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Communications Programming Concepts

RPC Language ping Program Example

The following is an example of the specification of a simple ping program described in the Remote Procedure Call language (RPCL):

/*
* Simple ping program
*/
program PING_PROG {
        /* Latest and greatest version */
        version PING_VERS_PINGBACK {
         void
        PINGPROC_NULL(void) = 0;
      /*
       * Ping the caller, 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 */

In this example, the first part of the ping program, PING_VERS_PINGBACK, consists of two procedures: PINGPROC_NULL and PINGPROC_PINGBACK. The PINGPROC_NULL procedure takes no arguments and returns no results. However, it is useful for computing round-trip times from the client to the server. By convention, procedure 0 of an RPC protocol should have the same semantics and require no kind of authentication. The second procedure, PINGPROC_PINGBACK, requests a reverse ping operation from the server. It returns the amount of time in microseconds that the operation used.

The second part, or original version of the ping program, PING_VERS_ORIG, does not contain the PINGPROC_PINGBACK procedure. The original version is useful for compatibility with older client programs. When the new ping program matures, this older version may be dropped from the protocol entirely.


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