Hooking Chat Messages

[bigblue]

The function "HookTest_ChatFrame_OnEvent(event)" is carried out up to 7 times if a message arrives.
Why? How can I prevent that?

local lOriginalChatFrame_OnEvent;

function HookTest_OnLoad()

   this:RegisterEvent("CHAT_MSG_CHANNEL");   
   lOriginalChatFrame_OnEvent = ChatFrame_OnEvent;
   ChatFrame_OnEvent = HookTest_ChatFrame_OnEvent;

end

function HookTest_ChatFrame_OnEvent(event)
   if (event == "CHAT_MSG_CHANNEL" and arg9 == "mmetestchan") then
      
      local msg = arg1;
      local plr = arg2;
      local cha = arg9;

      DEFAULT_CHAT_FRAME:AddMessage("["..cha.."]["..plr.."] "..msg, 1, 1, 1);
      return;
   end
   lOriginalChatFrame_OnEvent(event);
end

4 times with this change

local lOriginalChatFrame_OnEvent;
local hooktest=0;

function HookTest_OnLoad()

   this:RegisterEvent("CHAT_MSG_CHANNEL");   
   lOriginalChatFrame_OnEvent = ChatFrame_OnEvent;
   ChatFrame_OnEvent = HookTest_ChatFrame_OnEvent;

end

function HookTest_ChatFrame_OnEvent(event)
   if (event == "CHAT_MSG_CHANNEL" and arg9 == "mmetestchan" and hooktest==0) then
      
      local msg = arg1;
      local plr = arg2;
      local cha = arg9;

      hooktest=1;

      DEFAULT_CHAT_FRAME:AddMessage("["..cha.."]["..plr.."] "..msg, 1, 1, 1);
      return;
   end
   lOriginalChatFrame_OnEvent(event);
   hooktest=0;
end