event: allow blocking acks on event handling

call.go

@@ -13,7 +13,7 @@ import (
 )
 
 func (cli *Client) handleCallEvent(node *waBinary.Node) {
-	go cli.sendAck(node)
+	defer cli.maybeDeferredAck(node)
 
 	if len(node.GetChildren()) != 1 {
 		cli.dispatchEvent(&events.UnknownCallEvent{Node: node})

client.go

@@ -72,6 +72,8 @@ type Client struct {
 	// AutoReconnectHook is called when auto-reconnection fails. If the function returns false,
 	// the client will not attempt to reconnect. The number of retries can be read from AutoReconnectErrors.
 	AutoReconnectHook func(error) bool
+	// If SynchronousAck is set, acks for messages will only be sent after all event handlers return.
+	SynchronousAck bool
 
 	DisableLoginAutoReconnect bool
 

message.go

@@ -46,7 +46,7 @@ func (cli *Client) handleEncryptedMessage(node *waBinary.Node) {
 		if len(info.PushName) > 0 && info.PushName != "-" {
 			go cli.updatePushName(info.Sender, info, info.PushName)
 		}
-		go cli.sendAck(node)
+		defer cli.maybeDeferredAck(node)
 		if info.Sender.Server == types.NewsletterServer {
 			cli.handlePlaintextMessage(info, node)
 		} else {

notification.go

@@ -377,7 +377,7 @@ func (cli *Client) handleNotification(node *waBinary.Node) {
 	if !ag.OK() {
 		return
 	}
-	go cli.sendAck(node)
+	defer cli.maybeDeferredAck(node)
 	switch notifType {
 	case "encrypt":
 		go cli.handleEncryptNotification(node)
@@ -386,30 +386,30 @@ func (cli *Client) handleNotification(node *waBinary.Node) {
 	case "account_sync":
 		go cli.handleAccountSyncNotification(node)
 	case "devices":
-		go cli.handleDeviceNotification(node)
+		cli.handleDeviceNotification(node)
 	case "fbid:devices":
-		go cli.handleFBDeviceNotification(node)
+		cli.handleFBDeviceNotification(node)
 	case "w:gp2":
 		evt, err := cli.parseGroupNotification(node)
 		if err != nil {
 			cli.Log.Errorf("Failed to parse group notification: %v", err)
 		} else {
-			go cli.dispatchEvent(evt)
+			cli.dispatchEvent(evt)
 		}
 	case "picture":
-		go cli.handlePictureNotification(node)
+		cli.handlePictureNotification(node)
 	case "mediaretry":
-		go cli.handleMediaRetryNotification(node)
+		cli.handleMediaRetryNotification(node)
 	case "privacy_token":
-		go cli.handlePrivacyTokenNotification(node)
+		cli.handlePrivacyTokenNotification(node)
 	case "link_code_companion_reg":
 		go cli.tryHandleCodePairNotification(node)
 	case "newsletter":
-		go cli.handleNewsletterNotification(node)
+		cli.handleNewsletterNotification(node)
 	case "mex":
-		go cli.handleMexNotification(node)
+		cli.handleMexNotification(node)
 	case "status":
-		go cli.handleStatusNotification(node)
+		cli.handleStatusNotification(node)
 	// Other types: business, disappearing_mode, server, status, pay, psa
 	default:
 		cli.Log.Debugf("Unhandled notification with type %s", notifType)

receipt.go

@@ -16,6 +16,7 @@ import (
 )
 
 func (cli *Client) handleReceipt(node *waBinary.Node) {
+	defer cli.maybeDeferredAck(node)
 	receipt, err := cli.parseReceipt(node)
 	if err != nil {
 		cli.Log.Warnf("Failed to parse receipt: %v", err)
@@ -28,9 +29,8 @@ func (cli *Client) handleReceipt(node *waBinary.Node) {
 				}
 			}()
 		}
-		go cli.dispatchEvent(receipt)
+		cli.dispatchEvent(receipt)
 	}
-	go cli.sendAck(node)
 }
 
 func (cli *Client) handleGroupedReceipt(partialReceipt events.Receipt, participants *waBinary.Node) {
@@ -96,6 +96,17 @@ func (cli *Client) parseReceipt(node *waBinary.Node) (*events.Receipt, error) {
 	return &receipt, nil
 }
 
+func (cli *Client) maybeDeferredAck(node *waBinary.Node) func() {
+	if cli.SynchronousAck {
+		return func() {
+			go cli.sendAck(node)
+		}
+	} else {
+		go cli.sendAck(node)
+		return func() {}
+	}
+}
+
 func (cli *Client) sendAck(node *waBinary.Node) {
 	attrs := waBinary.Attrs{
 		"class": node.Tag,