11.1 An Example Service Described in the RPC Language

Here is an example of the specification of a simple ping program.

   program PING_PROG {
         /*
          * Latest and greatest version
          */
         version PING_VERS_PINGBACK {
            void
            PINGPROC_NULL(void) = 0;
            /*
             * Ping the client, return the round-trip time
             * (in microseconds). Returns -1 if the operation
             * timed out.
             */
            int
            PINGPROC_PINGBACK(void) = 1;
         } = 2;

         /*
          * Original version
          */
         version PING_VERS_ORIG {
            void
            PINGPROC_NULL(void) = 0;
         } = 1;
      } = 1;

      const PING_VERS = 2;      /* latest version */

The first version described is PING_VERS_PINGBACK with two procedures, PINGPROC_NULL and PINGPROC_PINGBACK. PINGPROC_NULL takes no arguments and returns no results, but it is useful for computing round-trip times from the client to the server and back again. By convention, procedure 0 of any RPC protocol should have the same semantics, and never require any kind of authentication. The second procedure is used for the client to have the server do a reverse ping operation back to the client, and it returns the amount of time (in microseconds) that the operation used. The next version, PING_VERS_ORIG, is the original version of the protocol and it does not contain PINGPROC_PINGBACK procedure. It is useful for compatibility with old client programs, and as this program matures it may be dropped from the protocol entirely.