ONC+ Developer's Guide

Dispatch Tables

Sometimes programs should have access to the dispatch tables used by the RPC package. For example, the server dispatch routine might check authorization and then invoke the service routine. Or, a client library might handle the details of storage management and XDR data conversion.

When invoked with the -T option, rpcgen generates RPC dispatch tables for each program defined in the protocol description file, proto.x, in the file proto_tbl.i. The suffix.i stands for “index.” You can invoke rpcgen with the -t option to build only the header file. You cannot invoke rpcgen in C-style mode (-N) with either the -T or -t flag.

Each entry in the dispatch table is a struct rpcgen_table, defined in the header file proto.h as follows:

struct rpcgen_table {
   char *(*proc)();
   xdrproc_t xdr_arg;
   unsigned len_arg;
   xdrproc_t xdr_res;
   xdrproc_t len_res


proc is a pointer to the service routine

xdr_arg is a pointer to the input (argument) xdr routine

len_arg is the length in bytes of the input argument

xdr_res is a pointer to the output (result) xdr routine

len_res is the length in bytes of the output result

The table, named dirprog_1_table for the dir.x example, is indexed by procedure number. The variable dirprog_1_nproc contains the number of entries in the table.

The find_proc() routine shows an example of how to locate a procedure in the dispatch tables.

Example 3–27 Using a Dispatch Table

struct rpcgen_table *
   rpcproc_t proc;
   if (proc >= dirprog_1_nproc)
       /* error */
      return (&dirprog_1_table[proc]);

Each entry in the dispatch table contains a pointer to the corresponding service routine. However, that service routine is usually not defined in the client code. To avoid generating unresolved external references, and to require only one source file for the dispatch table, the rpcgen service routine initializer is RPCGEN_ACTION(proc_ver).

Using this technique, the same dispatch table can be included in both the client and the server. Use the following define statement when compiling the client.

#define RPCGEN_ACTION(routine) 0

Use the following define when writing the server.

#define RPCGEN_ACTION(routine)routine