From 0c355293a7723724954b93aae401b68e5f9e2fae Mon Sep 17 00:00:00 2001
From: Ed Felten <ed@felten.com>
Date: Tue, 26 Nov 2019 07:00:04 -0500
Subject: [PATCH 1/2] Improve polling and subscription shutdown in
 arb-provider-go

---
 packages/arb-provider-go/connection.go | 56 +++++++++++++++-----------
 packages/arb-provider-go/go.mod        |  2 -
 2 files changed, 32 insertions(+), 26 deletions(-)

diff --git a/packages/arb-provider-go/connection.go b/packages/arb-provider-go/connection.go
index 3988880101..19b9ca42a7 100644
--- a/packages/arb-provider-go/connection.go
+++ b/packages/arb-provider-go/connection.go
@@ -224,12 +224,13 @@ const subscriptionPollingInterval = 5 * time.Second
 type subscription struct {
 	proxy            ValidatorProxy
 	firstBlockUnseen uint64
-	active           bool
 	logChan          chan<- types.Log
 	errChan          chan error
 	address          common.Address
 	topics           [][32]byte
 	unsubOnce        *sync.Once
+	closeChan        chan interface{}
+	wg               sync.WaitGroup
 }
 
 func _extractAddrTopics(query ethereum.FilterQuery) (addr common.Address, topics [][32]byte) {
@@ -309,44 +310,50 @@ func newSubscription(conn *ArbConnection, query ethereum.FilterQuery, ch chan<-
 	sub := &subscription{
 		conn.proxy,
 		0,
-		true,
 		ch,
 		make(chan error, 1),
 		address,
 		topics,
 		&sync.Once{},
+		make(chan interface{}),
+		sync.WaitGroup{},
 	}
+	sub.wg.Add(1)
 	go func() {
+		defer sub.wg.Done()
 		defer sub.Unsubscribe()
+		ticker := time.NewTicker(subscriptionPollingInterval)
+		defer ticker.Stop()
 		for {
-			time.Sleep(subscriptionPollingInterval)
-			if !sub.active {
+			select {
+			case <- sub.closeChan:
 				return
-			}
-			logInfos, err := sub.proxy.FindLogs(int64(sub.firstBlockUnseen), math.MaxInt32, sub.address[:], sub.topics)
-			if err != nil {
-				sub.errChan <- err
-				return
-			}
-			for _, logInfo := range logInfos {
-				outs, err := _decodeLogInfo(logInfo)
+			case <- ticker.C:
+				logInfos, err := sub.proxy.FindLogs(int64(sub.firstBlockUnseen), math.MaxInt32, sub.address[:], sub.topics)
 				if err != nil {
 					sub.errChan <- err
 					return
 				}
-				ok := true
-				for i, targetTopic := range topics {
-					if targetTopic != outs.Topics[i] {
+				for _, logInfo := range logInfos {
+					outs, err := _decodeLogInfo(logInfo)
+					if err != nil {
+						sub.errChan <- err
+						return
+					}
+					ok := true
+					for i, targetTopic := range topics {
+						if targetTopic != outs.Topics[i] {
+							ok = false
+						}
+					}
+					if outs.BlockNumber < sub.firstBlockUnseen {
 						ok = false
 					}
-				}
-				if outs.BlockNumber < sub.firstBlockUnseen {
-					ok = false
-				}
-				if ok {
-					sub.logChan <- *outs
-					if sub.firstBlockUnseen <= outs.BlockNumber {
-						sub.firstBlockUnseen = outs.BlockNumber + 1
+					if ok {
+						sub.logChan <- *outs
+						if sub.firstBlockUnseen <= outs.BlockNumber {
+							sub.firstBlockUnseen = outs.BlockNumber + 1
+						}
 					}
 				}
 			}
@@ -359,7 +366,8 @@ func newSubscription(conn *ArbConnection, query ethereum.FilterQuery, ch chan<-
 // and closes the error channel.
 func (sub *subscription) Unsubscribe() {
 	sub.unsubOnce.Do(func() {
-		sub.active = false
+		close(sub.closeChan)
+		sub.wg.Wait()
 		close(sub.errChan)
 	})
 }
diff --git a/packages/arb-provider-go/go.mod b/packages/arb-provider-go/go.mod
index 8b28be621d..6afdb1587f 100644
--- a/packages/arb-provider-go/go.mod
+++ b/packages/arb-provider-go/go.mod
@@ -8,8 +8,6 @@ require (
 	github.com/gorilla/mux v1.7.0
 	github.com/gorilla/rpc v1.2.0
 	github.com/miguelmota/go-solidity-sha3 v0.1.0
-	github.com/modern-go/concurrent v0.0.0-20180306012644-bacd9c7ef1dd // indirect
-	github.com/modern-go/reflect2 v1.0.1 // indirect
 	github.com/offchainlabs/arbitrum/packages/arb-util v0.2.0
 	github.com/offchainlabs/arbitrum/packages/arb-validator v0.2.0
 )

From 421be44db0cc93bc1f005b16eebd10a583073c46 Mon Sep 17 00:00:00 2001
From: Ed Felten <ed@felten.com>
Date: Tue, 26 Nov 2019 07:07:22 -0500
Subject: [PATCH 2/2] Implement FilterLogs in arb-provider-go

---
 packages/arb-provider-go/connection.go | 23 ++++++++++++++++++++++-
 1 file changed, 22 insertions(+), 1 deletion(-)

diff --git a/packages/arb-provider-go/connection.go b/packages/arb-provider-go/connection.go
index 19b9ca42a7..5bc33c6d17 100644
--- a/packages/arb-provider-go/connection.go
+++ b/packages/arb-provider-go/connection.go
@@ -206,7 +206,28 @@ func (conn *ArbConnection) SendTransaction(ctx context.Context, tx *types.Transa
 //
 // TODO(karalabe): Deprecate when the subscription one can return past data too.
 func (conn *ArbConnection) FilterLogs(ctx context.Context, query ethereum.FilterQuery) ([]types.Log, error) {
-	return nil, _nyiError("FilterLogs")
+	var ret []types.Log
+	address, topics := _extractAddrTopics(query)
+	logInfos, err := conn.proxy.FindLogs(0, math.MaxInt32, address[:], topics)
+	if err != nil {
+		return nil, err
+	}
+	for _, logInfo := range logInfos {
+		outs, err := _decodeLogInfo(logInfo)
+		if err != nil {
+			return nil, err
+		}
+		ok := true
+		for i, targetTopic := range topics {
+			if targetTopic != outs.Topics[i] {
+				ok = false
+			}
+		}
+		if ok {
+			ret = append(ret, *outs)
+		}
+	}
+	return ret, nil
 }
 
 // SubscribeFilterLogs creates a background log filtering operation, returning