Add function to get size of message by command ID

include/message.h

@@ -259,3 +259,27 @@ enum MESSAGEERR {
 
 enum MESSAGEERR
 message_validate(const union Message* message);
+
+static
+inline
+size_t
+message_length(uint16_t cmd) {
+    switch(cmd) {
+        case SET_SDK_CONNECTION_CMD:
+            return sizeof(struct SetSdkConnectionReq);
+        case SDK_HEARTBEAT_CMD:
+            return sizeof(struct SdkHeartbeatReq);
+        case SET_SDK_MODE_CMD:
+            return sizeof(struct SetSdkModeReq);
+        case SET_SYSTEM_LED_CMD:
+            return sizeof(struct SetSystemLedReq);
+        case SET_ROBOT_MODE_CMD:
+            return sizeof(struct SetRobotModeReq);
+        case SUBNODE_RESET_CMD:
+            return sizeof(struct SubNodeResetReq);
+        case SUBSCRIBE_ADD_NODE_CMD:
+            return sizeof(struct SubscribeAddNodeReq);
+        default:
+            return 0;
+    }
+}