
 	"net/http"
@@ -16,6 +17,7 @@ import (
 	"time"
 
 	"github.com/google/uuid"
+	"github.com/gorilla/websocket"
 	"github.com/nspcc-dev/neo-go/internal/testchain"
 	"github.com/nspcc-dev/neo-go/pkg/config"
 	"github.com/nspcc-dev/neo-go/pkg/core"
@@ -2132,11 +2134,42 @@ func TestWSClient_WaitWithLateSubscription(t *testing.T) {
 	// Firstly, accept the block.
 	blocks := getTestBlocks(t)
 	b1 := blocks[0]
-	b2 := blocks[1]
 	tx := b1.Transactions[0]
 	require.NoError(t, chain.AddBlock(b1))
 
-	// After that, subscribe for AERs/blocks.
+	// After that, wait and get the result immediately.
+	aer, err := act.Wait(tx.Hash(), tx.ValidUntilBlock, nil)
+	require.NoError(t, err)
+	require.Equal(t, tx.Hash(), aer.Container)
+	require.Equal(t, trigger.Application, aer.Trigger)
+	require.Equal(t, vmstate.Halt, aer.VMState)
+}
+
+func TestWSClient_WaitWithMissedEvent(t *testing.T) {
+	chain, rpcSrv, httpSrv := initClearServerWithServices(t, false, false, true)
+	defer chain.Close()
+	defer rpcSrv.Shutdown()
+
+	url := "ws" + strings.TrimPrefix(httpSrv.URL, "http") + "/ws"
+	c, err := rpcclient.NewWS(context.Background(), url, rpcclient.Options{})
+	require.NoError(t, err)
+	require.NoError(t, c.Init())
+	acc, err := wallet.NewAccount()
+	require.NoError(t, err)
+	act, err := actor.New(c, []actor.SignerAccount{
+		{
+			Signer: transaction.Signer{
+				Account: acc.ScriptHash(),
+			},
+			Account: acc,
+		},
+	})
+	require.NoError(t, err)
+
+	blocks := getTestBlocks(t)
+	b1 := blocks[0]
+	tx := b1.Transactions[0]
+
 	rcvr := make(chan *state.AppExecResult)
 	go func() {
 		aer, err := act.Wait(tx.Hash(), tx.ValidUntilBlock, nil)
@@ -2150,23 +2183,33 @@ func TestWSClient_WaitWithLateSubscription(t *testing.T) {
 	require.Eventually(t, func() bool {
 		rpcSrv.subsLock.Lock()
 		defer rpcSrv.subsLock.Unlock()
-		if len(rpcSrv.subscribers) == 1 { // single client
-			for s := range rpcSrv.subscribers {
-				var count int
-				for _, f := range s.feeds {
-					if f.event != neorpc.InvalidEventID {
-						count++
-					}
-				}
-				return count == 2 // subscription for blocks + AERs
-			}
-		}
-		return false
+		return len(rpcSrv.subscribers) == 1
 	}, time.Second, 100*time.Millisecond)
 
-	// Accept the next block to trigger event-based waiter loop exit and rollback to
-	// a poll-based waiter.
-	require.NoError(t, chain.AddBlock(b2))
+	rpcSrv.subsLock.Lock()
+	// Suppress normal event delivery.
+	for s := range rpcSrv.subscribers {
+		s.overflown.Store(true)
+	}
+	rpcSrv.subsLock.Unlock()
+
+	// Accept the next block, but subscriber will get no events because it's overflown.
+	require.NoError(t, chain.AddBlock(b1))
+
+	overEvent, err := json.Marshal(neorpc.Notification{
+		JSONRPC: neorpc.JSONRPCVersion,
+		Event:   neorpc.MissedEventID,
+		Payload: make([]interface{}, 0),
+	})
+	require.NoError(t, err)
+	overflowMsg, err := websocket.NewPreparedMessage(websocket.TextMessage, overEvent)
+	require.NoError(t, err)
+	rpcSrv.subsLock.Lock()
+	// Deliver overflow message -> triggers subscriber to retry with polling waiter.
+	for s := range rpcSrv.subscribers {
+		s.writer <- overflowMsg
+	}
+	rpcSrv.subsLock.Unlock()
 
 	// Wait for the result.
 waitloop: