From 7c902669bf95fedb924267b45dc4f1463839140f Mon Sep 17 00:00:00 2001
From: Roman Khimov <roman@nspcc.ru>
Date: Fri, 7 May 2021 12:19:48 +0300
Subject: [PATCH] stateroot: implement exponential vote resends

---
 pkg/services/stateroot/service.go    |  8 +++++++-
 pkg/services/stateroot/signature.go  |  5 +++++
 pkg/services/stateroot/validators.go | 30 ++++++++++++++++++++++++++--
 3 files changed, 40 insertions(+), 3 deletions(-)

diff --git a/pkg/services/stateroot/service.go b/pkg/services/stateroot/service.go
index 636702450..90b4a64ab 100644
--- a/pkg/services/stateroot/service.go
+++ b/pkg/services/stateroot/service.go
@@ -3,6 +3,7 @@ package stateroot
 import (
 	"errors"
 	"sync"
+	"time"
 
 	"github.com/nspcc-dev/neo-go/pkg/config"
 	"github.com/nspcc-dev/neo-go/pkg/config/netmode"
@@ -45,6 +46,8 @@ type (
 		srMtx           sync.Mutex
 		incompleteRoots map[uint32]*incompleteRoot
 
+		timePerBlock    time.Duration
+		maxRetries      int
 		relayExtensible RelayCallback
 		blockCh         chan *block.Block
 		done            chan struct{}
@@ -58,14 +61,17 @@ const (
 
 // New returns new state root service instance using underlying module.
 func New(cfg config.StateRoot, log *zap.Logger, bc blockchainer.Blockchainer, cb RelayCallback) (Service, error) {
+	bcConf := bc.GetConfig()
 	s := &service{
 		StateRoot:       bc.GetStateModule(),
-		Network:         bc.GetConfig().Magic,
+		Network:         bcConf.Magic,
 		chain:           bc,
 		log:             log,
 		incompleteRoots: make(map[uint32]*incompleteRoot),
 		blockCh:         make(chan *block.Block),
 		done:            make(chan struct{}),
+		timePerBlock:    time.Duration(bcConf.SecondsPerBlock) * time.Second,
+		maxRetries:      bcConf.ValidatorsCount + 1,
 		relayExtensible: cb,
 	}
 
diff --git a/pkg/services/stateroot/signature.go b/pkg/services/stateroot/signature.go
index 980389bc9..627193dfd 100644
--- a/pkg/services/stateroot/signature.go
+++ b/pkg/services/stateroot/signature.go
@@ -8,6 +8,7 @@ import (
 	"github.com/nspcc-dev/neo-go/pkg/core/transaction"
 	"github.com/nspcc-dev/neo-go/pkg/crypto/keys"
 	"github.com/nspcc-dev/neo-go/pkg/io"
+	"github.com/nspcc-dev/neo-go/pkg/network/payload"
 	"github.com/nspcc-dev/neo-go/pkg/smartcontract"
 	"github.com/nspcc-dev/neo-go/pkg/vm/emit"
 )
@@ -23,6 +24,10 @@ type (
 		root *state.MPTRoot
 		// sigs contains signature from every oracle node.
 		sigs map[string]*rootSig
+		// myVote is an extensible message containing node's vote.
+		myVote *payload.Extensible
+		// retries is a counter of send attempts.
+		retries int
 	}
 
 	rootSig struct {
diff --git a/pkg/services/stateroot/validators.go b/pkg/services/stateroot/validators.go
index bcfd78176..8fd8fead7 100644
--- a/pkg/services/stateroot/validators.go
+++ b/pkg/services/stateroot/validators.go
@@ -1,6 +1,8 @@
 package stateroot
 
 import (
+	"time"
+
 	"github.com/nspcc-dev/neo-go/pkg/core/state"
 	"github.com/nspcc-dev/neo-go/pkg/core/transaction"
 	"github.com/nspcc-dev/neo-go/pkg/io"
@@ -10,6 +12,8 @@ import (
 	"go.uber.org/zap"
 )
 
+const firstVoteResendDelay = 3 * time.Second
+
 // Run runs service instance in a separate goroutine.
 func (s *service) Run() {
 	s.log.Info("starting state validation service")
@@ -61,11 +65,11 @@ func (s *service) signAndSend(r *state.MPTRoot) error {
 	sig := acc.PrivateKey().SignHashable(uint32(s.Network), r)
 	incRoot := s.getIncompleteRoot(r.Index)
 	incRoot.Lock()
+	defer incRoot.Unlock()
 	incRoot.root = r
 	incRoot.addSignature(acc.PrivateKey().PublicKey(), sig)
 	incRoot.reverify(s.Network)
 	s.trySendRoot(incRoot, acc)
-	incRoot.Unlock()
 
 	msg := NewMessage(VoteT, &Vote{
 		ValidatorIndex: int32(myIndex),
@@ -92,10 +96,32 @@ func (s *service) signAndSend(r *state.MPTRoot) error {
 	buf := io.NewBufBinWriter()
 	emit.Bytes(buf.BinWriter, sig)
 	e.Witness.InvocationScript = buf.Bytes()
-	s.relayExtensible(e)
+	incRoot.myVote = e
+	incRoot.retries = -1
+	s.sendVote(incRoot)
 	return nil
 }
 
+// sendVote attempts to send vote if it's still valid and if stateroot message
+// was not sent yet. It must be called with ir locked.
+func (s *service) sendVote(ir *incompleteRoot) {
+	if ir.isSent || ir.retries >= s.maxRetries ||
+		s.chain.HeaderHeight() >= ir.myVote.ValidBlockEnd {
+		return
+	}
+	s.relayExtensible(ir.myVote)
+	delay := firstVoteResendDelay
+	if ir.retries > 0 {
+		delay = s.timePerBlock << ir.retries
+	}
+	_ = time.AfterFunc(delay, func() {
+		ir.Lock()
+		s.sendVote(ir)
+		ir.Unlock()
+	})
+	ir.retries++
+}
+
 // getAccount returns current index and account for the node running this service.
 func (s *service) getAccount() (byte, *wallet.Account) {
 	s.accMtx.RLock()