feat: introduce `MessagesIterator`

Enables customization of iteration strategy for retrieved messages.

protocol/messages_iterator.go

@@ -0,0 +1,40 @@
+package protocol
+
+import (
+	"golang.org/x/exp/maps"
+
+	"github.com/status-im/status-go/eth-node/types"
+	"github.com/status-im/status-go/protocol/transport"
+)
+
+type MessagesIterator interface {
+	HasNext() bool
+	Next() (transport.Filter, []*types.Message)
+}
+
+type DefaultMessagesIterator struct {
+	chatWithMessages map[transport.Filter][]*types.Message
+	keys             []transport.Filter
+	currentIndex     int
+}
+
+func NewDefaultMessagesIterator(chatWithMessages map[transport.Filter][]*types.Message) MessagesIterator {
+	return &DefaultMessagesIterator{
+		chatWithMessages: chatWithMessages,
+		keys:             maps.Keys(chatWithMessages),
+		currentIndex:     0,
+	}
+}
+
+func (it *DefaultMessagesIterator) HasNext() bool {
+	return it.currentIndex < len(it.keys)
+}
+
+func (it *DefaultMessagesIterator) Next() (transport.Filter, []*types.Message) {
+	if it.HasNext() {
+		key := it.keys[it.currentIndex]
+		it.currentIndex++
+		return key, it.chatWithMessages[key]
+	}
+	return transport.Filter{}, nil
+}

protocol/messenger.go

@@ -181,6 +181,9 @@ type Messenger struct {
 	// used to track unhandled messages
 	unhandledMessagesTracker func(*v1protocol.StatusMessage, error)
 
+	// enables control over chat messages iteration
+	retrievedMessagesIteratorFactory func(map[transport.Filter][]*types.Message) MessagesIterator
+
 	peersyncing         *peersyncing.PeerSyncing
 	peersyncingOffers   map[string]uint64
 	peersyncingRequests map[string]uint64
@@ -577,8 +580,9 @@ func NewMessenger(
 			func() error { _ = logger.Sync; return nil },
 			database.Close,
 		},
-		logger:                logger,
-		savedAddressesManager: savedAddressesManager,
+		logger:                           logger,
+		savedAddressesManager:            savedAddressesManager,
+		retrievedMessagesIteratorFactory: NewDefaultMessagesIterator,
 	}
 
 	if c.rpcClient != nil {
@@ -3735,7 +3739,10 @@ func (m *Messenger) handleRetrievedMessages(chatWithMessages map[transport.Filte
 		logger.Info("failed to retrieve admin communities", zap.Error(err))
 	}
 
-	for filter, messages := range chatWithMessages {
+	iterator := m.retrievedMessagesIteratorFactory(chatWithMessages)
+	for iterator.HasNext() {
+		filter, messages := iterator.Next()
+
 		var processedMessages []string
 		for _, shhMessage := range messages {
 			logger := logger.With(zap.String("hash", types.EncodeHex(shhMessage.Hash)))