IDoc user exits

Hi Experts,

We have a requirement to find the correct user exits to change the below IDoc messages.

1. Orders message(ORDERS01):

It is a inbound message, hence we need to find the user exit to change message data before creating sales order in R/3.

2. ORDERCON(ORDERS01), DESADV01,and INVOIC01:

these are outbound messages, hence we need find the user exit for each IDoc type after creating the IDoc and before posting it from R/3.

please suggest on how to find the right user exit to implement the client requirments.

Thanks,

MK