Merge branch 'XX-4193/GroupChatMessageCallback' into 'release'

Add group chat MessageReceive documentation

See merge request !375

bindings/group.go

@@ -410,6 +410,7 @@ type GroupRequest interface {
 }
 
 // GroupChatProcessor manages the handling of received group chat messages.
+// The decryptedMessage field will be a JSON marshalled GroupChatMessage.
 type GroupChatProcessor interface {
 	Process(decryptedMessage, msg, receptionId []byte, ephemeralId,
 		roundId int64, err error)
@@ -422,13 +423,53 @@ type groupChatProcessor struct {
 	bindingsCb GroupChatProcessor
 }
 
+// GroupChatMessage is the bindings layer representation of the
+// [groupChat.MessageReceive].
+//
+// GroupChatMessage Example JSON:
+//  {
+//    "GroupId": "AAAAAAAJlasAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAE",
+//    "SenderId": "AAAAAAAAB8gAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAD",
+//    "MessageId": "Zm9ydHkgZml2ZQAAAAAAAAAAAAAAAAAAAAAAAAAAAAA=",
+//    "Payload": "Zm9ydHkgZml2ZQ==",
+//    "Timestamp": 1663009269474079000
+//  }
+type GroupChatMessage struct {
+	// GroupId is the ID of the group that this message was sent on.
+	GroupId []byte
+
+	// SenderId is the ID of the sender of this message.
+	SenderId []byte
+
+	// MessageId is the ID of this group message.
+	MessageId []byte
+
+	// Payload is the content of the message.
+	Payload []byte
+
+	// Timestamp is the time this message was sent on.
+	Timestamp int64
+}
+
+// convertMessageReceive is a helper function which converts a
+// [groupChat.MessageReceive] to the bindings-layer representation GroupChatMessage.
+func convertMessageReceive(decryptedMsg gc.MessageReceive) GroupChatMessage {
+	return GroupChatMessage{
+		GroupId:   decryptedMsg.GroupID.Bytes(),
+		SenderId:  decryptedMsg.SenderID.Bytes(),
+		MessageId: decryptedMsg.ID.Bytes(),
+		Payload:   decryptedMsg.Payload,
+		Timestamp: decryptedMsg.Timestamp.UnixNano(),
+	}
+}
+
 // convertProcessor turns the input of a groupChat.Processor to the
 // binding-layer primitives equivalents within the GroupChatProcessor.Process.
 func convertGroupChatProcessor(decryptedMsg gc.MessageReceive, msg format.Message,
 	receptionID receptionID.EphemeralIdentity, round rounds.Round) (
 	decryptedMessage, message, receptionId []byte, ephemeralId, roundId int64, err error) {
 
-	decryptedMessage, err = json.Marshal(decryptedMsg)
+	decryptedMessage, err = json.Marshal(convertMessageReceive(decryptedMsg))
 	message = msg.Marshal()
 	receptionId = receptionID.Source.Marshal()
 	ephemeralId = receptionID.EphId.Int64()