Changing the Message Content

Message data is presented to exit IXZXIT02, through mapping macro IXZ$XPL, by a pair of fields:

XIT02_MESSAGE provides a pointer to the message data
XIT02_MESSAGE_LEN provides the length of that data.

To change the data, your exit routine must:

Obtain storage to contain the new copy of the data
This storage must be obtained from subpool 0. That is, do not specify a subpool. (IBM recommends using the STORAGE macro rather than $GETMAIN (for JES2) or AGETMAIN (for JES3) when obtaining this storage.)
Save the address of that storage in XIT02_MESSAGE_UPADDR
Save the length of that storage in XIT02_MESSAGE_UPLEN
Update XIT02_MAX_ADD in IXZ$XPL to reflect the message size change. XIT02_MAX_ADD contains the maximum number of bytes that can still be added to a message packet. Be certain to decrease its size as the message packet grows.
Copy the data into the storage and change the data as required
Set the indicator bit, XIT02_MESSAGE_UP, in IXZ$XPL to inform JES XCF of the changes.

JES XCF delivers the revised message rather than the original message data. Following message processing, JES XCF frees the storage obtained by this exit.