multi: add reset closure to kvdb.View

This commit adds a reset() closure to the kvdb.View function which will
be called before each retry (including the first) of the view
transaction. The reset() closure can be used to reset external state
(eg slices or maps) where the view closure puts intermediate results.

discovery/gossiper_test.go

@@ -1117,6 +1117,9 @@ func TestSignatureAnnouncementLocalFirst(t *testing.T) {
 			number++
 			return nil
 		},
+		func() {
+			number = 0
+		},
 	); err != nil {
 		t.Fatalf("unable to retrieve objects from store: %v", err)
 	}
@@ -1150,6 +1153,9 @@ func TestSignatureAnnouncementLocalFirst(t *testing.T) {
 			number++
 			return nil
 		},
+		func() {
+			number = 0
+		},
 	); err != nil && err != channeldb.ErrWaitingProofNotFound {
 		t.Fatalf("unable to retrieve objects from store: %v", err)
 	}
@@ -1219,6 +1225,9 @@ func TestOrphanSignatureAnnouncement(t *testing.T) {
 			number++
 			return nil
 		},
+		func() {
+			number = 0
+		},
 	); err != nil {
 		t.Fatalf("unable to retrieve objects from store: %v", err)
 	}
@@ -1355,6 +1364,9 @@ func TestOrphanSignatureAnnouncement(t *testing.T) {
 			number++
 			return nil
 		},
+		func() {
+			number = 0
+		},
 	); err != nil {
 		t.Fatalf("unable to retrieve objects from store: %v", err)
 	}
@@ -1466,6 +1478,9 @@ func TestSignatureAnnouncementRetryAtStartup(t *testing.T) {
 			number++
 			return nil
 		},
+		func() {
+			number = 0
+		},
 	); err != nil {
 		t.Fatalf("unable to retrieve objects from store: %v", err)
 	}
@@ -1570,6 +1585,9 @@ out:
 			number++
 			return nil
 		},
+		func() {
+			number = 0
+		},
 	); err != nil && err != channeldb.ErrWaitingProofNotFound {
 		t.Fatalf("unable to retrieve objects from store: %v", err)
 	}
@@ -1754,6 +1772,9 @@ func TestSignatureAnnouncementFullProofWhenRemoteProof(t *testing.T) {
 			number++
 			return nil
 		},
+		func() {
+			number = 0
+		},
 	); err != nil && err != channeldb.ErrWaitingProofNotFound {
 		t.Fatalf("unable to retrieve objects from store: %v", err)
 	}
@@ -2583,6 +2604,9 @@ func TestReceiveRemoteChannelUpdateFirst(t *testing.T) {
 			number++
 			return nil
 		},
+		func() {
+			number = 0
+		},
 	); err != nil {
 		t.Fatalf("unable to retrieve objects from store: %v", err)
 	}
@@ -2612,6 +2636,9 @@ func TestReceiveRemoteChannelUpdateFirst(t *testing.T) {
 			number++
 			return nil
 		},
+		func() {
+			number = 0
+		},
 	); err != nil && err != channeldb.ErrWaitingProofNotFound {
 		t.Fatalf("unable to retrieve objects from store: %v", err)
 	}

discovery/message_store.go

@@ -199,7 +199,7 @@ func readMessage(msgBytes []byte) (lnwire.Message, error) {
 // Messages returns the total set of messages that exist within the store for
 // all peers.
 func (s *MessageStore) Messages() (map[[33]byte][]lnwire.Message, error) {
-	msgs := make(map[[33]byte][]lnwire.Message)
+	var msgs map[[33]byte][]lnwire.Message
 	err := kvdb.View(s.db, func(tx kvdb.RTx) error {
 		messageStore := tx.ReadBucket(messageStoreBucket)
 		if messageStore == nil {
@@ -224,6 +224,8 @@ func (s *MessageStore) Messages() (map[[33]byte][]lnwire.Message, error) {
 			msgs[pubKey] = append(msgs[pubKey], msg)
 			return nil
 		})
+	}, func() {
+		msgs = make(map[[33]byte][]lnwire.Message)
 	})
 	if err != nil {
 		return nil, err
@@ -262,6 +264,8 @@ func (s *MessageStore) MessagesForPeer(
 		}
 
 		return nil
+	}, func() {
+		msgs = nil
 	})
 	if err != nil {
 		return nil, err
@@ -272,7 +276,7 @@ func (s *MessageStore) MessagesForPeer(
 
 // Peers returns the public key of all peers with messages within the store.
 func (s *MessageStore) Peers() (map[[33]byte]struct{}, error) {
-	peers := make(map[[33]byte]struct{})
+	var peers map[[33]byte]struct{}
 	err := kvdb.View(s.db, func(tx kvdb.RTx) error {
 		messageStore := tx.ReadBucket(messageStoreBucket)
 		if messageStore == nil {
@@ -285,6 +289,8 @@ func (s *MessageStore) Peers() (map[[33]byte]struct{}, error) {
 			peers[pubKey] = struct{}{}
 			return nil
 		})
+	}, func() {
+		peers = make(map[[33]byte]struct{})
 	})
 	if err != nil {
 		return nil, err