events: include unavailable type in undecryptable messages

message.go

@@ -219,10 +219,12 @@ func (cli *Client) handlePlaintextMessage(info *types.MessageInfo, node *waBinar
 }
 
 func (cli *Client) decryptMessages(info *types.MessageInfo, node *waBinary.Node) {
-	if len(node.GetChildrenByTag("unavailable")) > 0 && len(node.GetChildrenByTag("enc")) == 0 {
-		cli.Log.Warnf("Unavailable message %s from %s", info.ID, info.SourceString())
+	unavailableNode, ok := node.GetOptionalChildByTag("unavailable")
+	if ok && len(node.GetChildrenByTag("enc")) == 0 {
+		uType := events.UnavailableType(unavailableNode.AttrGetter().String("type"))
+		cli.Log.Warnf("Unavailable message %s from %s (type: %q)", info.ID, info.SourceString(), uType)
 		go cli.delayedRequestMessageFromPhone(info)
-		cli.dispatchEvent(&events.UndecryptableMessage{Info: *info, IsUnavailable: true})
+		cli.dispatchEvent(&events.UndecryptableMessage{Info: *info, IsUnavailable: true, UnavailableType: uType})
 		return
 	}
 

types/events/events.go

@@ -244,6 +244,13 @@ const (
 	DecryptFailHide DecryptFailMode = "hide"
 )
 
+type UnavailableType string
+
+const (
+	UnavailableTypeUnknown  UnavailableType = ""
+	UnavailableTypeViewOnce UnavailableType = "view_once"
+)
+
 // UndecryptableMessage is emitted when receiving a new message that failed to decrypt.
 //
 // The library will automatically ask the sender to retry. If the sender resends the message,
@@ -256,6 +263,8 @@ type UndecryptableMessage struct {
 	// IsUnavailable is true if the recipient device didn't send a ciphertext to this device at all
 	// (as opposed to sending a ciphertext, but the ciphertext not being decryptable).
 	IsUnavailable bool
+	// Some message types are intentionally unavailable. Such types usually have a type specified here.
+	UnavailableType UnavailableType
 
 	DecryptFailMode DecryptFailMode
 }