data property

Pointer to buffer which holds the message body data. For incoming messages, the parser will fill in this member with the pointer to the body string.

When sending outgoing message, this member doesn't need to point to the actual message body string. It can be assigned with arbitrary pointer, because the value will only need to be understood by the print_body() function. The stack itself will not try to interpret this value, but instead will always call the print_body() whenever it needs to get the actual body string.