Data exchanged between systems engaged in ONC RPC must always flow
in a standard format specified by XDR, because different machine architectures
have different representations of the same information.
Both client and server use XDR routines to convert the input
and output parameters between XDR format and the local data format.
You either write these yourself, or specify an XDR library function,
as described below. In Figure 1, inproc and outproc are
the XDR routines. Figure 1. XDR routines used in
a remote procedure call
Notice that in Figure 1, the same
XDR routine, inproc, is used to encode and decode the data
as it flows from client to server, and similarly for outproc as
it flows back to the client. The source for inproc is the same
in the client and server, but XDR library functions in the routines
are compiled to encode or decode as appropriate. Such routines are
termed bidirectional, and they help to ensure that the encoding
and decoding is done symmetrically in the two routines.
