Added new fields to the ARTMessage.

Source/ARTBaseMessage.m

@@ -21,6 +21,7 @@ - (id)copyWithZone:(NSZone *)zone {
     message->_data = [self.data copy];
     message->_connectionId = self.connectionId;
     message->_encoding = self.encoding;
+    message->_extras = self.extras;
     return message;
 }
 

Source/ARTJsonLikeEncoder.m

@@ -275,6 +275,8 @@ - (ARTMessage *)messageFromDictionary:(NSDictionary *)input {
     ARTMessage *message = [[ARTMessage alloc] init];
     message.id = [input artString:@"id"];
     message.name = [input artString:@"name"];
+    message.action = ([input artNumber:@"action"] ?: [[NSNumber alloc] initWithInt:ARTMessageActionCreate]).integerValue;
+    message.serial = [input artString:@"serial"];
     message.clientId = [input artString:@"clientId"];
     message.data = [input objectForKey:@"data"];
     message.encoding = [input artString:@"encoding"];;

Source/ARTMessage.m

@@ -40,7 +40,8 @@ - (NSString *)description {
 - (id)copyWithZone:(NSZone *)zone {
     ARTMessage *message = [super copyWithZone:zone];
     message.name = self.name;
-    message.extras = self.extras;
+    message.action = self.action;
+    message.serial = self.serial;
     return message;
 }
 

Source/include/Ably/ARTMessage.h

@@ -4,6 +4,41 @@
 #import <Ably/ARTTypes.h>
 #import <Ably/ARTChannelOptions.h>
 
+/**
+ * The namespace containing the different types of message actions.
+ */
+NS_SWIFT_SENDABLE
+typedef NS_ENUM(NSUInteger, ARTMessageAction) {
+    /**
+     * Message action has not been set.
+     */
+    ARTMessageActionUnset,
+    /**
+     * Message action for a newly created message.
+     */
+    ARTMessageActionCreate,
+    /**
+     * Message action for an updated message.
+     */
+    ARTMessageActionUpdate,
+    /**
+     * Message action for a deleted message.
+     */
+    ARTMessageActionDelete,
+    /**
+     * Message action for a newly created annotation.
+     */
+    ARTMessageActionAnnotationCreate,
+    /**
+     * Message action for a deleted annotation.
+     */
+    ARTMessageActionAnnotationDelete,
+    /**
+     * Message action for a meta-message that contains channel occupancy information.
+     */
+    ARTMessageActionMetaOccupancy,
+};
+
 NS_ASSUME_NONNULL_BEGIN
 
 /**
@@ -14,6 +49,12 @@ NS_ASSUME_NONNULL_BEGIN
 /// The event name, if available
 @property (nullable, readwrite, nonatomic) NSString *name;
 
+/// The action type of the message, one of the `ARTMessageAction` enum values.
+@property (readwrite, nonatomic) ARTMessageAction action;
+
+/// This message's unique serial.
+@property (nullable, readwrite, nonatomic) NSString *serial;
+
 /**
  * Construct an `ARTMessage` object with an event name and payload.
  *